Chapter 14
Macroevolution: the long run
Correlation vs. Causation
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3
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
Number of subtaxa within a higher taxon
species diversity
generic diversity
What might some problems be with measuring
species diversity? Would they be more pronounced
with genus diversity?
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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
End Spring 2015
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