Population Distributions

Geographic range

A measure of the total area covered by a population.

Geographic range factor

Any environmental, biological, or physical condition that determines where a species lives and where its boundaries stop

Spatial structure

The pattern of density and spacing of individuals in a population.

Fundamental niche

The range of abiotic conditions under which species can persist.

Realized niche

The range of abiotic and biotic conditions under which a species persists.

Endemic species

Species that live in a single, often isolated, location.

Cosmopolitan

Species with very large geographic ranges that can span several continents.

Ecological niche modeling

The process of determining suitable habitat conditions for a species.

Ecological envelope

The range of ecological conditions predicted to be suitable for a species.

Abundance

The total number of individuals in a population within a defined area.

Density

The number of individuals in a population per unit of area or volume.

Dispersion

The spacing of individuals with respect to one another within a geographic range.

Clustered dispersion

A dispersion pattern where individuals are aggregated in discrete groups.

Evenly spaced dispersion

A dispersion pattern where each individual maintains a uniform distance from neighbors.

Random dispersion

A dispersion pattern where the position of each individual is independent of others.

Dispersal

The movement of individuals from one area to another, essential for colonization.

Dispersal limitation

A substantial barrier that prevents dispersal between suitable habitats.

Lifetime dispersal distance

The average distance an individual moves from birth place to where it reproduces.

Habitat corridor

A strip of favorable habitat between two patches that facilitates dispersal.

Census

A count of every individual in a population.

Mark-recapture survey

A population estimation method involving capturing, marking, releasing, and recapturing a subset.

Positively correlated; highest abundance species have largest geographic ranges.

Abundance and geographic range

Negatively correlated; smallest-bodied species live at the highest densities.

Body mass and population density

Ideal free distribution

When individuals distribute among habitats to achieve the same per capita benefit.