AP Biology Unit 8 - Ecology

Population

A group of individuals of the same species living in the same area.

Carrying capacity

The point where resources become limited and the population stops growing rapidly.

Exponential growth

Population growth under ideal conditions with unlimited resources, producing a J-shaped curve.

Logistic growth

Population growth that slows as the population approaches carrying capacity, producing an S-shaped curve.

Lag phase

The beginning of population growth when the population is small and growth is slow.

Exponential phase / biotic potential

The period of fastest population growth.

Carrying capacity phase

The phase where the population levels off around K.

Biotic potential

The maximum rate at which a population can grow under ideal conditions.

Limiting factor

Anything that restricts the size of a population.

Density-dependent factor

A limiting factor whose effect becomes stronger as population density increases, such as competition, disease, predation, and parasitism.

Density-independent factor

A limiting factor that affects a population regardless of its density, such as drought, flood, hurricane, fire, and temperature.

r-selected species

Organisms that reproduce quickly, produce many offspring, provide little or no parental care, are usually small, adapt quickly to changing environments, evolve rapidly, and are less likely to become endangered.

K-selected species

Organisms that reproduce slowly, produce few offspring, provide high parental care, are usually large, have more stable populations, and are more likely to become endangered if conditions change.

Organism

One individual living thing.

Community

All the different populations in an area.

Ecosystem

The community plus the nonliving environment.

Biome

A large region with similar climate and organisms.

Biosphere

All ecosystems on Earth.

Food chain

A simple sequence showing who eats whom.

Food web

A network of many connected food chains.

Producer (autotroph)

An organism that makes its own food, usually through photosynthesis.

Primary consumer

An herbivore that eats producers.

Secondary consumer

An organism that eats primary consumers.

Tertiary consumer

An organism that eats secondary consumers.

Decomposer

An organism that breaks down dead organisms and returns nutrients to the environment.

10% rule

Only about 10% of the energy from one trophic level passes to the next.

Trophic level

A feeding level in a food chain or food web.

Energy pyramid

A diagram showing the decrease in energy at higher trophic levels.

Predator removal

If a predator is removed, the prey population usually increases.

Prey overpopulation

If prey overpopulate, they may use up resources and damage the ecosystem.

Producer removal

If a producer is removed, all higher trophic levels may decrease.

Dependency effect

If one species decreases, organisms that depend on it may also decrease.

Gross primary productivity (GPP)

The total amount of energy captured by producers.

Net primary productivity (NPP)

The amount of energy left after producers use some for respiration.

Formula

GPP - CR = NPP

Energy increase effect

If GPP increases, more energy is available for the ecosystem, so more organisms can survive.

Niche

The role of an organism in its ecosystem, including how it gets food, where it lives, and how it interacts with other organisms.

Competition

When organisms try to use the same limited resource.

Intraspecific competition

Competition between members of the same species.

Interspecific competition

Competition between different species.

Resource partitioning

When species avoid competition by using resources in different ways, places, or times.

Symbiosis

A close relationship between two species.

Mutualism

Both species benefit.

Commensalism

One species benefits and the other is unaffected.

Parasitism

One species benefits and the other is harmed.

Predator

An organism that hunts and eats another organism.

Prey

The organism being eaten.

Predator-prey balance

Predator and prey populations affect each other; if prey increase, predators may increase, and if predators increase too much, prey may decrease.

Balanced herbivory

Herbivores eat enough plants to survive without destroying the plant population.

Keystone species

A species with a very large effect on its ecosystem, even if it is not very common; removing it can cause major ecosystem collapse.

Biodiversity

The variety of life in an ecosystem; more biodiversity usually means a healthier and more stable ecosystem.

Succession

The gradual change in a community over time.

Primary succession

Succession that begins where there is no soil, such as bare rock after a volcanic eruption.

Secondary succession

Succession that begins where soil is already present, such as after a forest fire.

Carbon cycle

The movement of carbon through the atmosphere, organisms, and Earth.

Photosynthesis

The process by which producers take in carbon dioxide and use it to make glucose.

Respiration

The process by which organisms release carbon dioxide back into the atmosphere.

Decomposition

The process by which decomposers break down dead matter and release carbon.

Phosphorus cycle

The movement of phosphorus through rocks, soil, water, and organisms; it has no gas phase and is often a limiting factor.

Nitrogen cycle

The movement of nitrogen through the atmosphere, soil, and living things; nitrogen is needed to make proteins and DNA.

Nitrogen fixation

The process that changes nitrogen gas (N₂) into ammonia (NH₃), usually done by bacteria.

Extinction

When a species no longer exists.

Background extinction

The normal, slow rate of extinction over time.

Mass extinction

A period when many species go extinct in a short amount of time.

Endangered tendency

Large, slow-reproducing, K-selected species are most likely to become endangered, while species with many offspring and fast reproduction are less likely to become endangered.

Habitat destruction

When humans damage or remove habitats.

Invasive species

A species introduced into a new area where it has few or no natural predators and can spread quickly and disrupt ecosystems.

Pollution

Harmful substances entering the environment.

Bioaccumulation

When pollutants build up inside one organism over time.

Biomagnification

When the concentration of pollutants increases at higher trophic levels in a food chain, so top predators have the highest concentration of toxins.