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Transcript
Biogeography
Chapter 10
The Geography of Diversity
Species Diversity
Richness – The number of species
in a census
► Species
§ 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
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.
► Alpha
Patterns in Biogeography and
Gradients
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
► The
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
– 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)
► Macroecology
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