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Chapter 14Macroevolution: the long run
Correlation vs. Causation
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Microevolution and macroevolution
• Microevolution: evolution occurring within populations – Adaptive and neutral changes in allele
frequencies • Macroevolution: evolution above the
species level – Origination, diversification, and extinction
Interplay between speciation and extinction determines diversity
D1 (diversity) + originations – extinctions = D2 (new diversity)
Calculating rates of origination and extinction
Definition of Biological Diversity
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Number of subtaxa within a higher taxon
species diversitygeneric diversity
What might some problems be with measuring species diversity? Would they be more pronounced with genus diversity?
Diverse taxa have higher origination rate than extinction rate
α = origination rate; Ω = extinction rate"An inordinate fondness for beetles."
Extinction rate often tracks origination rate
Causes of decline in diversity
• Diversity can decline when extinction increases or origination decreases – Drop in origination rate contributed to dinosaur
extinction
Key Concepts
• Extinction occurs when the last member of a clade dies – Can be species or higher taxon
• Mass extinction in a clade can have two causes: – Drop in origination rate – Increase in extinction rate
Biogeography: the study of geographical patterns of diversity
Map of biogeographical regions
Clades can become isolated through vicariance
Marsupials evolved through a mix of vicariance and dispersal
Key Concepts
• Biogeography is a multidisciplinary field that explores the roles of geography and history in explaining the distribution of species
Estimating diversity through time is a complicated task
Chance fluctuations in diversity can produce trend-like patterns
Some ecological marine communities have become more diverse
Three “evolutionary faunas”
Crinoids
Caveats to diversity studies
• Most taxa studied are not species – Assignments to higher taxonomic groups
somewhat arbitrary • Phylogenetic relationships among groups
uncertain • Large-scale patterns may obscure
interesting regional patterns
Adaptive radiation in Hawaiian honeycreepers
Phylogenetic signatures of adaptive radiation
Adaptive radiation and convergent evolution
Adaptive radiation of animals
Rapid diversification of animals corresponds to major environmental changes
• Warming and retreat of glaciers • Oxygenation of ocean
Fossil record reveals how major transitions occurred
Key Concepts
• Most adaptive radiations involve exploitation of environments not occupied by competitors
• Key innovations can transform how organisms interact with their environment – Paves the way for adaptive radiation
Pace of extinctions
• Background extinction: the normal rate of extinction for a taxon or biota
• Mass extinction: a statistically significant increase above background extinction rate
Five large mass extinctions
You only need to now 2
Mass extinction can result from climate change
Rising carbon dioxide from volcanic activity may have led to Permian extinction
K-T boundary extinction may have been caused by asteroid impact
Traces of impact along Mexican coast
Key Concepts
• The big five extinctions had different causes that impacted different organisms
Humans may be driving a sixth mass extinction
Habitat loss contributes to extinction
Current extinction rates are on par with previous mass extinctions
Increasing carbon dioxide correlates with warming temperatures
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Key Concept
• Although a single extinction event may have minimal impacts on an ecosystem a mass extinction can have cascading effects
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End Spring 2015