Community Biology Ch 53 U115PP

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Community Biology- Ch 53 U115PP
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• Concept 53.4 Biogeographic factors affect
  community diversity
• Two key factors correlated with a communitys
  species diversity
• Are its geographic location and its size

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Equatorial-Polar Gradients

• The two key factors in equatorial-polar gradients
  of species richness
• Are probably evolutionary history and climate

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• Species richness generally declines along an
  equatorial-polar gradient
• And is especially great in the tropics
• The greater age of tropical environments
• May account for the greater species richness
• Higher productivity, longer growing season
• Spatial heterogeneity- more microhabitats

700 species of birds in Central America fewer
than 50 toward the poles 711 tree species in
Malaysia 10-15 in Michigan 200 ant species in
Brazil 7 in Alaska

• Climate
• Is likely the primary cause of the latitudinal
  gradient in biodiversity
• What components make up climate?

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• The two main climatic factors correlated with
  biodiversity
• Are solar energy input and water availability

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Area Effects

• The species-area curve quantifies the idea that
• All other factors being equal, the larger the
  geographic area of a community, the greater the
  number of species

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• A species-area curve of North American breeding
  birds
• Supports this idea

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Island Equilibrium Model

• Species richness on islands
• Depends on island size, distance from the
  mainland, immigration, and extinction

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• The equilibrium model of island biogeography
  maintains that
• Species richness on an ecological island levels
  off at some dynamic equilibrium point

Figure 53.27ac
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• Studies of species richness on the Galápagos
  Islands
• Support the prediction that species richness
  increases with island size