Evolution__3rd_Edition

518 PART 4 / Evolution and Diversity
Summary
1 Species, and higher taxa, have geographic distributions,
and biogeographers aim to describe and explain
them.
2 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.
Other taxa, such as plants, form slightly different
regional divisions.
3 The distributions of species are influenced by historic
accidents of where species happened to be at
certain times, and by their ecological tolerances.
4 The ranges of species may be altered by dispersal
(when a species moves in space) and by plate tectonics
(when movement of the land subdivides the ranges
of species). The splitting of a species range is called
vicariance.
5 When climates cooled in the most recent ice age, the
ranges of species in the northern hemisphere moved
to the south. In Europe, many species formed glacial
refuges in Spain, Italy, and the Balkans. After the ice
age they expanded north, resulting in a distrbution
with a three-clade intraspecific phylogeny, and in
suture zones, where several species form hybrid zones.
Further reading
6 Some taxa have undergone local adaptive radiations
on island archipelagos. The course of the radiation can
be studied by molecular phylogenetic techniques.
7 The species of an area tend to be more closely
related to other species in the same area than to ecologically
more similar species elsewhere in the globe.
Darwin used this observation to argue his case for
evolution.
8 An area cladogram shows the geographic areas
occupied by a group of phylogenetically related set of
taxa.
9 Vicariance biogeography suggests that geographic
distributions are determined mainly by splits in the
ranges of ancestral species, not by dispersal. It predicts
that the area cladogram of a taxon should match the
geological history of the area, and the area cladograms
of different taxa in an area should have compatible
(congruent) area cladograms.
10 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.
Cox & Moore (2000) is an introductory textbook, and Brown & Lomolino (1998) is
more comprehensive. Avise (1999) is a text on phylogeography, and Hare (2001) looks
at recent advances in phylogeography.
Simpson (1983) explains how the great faunal regions of the world were discovered,
as well as the importance of movement, and how to measure faunal (and floral) similarity.
Brown et al. (1996) review ecological ranges. For ecological influences, see an
ecology text, such as as Ricklefs & Miller (2000). On niche concepts, see the entries by
Griesemer and Colwell in Keller & Lloyd (1992). On Krakatau, see Thornton (1996)
and the narrative in Wilson (1992). Van Oosterzee (1997) is a book about Wallace’s
line.
On ice age biogeography see Pielou (1991), and the general references above, which
include a chapter in Cox & Moore (2000). See also Davies & Shaw (2001) on range
..