Biology Reference
In-Depth Information
Europe. The trans-Saharan migratory population of the European quail,
in particular, has declined in abundance in recent decades, and behavioral
evidence for hybridization in field populations exists in France and Spain.
Interaction of Competition and Hybridization
Interspecific hybridization is clearly becoming a more frequent compo-
nent of the impact of alien species. Many of the related species being
brought together evolved their differences in geographic isolation, under
conditions in which reproductive isolation was not a significant target of
selection.
Huxel (1999) examined the interaction of competition and hybridiza-
tion for simple two-species evolutionary systems.When competition acts
alone, the outcome depends on the fitness differential between the species
and the rate of immigration. If the fitness advantage of the alien is small
and its immigration rate low, the likelihood of the alien succeeding is
small. On the other hand, an alien species with greater relative fitness or
a high rate of immigration is likely to displace its native competitor. A
high rate of immigration, even when the alien had lower relative fitness,
also can enable the alien to displace its native competitor.
With introgressive hybridization and competition, the outcome also
depends on the fitness of hybrid genotypes. If hybrids are not favored or
are disadvantaged, the outcome is similar to that without hybridization. If
hybrid individuals have a fitness disadvantage, however, the displacement
of the native is speeded. If hybrid individuals show greater fitness, or
hybrid vigor, the complete displacement of the pure native species is pre-
vented unless the invasion rate of the alien is very high.This last case cor-
responds to genetic assimilation, in which the native effectively becomes
extinct by being absorbed into the gene pool of the alien.This appears to
be the case in Trout Lake,Wisconsin, where the introduced
Orconectes rus-
ticus
both competes with and interbreeds with the native
O. propinquus
(Perry et al. 2001a).The hybrids between the two appear to be competi-
tively superior to both parents but equivalent in fecundity. The outcome
thus is likely to be a population morphologically much like
O. rusticus
but
with a component of genes from
O. propinquus
. Both competition and
hybridization may be responsible for the replacement of native North
American subspecies of red foxes (
Vulpes vulpes
) by European red foxes
introduced to eastern North America beginning in the 1700s (Kamler
and Ballard 2002).
