Biogeography Chapter 10 The Geography of Diversity.
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BiogeographyChapter 10 The Geography of Diversity
Species DiversitySpecies Richness The number of species in a censusRare species are as important as dominant speciesWorking with census listsShannon Diversity IndexH=(Nj/N)ln(Nj/N)http://www.changbioscience.com/genetics/shannon.html http://monticello.bc.edu/uei/sh_weave.php
Scales of DiversityAlpha Diversity Species richness of a local ecological community (e.g. defined as a study plot such as a hectare)Beta Diversity Change (or turnover) in species composition between two distinct communitiesGamma Diversity Total species richness over a large geographic area such as a biome.
Patterns in Biogeography and GradientsThe Latitudinal Gradient Increasing diversity towards the equatorThe Peninsula Gradient Decreasing diversity away form the mainlandThe Elevation Gradient Species diversity decreases with elevationThe Aridity Gradient Species diversity decreases with diminishing water availabilityAquatic Environments Similar patterns
Species diversity studies reveal a pattern of higher diversity near the equator. The following are a few hypotheses attempting to explain this pattern.
The Peninsula Effect - Variation in species richness of three difference groups of organisms in Baja California, showing a variety of patterns
Causes of these PatternsNonequilibrium MechanismsGlaciationClimate ChangePlate TectonicsEquilibrium MechanismsProductivityHarshness and Abiotic StressClimatic StabilityHabitat HeterogeneityAreaBiotic Interactions
Ecogeographic RulesBergmanns Rule (1847) Animals with larger body forms occur at high latitudes. Larger animals have a lower surface area to volume ration.Allens Rule (1877) Endothermic vertebrates that live in warmer climates have longer appendages.Glogers Rule (1883) Coloration of related forms is correlated to humidity with darker coloration occurring in more humid regions. Most likely driven by crypsis (camouflage)
Bergmanns Rule and adaptation to temperature in the Bushy-tailed woodrat (Neotomoa nicerea), over both geographic space and evolutionary time.
Allens Rule showing ear length in rabbits and foxes where the organism on the left occurs in a hot desert habitat and the one on the right occurs in a cold tundra environment
Macroecology: Assembly of Continental BiotasMacroecology A quantitative and statistical approach that tries to identify general ecogeographic patterns and to understand the underlying mechanisms of the distributions of ecological particles (organism, species, biotas, or replicated sample plots; Brown 1995)
Relationship between area of range and body size showing that there are few large species with small geographic ranges
Natural ExperimentsThe Great American Interchange Isolated from 160 million years before present Formation of the Central American landbridge at 3.5 million years agoSee the effects of dispersal , interspecific interaction, extinction, and evolutionHalf of South American species are derived from North American while only 10% of North American species are derived from South American
The Great American InterchangeNorthern species had three advantagesThey were better migratorsThe were better survivors and speciatorsThe were better competitors
Organisms that crossed or were filtered out by the Central American Landbridge