Lecture 19 SPECIES DIVERSITY- REGIONAL TO GLOBAL LEVELS
MAJOR CONCEPTS
1.Equilbrium theories of diversity (e.g. Island Biogeography Theory) balance factors that
add (speciation + immigration) and remove species (extinction + emigration).
2. Regional patterns of diversity reflect habitat heterogeneity, climate change, tolerance
of physical conditions, and isolation from centers of diversity.
2.Numerous hypotheses explain the increase in species diversity with decreasing
latitude.
3.History, including continental drift and building of land bridges, account for patterns
of species distribution on continents.
4.Biogeographic regions reflect the long-term evolutionary isolation of large areas.
5.Catastrophes have caused major changes in the direction of evolution.
6.Climate changes have shifted the distributions of plants and animals.
Local to Regional Scale: Diversity
Effect of regional-scale on local-scale
Local diversity is a function of regional diversity.
Compare diversities in similar habitats in different regions  reveals regional effects
Saturation of local communities is seen if local diversity levels off rather than having
local diversity on same trajectory as regional diversity. 21.14
Comparisons of tree diversity among regions with unique geographic positions 21.16
effects of loss of habitat during glaciation (e.g. in Europe)
gains due to building stepping stones for dispersal + connections to tropics (e.g. Asia)
Regional Scale: Diversity
Equilibrium theory: number of species is a balance of
Additions (e.g. immigration and speciation) minus
Subtractions (e.g. emigration and extinctions)
E.g. Theory of Island Biogeography
Number of species at equilibrium results from balance of
immigration on regional scale and extinction on local scale 20.19
Island area: affects extinction rate so no. species > large than small islands 20.20
Distance from mainland: affects immigration rate so no. species > near than far 20.21
Applicability to ‘terrestrial habitat’ islands too
Other factors affecting patterns of species diversity 20.5
Habitat heterogeneity and range of conditions used
Suitability of physical conditions
Isolation from centers of diversity
Patterns of species richness over regional areas differ among taxa 20,6
Past climate change affects regional diversity today.
Latitudinal-scale
Increase in diversity with decrease in latitude
Hypotheses to explain high species richness in tropics (see biotic factors at local scale)
Add one more = tropics have been stable for longer time; time to add species and
less extinction?
Continental/global-scale
How do history, biogeography, and climate influence species diversity? 21.1, 21.3
Diversity has not been constant over geological time; communities not in constant
equilibrium 21.21
Catastrophes (e.g. meteorite hits; volcanic explosions) have caused major changes
in species diversity
Equilibrium Theory of Continental Communities: # species affected by balance of
speciation and extinction on continental scale 20.23
Diversification (additions-extinctions) may have been faster in tropics than temperate
area –> more species 21.19
Historical roots affect current species distributions
Continental drift/Plate tectonics 21.4
Altered positions of continents; some separations; some joining
Changed routes of dispersal
Drift separated lineages onto different continents subsequent divergence 21.5
Result = organisms not distributed uniformly over earth 20.1
Zoogeographic regions reflect long-term evolutionary isolation (e.g. 6 regions) 21.6
New land bridges arose connecting land masses 21.7
Exchanges of biotas possible; affected migration and extinctions
Climatic history influences geography of evolution and determines species
distributions
Climate zones have shifted historically from more to less tropical 21.18
Diversification is more likely to occur in ecological zone of origin (e.g. tropics)
hard to diversify into more stressful environments (e.g. at higher latitudes) 21.20
Climate change shifted biomes and evolution of animals dependent on biome 21.22
Glaciations and intolerance of low temperatures 21.17
Caused extinctions in Europe because of dispersal barriers as moved N to S; no refuges
Some species had limited dispersal and could not expand area post-glacial 21.9, 21.10
Species in N.A. behaved individualistically  shifts in community composition 21.8
Summary: 1, 3-7, 11-13