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Chapter 4

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evolution
genetically based change in the appearance, functioning, &/or behavior of organisms across generations, often by the process of natural selection
natural selection
the process by which inherited characteristics that enhance survival & reproduction are passed on more frequently to future generations than those that don't, thus altering the genetic makeup of populations through time
Charles Darwin & Alfred Russel Wallace
each independently proposed the concept of natural selection as a mechanism for evolution & as a way to explain the great variety of living things; keen naturalists from England who had studied plants & animals in exotic locales
adaptive trait/an adaptation
a trait that promotes success
mutations
accidental alterations that arise during DNA replication that give rise to genetic variation among individuals
recombination
process by which organisms mix their genetic material (as during sexual reproduction), so that some of each parent's genes are included in the genes of the offspring; produces novel combos of genes, generating variation among individuals
adaptive radiation
the burst of a species formation due to natural selection
selective breeding
the choosing of animals w/ traits we like & breeding them & not breeding animals w/ variants we don't like; results in the exaggeration of particular traits preferred
artificial selection
natural selection conducted under human direction (e.g. the selective breeding of crop plants, pets, & livestock)
biodiversity
the sum total of all organisms in an area, taking into account the diversity of species, their genes, their populations, & their communities
population
a group of individuals of a particular species that live in the same area
species
a population or groups of populations whose members share certain traits & can freely breed w/ one another & produce fertile offspring
speciation
the process by which new species are generated
allopatric speciation
species formation due to the physical separation of populations over some geographic distance
phylogenetic trees
a treelike diagram that represents the history of divergence of species or other taxonomic groups of organisms
fossil
the remains, impression, or trace of an animal or plant of past geological ages that has been preserved in rock or sediments
fossil record
the cumulative body of fossils worldwide, which paleontologists study to infer the history of past life on Earth
extinction
the disappearance of an entire species from the face of the Earth
endemic
native or restricted to a particular geographic region
background extinction rate
the average rate of extinction that occurred before the appearance of humans
mass extinction events
the extinction of a large proportion of the world's species in a very short time period due to some extreme & rapid change or catastrophic event; there have been 5 in the past half-billion years
ecology
the study of interaction among organisms & between organisms & their environments
biosphere
the cumulative total of living things on Earth & the areas they inhabit
ecologists
study relationships in the hierarchy of levels of life
population ecology
investigates the quantitative dynamics of how individuals within a species interact
community ecology
focuses on interactions among species
habitat
the specific environment in which an organism lives, consisting of the living & nonliving elements; are scale-dependent
habitat use
the process by which organisms use habitats from among the range of options they encounter
habitat selection
the process by which organisms select habitats among the range of options they encounter
niche
reflects an organism's use of resources & its functional role in a community; includes habitat use, its consumption of certain foods, its role in the flow of energy & matter, & its interactions w/ other organisms; a multidimensional concept
specialists
species w/ narrow breadth & very specific requirements
generalists
species w/ broad tolerances & are able to use a wide array of habitats & resources
population size
expressed as the number of individual organisms present at a given time; it may increase, decrease, undergo cyclical change, or remain the same over time
population density
describes the number of individuals within a population per unit area
population distribution/population dispersion
describes the spatial arrangement of organisms within an area; three types- random, uniform, & clumped
random distribution
indivuduals are located haphazardly in space in no particular pattern; occurs when resources are found throughout an area & other organisms don't strongly influence where members of a population settle
uniform distribution
individuals are evenly spaced; occurs when individuals hold territories or otherwise compete for space
clumped distribution
organisms arrange themselves according to the availability of the resources they need to survive; the pattern most common in nature; often indicates habitat selection
sex ratio
a population's proportion of males to females
age distribution/age structure
describes the relative numbers of organisms of each age within a population
age structure diagrams/age pyramids
visual tools scientists use to show the age structures of populations
demographers
scientists who study human populations
natality
births within the population
mortality
deaths within the population
immigration
arrival of individuals from outside the population
emigration
departure of individuals from the population
growth rate
the net change in a population's size, per 1,000 individuals; = (birth rate + immigration rate) - (death rate + emigration rate)
exponential growth
when a population increases by a fixed percentage each year
limiting factors
physical, chemical, & biological characteristics of the environment that restrain population growth
carrying capacity
the maximum population size of a species that a given environment can sustain
logistic growth curve
shows how an initial exponential increase is slowed & finally brought to a standstill by limiting factors; it rises sharply at first but then begins to level off as the effects of limiting factors become stronger
environmental resistance
the force of limiting factors that eventually stabilize the population size at carrying capacity
density-dependent
a limiting factor whose effects on a population increase or decrease depending on the population density
density-independent
a limiting factor whose effects on a population are constant regardless of population density
biotic potential
the ability to produce offspring
k-selected
term denoting a species w/ low biotic potential whose members produce a small number of offspring & take a long time to gestate & raise each of their young, but invest heavily in promoting the survival & growth of these few offspring; generally regulated by density-dependent factors
r-selected
term denoting a species w/ high biotic potential whose member produce a large number of offspring in a relatively short time but don't care for their young after birth; generally regulated by density-independent factors; quantity not quality