Biology Reference
In-Depth Information
once completely migratory are now partial migrants (Berthold 1999).
Berthold (2001) showed that the change from a fully migratory to a per-
manent resident songbird can occur within 25 generations.Thus, many of
the recent changes in ranges and migratory times of birds probably have
an evolutionary basis. Selection for earlier breeding has also contributed
to the advancement of egg laying by more than 1 wk during the past 20
yr in The Netherlands (Coppack and Both 2002).
Other signs of evolutionary adaptation to climatic change are now
being seen. In Israel, for example, where minimum summer temperatures
have increased more than 1°C during the last half of the twentieth cen-
tury,Yom-Tov (2001) showed that the body mass of several resident birds
has decreased. Jarvinen (1994) found an increase in egg volume of the
pied flycatcher (
Ficedula hypoleuca
) in northern Finland from 1975 to 1993
and attributed the change to the warming temperatures in this region. For
plants, Beering and Kelly (1997) noted increases in stomatal density for
herbaceous species of temperate forest over 70-200 yr. Although the
degree of genetic control is uncertain for some of these changes, it is clear
that global climate change will favor many physiological adjustments of
species within their present ranges.
Adaptive shifts in the ranges of species, whether they be native or
alien, in response to changing climate in many cases thus require evolu-
tionary adjustments as well as successful dispersal capabilities. Further-
more, populations at the expanding edge of the range of a species may
possess greater variability than those at the receding edge (Davis and Shaw
2001). Expanding edge populations receive pollen and seeds from popu-
lations away from the expanding edge but adapted to conditions ahead of
the expansion front (fig. 20.1). Populations at the receding edge depend
only on their own genetic variability to adapt to changing climate and are
more likely to fail and become extirpated.
Conservation in an Era of Rapid Evolution
This constellation of new relationships demands a new view of biotic
communities and their management. Many intercontinental aliens are so
fully integrated into ecosystems that their eradication is impossible, or
even undesirable.The majority of these are not invasive and are not eco-
logically disruptive. Some are beneficial through their roles in nutrient
cycling, biocontrol, and mutualistic interactions with native species.Thus,
in practice, we must assess the ecological and evolutionary processes
