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BIOL 4150
Scott Brandon

How Do Species Interaction Cause Trophic Cascades?  A progression of indirect effects across successively lower trophic levels  trophic cascade. One predator can affect many different species  Trophic cascades may have effects across multiple and very different ecosystems because individuals of many species move from one habitat type to another. Keystone species have wide-ranging effects  A species that exerts an influence out of proportion to it abundance is called a keystone species; may influence both the species richness of communities and the flow of energy and materials through ecosystems.  Keystone species are not necessarily predators. A plant species that serves as food for many different animals can also be a key stone species. How Do Disturbances Affect Ecological Communities?  Disturbance is an event that changes the survival rate of one or more species in an ecological community; may remove some species from a community, but may open up space and resources for other species.  Keystone species generate disturbance, so do physical events. Succession is a change in a community after a disturbance  Change in composition of an ecological community following a disturbance is called succession.  Primary succession begins on sites that lack living organisms.  Secondary succession begins on sites where some organisms have survived the most recent disturbance.  Species that colonize a site soon after the disturbance often alter environmental conditions for other species that come after them.  Secondary succession may begin with the dead parts of organisms. Species richness is greatest at intermediate levels of disturbance  Intermediate disturbance hypothesis: explains the low species richness in area with high disturbance levels by suggesting that only species with great dispersal abilities and high reproductive rates can persist in such areas; e
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