Chapter 10 The Geography of Diversity Biogeography Chapter 10 The Geography of Diversity

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) http://www.changbioscience.com/genetics/shannon.html http://monticello.bc.edu/uei/sh_weave.php

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.

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

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

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)

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

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

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)

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

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

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

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

Biomes http://www.ucmp.berkeley.edu/exhibits/biomes/index.php