Assimilation efficiencyA percentage expressing the proportion of ingested energy
that is absorbed into the bloodstream.
AutecologyStudy of the individual in relation to environmental conditions.
AutochthonousOriginating within a system, such as organic matter produced, and
minerals cycled, within streams and lakes. (Cf. allochthonous.)
AutotrophOrganism that obtains energy from the sun and materials from inorganic
sources. Most plants are autotrophs. (Cf. heterotroph.)Basal metabolic rate (BMR) The energy expenditure of an organism that is at rest,
fasting, and in a thermally neutral environment.
Beta diversityThe reciprocal of the mean number of habitats or localities occupied
by a species. Also defined as the proportional difference in species composition
between habitats, that is, the turnover of species among habitats.
BiodiversityThe variety of types of organisms, habitats, and ecosystems on earth or
in a particular place.
BiomassWeight of living material, usually expressed as a dry weight, in all or part
of an organism, population, or community. Commonly presented as weight per
unit of area, or biomass density.
BiomeA major category of ecological communities (e.g. tundra biome).
Biosphere The whole-earth ecosystem, also called the ecosphere. Divided into
biomes.
BiotaAll species living in a defined area.
Biotic factors Environmental influences caused by plants or animals. (Cf. abiotic
factors.)
Birth rate (bx)The average number of offspring produced per individual per unit
time, often expressed as a function of age (x).
BrowsersOrganisms that consume parts of woody plants. (Cf. grazers.)
By-catchThe incidental capture of prey by predators or humans whose efforts are
dependent on, or focus on, other more abundant prey.CarnivoreFlesh eater; organism that eats other animals. (Cf. herbivore.)
Carrying capacityThe number of individuals in a population that the resources of
a habitat can support; the asymptote, or plateau, of the logistic and other sigmoid
equations for population growth.
ChromosomesRod-like structures in eukaryotic cells on which genes reside.
ClimaxThe endpoint of a successional sequence, or sere; a community that has reached
a steady state under a particular set of environmental conditions.
ClineA gradual change in population characteristics or adaptations over a geographic
area.
CoexistenceOccurrence of two or more species in the same habitat; usually applied
to potentially competing species.
CohortA group of individuals of the same age recruited into a population at the
same time.
Cohort life tableSee dynamic life table.
CommunityAn association of interacting populations, usually defined by the nature
of their interaction or by the place in which they live.
CompetitionOccurs when a number of organisms of the same or different species
utilize common resources that are in short supply (exploitation competition); if390 GLOSSARY
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