BILD 3 Lecture Notes - Lecture 21: Foundation Species, Insular Biogeography, Keystone Species

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13 Mar 2017
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Field studies of sea stars: exhibit their role as a keystone species in intertidal communities. Some organisms exert their influence: by causing physical changes in the environment that affect community structure. Some foundation species act as facilitators: that have positive effects on the survival and reproduction of some of the other species in the community. Bottom-up and top-down controls: the bottom-up model of community organization, proposes a unidirectional influence from lower to higher trophic levels. Is an even that changes a community: removes organisms from a community, alters resource availability. Is a significant disturbance in most terrestrial ecosystems. Is often a necessity in some communities: the large scale fire in yellowstone national park in 1988, demonstrated that communities can often respond very rapidly to a massive disturbance. Is the sequence of community and ecosystem changes after a disturbance: primary succession, occurs where no soil exists when succession begins.

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