When two species with similar requirements overlap geographically, the less competitive species often is driven from the common area. A different result sometimes occurs, though: a phenomenon known as character displacement.
Virtually all populations have a large amount of genetic variation.
Sometimes, when two species are competing vigorously for the necessities of life,
individuals of the two species who are most different from members of the other species
do better than those who are nearly identical. With the individuals most different from
each other surviving more often and producing more offspring each generation, the two
species in the area of overlap become more and more different from each other through
time. In those parts of the geographic ranges where the two species do not overlap,
there is no competition and thus no such natural selection. The overall result is that
the individuals of two very closely related species may be easy to tell apart in an
area where they overlap, but individuals from different parts of their geographic
ranges may be so similar as to defy easy identification.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.