8 – Population Distribution and Abundance

Population

A group of individuals of a single species inhabiting a specific area.

4 key considerations when studying a population

Conservation, pest control (diseases), resource management, and human growth.

3 characteristics shared by all populations

Distribution, Density, and Abundance.

Population Distribution

The size, shape, and location that a given population occupies.

Population Density

The number of individuals per unit area.

Population Abundance

Total number of individuals or biomass of a species in a specified area.

Niche

The environmental factors influencing the growth, survival, and reproduction of a species.

Fundamental vs. Realized Niche

Fundamental is where a species could theoretically live; Realized is where it actually lives.

Example of niche restriction: Barnacles

Chthalamus is restricted to the upper intertidal due to competition; Balanus is restricted to lower levels due to desiccation (drying).

Small scale vs. Large scale in ecology

Small scale has little environmental change; Large scale has substantial change/gradients (e.g., mountains).

3 patterns of distribution in nature

Random, Regular (uniform), and Clumped.

3 determinants of distribution patterns

Physical environment, interactions between individuals, or a combination of both.

Interaction: Individuals ignore each other;

Result: Random distribution.

Interaction: Individuals repel each other

Result: Regular (uniform) distribution.

Interaction: Individuals attract each other

Result: Clumped distribution.

Distribution example Stingless bees

Aggressive species are regular; non-aggressive species are random.

Distribution example Desert shrubs

Changes as they grow; root competition leads to regular distribution.

Distribution: Local vs. Large scale

Local scales are determined by colonization/interactions; Large scales are typically clumped.

Relationship between body size and population density

Densities decrease as the size of the organism increases.

Why is the size-density relationship important?

It helps evaluate rarity and predicts the likelihood of extinction.

3 factors determining rarity/commonness

Geographic range (extensive/restricted)

Habitat tolerance (broad/narrow),

Local population size (large/small).

Rarity Example: Peregrine Falcon

Extensive range, broad habitat, but small populations.

Rarity Example: Passenger Pigeon

Extensive range, large populations, but narrow habitat (extinct 1914).

Rarity Example: Mountain Gorilla/California Condor

Restricted range, narrow habitat, and small populations.