APBI 418 Lecture : Biol 121- 2010.01.18- Ecology- Community Ecology- Species Richness, Energy Flow (Ch. 53-54).docx
Document Summary
Immigration and extinction rates and the theory of island biogeography. Why does a strong latitudinal gradient in species diversity exist? (higher species richness near equator, and decreasing numbers going south or north) Is a simple count of how many species are present in a given community. Is a weighted measure that incorporates a species" relative abundance as well as its presence or absence. Hard to do on relatively small study plots. Larger patches of habitat contain more species than do smaller patches large areas contain more types of niches and therefore support higher number of species. Immigration rates should decline as the number of species in an area increases individuals that arrive are more likely to represent a species already present. Extinction rates should increase as species richness increases niche overlap and competition becomes more intense. The result is an equilibrium balance between arrival of new species and extinction of existing ones.