Geography Reference
In-Depth Information
ive connections or corridors are rare. Thus “filter bridges” are the best fit for
the zoological evidence. For the instances of dispersal of single groups or
unbalanced faunas that do not meet the criteria for filter bridge connections,
Simpson postulated the existence of “sweepstake routes,” which depending
on chance may allow the dispersal of particular taxa.
Figure 3.2
Model postulated to explain the expansion and contraction of a taxon.
Lines 1-11 represent distributional limits at different times; 1-5, primary expansion of
the group on the landmass where it originally evolved; 5-8, expansion on a second
landmass; 8-11, contraction. After 8 it is extinct in its homeland but survives abroad,
and after 11 it is extinct everywhere (modified from Simpson 1940:145).
Simpson's (1953)
Evolution and Geography
represents an essay on
biogeography, where he formalized some key terms, such as
fauna.
For
Simpson,
The fauna of any one area is made up of numerous species which
have evolved from diverse ancestral groups, which interact with each
other in various ways, which (either as such or in ancestral forms)
have been in the region for different lengths of time, which have
come from different geographic sources, and which have at present
different relationships to species existing in other regions. (Simpson
1953:31)
