Population Ecology and Demography Overview

Population ecology

The study of factors that affect population size and how these factors change over space and time.

Population

A group of interbreeding individuals of the same species occupying the same area at the same time.

Demography

The study of birth rates, death rates, age distributions, and sizes of populations.

Density

The number of organisms in a given unit area or volume.

Dispersion

The way individuals are spaced within the population's living area.

Growth rates

The overall number of individuals (birth vs death).

Population density

Defined as the number of organisms of a given species in a given unit area or volume.

Methods to quantify population density

Includes simple visual count, various sampling devices, traps, and capture techniques.

Clumped dispersion

Individuals live close together in groups; this is the most common pattern.

Uniform dispersion

Individuals live at a constant distance from one another.

Random dispersion

Individuals live at variable and random distances from one another; this is the rarest pattern.

Rate of natality

Number of organisms that are born.

Rate of fatality

Number of organisms that die.

Rate of immigration

Number of organisms entering population.

Rate of emigration

Number of organisms leaving population.

Life table

A record of survival and reproductive rates in a population, broken down by age, size, or developmental stage.

Survivorship curve

Provides information of the numbers of surviving individuals for each age class in a population.

Factors affecting population growth

Includes age at first reproduction, frequency of reproduction, average number of offspring, reproductive life span, and average death rate.

Availability of resources

Refers to whether resources like food, energy, and space are limited or not.

Density-dependent factors

Includes parasitism, predation, and competition.