Week8 - Species Diversity in Continental and Marine...

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Species Diversity in Continental and Marine Habitats Questions: 1) What determines the numbers and kinds of species that occur together in one place? 2) Why do the numbers and kinds of species vary from one place to another? Species richness: the number of species in a local area or geographic region Alpha diversity: the species richness of a local ecological community Beta diversity: the change (turnover) in species composition over a relatively small distance - often between different but adjacent habitats Gamma diversity: total species richness of a large geographic region Species richness increases in most groups in a latitudinal gradient from temperate to tropical regions. Organisms restricted to temperate regions show an exception to this pattern (e.g., Pinaceae has highest diversity at the mid latitudes). Comparisons for #’s of tree species: Northern Canada -- 1 - 5 spp per hectare Eastern N. America -- 10 - 30 spp per hectare South/Central America -- 40 - 100 spp per hectare Animals that depend on plants will probably show comparable patterns of diversity shown for plants in Table 15.1 . Similar latitudinal gradients demonstrated for continents are also found in the oceans. Tropical coral reefs support the most diversity. Ditto for freshwater systems. What processes explain these patterns? Many hypotheses have been proposed ( Table 15.2 ). These hypotheses are not necessarily mutually-exclusive, and they can be divided into two classes: Equilibrial: adjustments of biota to current geological, climatic, and oceanographic conditions Nonequilibrial: reflect perturbations of the past (e.g., glaciation) Global patterns to consider: the amount of sunlight changes with latitude (hypotheses about productivity, harshness, climatic stability, habitat heterogeneity); 8 - 1
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so does the surface area (hypotheses about habitat heterogeneity) Patterns of Diversity for particular geographic features Peninsulas can be thought of as an island connected to a mainland. Diversity decreases with increasing distance to connection to continent. latitudinal gradient may confuse the pattern, though.
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This note was uploaded on 07/17/2008 for the course EEOB 700 taught by Professor Wolfe during the Winter '05 term at Ohio State.

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Week8 - Species Diversity in Continental and Marine...

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