Ess Ib Definitions Topic 4

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Biodiversity

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The amount of biological or living diversity per unit area. It includes the concepts of species, habitat and genetic diversity.

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Climax community

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A community of organisms that is more or less stable, and that is in equilibrium with natural environmental conditions such as climate; the end point of ecological succession.

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Correlation

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A measure of the association between two variables.

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Diversity

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A generic word for heterogeneity; it may refer to species, habitat, or genetic heterogeneity.

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Genetic diversity

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The range of genetic material present in a gene pool or population of a species.

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Habitat diversity

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The range of different habitats or number of ecological niches per unit area in an ecosystem, community or biome.

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Diversity index

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A numerical measure of species diversity that is derived from both the number of species (variety) and their proportional abundance.

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Species diversity

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The variety of species per unit area. This includes both the number of species present and their relative abundance.

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Evolution

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The cumulative, gradual change in the genetic characteristics of successive generations of a species or race of an organism, ultimately giving rise to species or races different from the common ancestor. Evolution reflects changes in the genetic composition of a population over time.

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Isolation

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The process by which two populations become separated by geographical, behavioural, genetic or reproductive factors. If gene flow between the two subpopulations is prevented, new species may evolve.

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Plate tectonics

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The movement of the eight major and several minor internally rigid plates of the Earth’s lithosphere in relation to each other and to the partially mobile asthenosphere below.

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Sere

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The set of communities that succeed one another over the course of succession at a given location.

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Speciation

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The process through which new species form.

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Succession

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The orderly process of change over time in a community. Changes in the community of organisms frequently cause changes in the physical environment that allow another community to become established and replace the former through competition. Often, but not inevitably, the later communities in such a sequence or sere are more complex than those that appear earlier.

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Zonation

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The arrangement of plant communities or ecosystems into parallel or sub‐parallel bands in response to change, over a distance, in an environmental factor. The main biomes display zonation in relation to latitude and climate. Plant communities may also display zonation with altitude on a mountain, or around the edge of a pond in relation to soil moisture.