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Evolution__3rd_Edition

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518 PART 4 / <strong>Evolution</strong> and Diversity<br />

Summary<br />

1 Species, and higher taxa, have geographic distributions,<br />

and biogeographers aim to describe and explain<br />

them.<br />

2 The similarity of the flora or fauna of two regions<br />

can be measured by indexes of similarity. The world<br />

can be divided up into six main faunal regions, based<br />

on the distributions of bird and mammal species.<br />

Other taxa, such as plants, form slightly different<br />

regional divisions.<br />

3 The distributions of species are influenced by historic<br />

accidents of where species happened to be at<br />

certain times, and by their ecological tolerances.<br />

4 The ranges of species may be altered by dispersal<br />

(when a species moves in space) and by plate tectonics<br />

(when movement of the land subdivides the ranges<br />

of species). The splitting of a species range is called<br />

vicariance.<br />

5 When climates cooled in the most recent ice age, the<br />

ranges of species in the northern hemisphere moved<br />

to the south. In Europe, many species formed glacial<br />

refuges in Spain, Italy, and the Balkans. After the ice<br />

age they expanded north, resulting in a distrbution<br />

with a three-clade intraspecific phylogeny, and in<br />

suture zones, where several species form hybrid zones.<br />

Further reading<br />

6 Some taxa have undergone local adaptive radiations<br />

on island archipelagos. The course of the radiation can<br />

be studied by molecular phylogenetic techniques.<br />

7 The species of an area tend to be more closely<br />

related to other species in the same area than to ecologically<br />

more similar species elsewhere in the globe.<br />

Darwin used this observation to argue his case for<br />

evolution.<br />

8 An area cladogram shows the geographic areas<br />

occupied by a group of phylogenetically related set of<br />

taxa.<br />

9 Vicariance biogeography suggests that geographic<br />

distributions are determined mainly by splits in the<br />

ranges of ancestral species, not by dispersal. It predicts<br />

that the area cladogram of a taxon should match the<br />

geological history of the area, and the area cladograms<br />

of different taxa in an area should have compatible<br />

(congruent) area cladograms.<br />

10 In the encounter between the North and South<br />

American faunas when the Isthmus of Panama formed<br />

3 million years ago, similar proportions of mammals<br />

initially moved in both directions, but the immigrant<br />

North American mammals in the south proliferated at<br />

a greater rate.<br />

Cox & Moore (2000) is an introductory textbook, and Brown & Lomolino (1998) is<br />

more comprehensive. Avise (1999) is a text on phylogeography, and Hare (2001) looks<br />

at recent advances in phylogeography.<br />

Simpson (1983) explains how the great faunal regions of the world were discovered,<br />

as well as the importance of movement, and how to measure faunal (and floral) similarity.<br />

Brown et al. (1996) review ecological ranges. For ecological influences, see an<br />

ecology text, such as as Ricklefs & Miller (2000). On niche concepts, see the entries by<br />

Griesemer and Colwell in Keller & Lloyd (1992). On Krakatau, see Thornton (1996)<br />

and the narrative in Wilson (1992). Van Oosterzee (1997) is a book about Wallace’s<br />

line.<br />

On ice age biogeography see Pielou (1991), and the general references above, which<br />

include a chapter in Cox & Moore (2000). See also Davies & Shaw (2001) on range<br />

..

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