5.4.3.2. Model Projections of Wildlife Responses
Invertebrates: Because changes in the distribution of disease vectors, such
as mosquitoes, and crop and forest pests can have major human health and economic
impacts, most modeling of changes in insect range and abundance have focused
on pest species (Sutherst et al., 1995). In southern Africa, models project
changes in the ranges of tsetse flies, ticks, and mosquitoes (Rogers, 1996).
Potential range changes of other disease vectors are discussed in Chapter
9.
High proportions of boreal forest insect pests overwinter as eggs. The strong
link between patterns of minimum temperature and the location of outbreaks are
best explained by the fact that eggs are killed when temperatures dip below
a species' tolerance threshold (Sullivan, 1965; Austara, 1971; Virtanen
et al., 1996). Modeling work that is based on these observations and projected
climate data suggests that increasing nighttime winter temperatures may increase
the frequency of these pest species in northern areas (Tenow, 1996; Virtanen
et al., 1996, 1998), although warmer summer temperatures may reduce the intensity
of outbreaks (Niemelä, 1980; Neuvonen et al., 1999; Virtanen and Neuvonen,
1999; but see Ayres, 1993).
Amphibians and Reptiles: In studies on altitudinal (Pettus and Angleton, 1967;
Licht, 1975; Bizer, 1978; Berven, 1982a,b) and latitudinal (Collins, 1979) gradients,
a general pattern of faster metamorphosis at smaller sizes occurs at high elevations
and northern latitudes. Changes in these life history attributes may affect
species' abundances as a result of susceptibility to predators or environmental
extremes or changes in reproductive output (Calef, 1973; Travis, 1981). Species
that inhabit high-altitude areas may be at particular risk from climate change
because as temperatures increase, their habitats may disappear (Hamilton, 1995;
Pounds et al., 1999). In Australia, frog distributions are strongly correlated
with patterns of annual rainfall, implying that frogs in these areas may be
able to expand their ranges if precipitation increases (Tyler, 1994). Reptile
ranges often correlate with temperature (Nix, 1986; Owen and Dixon, 1989; Yom-Tov
and Werner, 1996), suggesting that ranges may shift with temperature change.
Desert tortoises (Testudo graeca graeca) in southern Morocco already have shifted
their ranges in response to drier conditions possibly resulting from land-use
changes (Bayley and Highfield, 1996).
Birds: In the prairie pothole region of the United States and Canada, a significant
correlation between wetlands, duck numbers, and the Palmer Drought Severity
Index has been found (Sorenson et al., 1998). Projections of warming and drying
for this region suggest that the number of wetlands and, correspondingly, the
number of breeding ducks could be reduced. Similar losses of wetlands have been
projected for Africa (Magadza, 1996) and Australia (Hassal and Associates, 1998).
Mammals: Population reductions in mammals in African arid lands are possible
if the incidence of drought increases (IPCC, 1998). In Australia, declines in
several mammal species may occur if droughts increase in frequency or intensity
(Caughley et al., 1985; Roberston, 1986; Gordon et al., 1988). Mountains (see
Section 5.4.3.1), patchy habitats, and oceans can
be barriers to range shifts. The Arctic Ocean is an obstacle to 25 species of
Canadian mammals, with the collared lemming (Dicrostonyx groenlandicus) possibly
losing at least 60% of its available habitat to climate change (Kerr and Packer,
1998).
The nutritional quality of some plant species has been found to decrease with
increased CO2 availability (Bazzaz, 1996). This could mean that herbivores might
have to eat more. Most studies have dealt with insect or domestic mammals, but
similar results are likely to hold for wild herbivorous mammals (Baker et al.,
1993; Bolortsetseg and Tuvaansuren, 1996). Relative changes in major plant lifeforms
also can affect species distributions and populations densities; for example,
in high-latitude rangelands, shrub abundance may increase and forb abundance
may decrease (Chapin et al., 1995), possibly leading to limitations on food
supplies available to migrating caribou (White and Trudell, 1980).
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