region where two communities come together with a relatively sharp boundary indicated by a rapid replacement of species
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serpentine soils
soils toxic to many plants due to the concentration of heavy metals and lack of nutrients
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interdependent communities
species depend on each other to exist
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independent communities
species do not depend on each other to exist
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species richness
the number of species in a community
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absolute abundance
the number of individuals of each species that are counted
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relative abundance
the proportion of individuals in a community represented by each species
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log-normal distribution
a normal, bell-shaped distribution that uses a logarithmic scale on the x axis
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rank-abundance curves
show the relative abundance of each species in a community in rank order from the most abundant to the least abundant
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species eveness
comparison of the relative abundance of each species in a community
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keystone species
a species that substantially affects the structure of communities despite the fact that individuals of the species might not be particularly numerous
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intermediate disturbance hypothesis
more species are present in a community that experiences occasional disturbances than in a community that experiences frequent or rare disturbances
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food chain
linear representations of how species in a community consume each other and therefore how they transfer energy and nutrients from one group to another in an ecosystem
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food webs
complex and realistic representations of how species feed on each other in a community and include links among many species of producers, consumers, detritivorest, scavengers, and decomposers
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trophic levels
levels in a food chain or food web of an ecosystem
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primary consumers
species that eat producers
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secondary consumers
species that eat primary consumers
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tertiary consumers
species that eats secondary consumers
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omnivores
species that feeds at several trophic levels
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guild
within a given trophic level, a group of species that feeds on similar items
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direct effect
an interaction between two species that does not involve other species
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indirect effect
when two species interact in a way that involves one or more intermediate species
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trophic cascade
when indirect effects are initiated by a predator
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density mediated indirect effect
an indirect effect caused by changes in the density of an intermediate species
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trait mediated indirect effect
indirect effects that are caused by changes in the traits of an intermediate species
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bottom-up control
when the abundances of trophic groups in nature are determined by the amount of energy available from the producers in the community
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top-down control
when the abundance of trophic groups is determined by the existence of predators at the top of the foodweb