76 terms

AP Biology Barron's Chapter 15--Ecology

Study of the interactions of organisms with their physical environment and with each other.
A group of individuals of one species living in one area who have the ability of interbreeding and interacting with each other.
Consists of all the organisms living in one area
Includes all the organisms in a given area as well as the abiotic (nonliving) factors with which they interact
Abiotic Factors
Nonliving and include temperature, water, sunlight, wind, rocks, and soil
Global ecosystem
Five Properties of Populations
1. Size
--Total number of individuals in a population and is represented by N

2. Density
--Number of individuals per unit area of volume. Counting the number of organisms inhabiting a certain area is often very difficult, if not impossible. Instead of counting each organism scientists use sampling techniques to estimate the number of organisms living in one area. One technique that is used is called mark and recapture which is when organisms are captured, tagged, and then released. Some time later, the same process is repeated and the following formula is used for the collected data:
N= Number marked in first catch x total number in second catch/ number of recaptures in second catch

3. Dispersion
--The pattern of spacing of individuals within the area the population inhabits. The most common pattern of this is CLUMPED. Some populations are spread in a UNIFORM pattern. RANDOM spacing occurs in the absence of any special attractions or repulsions.

4. Survivorship/ Mortality Curves
--Show the size and composition of a population
>Three types:
1. Type I curves show organisms with low death rates in young and middle age and high mortality rates in old age. There is a great deal of parenting, which accounts for the high survival rates of the young. This is characteristic of humans.
2. Type II curves describe a species with a death rate that is constant over the life span. This describes the hydra, reptiles, and rodents.
3. Type 3 curves show a very high death rate among the young but then shows that death rates decline for those few individuals that have survived to a certain age. This is characteristic of fish and invertebrates that release thousands of eggs, have external fertilization, and have no parenting.

5. Age Structure Diagrams--Show the relative numbers of individuals at each age.

Developing countries have a pyramid shaped graph (India) and developed countries have zero population growth where the number of people at each age group is about the same and the birth rates and the death rates are about equal (USA).
Population Growth
Every population has a characteristic BIOTIC POTENTIAL, the maximum rate at which a population could increase under ideal conditions.

Different population have different biotic potentials, which are influenced by several factors.

These factors include: age at which reproduction begins, the life span during which the organisms are capable of reproducing, the number of reproductive periods in the lifetime, and the number of offspring the organism is capable of reproducing.

Regardless of whether a population has a large or small biotic potential, certain characteristics about growth are common to all organisms.
Exponential Growth
This is the simplest model for population growth.

It is an environment with no predation, parasitism, or competition. It has no immigration or emigration and is in an environment with unlimited resources. This is characteristic of a population that has been recently introduced into an area.

Exponential growth is usually short lived, the human population has been in the exponential growth phase for over 300 years.
Carrying Capacity
The limit to the number of individuals that can occupy one area at a particular time.

Each particular environment has its own carrying capacity around which the population size oscillates.

It changes as the environmental conditions change.
Limiting Factors
The factors that limit population growth.
What are the two categories of population growth?
Density-dependent and density-independent factors
Density-Dependent Factors
Factors that increase directly as the population density increases. They include competition for food, the buildup of wastes, predation, and disease.
Density-Independent Factors
Factors whose occurrence is unrelated to the population density. These include earthquakes, storms, and naturally occurring fires and floods.
Growth Patterns
Some species are opportunistic; they reproduce rapidly when the environment is uncrowded and resources are vast. They are referred to as r-strategists. Other organisms, the K-strategists, live at a density near the carrying capacity.
Many young
little to no parenting
Rapid maturation
Small young
Reproduce once
Few young
Intensive parenting
Slow maturation
Large young
Reproduce many times
What are communities made up of?
Populations that interact with the environment and with each other.
How are communities characterized?
How diverse they are and how dense they are.
What are the two components of species diversity?
1. Species richness= the number of different species in the community
2. Relative abundance
Why are diverse communities more productive?
More sable and survive for longer periods of time. They are also better able to withstand and recover from environmental stresses such as drought or an incursion by invasive species.
Competitive Exclusion Principle
Developed by G.F. Gause after studying the effects of interspecific competition in a laboratory setting. He worked with two very similar species. When he cultured them separatley, each population grew rapidly and then leveled off at the carrying capacity. However, when he put the two cultures together, the one with the advantage drove the other species to extinction.

Therefore his principle states that two species cannot coexist in a community if they share a niche, meaning if they use the same resources.
What are the possible outcomes if two species inhibit the same niche and therefore compete for resources?
1. Species will evolve through natural selection to exploit different resources (resource partitioning)
2. Occurred on the Galapagos Islands when finches evolved different beak sizes through natural selection and were able to eat different kinds of seeds and avoid competition. The divergence in body structure is called character displacement.
Can refer to one animal eating another, or it can refer to animals eating plants. For their protection, animals and plants have evolved defenses against predation.
What adaptations have plants created to defend themselves against predation?
Evolved spines and thorns and chemical poisons such as strychnine, mescaline, morphine, and nicotine to fend off attack by animals
What adaptations have animal created to fend off predation?
Evolved active defenses such as hiding, fleeing, or defending themselves. These can be very costly in energy. Therefore they evolved passive defenses such as cryptic coloration or camouflage that make the prey difficult to spot.
What are three kinds of passive defense that animals utilize?
1. Aposematic coloration
2. Batesian mimicry
3. Mullerian mimicry
Aposematic Coloration
The very bright, often red or arrange coloration of poisonous animals as a warning that possible predators should avoid them.
Batesian mimicry
Copycat coloration where one harmless animal mimics the coloration of one that is poisonous. One example is the viceroy butterfly which is harmless but looks very similar to the monarch butterfly, which stores poisons in its body from the milkweed plant.
Mullerian Mimicry
Two or more poisonous species, such as the cuckoo bee and the yellow jacket, resemble each other and gain an advantage from their combined numbers. Predators learn more quickly to avoid any prey with that appearance.
Is a symbiotic relationship where both organisms benefit (+/+). An example is the bacteria that live in the human intestine and produce vitamins.
A symbiotic relationship where one organism benefits and one is unaware of the other organism (+/o). Barnacles that attach themselves to the underside of a whale benefit by gaining access to a variety of food sources as the whale swims into different areas. In addition, the whale is unaware of the barnacles.
A symbiotic relationship (+/-) where one organism, the parasite, benefits while the host is harmed. A tapeworm in the human intestine is an example.
How much solar radiation is converted to chemical bond energy by photosynthesis?
less than 1%
Gross primary productivity (GPP)
Amount of light energy that is converted to chemical energy by photosynthesis per unit time.
Net primary productivity (NPP)
Equal to the GPP minus the energy used by producers for their own cellular respiration
What are the most productive terrestrial ecosystems?
Tropical rain forests; they contribute a large portion of Earth's overall net primary production because they cover a lot of the earth's surface
Do coral reefs contribute to global NPP?
No because they don't occupy a lot of the planet.
Open Oceans PNN
NPP is very low per unit area, but they make up 3/4 of the globe, so their global PNN is higher than that of any other biome.
Food Chain
Pathway along which food is transferred from one trophic or feeding level to another. Energy, in the form of food, moves from the producers to the herbivores to the carnivores.
How much energy is stored transferred from one trophic level to the next? What is the result of this?
10%; as a result food chains are rather short
Which are more stable: long or short food chains?
Long food chains are less stable because population fluctuations at lower trophic levels are magnified at higher levels, causing local extinction of top predators.
Food pyramid
Good model to demonstrate the interaction of organisms in the food chain and the loss of energy
-Green plants
-Convert light energy to chemical bond energy
-Have the greatest biomass of any trophic level
-Examples:diatoms and phytoplankton
Primary Consumers
-Eat the producers
-Examples: grasshoppers, zooplankton
Secondary consumers
-Eat the primary consumers
-Examples: frogs, small fish
Tertiary consumers
-Eat the secondary consumers
-Top of the food chain
-Have the least biomass of any other trophic level in the food chain
-Least stable trophic level and most sensitive to fluctuations in populations of the other trophic levels
-Example: hawk
Dominant species
A community are the species that are the most abundant or that collectively have the highest biomass. They exert control over the abundance and distribution of other species.
Keystone species
Not abundant in a community. However, they exert major control over other species in the community.
Biological Magnification
Organisms at higher trophic levels have greater concentrations of accumulated toxins stores in their bodies than those at lower trophic levels.
Bacteria and fungi. Without decomposers to recycle nutrients back to the soil to nourish plants, there would be no food chain and no life.
Ecological Succession
Most communities are dynamic, not stable. Things occur that suddenly and drastically destroy a community or an entire ecosystem.

Ecological succession is the process of sequential rebuilding of the ecosystem after destruction.

If the rebuilding begins in a lifeless area where even soil has been removed, the process is called PRIMARY ECOLOGICAL SUCCESSION. The essential and dominant characteristic of primary succession is soil building.
After an ecosystem is destroyed, what are the first organisms to inhabit a barren area?
Pioneer organisms like lichens and mosses
Climax community
Final stable community that remains
Secondary succession
Occurs when an existing community has been cleared by some disturbance that leaves the soil intact.
Very large regions of the earth whose distribution depends on the amount of precipitation and temperature in an area.

Each biome is characterized by dominant vegetation and animal life.
Tropical Rain Forest
-Found near the equator with abundant rainfall, stable temperatures, and high humidity
-Although these forests cover only 4 percent of the earth's land surface, they account for more than 20% of the earth's net carbon fixation
-The most diversity of species of any biome on earth.
-Dominant trees are very tall with interlacing tops that form a dense canopy, keeping the floor of the forest dimly lit even at midday. The canopy also prevents rain from falling directly onto the forest floor, but leaves drip rain constantly.
-Many trees are covered with epiphytes, photosynthetic plants that grow on other trees rather than supporting themselves. They are not parasites but may kill the trees inadvertently by blocking the light
-The most diverse animal species of any biome, including birds, reptiles, mammals, and amphibians.
-Some are biodiversity hotspots, meaning that many species are endangered
-Less than 10 inches of rainfall per year, not even grasses can survive
-Experiences the most extreme temperature fluctuations of any biome
-Characteristic plants are the drought-resistant adaptations
-Small annual plants that germinate only after a hard rain
-Most animals are active at night or during a brief early morning period or late afternoon. During the day they remain cool by burrowing underground or hiding in the shade
Temperate Grasslands
Temperate Deciduous Forest
Conifer Forest--Taiga
Freshwater Biomes
The Water Cycle
Water evaporates from the earth, forms clouds, and rains over the oceans and land. Some rain percolates through the soil and make it way back to the seas. Some evaporates directly from the land, but most evaporates from plants by transpiration.
The Carbon Cycle
1. Cell respiration by animals and bacterial decomposers adds CO2 to the air and removes O2
2. Burning of fossil fuels adds Co2 to the air
3. Photosynthesis removes CO2 from the air and adds O2

The major reservoir of carbon is fossil fuels, plant, and animal biomass. Also found in soil.
Nitrogen Cycle
1. Nitrogen-fixing bacteria live in the nodules in the roots of legumes and convert free nitrogen into the ammonium ion (NH4+)
2. Nitrifying bacteria convert the ammonium ion into nitrites and then into nitrates
3. Denitrifying bacteria convert nitrates into free atmospheric nitrogen
4. Bacteria of decay decompose organic matter into ammonia

The main reservoir is the atmosphere.
Runoff from sewage and manure from pastures increase nutrients in lake and cause excessive growth of algae and other plants.

Organic material accumulates on the lake bottom and reduces the depth of the lake. Also detrivores use up oxygen as they decompose the dead organic matter. Lower oxygen levels make it impossible for some fish to live. As fish die, decomposers expand their activity and oxygen levels continue to decrease. The process continues until the lake disappears.
Acid Rain
Caused by pollutants in the air from combustion of fossil fuels.
Nitrogen and sulfur pollutants in the air turn into nitric, nitrous, sulfurous, and sulfuric acids, which cause the pH of the rain to be less than 5.6. This kills the organisms in lakes and damages ancient stone architecture.
Toxins from industry have gotten into the food chain. Most cattle and chicken feed contains antibiotics and hormones to accelerate animal growth by may have serious ill affects on humans who eat the chicken and beef.

Any carcinogens and teratogens that get into the food chain accumulate and remain in the human body's fatty tissues because we occupy the top of the food chain. This is called biological magnification.
Greenhouse Effect
Global warming
Acidification of the Oceans
Depleting the Ozone Layer
Introducing new species
Pesticides vs. Biological control