• Species, and higher taxa, have geographic distributions, and biogeographers aim to describe and explain them.

• The similarity of the flora or fauna of two regions can be measured by indexes of similarity. The world can be divided up into six main faunal regions, based on the distributions of bird and mammal species. Different taxa imply different regional divisions.

• The ecological properties of a species set limits on where it can live.

• The distributions of species are influenced by historical accidents, of where species happened to be at certain times, as well as their ecological tolerances.

• The ranges of species may be altered by dispersal (when a species moves in space) and by continental drift (when movement of the land subdivides the ranges of species). The splitting of a species range is called vicariance.

• When climates cooled in the Ice Age, the ranges of species in the northern hemisphere moved to the south. The ranges of tropical forests may have been fragmented into localized refuges.

• An area cladogram shows the geographic areas occupied by a group of phylogenetically related set of taxa.

• In the encounter between the North and South American faunas when the Isthmus of Panama formed 3 million years ago, similar proportions of mammals initially moved in both directions; but the immigrant north American mammals in the south proliferated at a greater rate.