Biogeography

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Biogeography

• Chapter 10The Geography of Diversity

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Species Diversity

• Species Richness The number of species in a
  census
• Rare species are as important as dominant species
• Working with census lists
• Shannon Diversity Index
• HS(Nj/N)ln(Nj/N)

http//www.changbioscience.com/genetics/shannon.ht
ml
http//monticello.bc.edu/uei/sh_weave.php
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Scales of Diversity

• Alpha 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 communities
• Gamma Diversity Total species richness over a
  large geographic area such as a biome.

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Patterns in Biogeography and Gradients

• The Latitudinal Gradient Increasing diversity
  towards the equator
• The Peninsula Gradient Decreasing diversity
  away form the mainland
• The Elevation Gradient Species diversity
  decreases with elevation
• The Aridity Gradient Species diversity
  decreases with diminishing water availability
• Aquatic Environments Similar patterns

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Species diversity studies reveal a pattern of
higher diversity near the equator. The following
are a few hypotheses attempting to explain this
pattern.
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The Peninsula Effect - Variation in species
richness of three difference groups of organisms
in Baja California, showing a variety of patterns
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Causes of these Patterns

• Nonequilibrium Mechanisms
• Glaciation
• Climate Change
• Plate Tectonics
• Equilibrium Mechanisms
• Productivity
• Harshness and Abiotic Stress
• Climatic Stability
• Habitat Heterogeneity
• Area
• Biotic Interactions

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Ecogeographic Rules

• Bergmanns 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)

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Bergmanns Rule and adaptation to temperature in
the Bushy-tailed woodrat (Neotomoa nicerea), over
both geographic space and evolutionary time.
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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
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Macroecology Assembly of Continental Biotas

• Macroecology 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)

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Relationship between area of range and body size
showing that there are few large species with
small geographic ranges
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Natural Experiments

• The Great American Interchange
• Isolated from 160 million years before present
• Formation of the Central American landbridge at
  3.5 million years ago
• See the effects of dispersal , interspecific
  interaction, extinction, and evolution
• Half of South American species are derived from
  North American while only 10 of North American
  species are derived from South American

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The Great American Interchange

• Northern species had three advantages
• They were better migrators
• The were better survivors and speciators
• The were better competitors

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Organisms that crossed or were filtered out by
the Central American Landbridge
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Biomes
http//www.ucmp.berkeley.edu/exhibits/biomes/index
.php
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