Environmental Engineering Reference
In-Depth Information
month in advance of previous dates (Parmesan andYohe 2003).Amphibians
in the United Kingdom now breed two to seven weeks in advance of breed-
ing schedules from earlier in the century. Insects are passing through larval
stages faster and are becoming adults earlier.This may have particular im-
portance for the expansion of pest species ranges, and the extent of dam-
age they are able to inflict on agricultural crops and on naturally occurring
species.
Changes in the timing of life-history events due to climate change may
not necessarily lead to species declines, however. We need to view these
events in an environmental context to determine the important implica-
tions these life-history shifts may have for the populations and communi-
ties that are involved. For example, amphibians that are able to breed earlier
may be relieved from a serious summer bottleneck (pond drying), allow-
ing more individuals to metamorphose into adults.The effect of climate
change may be that there is greater population recruitment than under cur-
rent conditions.Alternatively, it is also important to realize that any benefit
of earlier breeding may be offset if pond drying also occurs earlier in the
season, or if biotic shifts such as abundance of important prey species cause
environmental conditions to become less favorable. Also, a shift in earlier
breeding dates for birds may allow a greater proportion of the population
to produce multiple clutches during the breeding season, or to take advan-
tage of new insect prey that are only available at earlier dates in the season.
Thus uncommon species may become highly abundant.
The important point is that strong scientific evidence shows that human
activity is causing mean temperatures to rise globally. Such change stands to
impose strong natural selection on species. Some species may mitigate those
environmental changes by migrating to more favorable climatic conditions
but others will be constrained. Regardless, all species are being forced to
adapt to the changes through selection on life-history traits and dispersal
abilities. Such evolutionary response has been part of the natural cycle of
life on earth for millennia.The difference now is the rate at which the en-
vironment is changing relative to change in our geological past. Such rapid
change imposes very strong selection on species, many which may not have
the genetic capacity or life history traits to respond quickly enough, if at all.
Eventually natural selection may become so strong that individuals may fail
to survive or reproduce altogether.This may precipitate one of the highest
extinction events ever witnessed on earth (Thomas et al. 2004).
