lecture+15+community+ecology

Alpha diversity in terms of richness is the number of

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Alpha diversity (in terms of richness) is the number of species in a place; Beta diversity is how quickly species change as you move from place to place. Gamma is the combination. a * b = g (alpha times beta = gamma) In the figure below, which region has the greatest beta diversity?
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Diversity of Fungal Endophytes Total number of “species” (gamma) 4253 Mean number per site (alpha) 848 Largest number per site (max alpha) 1229 Beta Diversity 5.0 80% of diversity is Beta diversity
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Patterns and Controls of Diversity Two big patterns one geographical, one ecological. Geographically the Tropics are diverse! Multiple groups of organisms, land and sea. Part of the reason is the relative consistency of climate, over very long times; part is greater productivity, part of the explanation remains under study
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Ecological Patterns and Controls Ecologically (within a region), the strongest predictor for diversity is disturbance of intermediate frequency. With low disturbance, only good competitors are present; with high disturbance, only the most resilient species. At intermediate levels of disturbance, you get a mosaic with both extreme groups of species (and other species as well)
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Bird Diversity and Extinction ~12,000 species 2000 years ago ~ 9500 species survive now - Given fossil record, we would expect perhaps 10-50 extinctions in 2000 years - 2500 occurred > 20% of bird species have gone extinct, and the vast majority of these extinctions are human-caused
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