Glossary

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D

Decomposition
The breakdown of complex, energy-rich organic molecules to simple inorganic constituents.
Degradative succession
A temporal succession of species that occurs on a degradable resource.
Demographic process
A process capable of changing the size of a population, viz. birth, death or migration.
Density dependence
The tendency for the death rate in a population to increase, or the birth or growth rate to decrease, as the density of the population increases.
Density independence
The tendency for the death, birth or growth rate in a population neither to rise nor fall as the density increases.
Deoxyribonucleic acid (DNA)
The carrier of genetic information in cells; capable of self-replication as well as coding for RNA synthesis.
Desert
A desolate and barren region, usually deficient in available water, and with scant vegetation.
Deterministic forces
Forces which can be characterized exactly with no element of chance or probability (cf. Stochastic forces).
Detritivory
Consumption of dead organic matter (detritus) usually together with associated microorganisms.
Developmental threshold
The body temperature of an organism below which no development occurs.
Devonian period
A geological era lasting from approximately 400 to 360 million years ago.
Diapause
A state of arrested development or growth, accompanied by greatly decreased metabolism, often correlated with the seasons, usually applied only to insects.
Dicotyledon
A member of one of the two classes of flowering plants, distinguished by having seedlings with usually a pair of seedling leaves (cotyledons) and commonly with floral parts in fours or fives, leaves with net venation and ability to form wood by secondary (cambial) cell division within the tissues.
Differential resource utilization
Normally used only in the context of interspecific competition, the use of different resources by two different species, or the use of the same resource at a different time, in a different place, or generally in a different manner.
Diffusion coefficient
A measure of the rate of movement of solutes or gases in response to a concentration gradient in the medium in which they are dissolved.
Dimorphism
The existence of two distinct forms of an organism or organ, e.g. winged and wingless generations in the life of aphids, winged and wingless seeds produced from the same flower.
Disaster
Major disturbances in the life of a community or population which occur sufficiently often to leave their record in the 'genetic memory' of the population (cf. Catastrophe).
Discrete generations
A series of generations in which, strictly, each one finishes before the next begins. Commonly, however, the early life cycle stages of the succeeding generation overlap with the end of the final stages of the preceding generation.
Disease
The disturbed or altered condition of an organism (malfunctioning) caused by the presence of an antagonist (toxin or pathogen) or the absence of some essential (e.g. micronutrient or vitamin).
Disjunct distribution
The geographical distribution of a species or other taxonomic class of which parts are widely separated.
Dispersal
The spreading of individuals away from each other, e.g. of offspring from their parents and from regions of high density to regions of lower density.
Dispersal polymorphism
Two or more types of dispersal structures found within a species or among the progeny of an individual.
Distribution
The spatial range of a species, usually on a geographic but sometimes on a smaller scale, or the arrangement or spatial pattern of a species over its habitat.
Disturbance
In community ecology, an event that removes organisms and opens up space which can be colonized by individuals of the same or different species.
Diversity
see Species diversity.
Diversity index
A mathematical index of species diversity in a community.
Dominant species
Species which make up a large proportion of community biomass or numbers.
Donor-controlled models
Mathematical models of predator - prey interactions in which the donor (prey) controls the density of the recipient (predator) but not the reverse.
Dormancy
An extended period of suspended or greatly reduced activity, e.g. aestivation and hibernation.
Dynamic equilibrium
The state of a system when it remains unchanged because two opposing forces are proceeding at the same rate.
Dynamically fragile
Describes a community which is stable only within a narrow range of environmental conditions.
Dynamically robust
Describes a community which is stable within a wide range of environmental conditions.

 
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