Biology Ii - Tarrant County College

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Community

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The assemblage of many populations that live in the same place at the same time.

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Community ecology

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The study of how groups of species interact and form functional communities.

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Organismic model

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Frederic Clements

View of the community with predictable and integrated associations of species separated by sharp boundaries, which depicts the ecological community as a superorganism.

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Individualistic model

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Henry Allen Gleason 1926

An assemblage of species coexisting primarily because of similarities in their physiological requirements and tolerances.

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Principle of species individuality

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Each species is distributed according to its physiological needs and population dynamics; most communities intergrade, or merge into one another gradually, and that competition does not create distinct vegetational zones.

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Area hypothesis

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The larger areas contain more species than smaller areas because they can support larger populations and a greater range of habitats.

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Species-area effect

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The relationship between the amount of available area and the number of species present.

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Productivity hypothesis

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Proposes that greater production by plants results in greater overall species richness.

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Evaporation rate

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The rate at which water moves into the atmosphere through the processes of evaporation.

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Intermediate-disturbance hypothesis

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Joseph Connell

Highest numbers of species are maintained in communities with intermediate levels of disturbance.

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Relative abundance

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Frequency of occurrence of species in a community.

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Metagenomics

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Field which seeks to identify and analyze the collecive microbial genomes contained in a community of organisms.

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Diversity-stability hypothesis

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Outbreaks of pests are often on cultivated land or land disturbed by humans, both of which are species-poor communities with few naturally occurring species.

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Succession

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The gradual and continuous change in species composition and community structure over time

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Primary succession

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Succession on a newly exposed site that has no biological legacy in terms of plants, animals, or microbes, such as bare ground caused by volcanic eruption or the sediment created by the retreat of glaciers.

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Secondary succession

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Succession on a site that has already supported life but has undergone a disturbance, such as a fire, tornado, hurricane, or flood.

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Climax community

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Succession as proceeding to a distinct end point.

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Sere

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each phase of a succession

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Facilitation

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Each colonizing species makes the environment a little different - a little shadier or a little richer in soil nitrogen - so that it becomes more suitable for other species, which then invade and outcompete the earlier residents.

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Inhibition

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Early colonists prevent colonization by other species

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Tolerance

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Joseph Connell & Ralph Slayter 1977

Third mechanism of succession

Any species can start succession, but the eventual climax communityis reached in a somewhat orderly fasion. The species that establish and remain do not change the environment in ways that either facilitate or inhibit subsequent colonists.

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Equilibrium model of island biogeography

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Robert MacArthur and E.O. Wilson 1960's

Model explains the process of succession on new islands, where gradual buildup of species proceeds from a sterile beginning.. Holds that the number of species on an island tends toward an equilibrium number that is determined by the balance between two factors: immigration rates and extinction rates.

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Source pool

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The pool of potential species available to colonize the island.

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Biosphere

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One giant interconnected ecosystem that unite the Earth and its living species via global nutrient cycles, such as the carbon, nitrogen, and sulfur cycles

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Eutrophication

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Process by which elevated nutrient levels lead to an overgrowth opf algae and the subsequent depletion of water oxygen levels

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Fossil fuels

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Material from primary producers is transformed into deposits of coal, gas, and oil.

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Nitrogen fixation

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Convert atmospheric nitrogen to forms usable by other organisms.

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Nitrification

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Soil bacteria convert NH3 or NH4+ to NO3-, a form of nitrogen commonly used by plants.

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Assimilation

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Inorganic substances are incorporated into organic molecules.

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Ammonification

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Conversion of organic nitrogen to NH3 and NH4+

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Denitrification

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The reduction of nitrate NO3- to gaseous nitrogen N2