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Eco Evo Exam 4(c.18)
Definitions
Term | Definition |
---|---|
Ecotone | A boundary created by sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species. |
Interdependent communities | Communities in which species depend on each other to exist. |
Independent communities | Communities in which species do not depend on each other to exist. |
Species richness | The number of species in a community. |
Relative abundance | The proportion of individuals in a community represented by each species. |
Log-normal distribution | A normal, or bell-shaped, distribution that uses a logarithmic scale on the x-axis. |
Rank-abundance curve | A curve that plots the relative abundance of each species in a community in rank order from the most abundant species to the least abundant species. |
Species evenness | A comparison of the relative abundance of each species in a community. |
Simpson's index | A measurement of species diversity. |
Shannon's index (H') | A measurement of species diversity. Also known as Shannon-Wiener index. |
Keystone species | A species that substantially affects the structure of communities despite the fact that individuals of that species might not be particularly numerous. |
Intermediate disturbance hypothesis | The hypothesis that more species are present in a community that occasionally experiences disturbances than in a community that experiences frequent or rare disturbaces. |
Food chain | A linear representation of how different species in a community feed on each other. |
Food web | A complex and realistic representation of how species feed on each other in a community. |
Trophic level | A level in a food chain or food web of an ecosystem. |
Primary consumer | A species that eats producers. |
Secondary consumer | A species that eats primary consumers. |
Tertiary consumer | A species that feeds at several trophic levels. |
Omnivore | A species that feeds at several trophic levels. |
Guild | Within a given trophic level, a group of species that feeds on similar items. |
Direct effect | An interaction between two species that does not involve other species. |
Indirect effect | An interaction between two species that involves one or more intermediate species. |
Trophic cascade | Indirect effects in a community that are initiated by a predator. |
Density-mediated indirect effect | An indirect effect caused by changes in the density of an intermediate species. |
Trait-mediated indirect effect | An indirect effect caused by changes in the traits of an intermediate species. |
Community stability | The ability of a community to maintain a particular structure. |
Community resistance | The amount that a community changes when acted upon by some disturbance, such as the addition or removal of a species. |
Community resilience | The time it takes after a disturbance for a community to return to its original state. |
Bottom-up control | When the abundances of trophic groups in nature are determined by the amount of energy available from the producers in a community. |
Top-down control | When the abundance of trophic groups is determined by the existence of predators at the top of the food web. |
Alternative stable state | When a community is disturbed so much that the species composition and relative abundance of populations in the community change, and the new community structure is resistant to further change. |