A Glossary of Ecology and Population Biology Terms

Chitral, or spotted deer, grazing.
Richard I'Anson / Getty Images

This glossary defines terms that are commonly encountered when studying ecology and population biology.

Character Displacement

Character displacement is a term used in evolutionary biology to describe the process by which differences are established among similar species with overlapping geographical distributions. This process involves a divergence of adaptations or other characteristics in the similar species in locations where the animals share a habitat. This divergence is spurred on by competition between the two species.


A demographic is a characteristic that is used to describe some aspect of a population and that can be measured for that population, such as growth rate, age structure, birth rate, and gross reproduction rate.

Density Dependent

A density-dependent factor influences individuals in a population to a degree that varies in response to how crowded or dense the population is.

Density Independent

A density-independent factor influences individuals in a population in a manner that does not vary with the extent of crowding present in the population.

Diffuse Competition

Diffuse competition is the sum-total effect of weak competitive interactions among species that are only distantly connected within their ecosystem.

Ecological Efficiency

Ecological efficiency is a measure of the amount of energy that is produced by one trophic level and is incorporated into the biomass of the next (higher) trophic level.

Ecological Isolation

Ecological efficiency is the isolation of competing species of organisms made possible by differences in each species food resources, habitat use, activity period, or geographical range.

Effective Population Size

The effective population size is the average size of a population (measured in the number of individuals) that can contribute genes equally to the next generation. The effective population size is in most cases less than the actual size of the population.


The term feral refers to an animal that comes from domesticated stock and that has subsequently taken up life in the wild.


 The degree to which a living organism is suited to a particular environment. The more specific term, genetic fitness, refers to the relative contribution the organism of a particular genotype makes to the next generation. Those individuals exhibiting higher genetic fitness are selected for and as a result, their genetic characteristics become more prevalent within the population.

Food Chain

The path that energy takes through an ecosystem, from sunlight to producers, to herbivores, to carnivores. Individual food chains connect and branch to form food webs.

Food Web

The structure within an ecological community that characterizes how organisms within the community acquire nutrition. Members of the food web are identified according to their role within it. For example, produces fix atmospheric carbon, herbivores consume producers, and carnivores consume herbivores.

Gene Frequency

The term gene frequency refers to the proportion of a particular allele of a gene in the gene pool of a population.

Gross Primary Production

Gross primary production (GPP) is the total energy or nutrients assimilated by an ecological unit (such as an organism, a population, or an entire community).


Heterogeneity is a term that refers to the variety of either an environment or population. For example, a heterogeneous natural area is composed of numerous different habitat patches that differ from one another in various ways. Alternatively, a heterogeneous population has high levels of genetic variation.


The term intergrading refers to the merging of characteristics of two populations where their ranges come into contact. The intergrading of morphological traits is often interpreted as evidence that the two populations are not reproductively isolated and should therefore be treated as a single species.


The term k-selected is used to describe organisms whose populations are maintianed near their carrying capacity (maximum number of individuals supported by an environment).


 A type of interaction between two different species that enables both species to benefit from their interaction and in which the interaction is necessary to both. Also referred to as symbiosis.


The role an organism occupies within its ecological community. A niche represents a unique way in which the organism relates to other biotic and abiotic elements of its surroundings.


A group of organisms of the same species that inhabit the same geographical location. 

Regulatory Response

A regulatory response is a set of behavioral and physiological adaptations that an organism makes in response to exposure to environmental conditions. Regulatory respones are temporary and do not involve modifications in morphology or biochemistry.

Sink Population

A sink population is a breeding population that does not produce enough offspring to maintain itself in coming years without immigrants from other populations.

Source Population

A source population is a breeding group that produces enough offspring to be self-sustaining and that often produces excess young that must disperse to other areas.

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Klappenbach, Laura. "A Glossary of Ecology and Population Biology Terms." ThoughtCo, Aug. 27, 2020, thoughtco.com/glossary-of-ecology-and-population-terms-130927. Klappenbach, Laura. (2020, August 27). A Glossary of Ecology and Population Biology Terms. Retrieved from https://www.thoughtco.com/glossary-of-ecology-and-population-terms-130927 Klappenbach, Laura. "A Glossary of Ecology and Population Biology Terms." ThoughtCo. https://www.thoughtco.com/glossary-of-ecology-and-population-terms-130927 (accessed March 22, 2023).