BiogeographyBiogeography

Chapter 10Chapter 10The Geography of DiversityThe Geography of Diversity

Species DiversitySpecies Diversity

►Species RichnessSpecies Richness – The number of species – The number of species in a censusin a census§ Rare species are as important as dominant Rare species are as important as dominant

speciesspecies§ Working with census listsWorking with census lists

►Shannon Diversity IndexShannon Diversity IndexH=H=ΣΣ(N(Njj/N)ln(N/N)ln(Njj/N)/N)

http://www.changbioscience.com/genetics/shannon.html

http://monticello.bc.edu/uei/sh_weave.php

Scales of DiversityScales of Diversity

► Alpha DiversityAlpha Diversity – Species richness of a local – Species richness of a local ecological community (e.g. defined as a study plot ecological community (e.g. defined as a study plot such as a hectare)such as a hectare)

► Beta DiversityBeta Diversity – Change (or turnover) in species – Change (or turnover) in species composition between two distinct communitiescomposition between two distinct communities

► Gamma DiversityGamma Diversity – Total species richness over a – Total species richness over a large geographic area such as a biome.large geographic area such as a biome.

Patterns in Biogeography and Patterns in Biogeography and GradientsGradients

►The Latitudinal GradientThe Latitudinal Gradient – Increasing – Increasing diversity towards the equatordiversity towards the equator

►The Peninsula GradientThe Peninsula Gradient – Decreasing – Decreasing diversity away form the mainlanddiversity away form the mainland

►The Elevation GradientThe Elevation Gradient – Species diversity – Species diversity decreases with elevationdecreases with elevation

►The Aridity GradientThe Aridity Gradient – Species diversity – Species diversity decreases with diminishing water availabilitydecreases with diminishing water availability

►Aquatic EnvironmentsAquatic Environments – Similar patterns – Similar patterns

Species diversity studies reveal a pattern of higher diversity Species diversity studies reveal a pattern of higher diversity near the equator. The following are a few hypotheses near the equator. The following are a few hypotheses

attempting to explain this pattern.attempting to explain this pattern.

The Peninsula EffectThe Peninsula Effect - Variation in species richness of three - Variation in species richness of three difference groups of organisms in Baja California, showing a difference groups of organisms in Baja California, showing a

variety of patternsvariety of patterns

Causes of these PatternsCauses of these Patterns

► Nonequilibrium MechanismsNonequilibrium Mechanisms§ GlaciationGlaciation§ Climate ChangeClimate Change§ Plate TectonicsPlate Tectonics

► Equilibrium MechanismsEquilibrium Mechanisms§ ProductivityProductivity§ Harshness and Abiotic StressHarshness and Abiotic Stress§ Climatic StabilityClimatic Stability§ Habitat HeterogeneityHabitat Heterogeneity§ AreaArea§ Biotic Interactions Biotic Interactions

Ecogeographic RulesEcogeographic Rules

► Bergmann’s RuleBergmann’s Rule (1847) – Animals with larger body forms (1847) – Animals with larger body forms occur at high latitudes. Larger animals have a lower occur at high latitudes. Larger animals have a lower surface area to volume ration.surface area to volume ration.

► Allen’s RuleAllen’s Rule (1877) – Endothermic vertebrates that live in (1877) – Endothermic vertebrates that live in warmer climates have longer appendages.warmer climates have longer appendages.

► Gloger’s RuleGloger’s Rule (1883) – Coloration of related forms is (1883) – Coloration of related forms is correlated to humidity with darker coloration occurring in correlated to humidity with darker coloration occurring in more humid regions. Most likely driven by crypsis more humid regions. Most likely driven by crypsis (camouflage) (camouflage)

Bergmann’s Rule and adaptation to temperature in the Bergmann’s Rule and adaptation to temperature in the Bushy-tailed woodrat (Bushy-tailed woodrat (Neotomoa nicereaNeotomoa nicerea), over both ), over both

geographic space and evolutionary time.geographic space and evolutionary time.

Allen’s Rule showing ear length in rabbits and foxes where Allen’s Rule showing ear length in rabbits and foxes where the organism on the left occurs in a hot desert habitat and the the organism on the left occurs in a hot desert habitat and the

one on the right occurs in a cold tundra environmentone on the right occurs in a cold tundra environment

Macroecology: Assembly of Macroecology: Assembly of Continental BiotasContinental Biotas

► MacroecologyMacroecology – A quantitative and statistical – A quantitative and statistical approach that tries to identify general approach that tries to identify general ecogeographic patterns and to understand the ecogeographic patterns and to understand the underlying mechanisms of the distributions of underlying mechanisms of the distributions of ecological particles (organism, species, biotas, or ecological particles (organism, species, biotas, or replicated sample plots; Brown 1995) replicated sample plots; Brown 1995)

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

Natural ExperimentsNatural Experiments

►The Great American Interchange The Great American Interchange § Isolated from 160 million years before present Isolated from 160 million years before present § Formation of the Central American landbridge at Formation of the Central American landbridge at

3.5 million years ago3.5 million years ago§ See the effects of dispersal , interspecific See the effects of dispersal , interspecific

interaction, extinction, and evolutioninteraction, extinction, and evolution§ Half of South American species are derived Half of South American species are derived

from North American while only 10% of North from North American while only 10% of North American species are derived from South American species are derived from South AmericanAmerican

The Great American InterchangeThe Great American Interchange

►Northern species had three advantagesNorthern species had three advantages§ They were better migratorsThey were better migrators§ The were better survivors and speciatorsThe were better survivors and speciators§ The were better competitorsThe were better competitors

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

BiomesBiomes

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