Biology Reference
In-Depth Information
Figure 20.1.
Adaptation by a species with a range expanding into a region of favor-
able climate and withdrawing from a region of unfavorable climate. (A) Curves of
phenotype frequencies (lower curve and lowercase letters) and fitness (upper curve
and capital letters) for a population occupying a portion of a climate gradient. The
highest frequency of phenotypes and optimal fitness coincide at c and C. (B) As the
climate gradient shifts, pollen and seed dispersal may help enable the species to
keep up with the shift in the fitness optimum at the advancing edge, but without
an evolutionary shift in the fitness optimum, the population cannot maintain itself
in areas where the climate has become unfavorable. (Reprinted with permission
from M. B. Davis and R. G. Shaw. 2001. Range shifts and adaptive responses to
quaternary climate change.
Science
292:673-679. © 2001 AAAS.)
involving both native and alien species and evaluate their influence on
community function.
Biotic communities that are changing in composition require that a
distinction be made between intracontinental and intercontinental aliens.
Serious threats are posed to many native species by the continuing inva-
sion of species from other continents. To fail to restrict these invasions is
obviously counter to conservation goals. In the modern world, however,
complete suppression of intercontinental invasions is impossible, so we
must recognize these invasions as part of global change. On the other
hand, we must recognize that the ranges of many species are shifting
within continents due to the effects of global change and direct human
modification of the environment. To treat such species as aliens as they
extend their ranges into areas that have become favorable as a result of cli-
matic change is also counter to the goal of conservation.
The dynamic nature of biotic communities in a changing world
means that conservation efforts must be flexible and in tune with biogeo-
graphic and evolutionary realities. To protect threatened and endangered
