Week2 - Patterns of Biodiversity Biogeography's central...

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Patterns of Biodiversity • Biogeography’s central tenet is that each species has a unique geographic range = basic unit of biogeography Range maps • Outline depicts the range as an irregular area within a boundary • Dot points plotted on map where spp has been recorded • Contour indicate variation in density in the range
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Populations factors that affect the size, density, and distribution of populations – environment – survival – reproduction – dispersal Thomas Malthus (1798) - Essay on the Principle of Population r = b + i - d - e r = per capita rate of growth b = birth rate d = death rate i = immigration e = emigration dN/dt = rN = exponential growth
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Multidimensional niche concept (Evelyn Hutchinson 1957) Geographic range is a reflection of the niche Joseph Connell’s study of barnacles (1961) - pioneered use of field experiments in ecology Three niche variables: desiccation, competition, predation Location of range boundaries thus depend on both abiotic and biotic factors Source and sink habitats • Metapopulation Distribution and Abundance Species tend to be most abundant where niche is favorable, and less abundant in less favorable habitats Range boundaries – affected by physical factors, disturbance, and interactions with other organisms
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Physical factors Justus von Liebig (1840): Liebeg’s law of the minimum - biological processes are limited by that single factor that is in shortest supply relative to demand, or for which the organism has the least tolerance may be too simplistic in light of multidimensional niche concept animals can generally disperse to better microclimates, whereas plants and sessile animals are more limited Disturbance Fires, hurricanes, volcanic eruptions, earthquakes, tornados, avalanche, landslide, tsunami Ecological succession: primary vs secondary Fire ecology: chaparral, prairie, forests, hurricane regimes: islands, offshore coral reefs; intertidal habitats Periodic disturbance may limit invasion of habitat by certain species Small scale disturbance also important -- leads to patchy microhabitats and increased diversity
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