Biol 303 Definitions

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Character Displacement

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A measurable physical difference between two species which has arisen by natural selection as a result of the selection pressures on one or both from competition with the other.

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Niche Differentiation

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The tendency for coexisting species to differ in their niche requirements.

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Competition coefficient

Back 3

In interspecific competition, a measure of the competitive effect of one species on another relative to the competitive effect of the second species on itself.

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Competitive release

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The expansion of the niche of a species associated with the lack of competition with other species; for instance, because it occurs on an island where competitors are absent.

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Density Dependence

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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.

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Density independence

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The tendency for the death, birth or growth rate in a population neither to rise nor fall as the density increases.

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Inverse density dependence

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occurs when a mortality due to a particular factor decreases in magnitude (or a fecundity factor increases) as density increases

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Fitness

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The contribution made to a population of descendants by an individual relative to the contribution made by others in its present population. The relative contribution that an individual makes to the gene pool of the next generation.

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Functional response Theory

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The relationship between a predator's consumption rate of prey and the density of those prey.

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Genet

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The organism developed from a zygote. The term is used especially for modular organisms and members of a clone to define the genetic individual and to contrast with 'ramet' the potentially physiologically independent part that may arise from the iterative process by which modular organisms grow.

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Ramet

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An offshoot or module formed by vegetative growth in some plants and modular invertebrates that is actually or potentially independent physiologically, e.g. the runners of the strawberry, the tubers of the potato, the polyps on a colonial hydroid.

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Interference

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Competition between two organisms in which one physically excludes the other from a portion of habitat and hence from the resources that could be exploited there.

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Exploitation

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Competition in which any adverse effects on an organism are brought about by reductions in resource levels caused by other, competing organisms.

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Intraspecific Competition

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Competition between individuals of the same species.

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Interspecific Competition

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Competition between individuals of different species.

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Law of Constant Final Yield

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The maximum yield (max. weight of plant maternal per unit area) will be reached at some threshold density, depending on the species: higher the initial density, the sooner that value is reached.

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Polymorphism

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The occurence together in the same habitat at the same time of two or more distinct forms of a species in such proportions the rarest of them cannot be maintained by recurrent mutation.

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Transient polymorphism

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The occurrence of two (or more) forms of a species or of genes (alleles) within a population while one form is being replaced by another.

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Stable polymorphism

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a system of genes in which two alleles are maintained in stable equilibrium because the heterozygote is more fit than either of the homozygote

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Regulation

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A tendency in a population for some factor(s) to cause density to increase when it is low and to decrease when it is high.

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Limitation

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a tendency in a population for some factor(s)to cause a change (usually a decrease) in average density.

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K (carrying capacity)

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The maximum population size that can be supported indefinitely by a given environment, at which intraspecific competition has reduced the per capita net rate of increase to zero. An idealized concept not to be taken literally in practice.

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R-Selection (Ruderals)

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associated with short life span & high seed production in highly disturbed but potentially productive environment

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C-Selection (Competitors)

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selected for high competitive ability which depends on plant characteristics which maximizes the capture of resources in productive, relatively undisturbed environments

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S-Selection (Stress-tolerators)

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has brought about reductions in both vegetative & reproductive vigor, adaptation which allow endurance of continually unproductive environment

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Optimal Diet-Choice

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Mathematical formulation of prey selection that would, in theory, provide the best energy returns to the consumer: used as a yardstick to assess actual performance.

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Marginal value theorem

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A proposed decision-rule (derived from theoretical exploration) for a predator foraging from patches of prey which it depletes, which states that the predator should leave all patches at the same rate of prey extraction, namely the maximum average overall rate for that environment as a whole.

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Stable Age Distribution

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provided the age specific birth & survival rates remain constant throug time, the population eventually reaches a stable age distribution (the proportion of individuals in each age grp also ramin unchanged)
All age classes grow or decline at the same rates & so does the total population.