AP Biology Ecology Unit

Population Ecology

the study of populations of organisms, especially how they interact with their environment and how factors like birth rates, death rates, immigration, and emigration affect population size and growth over time

Population

a group of individuals of the same species that live in the same area at the same time and can interbreed with one another.

Population Size

the number of individuals in a specific population at a given time

Population Distribution

describes how individuals in a population are spread out across a specific area. There are three main types:

• Clumped (individuals group together)

• Uniform (evenly spaced)

• Random (spread without a clear pattern)

Population Density

the number of individuals of a species per unit area or volume.

Birth Rate

the number of births in a population over a certain period of time

Death Rate

the number of deaths in a population over a certain period of time

Growth Rate

the change in population size over time. It depends on birth rate, death rate, immigration, and emigration

Exponential Growth

when a population grows rapidly because there are no limits on resources.
It makes a J-shaped curve on a graph

Logistic Growth

when a population grows rapidly at first, but then slows down and levels off as resources become limited. This makes an S-shaped curve on a graph

Limiting Factor

is anything that slows down population growth.
It can be:

• Density-dependent (like food, water, space, disease)

• Density-independent (like natural disasters, temperature

Density Dependent

affect a population more strongly as the population gets larger

Density Independent

affect a population regardless of its size or density.

Carrying Capcity

the maximum number of individuals in a population that an environment can support sustainably (without running out of resources)

Inflection Point

the point on a logistic growth curve where the population shifts from increasing faster to increasing slower

dN/dt=rmax*N

exponential growth equation

dN/dt=rmax*N((K-N)/K)

logistic growth equation

Community Ecology

the study of how different species interact with each other in the same area and how those interactions shape the structure and dynamics of the biological community

Community

all the different populations (species) that live and interact in the same area at the same time

Biotic Factor

the living parts of an ecosystem

Abiotic Factor

the non-living parts of an ecosystem

Disturbance

any event that changes an ecosystem, disrupting the community and possibly removing organisms or altering resources

Sucession

the natural, gradual process by which ecosystems change and develop over time, especially after a disturbance

Primary Sucession

• Happens in places with no soil or life to start with

• Example: After a volcanic eruption or glacier retreat

• Takes a long time because soil needs to form first

Secondary Sucession

• Happens in areas where a disturbance destroyed a community, but soil is still present

• Example: After a fire, flood, or farming

• Faster than primary succession

Pioneer Species

the first organisms to colonize a barren or disturbed area

Climax Community

a stable, mature community that has reached a final stage of succession