393 terms

Bio1 final


Terms in this set (...)

1. In 1831, Charles Darwin, a 22-year-old naturalist
accepted a position aboard the ship HMS Beagle that began a voyage around the world; it provided Darwin with many observations.
2. The pre-Darwinian world-view
was different from the post-Darwinian.
was determined by intractable theological beliefs.
The earth is young.
Each species was specially created and did not change over time.
Variations are imperfections varying from a perfectly-adapted creation.
Observations are to substantiate the prevailing worldview.
3) Darwin's ideas
Darwin, however, lived during a time of great change in scientific and social realms.
Darwin's ideas were part of a larger change in thought already underway among biologists; this concept would eventually be known as evolution.
A. Mid-Eighteenth-Century Contributions
Carolus Linnaeus and Taxonomy
Taxonomy is the science of classifying organisms; taxonomy had been a main concern of biology.
a.Carolus Linnaeus (1707-1778) was a Swedish taxonomist.
Linnaeus developed a binomial system of nomenclature (two-part names for each species [e.g., Homo sapiens]).
He developed a system of classification for all known plants.
3)Linnaeus believed in
Like other taxonomists of his time, Linnaeus believed in the ideas of special creation
Linnaeus thought that classification should describe the fixed features of species and reveal God's divine plan.
His ideas reflected the ideas of Plato and Aristotle: the ideal form can be deduced, and organisms can be arranged in order of increasing complexity.
His later work with hybridization suggested species might change with time.
a)special creation
special creation—each species had an "ideal" structure and function; and
b)fixity of species
fixity of species—each species had a place in the scala naturae, a sequential ladder of life.
2. Georges Louis Leclerc
Georges Louis Leclerc, known by his title, Count Buffon (1707-1788), was a French naturalist.
He wrote a 44-volume natural history of all known plants and animals.
He also provided evidence of descent with modification.
His writings speculated on influences of the environment, migration, geographical isolation, and the struggle for existence.
Buffon vacillated on whether he believed in evolutionary descent and he professed to believe in special creation and the fixity of species.
3.Erasmus Darwin (1731-1802)
Erasmus Darwin was Charles Darwin's grandfather.
He was a physician and a naturalist whose writings on both botany and zoology contained many comments that suggested the possibility of common descent.
b.He based his conclusions on
changes undergone by animals during development,
artificial selection by humans, and
the presence of vestigial structures (structures or organs that are believed to have been functional in an ancestor but are reduced and nonfunctional in a descendant).
Erasmus Darwin offered no mechanism by which evolutionary descent might occur.
B.Late Eighteenth-/Early-Nineteenth Century Contributions
Cuvier and Catastrophism
1.George Cuvier (1769-1832)
a French vertebrate zoologist, was the first to use comparative anatomy to develop a system of classifying animals.
He founded the science of paleontology—the study of fossils—and suggested that a single fossil bone was all he needed to deduce the entire anatomy of an animal.
To explain the fossil record, Cuvier proposed that a whole series of catastrophes (extinctions) and re-populations from other regions had occurred.
Cuvier was also a staunch advocate of special creation and fixity of species; this presented him with a problem when geological evidence of a particular region showed a succession of life forms in the earth's strata.
Catastrophism is the term applied to Cuvier's explanation of fossil history: the belief that catastrophic extinctions occurred, after which repopulation of surviving species occurred, giving an appearance of change through time.
2.Lamarck (1744-1829) Acquired Characteristics
Lamarck (1744-1829) was the first to state that descent with modification occurs and that organisms become adapted to their environments.
Lamarck, an invertebrate zoologist, held ideas at odds with Cuvier's.
Lamarck mistakenly saw "a desire for perfection" as inherent in all living things.
Inheritance of acquired characteristics was Lamarck's belief that organisms become adapted to their environment during their lifetime and pass these adaptations to their offspring.
Experiments fail to uphold Lamarck's inheritance of acquired characteristics; the molecular mechanism of inheritance shows phenotypic changes do not result in genetic changes that can be passed on to the next generation.
15.2 Darwin's Theory of Evolution
A.Darwin's Background
His nature was too sensitive to pursue medicine; he attended divinity school at Cambridge.
He attended biology and geology lectures and was tutored by the Reverend John Henslow.
3. Henslow arranged his five-year trip
on the HMS Beagle; Darwin was an observant student of nature.
B. Geology and Fossils
His study of geology and fossils caused him to concur with Lyell that the observed massive geological changes were caused by slow, continuous processes.
Darwin took Lyell's book on the voyage of the HMS Beagle.
In his book Principles of Geology, Charles Lyell presented arguments to support a theory of geological change proposed by James Hutton.
c.Hutton proposed
In contrast to catastrophists, Hutton proposed that the earth was subject to slow but continuous geological processes (e.g., erosion and uplifting) that occur at a uniform rate, a theory called uniformitarianism.
*The Argentina coast had raised beaches; he witnessed earthquakes raising the earth several feet.
*Marine shells occurred far inland and at great heights in the Andes.
*Fossils of huge sloths and armadillo-like animals suggested modern forms were descended from extinct forms with change over time; therefore species were not fixed.
Biogeography is the study of the geographic distribution of life forms on earth.
2. Biogeography evidence
Patagonian hares replaced rabbits in the South American grasslands.
*The greater rhea found in the north was replaced by the lesser rhea in the south.
4. Comparison of the animals of South America and the Galápagos Island
caused Darwin to conclude that adaptation to the environment can cause diversification, including origin of new species.
5.The Galápagos Islands
These volcanic islands off the South American coast had fewer types of organisms.
Island species varied from the mainland species, and from island-to-island.
Each island had a variation of tortoise; long and short necked tortoises correlated with different vegetation.
b.Darwin's Finches
*Finches on the Galápagos Islands resembled a mainland finch but there were more types.
*Galápagos finch species varied by nesting site, beak size, and eating habits.
*One unusual finch used a twig or thorn to pry out insects, a job normally done by (missing) woodpeckers (Darwin never witnessed this finch behavior).
4) finches posed questions
The variation in finches posed questions to Darwin: did they descend from one mainland ancestor or did islands allow isolated populations to evolve independently, and could present-day species have resulted from changes occurring in each isolated population?
D.Natural Selection and Adaptation
Darwin decided that adaptations develop over time; he sought a mechanism by which adaptations might arise.
*Because the environment is always changing, there is no perfectly-adapted organism.
2.Alfred Russel Wallace
Natural selection was proposed by both Alfred Russel Wallace and Darwin as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptation.
4.Natural selection is a process consisting of these conditions:
*The members of a population have random but heritable variations.
*In a population, many more individuals are produced each generation than the environment can support.
*Some individuals have adaptive characteristics that enable them to survive and reproduce better. Darwin called the ability to have more offspring, differential reproductive success.
d.The result of natural selection
* is a population adapted to its local environment.
*Natural selection can only utilize variations that are randomly provided; therefore there is no directedness or anticipation of future needs.
Extinction occurs when previous adaptations are no longer suitable to a changed environment.
E.Organisms Have Inheritable Variations
*In contrast to the previous worldview where imperfections were to be ignored, variations were essential in natural selection.
*Darwin suspected, but did not have today's evidence, that the occurrence of variation is completely random.
*New variations are as likely to be harmful as helpful.
*Variations that make adaptation possible are those that are passed on from generation to generation.
5.Darwin could not state the cause of variations because genetics was not yet established.
Natural selection only operates on variations that are already available in a population's gene pool.
F.Organisms Compete for Resources
1.Darwin and Wallace both read an essay by Thomas Malthus, a socioeconomist.
*Malthus proposed that human populations outgrow food supply and death and famine were inevitable.
*Darwin applied this to all organisms; resources were not sufficient for all members to survive.
2.Organisms Differ in Reproductive Success
Organisms whose traits enable them to reproduce to a greater degree have a greater fitness.
Fitness is a measure of an organism's reproductive success.
b. fitness example
Black western diamondback rattlesnakes are more likely to survive on lava flows; lighter-colored rattlesnakes are more likely to survive on desert soil.
2.Darwin noted that humans carry out artificial selection.
*Early humans likely selected wolf variants; consequently, desirable traits increase in frequency in subsequent generations and produced the varieties of domestic dogs.
*Russian scientists have produced silver foxes that allow themselves to be petted rather than running away from humans.
*Many crop plant varieties can be traced to a single ancestor.
1.H.Organisms Become Adapted
An adaptation is a trait that helps an organism be more suited to its environment.
*Unrelated organisms living in the same environment often display similar characteristics.
*Because of differential reproduction, adaptive traits increase in each succeeding generation.
I.On the Origin of Species by Darwin
*After the HMS Beagle returned to England in 1836, Darwin waited over 20 years to publish.
*He used the time to test his hypothesis that life forms arose by descent from a common ancestor and that natural selection is a mechanism by which species can change and new species arise.
3.Darwin was forced to publish Origin of Species
after reading a similar hypothesis by Alfred Russel Wallace.
J.Alfred Russel Wallace (Science Focus box)
1. Alfred Russel Wallace (1823-1913) was an English naturalist who independently and simultaneously proposed natural selection as a mechanism for evolution.
2. He and the entomologist Henry Walter Bates took a collecting trip to the Amazon, and then to the Malay Archipelago from 1854-1864)
3. After studying the animals from his trips, he divided the lislands into a western and eastn group. This sharp line dividing the two islands group is now known as Wallace's Line.
4. Wallace's Line is located near a deep channel between the Oriental and Australian regions. This area serves as an impassable barrier to animal dispersal.
5. In 1855 Wallace wrote an essay entitled, "On the Law Which Has Regulated the Introduction of New Species." At this point he saw that species share a common ancestry and that species also change over time.
6. In 1858 Wallace concluded changes in species are due to changes in the environment through natural selection.
7. Wallace wrote a manuscript of these findings and sent it to Charles Darwin for review. Darwin was shocked that Wallace had the same theories that he had. Darwin told Wallace to publish his manuscript at once.
8. Darwin published Origin of the Species one year later while Wallace was in the field.
9. Although Darwin overshadows Wallace, Wallace is still refered to as "England's Greatest Living Naturalist."
K.Natural Selection Can Be Witnessed
1. Darwin formed his natural selection hypothesis by observing the distribution of tortoises and finches on the Galapagos Islands.
2. Scientists are currently witnessing natural selection on the Galapagos Islands. Peter and Rosemary Grant have been observing finch beak size change with rainfall. During wet seasons, the offspring have smaller beaks to eat the small seeds, however, in drier seasons, offspring have larger beaks capable of breaking harder seeds that survive the dry weather.
3. Other examples of natural selection can be seen in marine snails, and the scarlet honeycreeper, plants and bacteria.
4. A common example of natural selection is industrial melanism. Prior to the industrial revolution in Great Britian, light-colored peppered moths were more common (90%) than the dark-colored peppered moths (10%).
Pepper colored moths
a. Following the industrial revolution and increase in pollution, dark-colored peppered moths reached 80% of the peppered moth population.
b. Once legislation regulated pollution reduction, dark-colored peppered moths reduced to 16% in one of th collecting sites.
15.3 Evidence for Evolution
Common Descent
The hypothesis of common descent is supported by many lines of evidence.
The more varied the evidence, the more certain it becomes.
Fossils Evidence
Fossils are the remains and traces of past life or any other direct evidence of past life.
*Fossils include skeletons, shells, seeds, insects trapped in amber, and imprints of leaves.
*Transitional fossils reveal links between groups.
a.Fossil examples
Archeopteryx is an intermediate between reptiles and birds.
*Ambulocetus natans is a whale with legs.
C.Biogeographical Evidence
Biogeography studies the distribution of plants and animals worldwide.
*Distribution of organisms is explained by related forms evolving in one locale and spreading to other accessible areas.
*Darwin observed South America had no rabbits; he concluded rabbits originated elsewhere.
*Biogeography explains the abundance of finch species on the Galápagos Islands lacking on the mainland.
b.Physical factors, such as the location of continents, determine where a population can spread
Cacti are restricted to North American deserts and euphorbia grow in African deserts.
Marsupials arose when South America, Antarctica, and Australia were joined; Australia separated before placental mammals arose, so only marsupials diversified in Australia.
D.Anatomical Evidence
Organisms have anatomical similarities when they are closely related because of common descent.
*Homologous structures in different organisms are inherited from a common ancestor.
*Analogous structures are inherited from unique ancestors and have come to resemble each other because they serve a similar function.
*Vertebrate forelimbs contain the same sets of bones organized in similar ways, despite their dissimilar functions.
*Vestigial structures are remains of a structure that was functional in some ancestors but is no longer functional in the organism in question.
a.Anatomical examples
Most birds have well-developed wings; some bird species have reduced wings and do not fly.
Humans have a tailbone but no tail.
c. Anatomical evidence supports common ancestor
Presence of vestigial structures is explained by the common descent hypothesis; these are traces of an organism's evolutionary history.
Embryological development reveals a unity of plan.
*During development, all vertebrates have a post-anal tail and paired pharyngeal pouches.
*In fishes and amphibian larvae, the pouches become gills.
*In humans, first pair of pouches becomes a cavity of middle ear and auditory tube; second pair becomes tonsils, while third and fourth pairs become thymus and parathyroid glands.
*The above features are explained if fishes are ancestral to other vertebrate groups.
1.Biochemical Evidence
All living organisms use the same basic biochemical molecules, e.g., DNA, ATP, and many identical or nearly identical enzymes.
*Organisms utilize the same DNA triplet code and the same 20 amino acids in their proteins.
*Many organisms share the same introns and types of repeats, which is remarkable since there is no obvious functional reason why these components need to be so similar.
*This is substantiated by the analysis of the degree of similarity in amino acids for cytochrome c among organisms.
Biochemical evidence supports common ancestor
These similarities can be explained by descent from a common ancestor.
*Life's vast diversity has come about by only a slight difference in the same genes.
Evolution a theory
Because it is supported by so many lines of evidence, evolution is no longer considered a hypothesis
*In science, theory is reserved for those conceptual schemes that are supported by a large number of observations or a large amount of experimental evidence and have not been found lacking.
Evolution unifying theory
Evolution is one of the great unifying theories of biology, similar in status to the germ theory of disease in medicine.
Natural selection
Natural selection favors the phenotype that is the most adaptive under the present environmental Circumstances. In this context, there are three types of natural selection: stabilizing, directional, or disruptive.
Stabilizing selection
Stabilizing selection occurs when extreme phenotypes are eliminated and the intermediate phenotype is favored.
a. The average number of eggs laid by Swiss starlings is four or five.
b. If the female lays more or less than this number, fewer survive.
c. Genes determining the physiology of yolk production and behavior are involved in clutch size.
Directional selection
Directional selection occurs when an extreme phenotype is favored; the distribution curve shifts that direction.
a. A shift to more colorful, later maturing male guppies with exposure to no predators compared to drab colored, early maturing male guppies.
Disruptive selection
Disruptive selection occurs when extreme phenotypes are favored and can lead to more than one distinct form.
a. British snails (Cepaea nemoralis) vary because a wide range causes natural selection to vary.
b. In forest areas, thrushes feed on snails with light bands.
c. In low-vegetation areas, thrushes feed on snails with dark shells that lack light bands.
5. Sexual Selection
Sexual selection
Sexual selection refers to adaptive changes in males and females that lead to an increased ability to secure a mate.
1) In males, this may result in an increased ability to compete with other males for a mate.
2) Females may select a mate with the best fitness (ability to produce surviving offspring), thereby increasing her own fitness.
Female Choice
a. Two hypothesis regarding a female's choice of a mate are:
1) The good genes hypothesis contends that females choose mates based on traits for improving the survival of offspring.
2) The runaway hypothesis states that females chose mates on the basis of traits that attract them to females; the trait can then become exaggerated until it is a handicap.
The Raggiana Bird of Paradise
b. The Raggiana Bird of Paradise is dimorphic (males and females differ in size and other traits)
1) The ornateness of the male is a factor in selection by a female.
2) More feathery Raggiana are parasite-free, and their selection by females would increase the chance for survival.
Male Competition
Male Competition
a. A cost-benefit analysis can be applied to determine if the benefit of access to mating is worth the cost of competition among males.
Baboons have a dominance hierarchy.
1) A dominance hierarchy is a ranking within a group where the higher ranking individuals acquire more resources.
2) Dominance is determined by confrontation where one animal gives way to the other.
3) Baboons are dimorphic: males are larger and have large canine teeth; they decide when the troop moves, and they defend it.
4) Females mate with dominant males when ovulation is near; the dominant males then protect all young.
5) The drawbacks to being large and in danger are outweighed by the chance of fathering young.
6) The subordinate males have less chance to mate but they do have avenues to have some offspring.
Red deer stake out a territory
an area that is defended against competitors.
1) Territoriality involves the type of behavior needed to defend a particular territory.
2) A stag competes for females that form a harem that mates only with him.
3) A stag remains at peak fighting ability for only a short time; one stag can only father about two dozen offspring.
Sexual Selection in Humans (Science Focus box)
a. Human Males Compete
b. Humans, like many other mammals, are dimorphic.
c. Males are larger and more aggressive, perhaps due to past sexual selection by females.
Females Choose
1. Females Choose
a. Male mating success correlates best with income—wealthy males attracted mates better than nonwealthy males.
b. Apparently, females prefer to mate with a male who is wealthy and has a successful career—this will ensure that the children will live to reproduce.
Men Also Have a Choice
2. Men Also Have a Choice
a. Men prefer women who will present them with children: health, age, "figure," faithfulness are all factors in a male's choice of a mate.
Modes of Speciation
*Allopatric speciation
Speciation is the splitting of one species into two more more species or the transformation of one species into a new species over time.
a. Researchers recognize two modes of speciation: geographic isolation and reproductive isolation.
Allopatric speciation
A. Allopatric speciation
1. Allopatric speciation occurs when new species result from populations being separated by a geographical barrier that prevents their members from reproducing with each other.
2. First proposed by Ernst Mayr of Harvard University.
3. While geographically isolated, variations accumulate until the populations are reproductively isolated.
Examples of Allopatric Speciation
a. An ancestral population of Ensatina salamanders migrated from northern California to southern California. The Central Valley prevented gene flow between the eastern and western populations of these salamanders. Genetic differences increased resulting in two distinct forms of Ensatina salamanders.
b. Green iguana of South America is believed to be the common ancestor for the marine iguanta on the Galapgagos Islands (to the west) and the rhinoceros iguana on Hispaniola (to the north). A few of these iguanas may have swam to the islands and over time formed populations separate from each other and from the parent population of South America.
c. Many sockeye salmon in Washington State were introduced into Lake Washington when some colonized an area of the lake near Pleasure Point Beach and others migrated into the Cedar River. Because of the difference in water current, over time, the salmon differed in shape and size due to the demands of reproducing in the different water currents.
Reinforcement of Reproductive Isolation
Reinforcement of Reproductive Isolation
a. A side effect to adaptive changes involving mating is reproductive isolation.
b. As populations become reproductively isolated, postzygotic isolating mechanisms may arise before prezygotic isolating mechanisms.
c. An example is a horse reproducting with a mule, a sterile donkey is produced.
d. Natural selection would favor any variation in populations that prevents the occurrence of hybrids when they do not have offspring.
e. Reinforcement refers to the process of natural selection favoring variations that lead to reproductive isolation.
Adaptive Radiation
Adaptive Radiation
1. Adaptive radiation is a type of allopatric speciation and occurs when a single ancestral species gives rise to a variety of species, each adapted to a specific environment.
2. An ecological niche is where a species lives and how it interacts with other species.
3. The case of Darwin's finches illustrates the adaptive radiation of 13 species from one founder mainland finch.
4. On the Hawaiian Islands, a wide variety of honeycreepers descended from one goldfinchlike ancestor; Hawaii is also the home of the silversword plants that radiated from ancestral tarweeds.
Sympatric speciation
Sympatric speciation would occur when members of a single population develop a genetic difference (e.g., chromosome number) that prevents them from reproducing with the parent type.
A polyploid
A polyploid is a eukaryote with three or more complete sets of chromosomes.
a. Polyploidy is predominantly seen in plants and makes a significant contribution to the evolution of new plants.
b. A polyploid plant can reproduce with itself, but cannot reproduce with the 2n population.
c. The two types of polyploidy are: aneuploidy and alloploidy.
3. Aneuploidy is the condition in which an organism gains or loses one or more chromosomes.
4. Monosomy (2n - 1) occurs when an individual has only one of a particular type of chromosome.
5. Trisomy (2n + 1)occurs when an individual has three of a particular type of chromosome.
6. Farmers may use produce sterile plants because their fruits do not have seeds and tend to be more favorable for the consumer.
Monosomy (2n - 1) occurs when an individual has only one of a particular type of chromosome.
Trisomy (2n + 1)occurs when an individual has three of a particular type of chromosome.
4. Alloploidy requires two different but related species of plants to hybridize.
a. When hybridization occurs, it is followed by chromosome doubling.
b. However the offspring that has parents with different numbered pairs of chromosomes will be sterile.
c. An exaple of alloploidy can be seen in the wheat plant used to produce bread. The parents of the present day bread wheat had 28 and 14 chromosomes. The hybrid with 21 chromosomes is sterile, but bread wheat with 43 chromosomes is fertile since the chromosomes can pair during meiosis.
The Burgess Shale Hosts a Diversity of Life (Science Focus box)
1. The Burgess Shale is a rock outcropping in Yoho National Park, British Columbia discovered by Charles Doolittle Walcott in 1909.
2. In this area there is a large quantity of fossils.
3. At the beginning of the excavation, it was difficult to extract the fossils from their matix, but now new methods that involve UV light and diluted acetic acid make it easy to free the fossils.
4. These marine fossils are thought to have lived around 540 million years ago (MYA), during the Precambrian period.
5. Many fossils found in the Burgess Shale are soft-bodied invertebrates, which is unusual since soft-bodied animals rarely fossilized.
6. When these organisms were alive, they all lived in the sea, and this area was subjected to mudslides. The mud entered the sea, buried the animals. Later the mud turned into shale and over time the shale was raised. Mud particles filled the spaces around the organisms, so the soft tissue was preserved and fossils became somewhat three-dimensional.
7. Organisms that have been preserved at the Burgess Shale are vertebrates, invertebrates, and unicellular organisms.
8. There is much dispute regarding the evolution of these species. Some scientist believe that evolution of these species happened slowly, while others believed it happened quickly and suddenly.
A. Macroevolution is evolution of new species and higher levels of classification.
B. Some evolutionists support a gradualistic model of macroevolution, meaning that speciation occurs after populations become isolated, with each group continuing slowly on its own evolutionary pathway.
1. According to this model, ancelstral species gradually gives rise to two separate species.
2. This model suggests that it is difficult to indicate when speciation occurred because there would be so many transitional links.
C. Other evolutionists support a punctuated equilibrium model to explain the pace of evolution.
a. According to this model, periods of equilibrium (no change) are punctuated (or interrupted) by speciation.
b. This model suggests that transitional links are less likely to become fossils and less likely to be found.
c. Speciation is more likely to involve only an isolated population at one locate, because a favorable genotype could spread more rapidly within such a population.
These two models could both assist in interpretation of the fossil record. For example, some species may fit into one model, and other species fit into the other model.
1. Developmental Genes and Macroevolution
a. Genes can bring about radical changes in body shapes and organs.
b. The Pax6 gene is involved in eye formation in all organisms.
c. Homeotic (Hox) genes determine the location of repeated structures in all vertebrates.
Gene Expression Can Influence Development
a. Gene expression influences organisms' developmental processes.
a. These genes can bring about changes in body shapes and organs.
b. Despite millions of years of divergent evolution, all animals share the same control switches for development
Development of the Eye
a. Although eyes of species vary in size, compound or simple, etc.
b. Despite these differences, there is one gene, Pax6, required for eye formation.
c. The gene Pax6 was dicvoered by Walter Gehrig and collegues in 1994.
d. Interestingly, the mouse Pax6 gene can cause an eye to develop in the leg of a fruit fly.
Development of Limbs
a. The Tbx5 gene helps in the development of limbs in humans and wings in birds.
b. Tbx5 triggers different genes in birds and humans, which may explain why the same protein is used in developing limbs in humans and wings in birds.
Development of Overall Shape
a. Hox genes control the number and appearances of repeated structures along the main body axes of vertebrates.
b. Shifts when the Hox gene is expressed can explain why some vertebrates, like the snake, have hundreds of vertebrae, and others, like the chick only have seven.
Pelvic-Fin Genes
a. An altered expression of a particular gene can reduce the pelvic-fin bud in the embryo.
b. Natural selection can lead to major skeletal changes in a relatively short period of time.
Human Evolution
a. Human DNA base sequencing is similar to that of chimpanzees, mice, and all vertebrates.
b. Scientist predict that differential gene expression and/or new functions for "old" genes will explain how humans evolved.
Macroevolution Is Not Goal-Oriented
1. The evolution of the horse, Equus, represents a gradual, straight-line evolution until its goal, the modern horse, has been achieved.
a. The trends seen in the evolution of the horse are: overall size, toe reduction, and change in tooth size and shape.
Horse example cont.
2. However, based on fossils, it is easier to see that the horse lineage is not a straight-line evolution, but rather forming a thick bush of many equine species.
3. One may have deducted that since the only genus that remains is Equus and the other genera have become extinct, that evolution was directed towards producing Equus. However, each of the ancesteral species was adapted to its environment.
4. Adaptation occurs because the members of a population with an advantage are able to have more offspring than other members.
5. Natural selection is not goal-oriented, but rather opportunistic.
Origin of life/Chemical evolution
Chemical evolution is the increase in complexity of chemicals that led to the first cells.
a. Today, we say that "life only comes from life."
b. However, the first cells had to arise from an increased complexity of chemicals.
The Early Earth
1. The Earth came into being about 4.6 BYA (BYA).
2. Heat from gravitation and radioactivity formed the Earth in several layers with iron and nickel in a liquid core, silicate minerals in a semi-liquid mantle, and upwellings of volcanic lava forming the first crust.
3. The Earth's mass provides a gravitational field strong enough to hold an atmosphere.
4. Early Earth's atmosphere differed from the current atmosphere, consisting of:
a. water vapor,
b. nitrogen,
c. carbon dioxide,
d. small amounts of hydrogen, methane, ammonia, hydrogen sulfide, and carbon monoxide.
5. The early atmosphere was formed by volcanic out-gassing characteristic of the young Earth.
6. The early atmosphere contained little free oxygen (O2) and was probably a reducing atmosphere with little free oxygen; a reducing atmosphere lacks free O2 and allows formation of complex organic molecules.
7. The early Earth was so hot that H2O only existed as a vapor in dense, thick clouds.
8. As the Earth cooled, H2O vapor condensed to form liquid H2O, and rain collected in oceans.
9. The Earth's distance from the sun allows H2O to exist in all phases: solid, liquid, and gas.
10. NASA photos seem to confirm that Earth is bombarded by comets adding substantial water vapor.
Monomers Evolve
Monomers Evolve
1. There are three hypotheses that explain how organic monomers could have evolved.
2. Hypothesis one: Monomers came from outer space
a. Comets and meteorites, perhaps carrying organic chemicals, have pelted the Earth throughout history.
b. A meteorite from Mars (ALH84001) that landed on Earth 13,000 years ago, may have fossilized bacteria.
Hypothesis two: monomers
3. Hypothesis two: monomers came from reactions in the atmosphere
a. Oparin/Haldane independently suggested organic molecules could be formed in the presence of outside energy sources using atmospheric gases.
b. Experiments performed by Miller and Urey (1953) showed experimentally that these gases (methane, ammonia, hydrogen, water) reacted with one another to produce small organic molecules (amino acids, organic acids).
c. Lack of oxidation and decay allowed organic molecules to form a thick, warm organic soup.
Hypothesis three: monomers
Hypothesis three: monomers came from reactions at hydrothermal vents
a. Ammonia may have been scarce in the early atmosphere; undersea thermal vents, which line ocean ridges, might have been responsible for converting nitrogen to ammonia.
Polymers Evolve
Polymers Evolve
1. Newly formed organic molecules polymerized to produce larger molecules.
a. Wachtershauser and Huber formed peptides using iron-nickel sulfides under ventlike conditions.
b. Such minerals have a charged surface that attracts amino acids and provides electrons so they bond together.
Protein-first Hypothesis
a. Sidney Fox demonstrated amino acids polymerize abiotically if exposed to dry heat.
b. Amino acids collected in shallow puddles along the rocky shore; heat of the sun caused them to form proteinoids (i.e., small polypeptides that have some catalytic properties).
c. When proteinoids are returned to water, they form cell-like microspheres composed of protein.
d. This assumes DNA genes came after protein enzymes; DNA replication needs protein enzymes.
The Clay Hypothesis
The Clay Hypothesis
a. Graham Cairns-Smith suggests that amino acids polymerize in clay, with radioactivity providing energy.
b. Clay attracts small organic molecules and contains iron and zinc atoms serving as inorganic catalysts for polypeptide formation.
c. Clay collects energy from radioactive decay and discharges it if temperature or humidity changes.
d. If RNA nucleotides and amino acids became associated so polypeptides were ordered by and helped synthesize RNA, then polypeptides and RNA arose at the same time.
RNA-first Hypothesis
RNA-first Hypothesis
a. Only the macromolecule RNA was needed at the beginning to lead to the first cell.
b. Thomas Cech and Sidney Altman discovered that RNA can be both a substrate and an enzyme.
c. RNA would carry out processes of life associated with DNA (in genes) and protein enzymes.
d. Supporters of this hypothesis label this an "RNA world" 4 BYA.
A Protocell Evolves
1. Before the first true cell arose, there would have been a protocell or protobiont.
2. A protocell would have a lipid-protein membrane and carry on energy metabolism.
3. Sidney Fox showed that if lipids are made available to microspheres, lipids become associated with microspheres producing a lipid-protein membrane
Oparin demonstrated a protocell could have developed from coacervate droplets.
Oparin demonstrated a protocell could have developed from coacervate droplets.
a. Coacervate droplets are complex spherical units that spontaneously form when concentrated mixtures of macromolecules are held in the right temperature, ionic composition, and pH.
b. Coacervate droplets absorb and incorporate various substances from the surrounding solution.
c. In a liquid environment, phospholipid molecules spontaneously form liposomes, spheres surrounded by a layer of phospholipids; this is called the "membrane-first" hypothesis.
d. A protocell could have contained only RNA to function as both genetic material and enzymes.
If a protocell was a heterotrophic
If a protocell was a heterotrophic fermenter living on the organic molecules in the organic soup that was its environment, this would indicate heterotrophs preceded autotrophs.
a. A heterotroph is an organism that cannot synthesize organic compounds from inorganic substances and therefore must take in preformed organic compounds.
b. An autotroph is an organism that makes organic molecules from inorganic nutrients.
protocell evolved at hydrothermal vents
6. If the protocell evolved at hydrothermal vents, it would be chemosynthetic and autotrophs would have preceded heterotrophs.
7. The first protocells may have used preformed ATP, but as supplies dwindled, natural selection would favor cells that could extract energy from carbohydrates to transform ADP to ATP.
8. Since glycolysis is a common metabolic pathway in living things, it evolved early in the history of life.
9. As there was no free O2, it is assumed that protocells carried on a form of fermentation.
first protocells had a limited ability
10. The first protocells had a limited ability to break down organic molecules; it took millions of years for glycolysis to evolve completely.
11. Fox has shown that a microsphere has some catalytic ability; Oparin found that coacervates incorporate enzymes if they are available in the medium.
A Self-Replication System Evolves
A Self-Replication System Evolves
1. In living systems, information flows from DNA → RNA → protein; it is possible that this sequence developed in stages.
The RNA-first hypothesis suggests that the first genes and enzymes were RNA molecules.
The RNA-first hypothesis suggests that the first genes and enzymes were RNA molecules.
a. These genes would have directed and carried out protein synthesis.
b. Ribozymes are RNA that acts as enzymes.
c. Some viruses contain RNA genes with a protein enzyme called reverse transcriptase that uses RNA as a template to form DNA; this could have given rise to the first DNA.
The protein-first hypothesis contends that proteins or at least polypeptides were the first to arise.
a. Only after the protocell develops complex enzymes could it form nucleic acids from small molecules.
b. Because a nucleic acid is complicated, the chance that it arose on its own is minimal.
c. Therefore, enzymes are needed to guide the synthesis of nucleotides and then nucleic acids.
Cairns-Smith suggests that polypeptides and RNA evolved simultaneously.
Cairns-Smith suggests that polypeptides and RNA evolved simultaneously.
a. The first true cell would contain RNA genes that replicated because of the presence of proteins; they become associated in clay in such a way that the polypeptides catalyzed RNA formation.
b. This eliminates the chicken-and-egg paradox; both events happen at the same time.
Once the protocell was capable of reproduction, it became a true cell and biological evolution began.
Once the protocell was capable of reproduction, it became a true cell and biological evolution began.
a. After DNA formed, the genetic code still had to evolve to store information.
b. Because the current code is subject to fewer errors than other possible codes, and because it minimizes mutations, it likely underwent a natural selection process.
origin of life steps
A Recap of the Steps
1. Most biologists suspect life evolved in basic steps.
a. Abiotic synthesis of organic molecules such as amino acids occurred in the atmosphere or at hydrothermal vents.
b. Monomers joined together to form polymers at seaside rocks or clay, or at vents; the first polymers could have been proteins or RNA or both.
c. Polymers aggregated inside a plasma membrane to make a protocell that had limited ability to grow; if it developed in the ocean it was a heterotroph, if at a hydrothermal vent, a chemoautotroph.
d. Once the protocell contained DNA genes or RNA molecules, it was a true cell.
Fossils tell a story
A fossil is the remains or traces of past life, usually preserved in sedimentary rock.
Most dead organisms are consumed by scavengers or decompose.
Paleontology is the study of fossils and the history of life, ancient climates, and environments.
Sedimentation has been going on since the Earth was formed; it is an accumulation of particles forming a stratum, a recognizable layer in a stratigraphic sequence laid down on land or in water.
5. The sequence indicates the age of fossils; a stratum is older than the one above it and younger than the one below it.
Relative Dating of Fossils
1. Strata of the same age in England and Russia may have different sediments.
2. However, geologists discovered that strata of the same age contain the same fossils, termed index fossils.
3. Therefore, fossils can be used for the relative dating of strata.
4. A particular species of fossil ammonite is found over a wide range and for a limited time period; therefore, all strata in the world that contain this ammonite are of the same age.
5. However, relative dating does not establish the absolute age of fossils in years.
Absolute Dating of Fossils
1. Absolute dating relies on radioactive dating to determine the actual age of fossils.
2. Radioactive isotopes have a half-life, the time it takes for half of a radioactive isotope to change into a stable element.
3. Carbon 14 (14C) is a radioactive isotope contained within organic matter.
a. Half of the carbon 14 (14C) will change to nitrogen 14 (14N) every 5,730 years.
b. Comparing 14C radioactivity of a fossil to modern organic matter calculates the age of the fossil.
c. After 50,000 years, the 14C radioactivity is so low it cannot be used to measure age accurately.
4. It is possible to determine the ratio of potassium 40 (40K) and argon 40 to date rocks and infer the age of a fossil.
The Precambrian Time
1. Geologists have devised the geological timescale, which divides the history of Earth into eras, and then periods and epochs.
2. Life arose in the Precambrian Era.
a. The Precambrian encompasses 87% of the geologic time scale.
b. Early bacteria probably resembled the archaea that live in hot springs today.
c. 3.8 BYA, the first chemical fingerprints of complex cells occur; at 3.46 BYA, photosynthetic prokaryotic cells appear.
d. Boulders called stromatolites from this early time resemble living stromatolites with cyanobacteria in the outer surface.
e. Oxygen-releasing photosynthesis by cyanobacteria in stromatolites caused the atmosphere to become oxidizing rather than reducing.
f. By 2 BYA, oxygen levels were high enough that anaerobic prokaryotes were declining.
g. Accumulation of O2 caused extinction of anaerobic organisms and the rise of aerobic organisms.
h. O2 forms ozone or O3 in the upper atmosphere, contributing to the ozone shield and blocking ultraviolet radiation from reaching the Earth's surface; this allowed organisms to live on land.
Eukaryotic Cells Arise
a. The eukaryotic cell, which arose 2.1 BYA, is always aerobic and contains a nucleus and organelles.
The Endosymbiotic Hypothesis
The Endosymbiotic Hypothesis states that a nucleated cell englulfed prokaryotes, which then became organelles. Evidence includes:
1) Present-day mitochondria and chloroplasts have a size that lies within the range of that for bacteria.
2) Mitochondria and chloroplasts have their own DNA and make some of their own proteins.
3) Mitochondria and chloroplasts divide by binary fission similar to bacteria.
4) The outer membrane of mitochondria and chloroplasts differ.
Multicellularity Arises
Multicellularity Arises
a. It is not known exactly when multicellular organisms appeared; they would have been microscopic.
b. Separating germ cells from somatic cells may have contributed to the diversity of organisms.
c. Fossils of the Ediacara Hills of South Australia, from about 600-545 MYA, were soft-bodied early invertebrates.
1) These bizarre animals lived on mudflats in shallow marine waters.
2) They lacked internal organs and could have absorbed nutrients from the sea.
The Paleozoic Era
1. The Paleozoic Era lasted over 300 million years and was a very active period with three major mass extinctions.
a. An extinction is the total disappearance of a species or higher taxonomic group.
b. Mass extinction is the disappearance of a large numbers of species or higher groups in a short geological time, just a few million years.
Cambrian Animals
Cambrian Animals
a. The Cambrian Period saw invertebrates flourish; invertebrates lack a vertebral column.
b. Today's invertebrates all trace their ancestry to the Cambrian Period, and possibly earlier.
c. A molecular clock, based on a fixed rate of changes in base pair sequences, allows us to trace backward how long current species have evolved separately.
d. Why fossils are easy to find in the Cambrian but not before is a complex question; most likely the animals evolved earlier but without outer skeletons.
e. Cambrian seafloors were dominated by trilobites, now extinct, that had armored exoskeletons.
f. Perhaps the evolution of exoskeletons was due to the presence of plentiful O2 in the atmosphere.
g. A skeleton may have been due to the increased pressures of predation.
Invasion of Land
Invasion of Land
a. Early in the Ordovician Period, marine algae expanded to freshwater.
b. In the Silurian Period, vascular plants invaded land and later flourished in warm swamps in the Carboniferous Period.
c. Spiders, centipedes, mites and millipedes all preceded the appearance of insects on land.
d. The appearance of wings on insects in the Carboniferous Period allowed insects to radiate into a diverse group.
e. The vertebrate line of descent began in the early Ordovician Period.
f. The Devonian Period is called the Age of Fishes and saw jawless and then jawed fishes, including both cartilaginous and ray-finned fishes.
g. The Carboniferous Period was an age of coal-forming forests with an abundance of club mosses, horsetails, and ferns.
1) It is called the "Age of the Amphibians" because amphibians diversified at this time.
2) Early vascular plants and amphibians were larger and more abundant during the Carboniferous Period; a climate change to colder and drier began the process that produced coal.
The Mesozoic Era
The Mesozoic Era
1. Although there was a mass extinction at the end of the Paleozoic, evolution of some plants and animals continued into the Triassic, the first period of the Mesozoic Era.
2. The Triassic period
a. Gymnosperms flourished, especially cycads; the Triassic and Jurassic are called the "Age of Cycads."
b. One group of reptiles, the therapsids, had the first mammal features.
c. Reptiles, originating in the Permian, underwent adaptive radiation.
3. The Jurassic Period
a. Many dinosaurs flourished in the sea, on land and in air.
b. Controversy surrounds dinosaurs being ectothermic or endothermic.
4. The Cretaceous Period
a. A new Chinese fossil, Jeholodens, reveals an early mammal with a long snout but sprawling reptile-like hind limbs.
b. The era of dinosaurs ended in a mass extinction in which dinosaurs, most reptiles, and many marine organisms perished.
The Cenozoic Era
The Cenozoic Era
1. The Cenozoic Era is divided into the Tertiary and the Quaternary Periods.
2. During the Cenozoic Era, mammals with hair and mammary glands diversified and human evolution began.
3. Mammalian Diversification
a. During the Paleocene Epoch, mammals were small and resembled rats.
b. In the Eocene Epoch, all of the modern orders of mammals had developed.
c. Many of the types of herbivores and carnivores of the Oligocene Epoch are extinct today.
Evolution of Primates
Evolution of Primates
a. Flowering plants were diverse and plentiful by the Cenozoic Era; primates were adapted to living in flowering trees.
b. The first primates were small squirrel-like animals; from them evolved the first monkeys and apes.
c. Apes diversified during the Miocene and Pliocene Epochs; this includes the first hominids, the group that includes humans.
d. During the Tertiary Period, the world's climate cooled with the last two epochs known as the Ice Age.
e. The Pleistocene Epoch saw many large sloths, beavers, wolves, bison, woolly rhinoceroses, mastodons, and mammoths; modern humans arose and may have contributed to extinction.
Factors That Influence Evolution
Continental drift
Plate techtonics
Mass extinctions
Continental Drift
Continental Drift
1. Earth's crust is dynamic, not immobile as was once thought.
2. In 1920, German meteorologist Alfred Wegener presented data from across disciplines supporting continental drift.
3. Continental drift was confirmed in the 1960s; the continents moved with respect to one another.
4. During the Permean Period, the continents were joined to form one supercontinent called Pangaea which later divided into Gondwana and Laurasia and then split to form today's configuration.
5. Continental drift explains why the coastlines of several continents (e.g., the outline of the west coast of Africa and that of the east coast of South America) are mirror images of each other.
6. The same geological structures (e.g., mountain ranges) are found in many areas where continents once touched.
7. Continental drift explains unique distribution patterns of several fossils (e.g., species of the seed fern Glossopteris).
8. Continental drift also explains why some fossils (e.g., reptiles Cynognathus and Lystrosaurus) are found on different continents.
9. Continental drift explains why Australia, South America, and Africa have distinctive mammals; current mammalian biological diversity is the result of isolated evolution on separate continents.
Plate Tectonics
B. Plate Tectonics
1. Plate tectonics is the study of the behavior of the Earth's crust in terms of moving plates that are formed at ocean ridges and destroyed at subduction zones.
2. Ocean ridges are ridges on ocean floors where oceanic crust forms; regions in oceanic crust where molten rock rises and material is added to the ocean floor result in seafloor spreading.
3. Seafloor spreading is the lateral movement of oceanic crust away from ocean ridges due to material added to the ocean floor.
4. Subduction zones are regions where oceanic crust collides with the continental crust, causing the oceanic crust to descend into the mantle where it is melted.
5. Where the ocean floor is at the leading edge of a plate, a deep trench forms bordered by volcanoes or volcanic island chains.
6. Two continents colliding form a mountain range (e.g., the Himalayas are the result of the collision of India and Eurasia).
7. Transform boundaries are regions where two crustal plates meet and scrape past one another resulting in relatively frequent earthquakes.
Mass Extinctions
Mass Extinctions
1. Five mass extinctions occurred at the ends of the Ordovician, Devonian, Permian, Triassic, and Cretaceous periods.
2. Mass extinctions have been attributed to tectonic, oceanic, and climatic changes.
3. Walter and Louis Alvarez proposed that the Cretaceous extinction was due to a bolide (an asteroid that explodes producing meteorites) striking the Earth.
a. A layer of iridium soot has been identified in the Cretaceous clay, the correct strata.
b. A huge crater near the Yucatan is the impact site.
c. The effect would have resembled a worldwide atomic explosion.
4. Continental drift contributed to Ordovician extinction; Gondwanaland arrived at the south pole and glaciers chilled oceans and land until Gondwanaland drifted away from the pole.
5. The Devonian extinction may have been a bolide event; this saw an end to 70% of the marine invertebrates; other possibilities include drifting back toward the south pole.
6. The Permian extinction was very severe; 90% of ocean species and 70% of land species disappeared perhaps due to an excess of carbon dioxide due to a change in ocean circulation due to a lack of polar ice caps.
7. The Triassic extinction has been attributed to meteorite collision with Earth; a crater in Central Quebec may have been the impact site.
. Systematics is a field of biology dedicated to understanding the evolutionary history of life on Earth
2. Taxonomy is the branch of biology concerned with identifying, naming, and classifying organisms.
Linnean Systematics
Linnean Systematics
1. A natural system of classification reflects the evolutionary history of organisms.
2. Naming and identifying organisms began with the Greeks and Romans.
3. In the Middle Ages, organisms were described using long Latin descriptions.
4. John Ray (1627-1705), a British naturalist, argued that each organism should have a set name.
The Binomial System
The Binomial System
1. The number of known organisms expanded greatly in mid eighteenth century due to European travel.
2. Carolus Linnaeus (1707-1778) developed the binomial system to name species.
binomial system of nomenclature naming
The binomial system of nomenclature names organisms using a two part Latin name.
a. First part is the genus; closely related species are assigned to the same genus.
b. Second part is the specific epithet; it usually provides something descriptive about an organism.
c. A scientific name consists of both genus and specific epithet (e.g., Lilium buibiferum and Lilium canadense).
d. Both names are italicized or underlined; the first letter of the genus name is capitalized.
e. The genus can be abbreviated when used with a specific epithet if the full name was given before.
Common names
Common names vary with different languages, lump many species under one name or have various names for the same species, and the same name may refer to different organisms in different regions.
The job of naming all species is far from finished.
a. There are estimated to be between 3 and 30 million species living on earth.
b. Currently, one million species of animals and a half million plant and microorganismic species have been named.
c. Some groups, such as birds, are nearly all known; some insect groups are mostly unknown.
Linnean Classification Categories
1. Aristotle classified life into 14 groups (e.g., mammals, birds, etc.), and subdivided them by size.
2. Ray grouped animals and plants according to how he thought they were related.
3. Linnaeus grouped plants by flower parts; his categories were published in Systema Naturae in 1735
4. Today, taxonomists use seven categories of classification: species, genus, family, order, class, phylum, and kingdom.
a. A higher category, the domain, has recently been added to these seven categories.
b. The higher the category, the more inclusive it is.
c. Members of a kingdom share general characters; members of a species share quite specific characters.
d. Since one taxonomic group exists inside another group, these categories are also termed nested.
A character is any structural, chromosomal, or molecular feature that distinguishes one group from another.
e. Additional levels of classification can be added by adding super , sub , or infra (e.g., suborder); thus, there are more than 30 categories of classification.
Phylogeny i
Phylogeny is the evolutionary history of a group of organisms.
phylogenetic tree
phylogenetic tree indicates common ancestors and lines of descent or lineages.
primitive character
primitive character is a trait that is present in a common ancestor and all members of a group.
derived character
derived character is present only in a specific line of descent
6. Different lineages diverging from a common ancestor have ancestral
characteristics—traits shared by the ancestor and the species in its lines of descent.
7. Because classification is hierarchical, it is possible to use classification categories to contrusct a phylogenetic tree.
8. When we say that two species are related, we mean that they share a common ancestor.
Cladistic systematics
Cladistic systematics is based on the work of Willi Hennig
Cladistics analyze primitive and derived characters and constructs cladograms on the basis of shared derived characters.
A cladogram
A cladogram is a diagram showing relationships among species based on shared, derived characters; a cladogram thus traces the evolutionary history of the group being studied.
Constructing a Cladogram
Constructing a Cladogram
a. First step: construct a table of characters of the taxa being compared.
b. Any character found in the outgroup as well as the ingroup is a shared primitive character.
c. Homologies shared by certain lineages are shared derived characters, or synapomorphies.
d. A clade is an evolutionary branch that includes a common ancestor and all its descendent species.
How to Judge a Cladogram
How to Judge a Cladogram
a. Cladists are guided by the principle of parsimony—the minimum number of assumptions is most logical.
b. The best cladogram is one in which the fewest number of shared derived characters are left unexplained or that minimizes the number of assumed evolutionary changes..
c. This approach is vulnerable if convergent evolution produces what appears to be common ancestry.
d. Statistical phylogenetic is a new branch of systematics that use statistical tools and not parisomy to help construct phylogenetic trees.
e. Reliability of cladograms is dependent on the knowledge and skill of a particular investigator gathering data.
How to Judge a Clade
How to Judge a Clade
a. A Monophyletic group is a grouping of species that includes a common ancestor and all the decendents of that ancestor.
b. A paraphyletic group contains a common ancestor and does not include all the decendents.
c. A polyphyletic group contains some of the descendants of more than one common ancestor and not all the common ancestors.
Tracing Phylogeny
*Fossil Record Data
*morphological data
*Behavioral Data
*Molecular Data
Fossil Record Data
1. Fossil Record Data
a. Because fossils can be dated, fossils can establish the age of a species.
b. It can be difficult to associate fossils with currently living groups; e.g., a new view of turtle fossils could place them closer to crocodiles.
c. The fossil record is often incomplete because soft bodied organisms do not fossilize well.
d. Most organisms decay and the chances of becoming a fossil are low.
Morphological Data
2. Morphological Data
a. Homology is character similarity that stems from having a common ancestor; homology helps indicate when species belong to a related group.
b. Homologous structures are related to each other through common descent but may differ in structure and function (e.g., the forelimbs of a horse and the wings of a bat).
c. Convergent evolution is acquisition of similar traits in distantly related lines of descent as a result of adaptation to similar environmental conditions; convergent evolution may make it difficult to distinguish homologous from analogous structures.
d. Analogous structures have the same function but are not derived from the same organ in a common ancestor (e.g., the wings of an insect and the wings of a bat).
Behavioral Data
Behavioral Data
1. Since many different species may display some common behaviors, this may substantiate the morphological data that some species are related through evolution.
Molecular Data
Molecular Data
1. Speciation occurs when mutations bring about changes in base pair sequences of DNA.
2. Each distinct lineage accumulates changes in DNA base pair sequences and amino acid sequences in proteins over time.
3. Advances in analyzing nucleotide and amino acid sequences make abundant data available to researchers.
4. Protein Comparisons
a. Earlier studies used immunological reactions to antibodies, made by injecting a rabbit with cells of one species, to determine the relatedness of two species.
b. Amino acid sequences are now used to determine the differences in proteins between two species.
1) Cytochrome c is a protein found in all aerobic organisms; the amino acid differences in cytochrome c between chickens and humans is 13 but between chickens and ducks is only 3.
c. Since the number of universal proteins is limited, most new studies use RNA and DNA.
DNA and RNA Comparisons
DNA and RNA Comparisons
a. DNA differences can substantiate data, help trace the course of macroevolution, and fill in the gaps of the fossil record.
e. Mitochondria DNA (mtDNA) mutates ten times faster than nuclear DNA; mtDNA is often used for closely related species; North American songbirds were found to have diverged well before retreating glaciation 250,000-100,000 years ago.
Molecular Clocks
Molecular Clocks
a. Nucleic acid changes are not tied to adaptation; the fairly constant changes provide a molecular clock.
b. Comparison of mtDNA sequences equated a 5.1% nucleic acid difference among songbird species to 2.5 million years.
c. The fossil record can then be used to calibrate the clock and confirm the hypothesis drawn from molecular data.
DNA Bar Coding of Life (Science Focus box)
1. The Consortium for the Barcode of Life (CBOL) believes that any scientist will be able to identify a species using a handheld scanner.
2. According to this Consortium, there will be a database of DNA sequences, and this scanner would tap into the database and identify an organism.
3. Paul Hebert and colleagues at the University of Guelph in Canada believe that it is possible to use the base sequence in DNA to develop a bar code for each living thing.
4. According to Herbert, the gene:
a. Should contain no more than 650 nucleotides so sequencing is easy and with no mistakes
b. Should be easy to extract from an organism's complete genome.
c. Should have mutated to the degree that each species has its own sequence of bases.
5. Herbert's team uses a mitochondrial gene, cytochrome c oxidase subunit I (COI), for a target gene in animals.
6. John Kress from the Smithsonian Institute in Washington, D.C. developed a potential method for bar coding plant species.
The Three-Domain System
1. Recent research suggests one group of prokaryotes is so distantly related it should be in a separate domain.
2. Sequencing of rRNA suggests all organisms evolved along three distinct lineages: domains Bacteria, Archaea, and Eukarya.
Domain Bacteria
3. Domain Bacteria
a. The bacteria are prokaryotic unicellular organisms that reproduce asexually.
b. Cyanobacteria are large photosynthetic prokaryotes.
c. Most bacteria are heterotrophic.
d. Bacteria are important in ecosystems because they break down organic remains, thereby keeping chemical cycling going.
e. Some bacteria are parasitic and cause disease.
Domain Archaea
4. Domain Archaea
a. Like bacteria, archaea are prokaryotic unicellular organisms that reproduce asexually.
b. The archaea live in extreme environments: methanogens in anaerobic swamps, halophiles in salt lakes, and thermoacidophiles in hot acidic environments.
c. The archaea cell wall is diverse but not the same as the bacterial cell wall.
Domain Eukarya
5. Domain Eukarya
a. Eukarytes are unicellular to multicellular organisms, always with a membrane-bound nucleus.
b. Sexual reproduction is common; various types of life cycles are seen.
c. Protists and fungi are eukarytes, as are plants and animals (these kingdoms will be studied in detail in later chapters in the text and in this instructor's manual).
1. are associated with a number of plant, animal, and human diseases;
2. can only reproduce by using the metabolic machinery of the host cell;
3. are noncellular;
4. may have a DNA or RNA genome.
5. In 1884, Pasteur suspected something smaller than bacteria caused rabies; he chose a Latin term for "poison."
6. In 1892, Russian biologist Dimitri Ivanowsky, working with the tobacco mosaic virus, confirmed Pasteur's hypothesis that an infectious agent smaller than a bacterium existed.
7. With the invention of the electron microscope, these infectious agents could be seen for the first time.
Viral Structure
Viral Structure
1. A virus is similar in size to a large protein, generally smaller than 200 nm in diameter.
2. Many viruses can be purified and crystallized, and the crystals stored for long periods of time.
3. Viral crystals become infectious when the viral particles they contain invade host cells.
4. The classification of viruses is based on
a. their type of nucleic acid, including whether they are single stranded or double stranded;
b. their size and shape; and
c. the presence or absence of an outer envelope.
All viruses have at least two parts
5. All viruses have at least two parts:
a. An outer capsid is composed of protein subunits.
b. An inner core contains either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid), but not both.
1) The viral genome at most has several hundred genes; a human cell, in comparison, contains thousands of genes.
2) The viral envelope is usually partly host plasma membrane with viral glycoprotein spikes.
3) Viral particles have proteins, especially enzymes (e.g., polymerases), to produce viral DNA or RNA.
4) Not all viruses have an envelope; such viruses are called naked viruses.
C. Parasitic Nature
Viruses are obligate intracellular parasites
Viruses are obligate intracellular parasites that cannot multiply outside a living cell; they must infect a living cell in order to reproduce.
a. Animal viruses in laboratories are raised in live chick embryos or in cell tissue culture.
b. Viruses infect all sorts of cells, from bacteria to human cells, but they are host specific.
1) The tobacco mosaic virus only infects certain plants.
2) The rabies virus infects only mammals.
3) The AIDS virus, HIV, infects only certain human blood cells.
4) The Hepatitis virus invades only liver tissues.
5) The Polio virus only reproduces in spinal nerve cells.
Prokaryotes include the bacteria and archaea.
1. Bacteria were discovered in the seventeenth century when Antonie van Leeuwenhoek examined scrapings from his teeth.
2. The "little animals" Leeuwenhoek observed were thought by him and others to arise spontaneously from inanimate matter.
3. Around 1850, Pasteur devised an experiment showing that the bacteria present in air contaminated the media.
4. A single spoonful of soil contains 1010 prokaryotes; these are the most numerous life forms.
Structure of Prokaryotes
1. Prokaryotes range in size from 1-10 µm in length and from 0.7-1.5 µm in width.
2. "Prokaryote" means "before a nucleus"—their cells lack a eukaryotic nucleus.
3. Prokaryotic fossils date back as far as 3.5—3.8 billion years ago.
4. Fossils indicate prokaryotes were alone on earth for 2 billion years; they evolved very diverse metabolic capabilities.
5. Prokaryotes adapted to most environments because they differ in the many ways they acquire and utilize energy.
6. Outside the plasma membrane of most cells is a rigid cell wall that keeps the cell from bursting or collapsing due to osmotic changes by peptidoglycan, a complex molecule containing a unique amino disaccharide and peptide fragments.
a. The cell wall may be surrounded by an organized capsule called a glycocalyx and/or by a loose gelatinous sheath called a slime layer.
b. In parasitic forms, these outer coverings protect the cell from host defenses.
7. Some prokaryotes move by means of flagella.
a. The flagellum has a filament composed of three strands of the protein flagellin wound in a helix and inserted into a hook that is anchored by a basal body.
b. The flagellum is capable of 360o rotation which causes the cell to spin and move forward.
8. Many prokaryotes adhere to surfaces by means of fimbriae.
a. Fimbriae are short hairlike filaments extending from the surface.
b. The fimbriae of Neisseria gonorrhoeae allow it to attach to host cells and cause gonorrhea.
Prokaryotic cells lack the membranous organelles of eukaryotic cells.
10. Various metabolic pathways are located on the plasma membrane.
A nucleoid is a dense area in prokaryotes where the chromosome is located; it is a single circular strand of DNA.
Plasmids are accessory rings of DNA found in some prokaryotes; they can be extracted and used as vectors to carry foreign DNA into bacteria during genetic engineering procedures.
Protein synthesis in prokaryotic cells
Protein synthesis in prokaryotic cells is carried out by thousands of ribosomes, which are smaller than eukaryotic ribosomes.
Reproduction in Prokaryotes
Reproduction in Prokaryotes
1. Binary fission is the splitting of a parent cell into two daughter cells; it is asexual reproduction in prokaryotes.
a. A single circular chromosome replicates; the two copies separate as the cell enlarges.
b. Newly formed plasma membrane and the cell wall separate the cell into two cells.
c. Mitosis, which involves formation of a spindle apparatus, does not occur in prokaryotes.
d. Because prokaryotes have a short generation time, mutations are generated and distributed through a population more rapidly.
e. Prokaryotes are haploid; mutations are therefore immediately subjected to natural selection.
In bacteria, genetic recombination can occur in three ways.
a. Conjugation occurs when a bacterium passes DNA to a second bacterium through a tube (sex pilus) that temporarily joins two cells; this occurs only between bacteria in the same or closely related species.
b. Transformation involves bacteria taking up free pieces of DNA secreted by live bacteria or released by dead bacteria.
c. In transduction, bacteriophages transfer portions of bacterial DNA from one cell to another.
d. Plasmids can carry genes for resistance to antibiotics and transfer them between bacteria by any of these processes.
The Bacteria
A. Characteristics of Bacterial Cells
1. Bacteria are the more common type of prokaryote
2. Bacterial cell walls are protected by peptidoglycan, a complex of polysaccharides linked by amino acids.
The Gram stain procedure (developed in the late 1880s by Hans Christian Gram) differentiates bacteria.
a. Gram positive bacteria stain purple, whereas Gram negative bacteria stain pink.
b. This difference is dependent on the thick or thin (respectively) peptidoglycan cell wall.
Bacteria and archaea have three basic shapes.
a. A spirillum is spiral shaped.
b. A bacillus is an elongated or rod shaped bacteria.
c. Coccus bacteria are spherical.
d. Cocci and bacilli tend to form clusters and chains of a length typical of the particular species.
Autotrophic Bacteria
Autotrophic Bacteria
a. Photoautotrophs
b. Chemoautotrophs
Photoautotrophs are photosynthetic and use light energy to assemble the organic molecules they require.
1) Primitive photosynthesizing bacteria (e.g., green sulfur bacteria and purple sulfur bacteria) use only photosystem I that contains bacteriochlorophyll; they do not give off O2 because hydrogen sulfide (H2S) is used as an electron and H+ donor instead of H2O.
2) Advanced photosynthesizing bacteria (e.g., cyanobacteria) use both photosystem I and II that contain the same types of chlorophylls found in plants; they do give off O2 because H2O is used as an electron and H+ donor.
Chemoautotrophs make organic molecules by using energy derived from the oxidation of inorganic compounds in the environment.
1) Deep ocean hydrothermal vents provide H2S to form chemosynthetic bacteria.
2) The methanogens are chemosynthetic bacteria that produce methane (CH4) from hydrogen gas and CO2; ATP synthesis and CO2 reduction are linked to this reaction and methanogens can decompose animal wastes to produce electricity as an ecological friendly energy source.
3) Nitrifying bacteria oxidize ammonia (NH3) to nitrites (NO2) and nitrites to nitrates (NO3).
Heterotrophic Bacteria
Heterotrophic Bacteria
a. Most free living bacteria are chemoheterotrophs that take in pre-formed organic nutrients.
b. As aerobic saprotrophs, there is probably no natural organic molecule that cannot be broken down by some prokaryotic species.
c. Bacteria produce chemicals including ethyl alcohol, acetic acid, butyl alcohol, and acetones.
d. Bacteria action produces butter, cheese, sauerkraut, rubber, cotton, silk, coffee and cocoa.
e. Antibiotics are produced by some bacteria.
Symbiotic Relationships
1. Bacteria and archaea form symbiotic relationshipa, forming relationships with members of other species; forms of symbiosis include mutualistic, commensalistic, and parasitic relationships.
Commensalism occurs when one population modifies the environment in such a way that a second population benefits. Commensalistic bacteria live in or on organisms of other species and cause them no harm.
Mutualistic bacteria that live in the intestines of humans benefit from undigested material and release vitamins K and B12, which we use to produce blood components.
Parasitic bacteria are responsible for a wide variety of infectious plant, animal and human diseases.
Parasitic bacteria that cause disease are called pathogens.
Some bacteria form resistant endospores in response to unfavorable environmental conditions.
1) Some cytoplasm and the chromosome dehydrate and are encased by three heavy, protective spore coats.
2) The rest of the bacterial cell deteriorates and the endospore is released.
3) Endospores survive in the harshest of environments: desert heat and dehydration, boiling temperatures, polar ice, and extreme ultraviolet radiation.
4) Endospores also survive very long periods of time; anthrax spores 1,300 years old can cause disease.
5) When environmental conditions are again suitable, the endospore absorbs water and grows out of its spore coat.
6) In a few hours, newly emerged cells become typical bacteria capable of reproducing by binary fission.
7) Endospore formation is not reproduction--it is a means of survival and dispersal to new locations.
Pathogens may be able to produce a toxin, and or adhere to surfaces and sometimes invade organs or cells.
1) Toxins
2) In almost all cases, the growth of the bacteria does not cause disease but instead the toxins they release cause the disease. Example: Clostridium tetani, the causative agent of tetanus.
3) Adhesion factors allow a pathogen to bind to certain cells, which determines which tissue in the body will be the host. Example: Shigella dysentariae releases a toxin and also sticks to the intestinal wall, making it a life-threatening form of dysentary.
4) Antibacterial compounds either inhibit cell wall synthesis or protein biosynthesis; increasingly, many pathogenic bacteria are becoming resistant to bacteria.
1) Toxins are small organic molecules, or small pieces of protein or parts of the bacterial cell wall, that are released when bacteria die.
1. Cyanobacteria are Gram negative bacteria with a number of unusual traits.
2. They photosynthesize in the same manner as plants, and thus are responsible for introducing O2 into the primitive atmosphere.
3. They were formerly mistaken for eukaryotes and classified with algae.
4. Cyanobacteria have pigments that mask chlorophyll; they are not only blue green but also red, yellow, brown, or black.
5. They are relatively large (1-50 µm in width).
6. They can be unicellular, colonial, or filamentous.
7. Some move by gliding or oscillating.
8. Some possess heterocysts, thick walled cells without a nucleoid, where nitrogen fixation occurs.
9. Cyanobacteria are common in fresh water, soil, on moist surfaces, and in harsh habitats (e.g., hot springs).
10. Some species are symbiotic with other organisms (e.g., liverworts, ferns, and corals).
11. Lichens are a symbiotic relationship where the cyanobacteria provide organic nutrients to the fungus and the fungus protects and supplies inorganic nutrients.
12. Cyanobacteria were probably the first colonizers of land during evolution.
13. Cyanobacteria "bloom" when nitrates and phosphates are released as wastes into water; when they die off, decomposing bacteria use up the oxygen and cause fish kills.
Archaea are prokaryotes with molecular characteristics that distinguish them from bacteria and eukaryotes; their rRNA base sequence is different from that in bacteria.
2. Because archaea and some bacteria are both found in extreme environments (hot springs, thermal vents, salt basins), they may have diverged from a common ancestor.
3. Later, the eukarya split from the archaea; archaea and eukarya share some ribosomal proteins not found in bacteria; initiate transcription in the same manner, and have similar types of tRNAs.
Structure of Archaea
Structure of Archaea
1. Archaea have unusual lipids in their plasma membranes that allow them to function at high temperatures: glycerol linked to hydrocarbons rather than fatty acids.
2. Cell walls of archaea do not contain the peptidoglycan found in bacterial cell walls.
Types of Archaea
Types of Archaea
1. Methanogens live under anaerobic environments (e.g., marshes) where they produce methane.
a. Methane is produced from hydrogen gas and carbon dioxide and is coupled to formation of ATP.
b. Methane released to the atmosphere contributes to the greenhouse effect.
c. About 65% of the methane found in our atmosphere is produced by methanogenic archaea.
2. Halophiles require high salt concentrations (e.g., Great Salt Lake).
a. Their proteins have unique chloride pumps that use halorhodopsin to synthesize ATP in the presence of light.
b. They usually require 12-15% salt concentrations; the ocean is only 3.5% salt.
3. Thermoacidophiles live under hot, acidic environments (e.g., geysers).
a. They survive best at temperatures above 80oC; some survive above boiling temperatures.
b. Metabolism of sulfides forms acidic sulfates; these bacteria grow best at pH of 1 to 2.
General Biology of Protists
A. Protists are classified in the domain Eukarya (they have eukaryotic cells) and the kingdom Protista.
The endosymbiotic hypothesis
1. The endosymbiotic hypothesis suggests how the eukaryotic cells arose.
a. It proposes that aerobic bacteria became mitochondria.
b. Cyanobacteria became chloroplasts after being taken up by eukaryotic cells.
c. Giardia lamblia has two nuclei but no mitochondria, suggesting that a nucleated cell preceded the acquisition of mitochondria.
protists are unicellular
2. Although many protists are unicellular, they are highly complex.
a. Amoeboids and ciliates possess unique organelles, such as contractile vacuoles.
Biology of Protists
3. Most protists are free-living; some are parasitic, some (e.g., slime molds) are saprophytic (feed on decaying plant material), and some are mixotrophic (combining autotrophic and heterotrophic nutrition modes).
4. Some protists are photoautotrophic; some are heterotrophic.
5. Most protists use asexual reproduction, but sexual reproduction occurs in some species.
a. Formation of spores allows free-living and parasitic protists to survive hostile environments.
b. A cyst is a dormant cell with a resistant outer covering; the cyst allows a free-living species to overwinter and helps certain parasitic species survive the host's digestive juices.
6. Some protists are of great medical importance because they cause disease; others are ecologically important.
7. Aquatic plankton serve as food for heterotrophic protists and animals.
8. Photosynthetic plankton produce much of the oxygen in the atmosphere.
9. Many protists enter symbiotic relationships; coral reefs rely on symbiotic photosynthetic protists.
Evolution and Diversity of Protists
Evolution and Diversity of Protists
1. Classification of protests has been based on modes of nutrition.
a. Algae are autotrophic, similar to land plants
b. Protozoans and slime molds are heterotrophic by ingestion, similar to animals
c. Water molds are heterotrophic by absorption, similar to fungi
2. Protozoans include photosynthetic, heterotrophic, and mixotrophic organisms and have some form of locomotion (flagella, pseudopods, cilia).
3. Currently, the most widely accepted method of categorizing protests is by assigning them to supergroups, which is a major eukarotic group. There are six protist supergroups.
Evoluation and Characteristics of Fungi
Evoluation and Characteristics of Fungi
1. The 80,000 species of the Kingdom Fungi are mostly multicellular eukaryotes that share a common mode of nutrition.
2. Like animals, fungi are heterotrophic and consume preformed organic matter.
3. Animals, however, are heterotrophic by ingestion while fungi are heterotrophic by absorption.
4. Fungal cells secrete digestive enzymes; following breakdown of molecules, the nutrients are absorbed.
5. Most fungi are saprotrophic decomposers, breaking down wastes or remains of plants and animals.
Evolution of Fungi
Evolution of Fungi
1. Fungi include club fungi, sac fungi, AM fungi, zygospore fungi, and chytrids.
2. Chytrids are unlike all the other fungi because they are aquatic and and they have flagellated spores and gamets.
3. The AM fungi only exist as mycchorizae in association with plant roots.
4. Molecular data shows that animals and fungi share a common ancestor after plants evolved.
5. The earliest fossil of fungi is dated 450 MYA.
Structure of Fungi
Structure of Fungi
1. Fungi can be unicellular (e.g., yeasts).
2. Most fungi are multicellular in structure.
a. The thallus (body) of most fungi is called a mycelium.
b. A mycelium is a network of hyphae comprising the vegetative body of a fungus.
c. Hyphae are filaments that provide a large surface area and aid absorption of nutrients.
d. When a fungus reproduces, a portion of the mycelium becomes a reproductive structure.
fungi made of chitin
Fungal cells lack chloroplasts and have a cell wall made of chitin, not cellulose.
a. Chitin, like cellulose, is a polymer of glucose molecules organized into microfibrils.
b. In chitin, unlike cellulose, each glucose has an attached nitrogen containing amino group.
energy reserve of fungi
The energy reserve of fungi is not starch, but glycogen, as in animals.
5. Except for aquatic chytrids, fungi are nonmotile; their cells lack basal bodies and do not have flagella at any stage in their life.
6. Fungi move to a food source by growing toward it; hyphae can grow up to a kilometer a day.
7. Nonseptate fungi lack septa, or cross walls, in their hyphae; nonseptate hyphae are multinucleated.
8. Septate fungi have cross walls in their hyphae; pores allow cytoplasm and organelles to pass freely.
9. The septa that separate reproductive cells, however, are complete in all fungal groups.
Reproduction of Fungi
Reproduction of Fungi
1. In general, fungal sexual reproduction involves the following:
haploid hyphae → dikaryotic stage → diploid zygote
↑-------------←-------- meiosis----←-----------↓
2. During sexual reproduction, haploid hyphae from two different mating types fuse.
3. If nuclei do not fuse immediately, the resulting hypha is dikaryotic (contains paired haploid nuclei,
n + n).
a. In some species, nuclei pair but do not fuse for days, months, or even years.
b. The nuclei continue to divide in such a way that every cell has at least one of each type of nucleus.
4. When the nuclei fuse, the resulting zygote undergoes meiotic cell division leading to spore formation.
5. Fungal spores germinate directly into haploid hyphae without embryological development.
6. Fungal Spore Formation
a. Spores are an adaptation to life on land and ensure that the species will be dispersed to new locations.
b. A spore is a reproductive cell that can grow directly into a new organism.
c. Fungi produce spores both during sexual and asexual reproduction.
d. Although nonmotile, the spores are readily dispersed by wind.
7. Asexual reproduction can occur by three mechanisms:
a. Production of spores by a single mycelium is the most common mechanism.
b. Fragmentation is when a portion of a mycelium becomes separated and begins a life of its own.
c. Budding is typical of yeasts; a small cell forms and gets pinched off as it grows to full size.
Lichens are a symbiotic association between a fungus and a cyanobacterium or a green alga.
2. The body of a lichen is composed of three layers:
a. a thin, tough upper layer and a loosely packed lower layer that shield the photosynthetic cells in the middle layer.
3. Special fungal hyphae penetrate or envelope the photosynthetic cells and transfer nutrients directly to the rest of the fungus.
4. Lichens can reproduce asexually by releasing fragments that contain hyphae and an algal cell.
Lichen parasitism
This association was considered mutualistic, but experimentation suggests a controlled parasitism by the fungus of the alga.
a. The algae grow faster when they are alone rather than when they are part of a lichen.
b. On the other hand, it is difficult to cultivate the fungus, which does not grow naturally alone.
c. Different lichen species are identified based on the fungal partner.
Lichen 3 kinds
Three types of lichens are recognized.
a. Compact crustose lichens are often seen on bare rocks or tree bark.
b. Foliose lichens are leaflike.
c. Fruticose lichens are shrublike.
Lichen biology
Lichens are efficient at acquiring nutrients; they survive with low moisture, temperature, or poor soil.
8. Lichens may live in extreme environments and on bare rocks; they help form soil.
9. Lichens also take up pollutants and cannot survive where the air is polluted.
1. Mycorrhizae are mutualistic relationships between soil fungi and roots of most plants.
2. The fungus enters the cortex of roots but does not enter the cytoplasm of plant cells.
3. Ectomycorrhizae, such as AM fungi, form a mantle that is exterior to the root, growing between cell walls.
4. It helps the roots absorb more minerals; in turn, the plant passes on carbohydrates to the fungus.
5. The truffle lives in association with oak and beech tree roots; it can be inoculated with the fungus.
6. The fossil record indicates that the earliest plants had mycorrhizae associated with them; mycorrhizae helped plants adapt to and flourish on land.
The Green Algal Ancestor of Plants
The Green Algal Ancestor of Plants
1. Plants are multicellular photosynthetic eukaryotes, whose evolution is marked by adaptations to a land existence.
2. Living on land requires adaptations, primarily dealing with the threat of desiccation.
3. The most successful land plants are those that protect all phases of reproduction from drying out and have an efficient means of dispersing offspring on land.
4. To conserve water, the land plant body is covered by a waxy cuticle that is impervious to water while still allowing carbon dioxide to enter so photosynthesis can continue.
5. In many plants, roots absorb water from the soil, and vascular system transports water in the body of the land plant.
6. Flowering plants have evolved in a way that employs animals to assist with reproduction and seed dispersal.
The Ancestry of Plants
The Ancestry of Plants
1. Plants are believed to have evolved from a freshwater green algal ancestor over 450 million years ago.
a. Both utilize chlorophylls a and b and various accessory pigments.
b. In both, the food reserve is starch.
c. The cell walls of both contains cellulose.
d. DNA base codes for rRNA suggest plants are most closely related to green algae known as charophytes.
The two group of charophytes
The two group of charophytes (Carales and Coleochate) have several features that would have promoted the evolution of multicellular land plants:
a. Cellulose cell walls of charophytes and land plant lineage are laid down by the same unique type of cellulose synthesizing compexes. The cell walls of both types of organisms are similar.
b. In charophytes, apical cells produce cells that allow their filaments to increase in length. At the notes other cells can divide asymmetrically to produce reproductive structures. Land plants have apical tissue that produces specialized tissues that add to or develop into new organs.
c. Plasmodesmata between cells provide a means of communication between neighboring cells and may have played a role in the evolution of specialized tissues in land plants.
d. A placenta (designed cells) transfers nutrients from haploid cells of the previous generation to the diploid zygote. Both charophytes and land plants retain and care for the zygote.
Alternation of Generations Life Cycle
Alternation of Generations Life Cycle
1. Land plants have a two generation life cycle called alternation of generations.
a. Embryophyta is an alternate name for the land plant clade since the 2n embryo are retained and protect the embryo from drying out.
b. The sporophyte is a diploid (2n) generation producing haploid spores by meiotic cell division. Spores have a wall that contains sporopollenin, a molecules that prevents drying out.
c. The gametophyte is a haploid (n) generation producing haploid gametes by mitotic division. A male gametangium is called an antheridium, and a female gametangium is called an archegonium.
d. In the plant life cycle, a spore undergoes mitosis and becomes a gametophyte.
d. Note that meiosis produces haploid spores.
e. Mitosis occurs as a spore becomes a gametophyte, and also as a zygote becomes a sporophyte.
f. The charophytes have a haploid life cycle. The zygote undergoes meiosis, and only four zoospores are produced per zygote.
gametophyte or sporophyte-is dominant.
Plants differ in which generation-gametophyte or sporophyte-is dominant.
a. In nonvascular plants, the gametophyte is dominant.
b. In the vascular groups, the sporophyte is dominant.
c. The shift to sporophyte dominance is an adaptation to life on land.
d. As the sporophyte gains dominance, the gametophyte becomes microscopic and dependent on the sporophyte.
Other Derived Traits of Land Plants
Other Derived Traits of Land Plants
1. Leaves and stems are covered by a waxy cuticle that holds in water but limits gas exchange; the thickness of the cuticle varies among different species of plants.
2. Leaves and some other tissues have openings (stomata) that regulate gas and water exchange.
3. Apical tissue has the ability to produce complex tissues and organs.
Evolution of Animals
Evolution of Animals
1. Members of the kingdom Animalia are multicellular heterotrophs that ingest their food.
2. Animals have the diploid life cycle, and usually reproduce sexually.
3. Muscle and nerve tissues characterize animals.
a. The evolution of these tissues enabled many types of animals search actively for their food and prey on other organisms.
4. Animals are monophyletic - meaning both invertebrates and vertebrates can trace their ancestry to the same ancestor.
5. Adult vertebrates have a spinal cord (or backbone), while invertebrates do not have a backbone.
Ancestry of Animals
Ancestry of Animals
1. The colonial flagellate hypothesis states that animals are descended from an ancestor that resembled a hollow spherical colony of flagellated cells.
2. The colonial flagellate hypothesis implies that radial symmetry preceded bilateral symmetry in the history of animals.
a. In a radially symmetrical animal, any longitudinal cut produces two identical halves.
b. In a bilaterally symmetrical animal, only one longitudinal cut yields two identical halves.
3. The choanoflagellates (collared flagellates) most likely resemble the last unicellular ancestor of living animals, and molecular data illustrates that they are the closest living relatives of animals.
4. A choanoflagellate is a single cell, 3-10 μm in diameter, with a flagellum surrounded by a collar of 30-40 microvilli.
5. As the water moves through the microvilli, they engulf bacteria and debris from the water.
Evolution of Body Plans
Evolution of Body Plans
1. As an animal develops, there are many possibilities regarding the number, position, size, and patterns of its body parts.
2. Slight shifts in genes called Hox (homeotic) genes are responsible for the major differences between animals that airse during development.
a. Maybe the changes in the expression of Hox developmental genes explans why all the animals groups of today had representations of the Cambrian seas
The Phylogenetic Tree of Animals
The Phylogenetic Tree of Animals
1. The phylogenetic tree of animals is based on molecular and morphological data.
2. It is assumed that the more closely related two organisms, the more rRNA nucleotide sequences they will have in common.
3. Molecular data have resulted in a phylogenetic tree that is quite different from the one based only on morphological characteristics.
Morphological Data animals
Morphological Data
1. Types of Symmetry
a. Asymmetry means there is no particular body shape (e.g., sponge).
b. Radial symmetry describes body parts arranged around an axis, like spokes of a wheel (e.g., starfish).
1) Radially symmetrical animals may be sessile (i.e., attached to a substrate or less motile).
2) This symmetry enables an animal to reach out in all directions from one center.
Bilateral symmetry
Bilateral symmetry describes a body having a right and left, or complementary halves.
1) Only one longitudinal cut down the center produces mirror halves.
2) Bilaterally symmetrical animals tend to be active and to move forward at an anterior end.
3) The development of a head to localize the brain and sensory organs at the anterior end is called cephalization.
Embryonic Development
Embryonic Development
a. The first three tissue layers are called germ layers because they give rise to the organs and organ systems of complex animals.
b. Animals (e.g. cnidarians) that have two tissues layers (ectoderm and endoderm) as embryos are diploblastic with the tissue level of organization.
c. Animals that develop further and have all three tissue layers (ectoderm, mesoderm, and endoderm) as embryos are triploblastic and have the organ level of organization.
1) Animals that have three tissue layers are either protostomes or deuterostomes.
d. Protostomes exhibit the following events during embryological development.
1) Spiral cleavage, in which the cells divide without an increase in size.
2) The fate of the cells is fixed - each contributes to development in only one particular way.
3) The blastopore is associated with the mouth.
4) A coelom forms by splitting of the mesoderm, which has arisen from cells near the blastopore.
Deuterostomes exhibit the following events during embryological development.
1) Radial cleavage, where the new daughter cells sit atop the previous cells; the fate of these cells is indeterminate.
2) The blastopore is associated with the anus; the mouth appears later.
3) A coelom forms by the fusion of mesodermal pouches from the primitive gut.
Protostomes are divided into two groups:
1) Ecdysozoans include roundworms and arthropods.
a. Both of these animals molt; they shed their outer covering as they grow.
2) Lophotrochozoa contains two groups
a. Lophophores have the same type of feeding apparatus.
b. Trochophores either have presently or their ancestors had a trochophore larva.
The Chordates
The Chordates
1. Chordates (phylum Chordata) are deuterostomes, and have an internal skeleton, with mucles attached to the outer surface.
At some time during their life, all chordates have four basic characteristics.
At some time during their life, all chordates have four basic characteristics.
a. Notochord
1) This supporting rod is located dorsally just below the nerve cord.
2) It provides support and is replaced by the vertebral column in vertebrates.
b. Dorsal Tubular Nerve Cord
1) This cord contains a fluid filled canal.
2) In vertebrates, this is the spinal cord and it is protected by vertebrae.
c. Pharyngeal Pouches
1) These openings function in feeding, gas exchange, or both.
2) They are seen only during embryonic development in most vertebrates.
3) In invertebrate chordates, fish, and amphibian larvae, they become functioning gills.
4) In terrestrial vertebrates, the pouches are modified for various purposes.
5) In humans, the first pair of pouches become the auditory tubes, the second become tonsils, and the third and fourth pairs become the thymus and parathyroid glands.
d. A postanal tail extends beyond the anus; in some, this only appear in embryos.
Nonvertebrate Chordates
Nonvertebrate Chordates
1. Lancelets
a. Lancelets are in the group cephalochords.
b. Lancelets are named are named for their resemblance to a lancet - a two edged surgical knife.
c. They inhabit shallow coastal waters; they filter feed partly buried in sandy substrates.
d. They feed on microscopic particles filtered from a constant stream of water that enters the mouth and exits through gill slits into an atrium that opens at the atriopore.
e. Lancelets retain the four chordate characteristics as adults.
f. The notochord extends from head to tail, accounting for their group name cephalochordates.
g. They possess segmented muscles and the dorsal hollow nerve cord has periodic branches.
2. Sea Squirts
a. Sea squirts belong in thr group urochordates.
b. Adults have a body composed of an outer tunic; an excurrent siphon squirts out water when it is disturbed.
c. The larvae are bilaterally symmetrical and have the four chordate characteristics.
d. The larvae undergo metamorphosis to develop into sessile adults.
e. Water passes into a pharynx and out numerous gill slits, the only chordate characteristic that remains in adults.
f. If the larvae became sexually mature without developing tunicate characteristics, the urochordate larva may have been ancestral to vertebrates.
Vertebrates features
1. As embryos, vertebrates have the four chordate characteristics.
2. Vertebrates also have these features:
a. Vertebral colum
1) The embryonic notochord is replaced by a vertebral column.
2) Remnants of the notochord are seen in the intervertebral disks.
3) The vertebral column is part of a flexible, strong endoskeleton that is also evidence of segmentation.
b. Skull
1) A skull is an anterior component of the main axis of vertebrate endoskeleton; it encases the brain.
2) The high degree of cephalization in vertebrates is accompanied by complex sense organs.
3) The eyes developed as outgrowths of the brain.
4) The ears—equilibrium devices in water—function as sound wave receivers in land vertebrates.
c. Endoskeleton
1) The endoskeleton and muscles together permit rapid and efficient movement.
2) The pectoral and pelvic fins of fish evolved into jointed appendages allowing vertebrates to move onto land.
d. Internal organs
1) Vertebrates possess a complete digestive system and a large coelom.
2) The circulatory system is closed and the blood is contained within blood vessels.
3) Gills or lungs provide efficient gas exchange.
4) The kidneys efficiently excrete nitrogenous waste and regulate water.
5) Reproduction is usually sexual with separate sexes.
Vertebrate Evolution
Vertebrate Evolution
1. Chordates (including vertebrates) appeared at the start of the Cambrian period.
2. The earliest vertebrates were fishes; most of which have jaws.
3. Jawed fish and other vertebrates are gnathostomes - animals with jaws.
4. Fish also had a bony skeleton, lungs, and fleshy fins, which were preadaptive for a land existence.
5. Amphibians are the first vertebrates to live on land and to have four limbs (tetrapods).
6. Amphibians are not fully adapted to living on land because they still have to reproduce in an aquatic environment.
7. Reptiles are fully adapted to living on land because they produce an amniotic egg.
8. Amniotes develop within an aquatic environment but of their own making.
9. In placental mammals, the fertilized egg develops inside the female, where it is surrounded by an amniotic membrane.
10. Another feature for living on land includes watertight skin, and can be seen in reptiles and mammals.
The Fishes
The Fishes
A. Jawless Fishes of w/jaws
1. Small, jawless, and finless ostracoderms are the earliest vertebrate fossils.
2. Today's jawless fishes, or agnathans have a cartilaginous skeleton and persistent notochord
3. They have smooth nonscaly skin.
4. They have cylindrical bodies and are up to a meter long.
5. Many lampreys are filter feeders similar to their ancestors.
6. Parasitic lampreys have a round muscular mouth equipped with teeth; they attach themselves to fish and suck nutrients from the host's circulatory system.
7. Marine parasitic lampreys entered the Great Lakes and devastated the trout population in the 1950s.
Fishes with Jaws
Fishes with Jaws
1. Fishes with jaws have:
a. Ectothermy - they depend on the environment to regulate their body temperature.
b. Gills are used for gas exchange.
1) Jawed fish have a single-looped, closed circulatory pathway with a heart that pumps the blood first to the gills (for oxygen exchange) and then to the rest of the body.
c. Cartilaginous or bony skeleton - the endoskeleton of jawed fishes include vertebral column, skull with jaws, and paired pectoral or pelvic fins.
1) Jaws evolved from the first pair of gill arches of agnathans; the second pair of arches became support structures for the jaws.
d. Scales cover and protect the fish skin.
2. Placoderms are extinct jawed fishes of the Devonian Period.
a. They were armored with heavy plates and had strong jaws.
b. Like extant fishes, they had paired pectoral and pelvic fins.
c. Paired fins allow a fish to balance and maneuver well in water; this helps predation.
Cartilaginous Fishes
Cartilaginous Fishes
1. Sharks, rays, skates, and chimaeras are marine cartilaginous fishs (chondrichthyes).
2. They have a cartilaginous skeleton rather than bone.
3. Five to seven gill slits are on both sides of the pharynx; they lack the gill covers found on bony fish.
4. They have many openings to the gill chamber located behind the eys called spiracles.
5. Their body is covered with dermal denticles.
6. The teeth of sharks are enlarged scales; there are many rows of replacement teeth growing behind the front teeth.
7. They have three well developed senses to detect electric currents in water, pressure (a lateral line system), and smell.
8. The largest sharks are filter feeders, not predators; the basking and whale sharks eat tons of crustacea.
9. Most sharks are fast, open sea predators; a great white shark eats dolphins, sea lions and seals.
10. Rays and skates live on the ocean floor; their pectoral fins are enlarged into winglike fins and they swim slowly.
11. Stingrays have a venomous spine.
12. Electric rays feed on fish that have been stunned with an electric shock that may reach over 300 volts.
13. Sawfish rays have a large anterior "saw" that they use to slash through schools of fish.
14. Chimaeras (ratfishes) live in cold marine waters and are known for their unusal shape and iridescent colors.
Bony Fishes
Bony Fishes
1. There are about 25,000 species of bony fishes (osteichthyes).
2. Bony fishes have a skeleton of bone; most are ray finned with thin, bony rays supporting the fins.
3. The gills of bony fishes do not open separately but instead are covered by an operculum.
4. The swim bladder is a gas filled sac whose pressure can be altered to regulate buoyancy and depth.
5. Bony fish have a single-loop, closed cardiovascular system.
6. They have a well-developed nervous system.
7. Fish sperm and eggs are usually shed into water.
8. For most fish, the fertilization and embryonic development occur outside the female's body.
9. The lobe finned fishes include six species of lungfishes and two species of coelacanth.
a. Their fleshy fins are supported by central bones.
b. Lungfishes have lungs and gills for gas exchange.
c. Lungfishes and lobe-finned fishes are grouped together as sarcopterygii.
d. Lungfishes live in stagnant fresh water or in ponds that dry up annually; they are found in Africa, South America, and Australia.
e. Coelacanths live in deep oceans; once considered extinct, more than 200 have been captured since 1938.
The Amphibians
The Amphibians
1. Today's amphibians are tetrapods; they have four limbs.
a. The skeleton is well-developed for locomotion.
2. Amphibians have smooth and nonscaly skin.
a. The moist skin plays an active role in water balance, respiration, and temperature regulation.
3. Amphibians usually have small lungs supplemented by gas exchange across porous skin.
4. The single loop circulatory path of fish is replaced by a closed double loop circulatory system; however oxygen-rich blood mixes with some oxygen-poor blood.
a. A three chambered heart with a single ventricle pumps mixed blood before and after it has gone to the lungs.
Amphibians bio
Amphibians have sense organs that are adapted to life on land.
a. The brain is larger than that of fishes; their cerebral cortex is more developed.
b. A specialized tongue is used for catching prey.
c. The eyelids keep their eyes moist.
d. Amphibian ears are adapted for detecting sound waves; in turn, the larynx produces sounds.
6. Amphibians are ectothermic, depending upon the environment to regulate body temperature.
a. If winter temperature drops too low, temperate ectotherms become inactive and enter torpor.
7. Amphibians return to the water to reproduce.
a. They shed eggs into the water for external fertilization.
b. Generally, amphibian eggs are protected by a coat of jelly but not by a shell.
c. The young hatch into aquatic larvae with gills (tadpoles).
d. The aquatic larvae usually undergo metamorphosis to develop into a terrestrial adult.
e. Some amphibians evolved mechanisms that allow them to bypass the aquatic larval stage and produce on land.The lobe finned fishes of Devonian are ancestral to amphibians.
Evolution of Amphibians
Evolution of Amphibians
1. Amphibians evolved from the lobe-finned fishes with lungs by way of transitional forms.
2. Two hypotheses describe evolution of amphibians from lobe finned fishes.
a. Lobe finned fishes that could move from pond to pond had an advantage over those that could not.
b. The supply of food on land and the absence of predators promoted adaptation to land.
3. Paleontologists found a fossil, Tiktallik roseae, from the late Devonian period in Arctic Canada that represents an intermediate between lobe-finned fishes and tetrapods with limbs.
Diversity of Living Amphibians
Diversity of Living Amphibians
1. Modern amphibians include three groups: salamanders and newts, frogs and toads, and caecilians.
2. Salamanders and newts have a long body and tail, and two pairs of legs
3. Their S-shaped locomotion is similar to fish movements.
4. Salamanders and newts are carnivorous, feeding on insects, snails, etc.
5. Salamanders practice internal fertilization; the males produce a spermatophore that females pick up with the cloaca (the common receptacle for the urinary, genital, and digestive canals).
6. Frogs and toads are tailless as adults; the hind limbs are specialized for jumping.
7. Some skin glands secrete poisons; those tropical species often have brilliant warning coloration.
8. Frogs and toads have the head and trunk fused; frogs live near or in fresh water while toads live in damp places away from water.
9. Caecilians are legless; most burrow in soil and feed on worms, etc.
The Reptiles
The Reptiles
1. Reptiles (class Reptilia) are a successful group of terrestrial animals.
2. Reptiles have many characteristics showing that they are fully adapted to living on land.
a. Reptiles have paired limbs and are adapted for climbing, running, paddling, or flying.
b. Reptiles have a thick, scaly skin that is impermeable to water.
1) Reptile's protective skin prevents water loss but it also requires several molts a year.
c. Reptile have efficient breathing - their lungs are more developed than in amphibians; air rhythmically moves in and out of the lungs due to an expandable rib cage.
d. Reptiles have efficient circulation - The heart prevents mixing of blood. Oxygen-rich blood is more fully separated from oxygen-poor blood.
e. Reptiles are ectothermic.
1) They require a fraction of the food per body weight of birds and mammals.
2) They are behaviorally adapted to warm their body temperature by sunbathing.
f. Reptiles have well-adapted reproduction.
1) The sexes are separate and fertilization is internal.
2) The amniotic egg contains extraembryonic membranes.
3) Extraembryonic membranes are not a part of the embryo and are disposed of after development.
4) They protect the embryo, remove nitrogenous wastes, and provide oxygen, food, and water.
5) The amnion is one extraembryonic membrane; it fills with fluid to provide a "pond" for embryo to develop.
Evolution of Amniotes
A. Evolution of Amniotes
1. The amniotes consist of three lineages:
a. The turtles, in which the skul has no openings behind the orbit - eye socket.
b. All the other repites, in which the skull has two openings behind the orbit
c. The mammals, in which the skull has one opening behind the orbit.
2. The reptiles have no common ancestor; they are a paraphyletic group and not a monophyletic group.
3. Other reptiles are diapsids have a skull with two openings behind the eyes.
4. Thecodonts are diapsids that gave rise to the ichthyosaurs, which returned to the aquatic environment, and the pterosaurs, which were terrestrial.
a. The pterosaurs of the Jurassic period had a keel for attachment of flight muscles and air spaces in bones to reduce weight.
b. The thecodonts gave rise to the crocodiles and dinosaurs.
Dinosaurs varied in size and behavior; some had a bipedal stance and gave rise to birds.
6. Dinosaurs dominated earth for about 170 million years; then most died out at the end of the Cretaceous period.
7. One theory of mass extinction:
a. A large meteorite or comet at the end of the Cretaceous Period could have set off earthquakes and fires, raising enough dust and smoke to block out the sun.
b. An iridium layer, a mineral common in meteorites, occurs in rocks at the end of this period.
Diversity of Living Reptiles
Diversity of Living Reptiles
a. Most reptiles today live in the tropics or subtropics; lizards and snakes live on soil; turtles, crocodiles and alligators live in water.
b. Turtles have a heavy shell fused to the ribs and to the thoracic vertebrae.
1) Turtles lack teeth but use a sharp beak.
2) Sea turtles must return to lay eggs onshore.
c. Lizards have four clawed legs and are carnivorous.
1) Marine iguanas on the Galapagos are adapted to spend long times in the sea.
2) Chameleons live in trees, have a long sticky tongue to catch insects, and change color.
3) Geckos are nocturnal and have adhesive pads on their toes.
4) Skinks have reduced limbs and shiny scales.
d. Snakes evolved from lizards and lost legs as an adaptation to burrowing.
1) Their jaws can readily dislocate to engulf large food.
2) A tongue collects airborne molecules to transfer them to Jacobson's organ for tasting.
3) Some snakes are poisonous and have special fangs to inject venom.
4) Snakes have internal ears that can detect low-frequency sounds and vibrations.
e. Tuataras are lizardlike animals found in New Zealand.
1) They possess a well-developed "third eye," which is light sensitive and buried beneath the skin in the upper part of the head.
2) They are the only member of an ancient group of reptiles that incuded the common ancestor of modern lizards and snakes.
f. Crocodiles and alligators are largely aquatic, feeding on fishes and other animals.
1) Their powerful jaws have numerous teeth; a muscular tail is both a paddle to swim and a weapon.
2) Male crocodiles bellow to attract mates; males of some species protect the eggs and young.
B. Birds
1. Birds share a common ancestor with crocodilians and have scales (feathers are modified scales), a tail with vertebrae, and clawed feed.
2. Feathers keep birds warm, and help birds fly and steer.
a. Feathers are modified scales.
b. Birds molt and replace their feathers annually.
3. Birds have a modified skeleton.
a. The collarbone and fused and sternum has a keel.
b. Other bones are fused to make the skeleton more rigid than the reptilian skeleton.
c. The breast muscles are attached to the keel.
Birds have modified respiration.
4. Birds have modified respiration.
a. Bird respiratory air sacs are extensive, even extending into some larger bones.
1) Using a one way flow of air, air sacs maximize gas exchange and oxygenation of blood.
2) Efficient supply of oxygen to muscles is vital for the level of muscle activity needed for flight.
5. Brids are endothermic; they have the ability to maintain a constant, relatively high body temperature.
6. Birds have well-developed sense organs and nervous system.
a. Birds have very acute vision.
b. Birds muscle reflexes are excellent.
c. Bird migration allows use of widespread food sources; an enlarged portion of the brain is responsible for instinctive behaviors.
Diversity of Living Birds
7. Diversity of Living Birds
a. Most birds can fly; some, however are flightless.
b. Bird classification is based on beak and foot types, and some on habitats and behaviors.
1) Birds of prey have notched beaks and sharp talons.
2) Shorebirds have long slender bills and long legs.
3) Waterfowl have webbed toes and broad bills.
Vertebrates and Human Medicine (Science Focus box)
Vertebrates and Human Medicine (Science Focus box)
1. There are many pharmaceutical products that come from vertebrates.
a. The venom of the Thailand cobra is the source of Immunokine, which has been used for ten years in multiple sclerosis patients.
b. ABT-594 from the poison dart frog is about 50 times more powerful than morphine without the addictive properties.
2. Animal pharming uses genetically altered vertebrates (mice, sheep, goats, cows, chickens, pigs) to produce medically useful pharmaceutical products.
a. The human gene for some useful product is inserted into the embryo of the vertebrate.
b. That embryo is implanted into a foster mother, which gives birth to the transgenic animal.
3. Xenotransplantation is the transplantation of nonhuman vertebrate tissues and organs into humans.
a. The use of transgenic vertebrates for medical purposes raises many health and ethical concerns.
The Mammals
The Mammals
1. The following characteristics distinguish mammals:
a. Hair
1) Hair provides insulation against heat loss.
2) Hair color can provide camouflage to blend into its surroundings.
3) Hair can serve sensory functions.
b. Mammary glands
1) Mammary glands enable females to feed young without deserting them to obtain food.
2) Nursing creates a bond between mother and offspring to ensure parental care while the young are helpless.
c. Skeleton
1) The mammal skull is bigger than reptiles', their teeth are differentiated into molars and premolars, and the vertebral column provides more movement.
d. Internal organs
1) Gas exchange is efficiently accomplished by lungs.
2) Mammals possess a four chambered heart and a double loop circulatory system.
3) Kidneys are adapted to conserving water.
4) The nervous system and sensory organs are highly developed.
e. Internal development
1) In most mammals, the young are born alive after a period of development in uterus.
Evolution of Mammals
Evolution of Mammals
1. Mammals evolved during the Mesozoic Era from mammal-like synapsids.
2. True mammals appeared during the Triassic period, about the same time as the first dinosaurs.
a. The first mammals were small, about the size of mice.
b. Some of the earliest mammalian groups were monotremes and marsupials.
c. Placental mammals evolved later to occupy habitats vacated by dinosaurs.
3. Monotremes
a. Monotremes are mammals that have a cloaca and lay hard shelled amniote eggs.
b. They are represented by the duckbill platypus and two species of the spiny anteaters.
c. A female duckbill platypus lays her eggs in a burrow in the ground where she incubates them.
d. After hatching, the young lick milk seeping from modified sweat glands on the abdomen.
e. The spiny anteater has a pouch formed by swollen mammary glands and muscle; the egg moves from cloaca to pouch and hatches; the young remain for 53 days and live in the burrow where the mother feeds them.
4. Marsupials
a. Marsupials begin development inside the mother's body but are then born in a very immature state.
b. The newborns crawl up into a pouch on their mother's abdomen.
c. Inside a pouch they attach to the nipples of the mother's mammary glands and continue to develop.
d. Today, most marsupials are found in Australia where they underwent adaptive radiation for several million years without competition from the placental mammals, only introduced recently.
Placental Mammals
Placental Mammals
a. Developing placental mammals are dependent on a placenta, an organ of exchange between maternal and fetal blood.
b. The placenta supplies nutrients to and removes wastes from the blood of developing offspring.
c. A placenta also allows a mother to move about while the offspring develop.
d. The placenta enables young to be born in a relatively advanced stage of development.
e. Placental mammals are very active animals; they possess acute senses and a relatively large brain.
f. The brains of placental animals have cerebral hemispheres proportionately larger than other animals.
g. The young go through a long period of dependency on their parents after birth.
h. Most are terrestrial, but some are aquatic, and bats can fly.
The main types of placental animals are:
a. Ungulates are hoofed animals, which make up about 1/3 of all living an extinct mammal groups.
1) They have a reduced number of toes and divided according to wheather an odd or even number of toes remain.
2) They have elongated limbs adapted for running across open grassland.
3) They are herbivorous and have large grinding teeth.
Carnivores are meat eaters with large and conical-shaped canine teeth.
1) Aquatic carnivores such as seals and sea lions must return to land to reproduce.
Primates tree-dwelling fruit eaters.
1) Their digits have nails, not claws; the thumb is more opposable.
2) Primates, particularly humans, have well developed brains.
d. Cetaceas are marine whales and dolphins.
1) They lack substantial hair or fur.
2) Baleen whales that strain plankton from the water.
3) Toothed whales feed on fish and squid.
e. Chiroptera are nocturnal flying bats.
1) Wings are layers of skin and connective tissue stretched between the elongated bones of all fingers but the first.
2) Many species use echolocation to locate their usual insect prey.
3) Some bats also eat birds, fish, frogs and plant tissues.
f. Rodents are most often small plant eaters.
1) Rodents have incisors that grow continuously.
g. Probiscideans are the herbivorous elephants.
1) They are the largest living land mammals.
2) The upper lip and nose have become elongated and muscularized to form a trunk.
Lagomorphans are rabbits, hares and pikas.
1) They resemble rodents but have two pairs of continuously growing incisors.
2) Their hind legs are longer than their front legs and they are herbivores.
Insectivores includes the shrews and moles, mammals with short snouts that live underground.
1) Insectivores were thought to be most like the original placentas. However, recent analysis suggests that the edentates (anteaters) and the pangolins (scaly anteaters) are the more primitive groups of placentals.
scope of Ecology
1. Ecology is the study of the interactions of organisms with other organisms and with the physical environment.
2. Ecology studies how environmental factors determine the distribution and abundance of populations.
3. Ecology and evolution are related because ecological interactions are natural selection pressures that have long term effects.
4. A habitat is the place where an organism exists
5. A population is a group of the same species occupying a certain area
6. A community consists of all populations at one locale (e.g., a coral reef population).
7. An ecosystem contains the community organisms and abiotic factors (e.g., energy flow, chemical cycling).
The biosphere
8. The biosphere is the layer on the earth where living organisms can live
Modern ecology
9. Modern ecology is both descriptive and predictive, with applications to wildlife management, agriculture, and many other problems
Demographics of Populations
Demographics of Populations
• Demography is the statistical study of a population, e.g., its density, distribution, rate of growth.
Density and Distribution
. Density and Distribution
1. The population density is the number of individuals per unit area.
2. The population distribution is the pattern of dispersal of individuals across an area.
3. Resources are nonliving and living components of an environment that support living organisms.
Limiting factors
4. Limiting factors are those environmental aspects that particularly determine where an organism lives.
a. Such factors include oxygen supply, light availability, space, temperature, and precipitation amounts.
5. Distribution can be due to biotic (living) factors.
a. Biotic factors can be illustrated by red kangaroos that are limited to inland Australia by the grasses that grow there.
6. Clumped, random, and uniform are terms used to describe patterns of distribution.
a. In certain cases, the pattern of distribution can change as the organisms under consideration mature; thus, distribution patterns are not necessarily constant.
7. Other factors, such as territoriality, seed dispersal, etc., can influence distribution patterns.
Population Growth
B. Population Growth
1. The rate of natural increase (r) is dependent on the number of individuals born every year and the number of individuals that die every year. (It is assumed that immigration and emigration are equal and are thus not considered.)
Biotic potential
2. The highest possible rate of natural increase for a population when resources are unlimited is called its biotic potential, and it depends on the following:
a. Usual number of offspring per reproduction
b. Chances of survival until age of reproduction
c. How often each individual reproduces
d. Age at which reproduction begins
3. Mortality Patterns
a. A cohort is all members of a population born at the same time.
b. Survivorship is the probability of newborn individuals of a cohort surviving to particular ages.
survivorship curve
c. A survivorship curve, obtained by plotting the number of individuals surviving at each age, is characteristic of each species.
1) In the Type I survivorship curve, most individuals live out their life span and die of old age (e.g., humans in well-developed countries).
2) In the Type II survivorship curve, individuals die at a constant rate across their lifespan (e.g., birds, rodents, and perennial plants).
3) In the Type III survivorship curve, most individuals die early in life (e.g., fishes, invertebrates, and plants).
Age Distribution
4. Age Distribution
a. A population contains three age groups: prereproductive, reproductive, and postreproductive.
age structure diagrams
b. Because populations differ according to what proportion of the population falls into each group, three different age structure diagrams are possible; an age structure diagram is a representation of the number of individuals in each age group in a population
*4) Information obtained from these graphs is used to determine past and future history of a population.
pyramid shape diagram
1) A pyramid shape indicates the population has high birthrates; the population is undergoing exponential growth.
bell shape diagram
2) A bell shape indicates that prereproductive and reproductive age groups are more nearly equal, with the postreproductive group being smallest due to mortality; this is characteristic of stable populations.
urn shaped diagram
3) An urn shaped diagram indicates the postreproductive group is largest and the prereproductive group is smallest, a result of the birthrate falling below the death rate; this is characteristic of declining populations.
Population Growth Models
1. There are two patterns of population growth.
a. In a pattern called semelparity, organisms reproduce once and cease to grow as adults; they expend energy in reproduction and then die.
b. In a pattern called iteroparity, organisms reproduce throughout their lifetime, which invests energy in their future survival.
Some organisms do not exactly fit these two patterns.
a. Aphids can switch between sexual and asexual reproduction according to the season.
b. Annual plants can reproduce both by seeds and by vegetative extensions.
Exponential Growth
Exponential Growth
1. The J shaped growth curve depicts exponential growth, and it has two phases.
a. In the lag phase, growth is slow because the population is small.
b. In the exponential growth phase, growth is accelerating.
2. A mathematical equation can be used to calculate the exponential growth and size for any population that has discrete generations.
3. With exponential growth, the number of individuals added each generation increases as the total number of females increases.
4. For exponential growth to continue unchecked, each member of the population has to have unlimited resources.
5. As the population increases in size so do the effects of competition between members, predation, parasites, and disease.
Logistic Growth
Logistic Growth
1. When growth encounters environmental resistance, populations experience logistic growth, and the growth curve has a characteristic sigmoidal or S shaped curve.
2. In addition to the lag phase and exponential growth phase, there is a deceleration phase where the rate of population growth slows, and a stable equilibrium phase with little if any growth, because births equal deaths.
3. This curve is called "logistic" because the exponential portion of the curve would plot as a straight line as log of N.
4. A mathematical equation calculates logistic growth.
5. Environmental resistance results in the deceleration phase and the stable equilibrium phase; population is at the carrying capacity of the environment.
Carrying Capacity
a. The carrying capacity (K) is the maximum number of individuals of a species that can be supported by the environment.
b. The closer population size gets to the carrying capacity, the greater is the environmental resistance.
c. When N is small, a large portion of the carrying capacity has not been utilized, but as N approaches K, population growth slows because K N is nearing zero.
d. For example, over-fishing drives a population into the lag phase.
e. It is best to maintain desirable populations in the exponential phase of the logistic growth curve.
f. Farmers can reduce the carrying capacity for a pest by alternating rows of different crops.
Regulation of Population Size
1. The J shaped and S shaped growth curve models do not always predict real populations.
a. In the winter moth, many eggs did not survive the winter and exponential growth did not occur.
b. The growth curve of a reindeer herd introduced to St. Paul Island in Alaska overshot its carrying capacity and crashed.
Factors That Regulate Population Growth
1. Some populations are considered to be regulated primarily by density independent factors; these are also considered abiotic factors.
a. The number of organisms present does not affect the influence of the factor.
b. The damage to a population from, for example, a flash flood does not change with or depend on the number of organisms present.
c. Thus, density independent factors show no correlation with the size of the population.
Populations regulated by density dependent factor
Populations regulated by density dependent factors are affected by the number of organisms present.
a. Predation, parasitism, and competition are considered density dependent; the more these organisms crowd together, the more damaging are the food shortages, the parasites, and the predators.
b. Thus, density dependent factors have some effect relative to the size of the population.
Other considerations
a. Intrinsic factors (e.g., anatomy, physiology, behavior) can also influence population size: territoriality, recruitment, immigration and emigration.
b. Populations can sometimes show extreme fluctuations in size and growth rates in spite of extrinsic and intrinsic regulating mechanisms—such wild fluctuations with no recurring pattern are termed chaos.
Life History Patterns
Life History Patterns
1. Populations vary on particulars such as:
a. Fecundity - the number of births per reproduction
b. Maturity - the age of reproduction
c. Parity - the number of episodes of reproductions
The logistic population model predicts two main life history patterns.
The logistic population model predicts two main life history patterns.
1. r Selection
a. Species that underwent selection to maximize their rate of natural increase are categorized as r selected.
b. These populations are often opportunistic species, and tend to be colonizers.
c. Their strategy for continued existence is based on individuals having the following traits:
1) small size,
2) short life span,
3) mature fast,
4) produce many offspring, and
5) engage in little care of offspring.
d. Such organisms rely on rapid dispersal to new unoccupied environments.
K Selection
2. K Selection
a. Species that hold their populations fairly constant near the carrying capacity are called K selected.
b. Such populations are equilibrium species; they are strong competitors, tend to be specialists rather than colonizers, and may become extinct when their evolved way of life is disrupted (e.g., the grizzly bear, Florida panther, etc.).
c. Their overall strategy for continued existence is based on having the following traits:
1) large size,
2) long life span,
3) slow to mature,
4) produce few offspring, and
5) expend considerable energy in care.
3. Most populations cannot be characterized as either r or K strategists; they have intermediate characteristics.
When a Population Grows Too Large (Ecology focus box)
When a Population Grows Too Large (Ecology focus box)
1. About 100 years ago the white-tailed deer population across the eastern United States was less than 500,000, and now, it is over 200 million deer.
2. The increase in population size can be attributed to the lack of predators.
a. Hunting is tightly controlled, or banned altogether.
b. Natural predators such as wolves and mountain lions are absent from most regions.
3. In areas where the deer populations have become too large, the deer suffer from starvation as they deplete their own food supply.
4. The large deer population also causes economic loss due to loss of agriculture, forestry, and even insurance claims due to deer-vehicle collisions.
5. Deer overpopulation also harms other species.
a. In areas where there are many deer, there are fewer understory plants.
b. The number of songbirds, insects, squirrels, mice, and other animals declines with an increasing deer population.
6. Some states are working on effective deer management plans.
a. Texas landowners can set aside a portion of their property for a deer herd, and in return, can charge people for the opportunity to hunt on their land.
Human Population Growth
Human Population Growth
1. The human population is now in an exponential part of a J shaped growth curve.
2. World population increases the equivalent of one medium sized city (216,000) per day and 79 million per year.
3. The doubling time is the length of time for a population size to double, now 53 years.
4. Zero population growth is when the birthrate equals the death rate and the population size remains steady.
5. The world population may level off at 8, 10.5 or 14.2 billion, depending on the decline in net reproductive rate.
More Developed Versus Less Developed Countries
More Developed Versus Less Developed Countries
1. The more developed countries underwent a demographic transition from 1950-1975; their growth rate is now low.
a. The more developed countries (MDCs) (e.g., Europe, North America, Japan, etc.) have low population growth and people enjoy a good standard of living.
b. Less developed countries (LDCs) (e.g., countries in Africa, Asia, and Latin America) are those in which population growth is expanding rapidly and the majority of people live in poverty.
c. LDC growth rate peaked at 2.5% between 1960-1965; it has been declining slowly to about 1.6%.
d. Demographic transition is a decline in death rate followed by declining birthrate; it results in slower growth, about 0.1%.
2. The less developed countries (LDCs) are now undergoing demographic transition.
3. Most of the explosive growth will occur in Africa, Asia and Latin America unless
a. family planning or birth control are strengthened,
b. the desire for more children is reduced, and
c. the onset of childbearing is delayed.
Age Distributions
Age Distributions
1. Age structure diagrams divide populations into: dependency, reproductive, and postreproductive.
2. Replacement reproduction, or each couple having just two children, will still cause population growth to continue due to the age structure of the population.
3. Mere replacement does not produce zero population growth (no increase in population) because more women enter reproductive years than leave them.
4. The LDCs have a higher growth rate because of a youthful age structure and more women entering reproductive ages than leaving.
5. The MDCs have a low growth rate because of a stabilized age structure.
Population Growth and Environmental Impact
C. Population Growth and Environmental Impact
1. Environmental Impact (E.I.)
a. Both the growing populations of LDCs and the high consumption of MDCs stress the environment.
b. An average American family, in terms of consumption and waste production, is equal to thirty people in India.
c. MDCs account for one-fourth the world population but provide 90% of the hazardous waste production.
d. Resource consumption affects the cycling of chemicals and contributes to pollution and extinction of species.
e. Conservation biology seeks sustainable practices to prevent mass extinction of species.
A community is a group
• A community is a group of populations that interact with one another in the same environment.
1. Communities vary in size and may have boundaries that are difficult to determine.
2. A fallen log supports a community but a passing bird can eat one of its members.
3. A forest may appear distinct but it gradually fades into the surrounding areas.
Community Structure
Community Structure
1. The species richness of a community is a listing of the species within a community; it does not reveal the relative abundance of organisms.
a. For example, a coniferous forest has a different composition from a tropical rain forest in species of plants and animals.
Species diversity of a community
Species diversity of a community includes not only a listing of the species in the community, but also the abundance of each species.
a. The greater the diversity, the greater the number and the more even the distribution of the species.
b. A forest with 36 poplar trees and 41 American elms is more diverse than a forest with 76 poplar trees but only one American elm.
Community Interactions
1. A habitat is where an organism lives and reproduces in the environment.
ecological niche
2. The ecological niche is the role an organism plays in its community, including its habitat and its interactions with other organisms.
a. The fundamental niche is the range of conditions under which it can survive and reproduce.
b. The realized niche is the set of conditions under which it exists in nature
Generalist species
3. Generalist species (e.g., raccoons, roaches, humans) have a broad range of niches.
a. They have a survival advantage when environmental conditions are apt to change.
Specialist species
4. Specialist species (e.g., pandas, spotted owls, freshwater dolphins) have a narrow range of niches.
a. They have a survival advantage in stable environments
Competition occurs when different species utilize a resource (e.g., light, nutrient) that is in limited supply.
6. If the resource is not in limited supply, there is no competition.
Lotka and Volterra (1920s)
Lotka and Volterra (1920s) developed a formula: competition favors one species and can eliminate the other.
8. Gause grew two species of Paramecium in one test tube; only one survived if they were grown together.
Competitive exclusion principle
Competitive exclusion principle: no two species can indefinitely occupy the same niche at the same time.
10. Over time, either one population replaces the other or the two species evolve to occupy different niches.
11. If it appears two species occupy the same niche, there must be slight differences; Gause found two species of paramecium coexisted if one fed on bacteria at the bottom of the tube and the other fed on suspended bacteria.
Resource partitioning
Resource partitioning occurs when species shift niches; they no longer directly compete.
a. Three species of Galapagos Island finches have three sizes of beaks for small, medium, and large seeds.
b. When species live on separate islands, their beak sizes are diversified; this is character displacement.
character displacement.
Five species of warblers in the same tree spent time in different tree zones to avoid competition; they had different niches.
d. Swallows, swifts, and martins fly in mixed flocks eating aerial insects but have different nesting sites, etc.
e. The above examples are deduced from already completed partitioning.
Joseph Connell
Joseph Connell studied the competition occurring in barnacles that consistently shift to match shoreline tidal zones.
1) By removing the larger Balanus barnacles from the lower zone, the smaller barnacles easily moved in.
2) The smaller barnacle is more resistant to drying out; but the larger one can overgrow it.
Predator Prey Interactions
Predator Prey Interactions
1. Predation occurs when one organism (predator) feeds on another (prey).
2. In a broad sense, it includes not only single predator prey kills, but also filter feeding whales that strain krill, parasitic ticks that suck blood, and even herbivorous deer that eat leaves.
Predator Prey Population Dynamics
Predator Prey Population Dynamics
a. Some predators reduce the densities of their prey.
1) When Gause reared the protozoans Paramecium caudatum and Didinium nasutum together in culture, Didinium ate all the Paramecium and then died of starvation.
2) When prickly-pear cactus was introduced to Australia from South America, it spread wildly without competition on the desert; a natural predator moth from South America was introduced and the cactus and moth populations plummeted dramatically.
Natural predator prey relationships
Natural predator prey relationships allow persistent populations of both predator and prey populations, though both may fluctuate over time.
1) Often a graph of predator prey population densities shows regular peaks and valleys with the predator population lagging slightly behind the prey; two reasons are possible.
a) The biotic potential of the predator may be great enough to overconsume the prey; the prey population declines and the predator population then follows.
b) Or the biotic potential of the prey is unable to keep pace and the prey population overshoots the carrying capacity and suffers a crash.
The Classic Case of the Snowshoe Hare and the Canadian Lynx
The Classic Case of the Snowshoe Hare and the Canadian Lynx
a. Careful records of pelts of both animals for over a century have demonstrated regular fluctuations.
b. To test whether the lynx or hare food supply was causing the cycling, three experiments were done.
1) A hare population was given a constant supply of food and predators were excluded; the cycling ceased.
2) The hare populations were given a constant food supply but predators were not excluded; the cycling continued.
3) Predators were then excluded but no extra food was added; the cycling continued.
c. The interpretation of these results is that both a hare food cycle and a predator hare cycle combine to produce the overall effect.
d. The grouse population also cycle, perhaps because the lynx switches to grouse when the hare populations decline; thus predators and prey do not normally exist as simple two species systems.
Prey Defenses
Prey Defenses
1. Prey have evolved a variety of antipredator defenses.
2. Plant adaptations for discouraging predation include:
a. Sharp spines,
b. Tough leathery leaves,
c. Poisonous chemicals in their tissues, and
d. chemicals that act as hormone analogues to interfere with insect larval development.
3. Animals have defenses that include:
a. Camouflage for concealment; this also requires behavior (stillness),
b. Cryptic coloration to blend into the surroundings,
c. Fright of the predator,
d. Warning coloration,
e. Vigilance and association with other prey for better warning.
1. Mimicry occurs if one species (the mimic) resembles another species (the model) possessing an antipredator defense.
2. Batesian mimicry, named for Henry Bates, is a form of mimicry in which one species that lacks defense mimics another that has successful defenses.
3. Müllerian mimicry, named for Fritz Müller, is where several different species with the protective defenses mimic one another (e.g., stinging insects all share same black and yellow color bands).
Symbiotic Relationships
Symbiotic Relationships
1. Symbiosis is a close relationship between members of two populations.
a. Parasitism is similar to predation; the parasite derives nourishment from the host.
b. Viruses are always parasitic; parasites occur in all kingdoms of life.
c. Endoparasites are small and live inside the host.
d. Ectoparasites are larger and remain attached to the body of hosts by specialized organs or appendages.
e. Many parasites have two hosts.
1) The primary host is the main source of nutrition.
2) The secondary host may serve to transport (vector) the parasite to other hosts.
f. Parasites are specific and require certain species as hosts.
a. In commensalism, one species benefits and the other is neither harmed nor benefitted.
b. It is difficult to determine true commensalism because it is difficult to ensure that the host is not harmed.
Commensalism Examples
Barnacles secure a home by attaching themselves to the backs of whales and the shells of horseshoe crabs.
d. Remora fish attach themselves to the bellies of sharks, securing a free ride and the remains of the shark's meals.
e. Epiphytes (Spanish moss) grow in the branches of trees to receive light but take no nourishment from the tree.
f. Clownfish live within the tentacles of sea anemones for protection.
true commensalism.
Some relationships are so loose that it is difficult to know if they are true commensalism.
1) Cattle egrets feed near cattle because the egrets flush insects as they graze.
2) Baboons and antelopes forage together for added protection.
a. In mutualism, both species benefit.
b. Mutualism can be found among organisms in all kingdoms of life.
Mutualism Examples
Examples include the following:
1) Bacteria in the human intestinal tract are provided with some of our food but also provide us with vitamins.
2) Termites can only feed on wood because their gut contains the protozoa that digest cellulose.
3) Mycorrhizae are symbiotic associations between the roots of fungal hyphae and plants.
4) Flowers and insect pollinators represent a shift from insects eating pollen to eating nectar.
5) Lichens are made of algae that produce food and fungi that preserve water, although the algae can survive alone.
Classic Example of the Ant and the Acacia Tree
Classic Example of the Ant and the Acacia Tree
1) In tropical America, the bullhorn acacia provides a home for ants in its hollow thorns.
2) The acacia also provides ants with food from its nectaries, and protein in nodules called Beltian bodies.
3) In return, the ant protects the plant from herbivores and other plants that might shade it.
4) When ants on an experimental tree were killed with insecticide, the tree also died.
Cleaning Symbiosis
Cleaning Symbiosis
1) Crustacea, fish, and birds act as cleaners to a variety of vertebrate clients; this is called cleaning symbiosis.
2) Large fish in coral reefs line up at cleaning stations and wait their turn to be cleaned by small fish.
3) The possibility of feeding on host tissues as well as on ectoparasites complicates this case of mutualism.
Interactions and Coevolution (Ecology focus box)
Interactions and Coevolution (Ecology focus box)
1. Coevolution occurs when two species adapt in response to selective pressure imposed by the other.
2. Symbiotic associations are especially prone to the process of coevolution.
a. An example of coevolution is between flowers and their pollinators. Flowers pollinated by animals have features that attract them.
b. Another example of coevolution occurs between predators and prey.
1) Cheetahs print forward to catch prey, and gazelles that are fast enough avoid capture. Over generations, a fast running speed may put selective pressure on the predator for an adaptation to the prey's defense mechanism.
c. Coevolution can also take form as the relationship between parasite and host.
1) When snails of the genus Succinea are parasitized by worms of the genus Leucochloridium, they are eaten by birds. As worm matures, they invade the snail's eyestalks, making them resemble edible caterpillars. The birds then eat the snails, and the parasites release their eggs.
Island Biogeography Pertains to Biodiversity (Science focus box)
Island Biogeography Pertains to Biodiversity (Science focus box)
1. Robert MacArthur and E. O. Wilson developed the general theory of island biogeography.
2. Nearby islands have more species because immigration is easier.
3. Larger islands have more species because a large island has more resources.
4. "Islands" can also include patches of forest surrounded by cropland, housing developments, etc.
a. The spatial heterogeneity model describes the patchiness of an environment.
b. The greater the number of habitat patches, the greater the diversity.
5. Stratification is an increase in vertical living spaces; a tree canopy provides a high rise habitat and vertical patchiness.
6. An equilibrium point is reached when the rate of species immigration matches the rate of species extinction.
7. An equilibrium point can be dynamic with many species arriving and departing, or steady unless disturbed.
Community Development
Community Development
• Communities change over both short and long intervals of time due to continental drift, glaciation, etc.
Ecological Succession
Ecological Succession
1. Ecological succession is a change involving a series of species replacements in a community following a disturbance.
Primary succession
Primary succession begins in a habitat lacking soil; this might occur following a volcanic eruption.
Secondary succession
Secondary succession begins when soil is already present but it has been disturbed and returns to a natural state, as in an abandoned cornfield.
a. In the first years, wild grasses and other pioneer species (plants that are invaders of disturbed areas) invade.
b. Soon sedges and shrubs invade.
c. Later, there is a mixture of shrubs and trees.
Clements proposed In 1916
In 1916, Clements proposed the climax pattern model of succession: that succession leads to a climax community that is characteristic for an area.
A climax community has a community composition that depends on climate.
A climax community has a community composition that depends on climate.
1) Dry climates eventually produce deserts.
2) Wet climates proceed to forests.
3) Intermediate moisture will result in grasslands, shrubs, etc.
4) Soils will also influence the developing community.
facilitation model
Each stage facilitates the occurrence of the next stage (called the facilitation model).
1) Shrubs cannot grow on dunes until the dune grass has developed the soil.
2) Therefore the grass shrub forest must occur sequentially.
The inhibition mode
The inhibition model challenged Clements's view of succession.
a. Colonists hold onto their space and inhibit the growth of other plants until the colonists die.
b. Death releases resources that allow different, longer lived species to invade.
The tolerance model provides yet another view of succession.
The tolerance model provides yet another view of succession.
a. Sheer chance may determine which seeds arrive first; in this case, the successional stages may merely reflect the maturation time.
b. Trees merely take more time to develop; however, both facilitation and inhibition of growth may be taking place.
7. All models are probably involved and succession may not often reach the same final potential natural community.
Dynamics of an Ecosystem
Dynamics of an Ecosystem
• In an ecosystem, populations interact among themselves and with the physical environment.
1. Autotrophs capture energy (e.g., sunlight) and use it, along with inorganic nutrients, to produce organic compounds; therefore they are also called producers.
2. Photosynthetic organisms possess chlorophyll and carry on photosynthesis.
a. Algae are the main producers in freshwater and marine environments.
b. Green plants are the main land photosynthesizers.
3. Chemoautotrophs are bacteria that obtain energy from the oxidation of inorganic compounds such as ammonia, nitrites, and sulfides; they synthesize carbohydrates and are found in cave communities and ocean depths.
1. Heterotrophs need a source of preformed organic nutrients and consume tissues of other organisms; they are called consumers.
2. Herbivores are animals that feed directly on green plants.
3. Carnivores are animals that eat other animals.
4. Omnivores can feed upon a variety of organisms, including plants and animals; humans are omnivores.
Decomposers are nonphotosynthetic bacteria and fungi that extract energy from dead matter, including animal wastes in the soil, and make nutrients available.
Some animals (e.g., earthworms) feed on detritus 3/4 the decomposing products of organisms—these organisms are called detritivores
Energy Flow and Chemical Cycling
Energy Flow and Chemical Cycling
1. All ecosystems are dependent upon solar energy flow and finite pools of nutrients.
2. Most ecosystems cannot exist without a continual supply of solar energy.
two fundamental laws of thermodynamics:
Energy flow in an ecosystem is a consequence of two fundamental laws of thermodynamics:
a. The first law of thermodynamics states energy can neither be created nor destroyed; it can only be changed from one form of energy to another.
b. The second law of thermodynamics states when energy is transformed from one form to another, there is always some loss of energy from the system, usually as low grade heat.
Energy Flow
Energy Flow
1. The complex trophic (feeding) relationships that exist in nature are called food webs.
2. A grazing food web begins with leaves, stems and seeds eaten by herbivores and omnivores.
3. A detrital food web begins with detritus, followed by decomposers (including bacteria and fungi).
4. Detrital food chains are connected to a grazing food chain when consumers of a grazing food chain feed on the decomposers of the detrital food chain.
5. In some ecosystems, more energy may move through the detrital food web than moves through the detritus food web.
food chain
A food chain represents a single path sequence of organisms that form links.
energy input and loss
A trophic level is a feeding level of one or more populations in a food web; those organisms in an ecosystem that are the same number of food chain steps from the energy input into the system:
a. First trophic level—primary producers,
b. Second trophic level—all the primary consumers,
c. Third trophic level—all the secondary consumers, etc.
8. About 10% of the energy at a particular trophic level is incorporated into the next trophic level.
a. Thus, 1,000 kg (or kcal in an energy pyramid) of plant material converts to 100 kg of herbivore tissue, which converts to 10 kg of first carnivores, which can support 1 kg of second level carnivores.
b. This rapid loss of energy is the reason food chains have from three to four links, rarely five.
c. This rapid loss of energy is also the reason there are few large carnivores.
ecological pyramid
An ecological pyramid shows this trophic structure of an ecosystem as a graph representing biomass, organism number, or energy content of each trophic level in a food web.
10. The base of the pyramid represents the producer trophic level, and from there the consumer trophic level is stacked, with the apex representing the highest consumer trophic level.
11. A pyramid of numbers is based on the number of organisms in each trophic level.
pyramid of biomass
A pyramid of biomass is based on the weight (biomass) of organisms at each trophic level at one time; this eliminates size of the organisms as a factor.
a. Usually a large mass of plants supports a medium mass of herbivores and a small mass of carnivores.
b. However, at one point in time at seashores, herbivores can have greater biomass feeding on algae that reproduce fast but are eaten, producing an inverted pyramid; over long time periods, the biomass is a normal pyramid.
13. One problem is where to fit in the decomposers; a large portion of energy becomes detritus in many ecosystems.
Chemical Cycling
Chemical Cycling
1. Biogeochemical cycles are the pathways by which chemicals circulate through the biotic and abiotic components of an ecosystem.
2. Some cycles are primarily gaseous cycles (carbon and nitrogen); others are sedimentary cycles, (phosphorus).
A reservoir is that portion of the earth that acts as a storehouse for the element
exchange pool
An exchange pool is the portion of the environment from which producers take chemicals, such as the atmosphere or soil.
biotic community
The biotic community is the pathway through which chemicals move through food chains.
The Water Cycle and transfer rate
The Water Cycle
1. A transfer rate is defined as the amount of a substance that moves from one component of the environment to another within a specified period of time.
Water or hydrologic cycle
2. In the water or hydrologic cycle, freshwater evaporates and condenses on the earth.
3. The evaporation of water from the oceans leaves behind salts; during condensation, a gas is exchanged into a liquid—vaporized fresh water rises into the atmosphere and returns to Earth in the form of precipitation.
4. Precipitation that percolates into the earth forms a water table at the surface of the groundwater.
5. An aquifer is an underground storage of fresh water in porous rock trapped by impervious rock.
6. Freshwater makes up about 3% of the world's supply of water and is considered a renewable resource.
7. However, freshwater becomes unavailable when consumption exceeds supply or is so polluted that it is not usable; when water withdrawal from aquifers exceeds replenishment, it is called "groundwater mining."
The Carbon Cycle
The Carbon Cycle
1. Both terrestrial and aquatic organisms exchange carbon dioxide with the atmosphere—this is called the carbon cycle.
2. On land, photosynthesis removes CO2 from the atmosphere; respiration then returns CO2 to the atmosphere.
3. CO2 from the air combines with water to produce bicarbonate (HCO3), which is a source of carbon for aquatic producers, primarily protists.
4. Similarly, when aquatic organisms respire, the CO2 they release combines with water to form bicarbonate ions (HCO3-).
5. The reservoir for the carbon cycle is largely composed of organic matter, calcium carbonate in shells, and limestone, as well as fossil fuels.
6. The transfer rates between photosynthesis and respiration (including decay) are about even.
7. Because we burn fossil fuels and forests, there is now more CO2 entering the atmosphere than is removed.
8. CO2, nitrous oxide, and methane are greenhouse gases that contribute to the rise in Earth's temperature, a phenomenon called global warming.
9. The above gases and water vapor increase the greenhouse effect that holds heat next to the Earth.
10. The increased heat may cause more clouds that in turn increase global warming.
11. Computer models cannot incorporate all variables; predictions are for 1.5-4.5oC increase by 2100.
12. Possible results may include glaciers melting, sea levels rising, a redistribution of dry and wet regions, and an increase in species extinctions.
The Phosphorus Cycle
The Phosphorus Cycle
1. In the phosphorus cycle, weathering makes phosphate ions (PO4 and HPO42 ) available to plants that take up phosphate from the soil.
2. Some of this phosphate runs off into aquatic ecosystems where algae incorporate it into organic molecules before it is entrapped in sediments.
3. Phosphate that is not taken up by algae is incorporated into sediments in the oceans.
4. Sediment phosphate only becomes available when geological upheaval exposes sedimentary rocks.
5. Phosphate taken up by producers is incorporated into a variety of organic compounds.
6. Animals eat producers and incorporate some of the phosphate into phospholipids, ATP, and nucleotides of DNA; however what is in teeth, bones, and shells does not decay for long periods.
7. Decay of organisms and decomposition of animal wastes eventually makes phosphate ions available again.
8. Available phosphate is generally taken up quickly; it is usually the limiting nutrient in most ecosystems.
9. Human Activities and the Phosphorus Cycle
a. Humans boost the supply of phosphate by mining phosphate ores for fertilizers, detergents, etc.
b. Run off of animal wastes from livestock feedlots and commercial fertilizers from cropland as well as discharge of untreated and treated municipal sewage can all add excess phosphate to nearby waters.
c. Eutrophication is the name of this over-enrichment that leads to algal blooms; when the algae die off, decomposers use up all of the oxygen and this can cause a massive fish kill.
The Nitrogen Cycle
The Nitrogen Cycle
1. Nitrogen gas (N2) is 78% of the atmosphere, yet nitrogen deficiency can limit plant growth.
2. In the nitrogen cycle, plants cannot incorporate N2 into organic compounds and they therefore depend on the various types of bacteria to make nitrogen available to them.
3. Nitrogen fixation occurs when N2 is converted to a form that plants can use.
a. Other nitrogen fixing bacteria, living in nodules on the roots of legumes, make reduced nitrogen and organic compounds available to a host plant.
b. Some cyanobacteria in water and the free living bacteria in soil are able to reduce N2 to ammonium (NH4+ ).
c. Plants take up both NH4+ and nitrate (NO3 ) from the soil.
d. After plants take up NO3, it is enzymatically reduced to NH4+ that is then used to synthesize amino and nucleic acids.
4. Nitrification is the production of nitrates (NO3).
a. Nitrogen gas is converted to NO3 in the atmosphere when cosmic radiation, meteor trails, and lightning provide the high energy for nitrogen to react with oxygen.
b. Nitrifying bacteria convert NH4+ to NO3.
c. Ammonium in the soil is converted to NO3 by nitrifying bacteria in the soil in a two step process that does not depend on nitrogen gas.
1) First, nitrite producing bacteria convert NH4+ to nitrite (NO3).
2) Then, nitrate producing bacteria convert NO2 to NO3.
5. Denitrification is conversion of NO3 to nitrous oxide (N2O) and N2.
a. There are denitrifying bacteria in both aquatic and terrestrial ecosystems.
b. Denitrification counterbalances nitrogen fixation, but not completely; more nitrogen fixation occurs.
Human Activities and the Nitrogen Cycle
6. Human Activities and the Nitrogen Cycle
a. Production of fertilizers and burning of fossil fuels adds three times the nitrogen oxides to the atmosphere as normal.
b. Acid deposition occurs when nitrogen oxides and sulfur oxides combine with water vapor in the atmosphere.
Ozone Shield Depletion
Ozone Shield Depletion (Science focus box)
1. In the stratosphere, ozone forms the ozone shield, which absorbs most of the ultraviolet (UV) rays of the sun so that fewer rays strike the Earth.
2. UV radiation can cause some harmful effects.
a. It causes mutations that can lead to skin cancer and make the eye lens develop cataracts.
b. UV radiation can adversely affect our immune system, making use more susceptible to infection.
c. UV radiation impairs crop and tree growth and skills algae and krill that are at the base of many food webs
ozone depletion was occurring world-wide and most serious above the Antarctic every spring.
In the 1980s, scientists became concerned that ozone depletion was occurring world-wide and most serious above the Antarctic every spring.
a. Ozone holes have also been detected above the Arctic, and within northern and southern latitudes, where many people live.
4. The cause of ozone depletion was found to be chlorine atoms (Cl), which can destroy up to 100,000 molecules of ozone before settling back to the Earth's surface.
5. Chlorine atoms entered the stratosphere from the breakdown of chlorofluorocarbons (CFCs)
a. The best-known CFC is Freon, which is a coolant found in refrigerators and air conditioners.
b. CFCs are also used in cleaning agents and in styrafoam inflation, insulation, and paddings.
6. The United States stopped the production of CFCs in 1995, and since then the amount of Clorine atoms in the stratosphere has started to decline.
7. However, currently there are more polar clouds (which contribute to ozone depletion) than previously thought.
a. As the surface of the Earth warms, due to global warming, less heat reradiates into the stratosphere.
b. It is speculated that once polar stratospheric clouds become twice as persistent, there could still be an ozone loss of 30%.
Climate is the prevailing weather conditions in a region over time.
2. Climate is primarily dictated by temperature and rainfall which is influenced by two factors:
a. variations in solar radiation due to the tilt of the spherical Earth, and
b. other effects such as topography and whether a body of water is nearby.
Effect of Solar Radiation
Effect of Solar Radiation
1. The Earth is a sphere; the sun's rays are more direct near the equator and spread out near the poles.
2. The tropics are therefore warmer than temperate areas.
3. The tilt of the Earth's axis as it rotates about the sun causes one pole to be more directly exposed to sunlight.
4. Cold air is heavy and sinks; hot air is lighter and rises.
a. Therefore if the Earth were standing still, equatorial air would rise and move toward the poles.
b. This would replace heavy polar air that sinks and flows toward the equator, now a low pressure area.
c. In a world that stood still, this would produce high winds moving toward the poles and surface winds moving toward the equator.
The Earth's Rotation Has an Effect
The Earth's Rotation Has an Effect
a. The wet equatorial air loses its moisture as it rises and cools near the equator.
b. By the time it moves 30o to the north, the air descends, reheats and is dry; this is a zone of deserts.
c. Because of the Earth's rotation, from the equator to 30o north and south, surface winds blow from east-southeast in the Southern Hemisphere and from the east-northeast in the Northern Hemisphere making east coasts wet.
d. Between 30o and 60o north and south, strong winds called the prevailing westerlies blow from west to east.
e. The west coasts of continents in these latitudes are wet as is the Pacific Northwest.
f. Weaker polar easterlies blow from east to west between 60o north or south and the respective poles.
g. The Earth's rotation, continents, and oceans alter the three circulation cells between the equator and poles.
Other Effects
Other Effects
1. Topography is the physical features or "lay" of the land.
2. Mountains cause rain and rain shadows.
a. Air blowing up over a mountain range rises and cools; the windward side therefore receives more rainfall.
b. The leeward side of the mountain range receives dry air; it is in a rain shadow.
c. The Hawaiian Islands experience over 750 cm of rain on the windward side but only average 50 cm in the rain shadow.
d. The western side of the Sierra Nevada Mountains is lush; the eastern side is a semidesert.
3. Coastal Breezes
a. Since the land heats up and cools down faster than oceans, it causes a daily pattern.
b. In the day, land heats up and warm air rises; then cool sea breezes blow inland to replace the rising air.
c. At night, the land cools first and the cold air sinks and blows out to sea.
Monsoon Climates
Monsoon Climates
a. The India and south Asia climate have a monsoon climate and generates wet ocean winds for almost half the year.
b. The land heats more rapidly than the waters of the Indian Ocean during spring.
c. The difference in temperature causes a gigantic circulation of air with warm air rising and cooler air continuously coming in from the ocean to replace it.
d. As the warm air rises, it loses its moisture and the monsoon season begins.
The "lake effect"
The "lake effect"
a. Winter Arctic winds blowing across the Great Lakes become warm and moisture laden.
b. When these winds rise and lose their moisture, a large amount of snow falls.
Biome Distribution
Biome Distribution
1. The biosphere is divided into large biogeographic units called biomes.
2. A biome has a particular mix of plants and animals adapted to live under certain environmental conditions.
3. The average temperature and rainfall influences where the different biomes are found on the surface of the Earth.
4. Climate, and mainly solar radiation and topography, is the principle determinant of the distribution of biomes.
5. A latitude temperature gradient is also seen when we consider altitude; the rain forest-deciduous forest-coniferous forest-tundra sequences are also seen when ascending a mountain.
a. The mountain coniferous forest is a montane coniferous forest.
b. The tundra near the peak is an alpine tundra.
1. The Arctic tundra encircles the Earth south of the ice-covered polar seas in the Northern Hemisphere.
2. Arctic tundra covers 20% of the Earth's land surface; it is cold and dark much of the year.
3. The tundra receives about 20 cm of rainfall annually; this would constitute a desert but the melting snow provides water during summer and very little evaporates.
4. Only the topmost layer of Earth thaws; the permafrost beneath is always frozen.
5. Trees are not found in the tundra because
a. the growing season is too short,
b. their roots cannot penetrate the permafrost, and
c. trees cannot become anchored in the boggy soil of summer.
6. In the summer, the ground is covered with sedges and short-grasses with patches of lichens and mosses.
7. Dwarf woody shrubs flower and seed quickly while there is sunlight for photosynthesis.
8. Only a few animals adapted to cold live in the tundra year-round (e.g., lemming, ptarmigan, and musk-ox).
9. During the summer, the tundra contains many insects, birds, and migratory animals (e.g., shore birds, waterfowl, caribou, reindeer, and wolves).
Coniferous Forests
Coniferous Forests
1. Conifer forests are found in three locations: taiga, montane coniferous forests, and temperate coniferous forests.
2. Taiga is coniferous forest extending across northern Eurasia and North America.
3. Near a mountain top is a similar conifer forest called a montane coniferous forest.
4. On the Pacific Coast from Canada down to California is part of the temperate rain forest.
5. Conifer forests contain great stands of spruce, fir, hemlock, and pine; these trees have thick protective leaves or needles and bark.
6. The needlelike leaves can withstand the heavy weight of snow.
7. There is a limited understory of plants; the floor is covered by low-lying mosses and lichens beneath the layer of needles.
8. Birds harvest the seeds of conifers; bears, deer, moose, beaver and muskrat live around the cool lakes and streams.
9. Major carnivores include wolves, wolverines, and mountain lions.
10. The temperate rain forest along the Pacific Coast has the largest trees in existence, some as old as 800 years.
Temperate Deciduous Forests
D. Temperate Deciduous Forests
1. Temperate deciduous forests are found south of the taiga in eastern North America, eastern Asia, and much of Europe.
2. Climate in these areas is moderate with a relatively high annual rainfall (75-150 cm).
3. The seasons are well-defined with a growing season that ranges between 140 and 300 days.
4. The trees of a deciduous forest (e.g., oak, beech, and maple) have broad leaves which they lose in the fall and grow again in the spring.
5. Enough sunlight penetrates the canopy to support a well-developed understory composed of shrubs, a layer of herbaceous plants, and a ground cover of mosses and ferns.
6. Stratification beneath the canopy provides a variety of habitats for insects and birds.
7. Deciduous forest contains many rodents that provide food for bobcats, wolves, and foxes.
8. Deciduous forest also contains deer and black bears.
9. Compared to the taiga, the winters are milder and allow many amphibians and reptiles to survive.
10. Minerals are washed into the ground and eventually brought back up by deep roots of trees.
Wildlife Conservation and DNA
Wildlife Conservation and DNA (Ecology focus box)
1. After DNA analysis, scientist discovered that 60% of loggerhead turtles drowning in the nets and hooks of fisheries in the Mediterranean Sea were from beaches in the southeastern United States.
a. More than half of the young turtles living in the Mediterranean Sea had hatched from nests in Florida, Georgia, and South Carolina.
2. DNA sequencing from Alaskan brown bears showed that there are two types of brown bears in Alaska.
a. One type of bear, who only resides in the Admiralty, Baranof, and Chichagof islands (ABC islands) may be important wildlife conservation effort.
b. The logging industry has expressed interest in logging the ABC islands.
c. The new DNA analysis, may have protected the ABC bear's habitat.
3. Another example of DNA sequencing was an experiment discretely conducted at sushi restaurants in Japan.
a. Scientists discovered that of the 16 pieces of whale sushi they examined, many were from whales that are endangered or protected under an international moratorium on whaling.
4. DNA sequencing is now being used in wildlife crimes in the United States and 122
Tropical Forests
Tropical Forests
1. Tropical rain forests are found in South America, Africa, and the Indo-Malayan region near the equator.
2. The climate is warm (20o-25o C) and rainfall is plentiful with a minimum of 190 cm per year.
3. This is probably the richest biome, both in number of species and in their abundance.
4. A tropical rain forest has a complex structure, with many levels of life.
5. Although there is animal life on the ground (e.g., pacas, agoutis, peccaries, and armadillos), most of the animals live in the trees.
6. Insects are abundant in tropical rain forests; the majority have not been identified.
7. Termites are critical in the decomposition of woody plant material.
8. Various birds tend to be brightly colored.
9. Amphibians and reptiles are represented by many species of frogs, snakes, and lizards.
10. Lemurs, sloths and monkeys feed on fruits.
11. The largest carnivores are cats (e.g., jaguars in South America and leopards in Africa and Asia).
12. Epiphytes are air plants that grow on other plants.
a. They have roots of their own to absorb moisture and minerals leached from the canopy.
b. Others catch rain and debris in hollows of overlapping leaf bases.
c. Common epiphytes are related to pineapples, orchids and ferns.
13. Tropical forests in India, Southeast Asia, West Africa, West Indies, and Central and South America are seasonal.
a. They have deciduous trees that shed leaves in the dry season; layers of undergrowth are below.
b. Certain of these forests contain elephants, tigers and hippopotami.
14. A year-long growing season and high temperatures mean productivity is high.
15. But the warm, moist climate that supports high productivity also promotes rapid recycling of litter.
16. The soil is called laterite and the iron and aluminum oxides give it a red color and a brick texture when it bakes in the hot sun.
17. Consequently the soil is relatively poor because the nutrients are rapidly cycled into the biomass; this makes a poor agricultural soil.
Shrubland is dominated by shrubs with small but thick evergreen leaves coated with a thick, waxy cuticle, and with thick underground stems that survive dry summers and frequent fires.
2. Shrubland is found more along the coasts in South America, western Australia, central Chile, and around the Mediterranean Sea..
3. The dense shrubland in California, where the summers are hot and very dry, is chaparral.
a. This Mediterranean-type shrubland lacks an understory and ground litter and is highly flammable.
b. Seeds of many species require heat and the scarring action of fire to induce germination.
4. West of the Rocky Mountains is a cold desert region dominated by sagebrush and dependent birds.
Grasslands occur where rainfall is greater than 25 cm but is insufficient to support trees.
2. In temperate areas with rainfall between 10 and 30 inches a year, grassland is the climax community; it is too wet for desert and too dry for forests.
3. Natural grasslands once covered over 40% of the Earth's land surface.
4. Most grasslands now grow crops, especially wheat and corn.
5. Grasses generally grow in different seasons; therefore some grassland animals migrate and ground squirrels hibernate when there is little grass.
6. The temperate grasslands include the Russian steppes, South American pampas, and North American prairies.
7. Tall-grass prairie occurs where moisture is not sufficient to support trees.
8. Short-grass prairie survives on less moisture and is between a tall-grass prairie and desert.
9. Animal life includes mice, prairie dogs, and rabbits and the animals that feed on them: hawks, snakes, badgers, coyotes, and foxes.
10. Prairies once contained large herds of buffalo and pronghorn antelope.
Savannas are tropical grasslands that contain some trees.
a. The savanna occurs in regions where a relatively cool dry season is followed by a hot, rainy one.
b. The savanna contains the greatest variety and numbers of herbivores (e.g., antelopes, zebras, wildebeests, water buffalo, rhinoceroses, elephants, and giraffes).
c. Any plant litter not consumed by grazers is attacked by termites and other decomposers.
d. Termites also build towering nests and tend fungal gardens.
e. The savanna supports a large population of carnivores (e.g., lions, cheetahs, hyenas, and leopards).
1. Deserts usually occur at latitudes about 30o both north and south of the equator.
2. Deserts have an annual rainfall of less than 25 cm because incoming descending winds lack moisture.
3. Lacking cloud cover, the desert days are hot and the nights are cold.
4. The Sahara and a few other deserts are nearly devoid of vegetation.
5. Most have a variety of plants, all adapted to heat and scarcity of water (e.g., succulents).
6. Animal life includes many insects, reptiles such as lizards and snakes, running birds (e.g., roadrunner), rodents (e.g., kangaroo rat), and a few larger birds and mammals such as hawks and coyotes.
Aquatic Ecosystems
Aquatic Ecosystems
1. Aquatic ecosystems are classified as freshwater (inland) or saltwater (marine).
2. Wetlands near the sea have mixed fresh and saltwater and are brackish.
3. Seawater evaporates and then precipitates and flows through lakes and ponds, streams and rivers, and groundwater.
a. The top of the saturation zone defines the water table.
b. Groundwater sometimes occurs in underground layers called aquifers.
4. Wetlands are areas that are wet for at least part of the year; they are generally classified by their vegetation.
5. Marshes are wetlands that are frequently or continually inundated by water; they are characterized by the presence of rushes, reeds, and other grasses.
6. Bogs are wetlands that a characterized by acidic waters, peat deposits, and sphagnum moss; they receive most of their water from precipitation and are nutrient-poor.
7. Wandering streams are often channelized into straight channels; this eliminates storage for flood control.
8. The elimination of wetlands removes unique habitat for fish, waterfowl and other wildlife.
9. Wetlands also filter toxic wastes and use excess nutrients.
1. Lakes are freshwater bodies classified by their nutrient status.
a. Oligotrophic (nutrient-poor) lakes have low organic matter and therefore low productivity.
b. Eutrophic (nutrient-rich) lakes are highly productive from natural nutrients or agricultural runoff.
c. Eutrophication occurs when added nutrients change an oligotrophic lake to eutrophic; this process is called eutrophication.
2. In the temperate zone, deep lakes are stratified in summer and winter.
a. Epilimnion is the surface layer warmed from solar radiation; it soon becomes nutrient-poor but photosynthesis keeps oxygen levels high.
b. At the thermocline, there is an abrupt drop in temperature.
c. The hypolimnion is the lower cold region; it becomes depleted in oxygen but is nutrient rich from detritus falling from above.
d. The less dense epilimnion floats on the heavier cold hypolimnion; this prevents mixing.
3. Fall and Spring Overturns
a. In the fall, the upper epilimnion waters become cooler than the hypolimnion.
b. This causes the surface water to sink and deep water to rise.
c. This fall overturn continues until the temperature is uniform.
d. In the winter, ice forms on top because ice is lighter; this provides an insulating cover and organisms can live through a harsh winter in this moderate water.
e. In spring, the ice melts and the cooler water on top sinks below the warmer water on the bottom.
f. After the spring overturn, water returns to a more uniform temperature and sun warms the surface.
g. Fish and other aquatic life are adapted to the strata and seasonal changes; for instance, cold water fish move deeper in the summer.
Life Zones
Life Zones
1. Plankton includes freshwater and marine microscopic organisms that freely drift in fresh or saltwater.
2. Phytoplankton are the photosynthetic plankton, including algae.
3. Zooplankton are animals that feed on phytoplankton.
4. The littoral zone is shallow and closest to shore; plants root in this zone and harbor some animals.
5. The limnetic zone is the open sunlit layer of body of a lake; it contains plankton, a few insect larvae, and fish.
6. The profundal zone is that portion of a lake below any significant sunlight penetration; it contains zooplankton and fishes that feed on the debris that falls from above.
7. The benthic zone is at the soil-water interface with the bottom-dwelling organisms; it includes worms, mollusks, and crustaceans.
Coastal Ecosystems Border the Oceans
Coastal Ecosystems Border the Oceans
1. An estuary is a partially enclosed body of water at the end of a river where the fresh water and sea water mix.
a. Not many organisms are tolerant of this mix of fresh river water and salty tidal water.
b. For organisms suited to the rapid changes in salinity, estuaries provide abundant nutrients.
c. Estuaries are a nutrient trap since nutrients are
1) delivered by the river,
2) brought in from the sea by tides, and
3) released from decaying vegetation.
d. Estuaries are a nursery estimated as spawning and rearing over half of all marine fishes.
2. Seashores are constantly bombarded by tidal seas.
a. The littoral zone is between high and low tide and is covered and uncovered daily.
b. The upper littoral is covered by barnacles.
c. The midportion harbors brown algae that may overlie barnacles.
d. The lower portion has oysters and mussels attached to rock by byssal threads; various snails hide in crevices or seaweed.
e. Below the littoral zone, seaweeds are the main photosynthesizers and are anchored to rocks by holdfasts.
f. Sandy beaches have no anchor holds; therefore permanent beach organisms are burrowing or tube-living.
1. Shallow ocean waters (called the euphotic zone) contain a greater concentration of organisms than the rest of the sea.
a. This contains a greater concentration of organisms than are in the oceanic province.
b. It is a more productive part of the ocean because of the concentration of sunlight and nutrients.
c. It provides the base of the food web leading to commercially valuable fishes (e.g., herring, cod, and flounder).
d. Coral reefs are areas of biological abundance found in shallow, warm waters just below the surface; there is much concern about future survival of coral reefs since they are vulnerable to environmental changes, temperature shifts, salinity, and light availability.
The pelagic division
The pelagic division includes the neritic and oceanic provinces.
a. The neritic province lies over the continental shelf.
b. The epipelagic zone extends from the surface to the maximum depth that photosynthesis significantly occurs.
1) It does not have a high concentration of phytoplankton because it lacks nutrients.
2) However, the numbers of producers in this zone still support a large assembly of zooplankton, which support large numbers of other marine organisms, when the entire ocean is considered.
3) The epipelagic animals include mackerels, tunas, and sharks.
c. The mesopelagic zone extends below maximum depth at which photosynthesis significantly occurs.
1) This zone is dominated by carnivores adapted to the absence of light (e.g., luminescent shrimps, squids, and fishes).
2) Organisms here tend to be translucent or red colored.
The bathypelagic zone
The bathypelagic zone is in absolute darkness except for an occasional flash of bioluminescent light.
1) Animals here are carnivores and scavengers.
2) This level supports a variety of very strange carnivores.
e. The abyssal plain is located on and immediately above the abyssal plane.
1) This is a region of extreme cold and intense pressure.
2) It contains a detrital food web in which the detritivores (e.g., sponges, worms, tube worms, sea cucumbers, sea lilies, and sea urchins) comprise the first trophic level.
3) Starfishes, crabs, brittle stars, and some bottom-dwelling fish occupy the upper trophic levels.
4) Hydrothermal vents are areas where seawater percolates through cracks.
a. The water is heated to about 350oC.
b. This causes sulfate to react with water to form hydrogen sulfide (H2S).
c. Chemosynthetic bacteria obtain energy by oxidizing hydrogen sulfide
Ocean Currents
Ocean Currents
1. Moisture that evaporates into the air carries the heat used to evaporate it with it.
2. Water is warm at the equator and cold at the poles due to the distribution of the sun's rays.
3. Air takes on the temperature of the water below and warm air moves from the equator toward the poles.
4. Therefore, the oceans make winds blow.
5. Oceans hold heat or remain cool longer than landmasses.
6. Winds generate ocean currents due to friction at the ocean surface.
7. Since ocean currents are bounded by land, they move in a circular path, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
8. Ocean currents take heat from the equator to the polar regions.
a. The Gulf Stream brings warmer tropical Caribbean water to the east coast of North America and to upper western Europe.
b. Without the Gulf Stream, Great Britain would be as cold as Greenland.
c. A major Atlantic Ocean current warms the eastern coast of South America.
d. The Humboldt Current in the Pacific flows toward the equator off the west coast of South America.
Upwellings occur when cold nutrient-rich water rises to supplant warm nutrient-poor water.
a. The Humboldt Current brings rich nutrients north; this supports rich marine life and the fisheries of Peru and northern Chile.
b. Seabirds deposit droppings (guano) on land where it is a major source of phosphorus mining.
c. When the Humboldt Current is not as cool as usual, upwelling does not occur, stagnation results, fisheries decline, and climate patterns change globally; this is called an El-Niño-Southern Oscillation.
El Niño-Southern Oscillation (Ecology focus box)
El Niño-Southern Oscillation (Ecology focus box)
1. El Niño-Southern Oscillation (ENSO) refers to a sever weather change brought on by an interaction between the atmosphere and the ocean currents.
2. Ordinarily, the southeast trade winds move along the coast of South America and turn east because of the Earth's daily rotation on its axis.
a. The winds bring warm ocean waters from east to west.
b. There is also an upwelling of nutrient-rich cold water from the depths of the ocean, resulting in a large Peruvian harvest of anchovies.
c. The warm ocean waters also bring monsoon rain to India and Indonesia.
3. During an El Niño, the northeast and southeast trade winds slacken.
a. There is no upwelling, and anchovy harvest plummets.
b. Waters from the east may never reach the west.
c. Winds lose moisture in the middle of the Pacific, rather than the Indian Ocean.
d. Drought occurs in India, Indonesia, Africa, and Australia.
4. Some parts of the United States benefit from an El Niño.
a. The Northeast is warmer than usual.
b. Fewer hurricanes hit the east coast.
c. Tornadoes decrease in the Midwest.
5. Following El Niño, normal conditions occur, which is known as La Niña.
6. As climate changes, the severity of El Niños remains somewhat unpredictable.