Geography Reference
In-Depth Information
were never in contact (Cowie and Holland 2006; De Queiroz 2005;
Waters and Roy 2004).
• Diffusion (also known as range expansion): gradual movement of pop-
ulations crossing adjacent suitable habitats over several generations.
There are several examples of species that expanded their distribution
in North America with the warming of the climate and the retreat of ice
at the end of the Pleistocene (MacDonald 2003).
• Secular migration: movement over a short distance that occurs so
slowly that the species evolves in the meantime.
• Geodispersal (also known as mass coherent dispersal, biotic dispers-
al, concerted dispersal, or predicted dispersal): simultaneous move-
ment of several taxa due to the effacement of a barrier, followed by the
emergence of a new barrier that produces subsequent vicariance. An
example of geodispersal occurred during the Pleistocene, when the
Bering Strait connected North America and Asia, allowing the dispers-
al of several taxa, including
Homo sapiens,
to the Americas (Lieber-
man 2004). As a result of geodispersal, biogeographic convergence
occurs (Hallam 1974). Its main consequence is the reticulated, nonhi-
erarchical evolution of biotic components.
Vicariance is the appearance of a barrier that allows fragmentation of
the distribution of an ancestral species, after which the descendant species
may evolve in isolation. The appearance of the barrier causes the disjunc-
tion, so both species have the same age. Area fragmentation is not the only
way to cause vicariance. The process known as dynamic vicariance (Zunino
and Zullini 1995) implies that climatic changes may act by displacing a biotic
component gradually in a certain direction, which finally finds a barrier that
causes vicariance. One example is the Mediterranean area, where the cli-
matic oscillations of the Pleistocene induced vicariance of formerly wide-
spread taxa in different European peninsulas (Zunino 2003). Another is the
South American Chacoan subregion, which developed gradually during the
Tertiary, splitting the former continuous Amazonian-Parana forest and leav-
ing a central diagonal of open vegetational formations (Morrone 2006).
Extinction is the local extirpation or total disappearance of a taxon (Mo-
rain 1984). It has the potential to obscure biogeographic patterns because
biotas may appear different simply because one region has experienced dif-
ferential extinction (Lieberman 2003a, 2005). Although extinction is a fact,
mechanisms explaining it usually do not concern biogeographers because
