Glossary
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Adapted from Watt et al. (1995), Ricklefs & Miller (2000), and Krebs (2001).Abiotic factorsCharacterized by the absence of life; include temperature, humidity,
pH, and other physical and chemical influences. (Cf. biotic factors.)
AdaptationA genetically determined characteristic that enhances the ability of
an individual to cope with its environment; an evolutionary process by which
organisms become better suited to their environments.
Adaptive radiationThe evolution of ecological and phenotypic diversity within a rapidly
multiplying lineage. It is the differentiation of a single ancestor into an array of
species that inhabit a variety of environments and that differ in the morpholo-
gical, physiological, and behavioral traits used to exploit those environments.
Age classThe individuals in a population of a particular age.
Age structureThe relative proportions of a population in different age classes.
AggregationOrganisms show an aggregated spatial distribution when they co-occur
significantly more than would be expected from a (completely random) Poisson
distribution. This clumping is reflected in a variance mean ratio significantly
greater than unity. Macroparasitesare usually aggregated in their host population,
the majority of hosts harboring a few or no parasites and a few hosts harboring
large parasite burdens. Aggregated distributions are often well described empiri-
cally by the negative binomial distribution; the degree of aggregation is inversely
proportional to the negative binomial parameter, k.
AlleleOne of a pair of characters that are alternative to each other in inheritance,
being governed by genes situated at the same locus on homologous chromosomes.
AllochthonousOriginating outside a system, such as minerals and organic matter
transported from marine to terrestrial habitats or from land into streams and lakes.
(Cf. autochthonous.)
AllopatricOccurring in different places; usually referring to geographic separation
of populations. (Cf. sympatric.)
Alpha diversityThe mean variety of organisms occurring in a particular place or
habitat; often called local diversity.
AmbientReferring to conditions of the abioticenvironment surrounding the organism.
AntibodyA protein produced in the blood of vertebrates in response to an antigen.
The antibody produced is able to bind specifically to that antigen, and plays a role
in its inactivation or removal by the immune system.
AntigenA substance, generally foreign, capable of inducing antibodyformation.
Apparent competitionA situation in which two or more species negatively affect
one another indirectly through their interaction with a common predator.WECD02 08/17/2005 04:54PM Page 389