Geography Reference
In-Depth Information
warm temperatures, have maximum species diversity for the general
part of the world where they are located, and harbor the most ad-
vanced species and genera of taxa that are well represented.
• On a worldwide basis, the study of major barriers separating biogeo-
graphic regions shows that species evolved in the centers of origin not
only can spread out to occupy large portions of such regions but also
can transgress the barriers and colonize adjacent regions. As a res-
ult, a given center of origin may eventually have a profound influen-
ce on the biotic composition of a large portion of the world. Because
thesecentersharbormoreadvancedandmorehighlycompetitivespe-
cies, they have very high resistance to invasion by species from other
areas.
• The kind of evolution that goes on in the centers of origin probably is
different from that which takes place in peripheral areas because they
have larger populations and individuals have higher levels of genet-
ic variation. The rate of evolutionary change is slower than in smaller,
isolated populations, but in terms of producing phyletic lines, they are
probably more successful.
• Data about the centers of origin and their probable mode of operation
indicate that someparts of the earth, interms of evolutionary progress,
have been much more important than others. The complex community
structure of the tropical areas is not well understood, yet many of their
biotas are being destroyed for agricultural and other purposes. In an
evolutionary sense, these areas represent the future of the living world
and therefore should be preserved.
From a different perspective, Bremer (1992, 1995) formalized a cladistic
method to estimate centers of origin or ancestral areas. Bremer reasoned
that the search for the ancestral area of a taxon was a valid part of the study
of its natural history. Ancestral area analysis assumes that areas inhabited
by the most plesiomorphic species and areas represented on numerous
branchesofthecladogramaremorelikelytorepresentpartsoftheancestral
area of the group. These assumptions are similar to Hennig's (1950) pro-
gression rule, so ancestral area analysis may be considered a formalization
of phylogenetic biogeography (Santos 2007). This new version of dispers-
alism assumes that the search for and identification of ancestral areas or
centers of origin constitute valid biogeographic objectives and that they can
found by determining which are the most basal areas in a cladogram and