Environmental Engineering Reference
In-Depth Information
two-thirds of the European butterfly species surveyed had shifted north (by
35-240 kilometers); only 3 percent shifted their range to the south. Like-
wise, birds in Britain and birds and mammals in North America have un-
dergone significant northward range shifts in the past decades (Parmesan
and Yohe 2003).
The Pace of Change
Although some species seem to be moving fairly rapidly, there is evidence
that even for some highly mobile species such as birds and butterflies, the
response to climate change is not as quick as would be expected were ani-
mals perfectly tracking shifts in climatic isotherms (Paremsan and Yohe
2003). For example, the European climatic isotherms have moved north 120
kilometers this century (+0.8° C), and a substantial portion of the nonmi-
gratory European butterflies have shifted only a portion of this distance
(Parmesan et al. 1999).A major constraint on migration may be availability
of habitat. For example, habitat may not exist in contiguous patches due to
urban development.
Whether or not human land development and/or natural barriers se-
verely impact the ability of species to respond to changing climatic condi-
tions will depend on the species' dispersal ability as well as the distribution
of habitat and land use practices around the habitat. For example, it has been
shown that for some species of butterflies dispersal will be seriously con-
strained because of habitat loss and habitat fragmentation, whereas other
species of butterflies may not be so encumbered (Parmesan et al. 1999).We
may also see evolution of morphologies designed to overcome barriers to
dispersal (i.e., longer wings in some insect species;Thomas et al. 2001).
The above analyses address only one component of fitness: the ability to
survive by seeking out more climatically favorable geographic locations.
Without knowing the effects of climate change on reproduction, one can-
not conclude that wildlife populations will remain viable simply because
habitat is still available. Likewise, we cannot conclude that wildlife species
will exhibit the same life-history traits under a doubling of atmospheric
CO
2
as they do under current climate regimes. Indeed, mounting empiri-
cal evidence suggests that climate warming is altering the timing of life-his-
tory events. Examples comparing historical to current records has indicated
shifts in breeding dates, body mass, and migration that are concurrent with
increased mean spring and winter temperatures. Many common bird species
have shown significantly earlier breeding dates ranging from a week to a
