Most organisms participate in mutualistic interactions..doc

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Biomedical Engineering
BMEN 515
William Huddleston

Most organisms participate in mutualistic interactions. 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; expla
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