Population Dynamics

Population

A group of organisms of the same species living in the same area at the same time.

Population Density

The number of individuals of a species in a specific area or volume. (e.g., 100 oak trees per acre).

Dispersion

How individuals in a population are spaced out in their habitat (clumped, random, or uniform).

Range

The total area over which a particular species is naturally found.

Population Growth Rate

How quickly a population is increasing or decreasing in size. (Calculated using births, deaths, immigration, and emigration).

Mortality Rate

The death rate; the number of individuals dying in a population over a specific time.

Birth Rate

The number of individuals born in a population over a specific time.

Zero Population Growth

When the birth rate equals the death rate, so the population size is stable (not growing or shrinking).

Immigration

Individuals moving INTO a population's area from elsewhere.

Emigration

Individuals moving OUT of a population's area to go elsewhere.

Carrying Capacity

The maximum number of individuals of a species that an environment can sustain indefinitely without damaging the environment.

Exponential Curve (J-Curve)

A graph showing unrestricted population growth where the population increases at an accelerating rate. It's shaped like a 'J'. This happens when resources are unlimited.

Logistic Curve (S-Curve)

A graph showing growth that starts fast but then slows down and levels off as the population approaches its carrying capacity. It's shaped like an 'S'.

Population Overshoot

When a population temporarily grows beyond its carrying capacity, using resources faster than they can be replenished.

Die Off

A rapid decline in population size that usually follows an overshoot because the environment can no longer support the high number of individuals.

Density Dependent Factor

A limiting factor (like disease or competition) that gets worse as the population density increases.

Density Independent Factor

A limiting factor (like a natural disaster or severe weather) that affects the population size regardless of how dense the population is.

Extinction

When all individuals of a species die out globally, and the species no longer exists.

Habitat Fragmentation

The breakup of a large, continuous habitat into smaller, isolated patches, often by human development, which threatens populations.

Interspecific Competition

Competition BETWEEN members of two different species for the same limited resource (e.g., lions and hyenas fighting over a carcass).

Intraspecific Competition

Competition AMONG members of the same species for the same limited resource (e.g., two male deer fighting over a female).

Dependent Variable

In an experiment or on a graph, this is the variable that changes in response to the independent variable (e.g., population size is often the dependent variable that changes over time).