1. Chapter 10 The Geography of Diversity
Biogeography
Chapter 10 The Geography of Diversity

2. 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
H=Σ(Nj/N)ln(Nj/N)

3. 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.

4. 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

5. Species diversity studies reveal a pattern of higher diversity near the equator. The following are a few hypotheses attempting to explain this pattern.

6. The Peninsula Effect - Variation in species richness of three difference groups of organisms in Baja California, showing a variety of patterns

7. 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

8. Ecogeographic Rules
Bergmann’s Rule (1847) – Animals with larger body forms occur at high latitudes. Larger animals have a lower surface area to volume ration.
Allen’s Rule (1877) – Endothermic vertebrates that live in warmer climates have longer appendages.
Gloger’s Rule (1883) – Coloration of related forms is correlated to humidity with darker coloration occurring in more humid regions. Most likely driven by crypsis (camouflage)

9. Bergmann’s Rule and adaptation to temperature in the Bushy-tailed woodrat (Neotomoa nicerea), over both geographic space and evolutionary time.

10. Allen’s 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

11. 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)

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

13. 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

14. The Great American Interchange
Northern species had three advantages
They were better migrators
The were better survivors and speciators
The were better competitors

15. Organisms that crossed or were filtered out by the Central American Landbridge

16. Biomes