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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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