FA2008 - BILD 3 - Lecture 10 (Community Ecology - 03)

FA2008 - BILD 3 - Lecture 10 (Community Ecology - 03) -...

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11/6/08 1 III. SPECIES DIVERSITY Species diversity : two components Species richness (number of species) Relative abundance of species (evenness) Certain species have an especially large impact on the structure of entire communities *highly abundant, or *they play a pivotal role in community dynamics Dominant species – Are those species in a community that are most abundant or have the highest biomass – Exert powerful control over the occurrence and distribution of other species Redwood forest Keystone species – Are not necessarily abundant in a community – Exert strong control on a community by their ecological roles, or niches
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11/6/08 2 Field studies of sea stars ( Pisaster ochraceous ) Exhibit their role as a keystone species in intertidal communities Why would species diversity in the intertidal decrease when Pisaster was removed? a. Pisaster was a superior competitor b. Pisaster predation kept superior competitors in check c. Competitive exclusion d. Resource partitioning Mytilus californicus (mussel) Pisaster ochraceous (sea star) Foundation Species - Ecosystem “Engineers” Some organisms exert their influence by causing physical changes in the environment Presence of black rush ( Juncus ) increases species number Evidence - removal experiments IV. TROPHIC STRUCTURE the feeding relationships between organisms in a community (what you eat and who eats you)
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