This document is written according to the IEB subject assessment guidelines. It is a complete summary of the population ecology section and is all that is needed for the IEB final examinations.
“ The study of the changes in number and size of organisms in populations, the factors that influence
these changes and the effect the changes have on that population and populations in the area”
Term Definition
**Individuals A single living organism
A group of organisms of the same species that occur in a
**Population
particular area and are able to interbreed freely
**Community A group of populations occurring in a particular area
A unit of biotic communities in interaction with each other as
**Ecosystem
well as with the abiotic factors in an area
A group of organisms that can reproduce successfully to
Species
produce fertile offspring
The specific type of environment in which a plant or animal
Habitat
species normally occurs
Describes the role and space that an organism occupies in
Ecological niche
an ecosystem
The birth rate of a population, usually expressed as the
Natality
number of live births per thousand individuals per year
Mortality The death rate of a population
The one-way movement of organisms into an area to settle
Immigration
there
The one-way movement of organisms out of an area to
Emigration
settle elsewhere
When a population moves out of its original habitat but
Migration
returns later, often driven by food availability
Factors that take effect when population size or density
Density-dependent factors
increases
Factors that limit population size regardless of its current
Density-independent factors
size
The maximum number of individuals an environment can
Carrying capacity
sustain
Factors that limit population growth and exceed its
Environmental resistance
maximum growth rate
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