Bio 221a: Biogeographic Evidence for Evolution

Biogeographic Evidence for Evolution

• Biogeography is the study of organisms' geographic distributions, with both historical and ecological components.
• Certain distributions are the consequence of long-term evolutionary history, while others are the result of current ecological factors.

Patterns of Distribution

• Biogeographic realms recognized by Wallace include Palearctic, Ethiopian, Oriental, Australian, Nearctic, and Neotropical.
• Examples of taxa endemic to the Neotropical biogeographic realm exist.
• Disjunct distributions occur, where related species are found in different geographic locations.

Historical Explanations of Geographic Distributions

• Historical processes affecting the distribution of a taxon include extinction, dispersal, and vicariance (fragmentation of a continuous distribution by the emergence of a barrier).
• These processes may be affected or accompanied by environmental change, adaptation, and speciation.
• Histories of dispersal or vicariance can often be inferred from phylogenetic data.
• Disjunct distributions are attributable to vicariance, but dispersal seems to be the more common cause.

Phylogeography

• Phylogeography is the description and analysis of the processes that govern the geographic distribution of lineages of genes, especially within species and among closely related species.
• Genetic patterns of geographic variation within species can provide information on historical changes in a species' distribution.

Geographic Range Limits: Ecology and Evolution

• The local distribution of species is affected by ecological factors, including abiotic aspects of the environment and biotic features such as competitors and predators.
• Why species do not enlarge their ranges indefinitely is a major question in evolutionary biology.
• Competition tends to prevent ecologically similar species from becoming sympatric.

Geographic Patterns of Diversity

• The latitudinal diversity gradient shows that the numbers of species (and of higher taxa such as genera and families) decline with increasing latitude, both on land and in the ocean.
• Three models of species accumulation have been proposed to account for the latitudinal diversity gradient.
• Geographic patterns in the number and diversity of species may stem partly from current ecological factors, but long-term evolutionary history also may explain them.

This quiz covers the biogeographic evidence for evolution, major patterns of distribution, and historical explanations of geographic distributions in the context of evolutionary biology.