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

Artificial clades

Real clades of brachiopods

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 know 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 affected 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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CO2, by definition, has a GWP of 1 regardless of the time period used, because it is the gas being used as the reference. CO2 remains in the climate system for a very long time: CO2 emissions cause increases in atmospheric concentrations of CO2 that will last thousands of years.

Methane (CH4) is estimated to have a GWP of 28–36 over 100 years (Learn why EPA's U.S. Inventory of Greenhouse Gas Emissions and Sinks uses a different value.). CH4 emitted today lasts about a decade on average, which is much less time than CO2. But CH4 also absorbs much more energy than CO2. The net effect of the shorter lifetime and higher energy absorption is reflected in the GWP. The CH4 GWP also accounts for some indirect effects, such as the fact that CH4 is a precursor to ozone, and ozone is itself a GHG.

Nitrous Oxide (N2O) has a GWP 265–298 times that of CO2 for a 100-year timescale. N2O emitted today remains in the atmosphere for more than 100 years, on average.

Chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are sometimes called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO2. (The GWPs for these gases can be in the thousands or tens of thousands.)

Key Concept

• Although a single extinction event may have minimal impacts on an ecosystem a mass extinction can have cascading effects