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Evidence for Evolution

Problems

Biogeography

Comparative Anatomy

Problem : In the , what is the number of species that will be present at equilibrium?

Figure%: the extinction and arrival rates for a habitat island

Approximately 25 species will be present at equilibrium.

Problem : How can you determine what species will be present at when a habitat reaches equilibrium?

You cannot determine which species will be present when a habitat reaches equilibrium because at equilibrium the number of species present remains the same, but the individual species will change.

Problem : How is an area cladogram constructed? What information does it give us?

An area cladogram is made by replacing the species names on a taxonomic tree with the geographic location in which they are found. This allows scientists to determine how the difference in environments has affected the evolutionary history of different species of common origin.

Problem : Describe the species richness equilibrium model.

The model begins with an uninhabited "island" (either a literal island or an area of like habitats completely surrounded by unlike habitats). All species available to colonize the new area are called the "species pool." As more and more new species enter the new area, the species pool becomes smaller and smaller, and the probability that any given species that moves into the area will be a new species, or the immigration rate, decreases. At the same time, the island is becoming more and more crowded and supplies become scarce, causing the extinction rate to increase. The point at which the extinction rate and the immigration rate are balanced is called the equilibrium point. The model predicts that changes in extinction and immigration rates will tend toward the equilibrium point, which is different for every island, depending on resources and degree of separation from other areas.

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