Findings indicate that many animals already may be responding to local climatic changes. Types of changes already observed include poleward and elevational movement of ranges, changes in animal abundance, changes in body size, and shifts in the timing of events such as breeding to earlier in the spring. These responses have been identified by a group of studies from around the world in a variety of different species (see Table 5-3). Far more information is available than can be summarized here. More detail on these changes is available in Hughes (2000) and Price et al. (2000).
Results from most studies that use large-scale data sets provide circumstantial (e.g., correlational) evidence about the association between changes in climate-related environmental factors and animal numbers or activities. Circumstantial evidence, though insufficient by itself, is highly suggestive when multiple studies examining a myriad of different species on all continents find similar results. Combined with smaller scale studies, experimental studies, and modeling studies that examine mechanistic connections between animals and climate change, the weight of evidence becomes even stronger. Such is the case for wildlife already exhibiting change related to climate forcings (see Table 5-3). The information given in the following subsections is a sampling of the types of studies that have examined the potential impacts of climate change on animals. The studies were selected for taxonomic and geographic inclusiveness and are not inclusive of the breadth of range of published studies. Information on more studies can be found in Table 5-3 and in Price et al. (2000).
Box 5-6. Penguins as Indicators of Climate Warming in Western Antarctic
Midwinter surface air temperatures in the Western Antarctic Peninsula (WAP) region have increased by 4-5°C over the past 50 years (Smith et al., 1996b). Studies confirm that the spatial and temporal patterns of winter sea-ice development in the WAP have changed during this time in response to rapid warming (Fraser et al., 1992; de la Mare, 1997; Jacobs and Comiso, 1997; Loeb et al., 1997). Chinstrap (Pygoscelis antarctica) and Adélie (P. adeliae) penguin populations also have changed during the past 25 years.
Although these two species are ecologically very similar, with diets and breeding ranges that overlap in the WAP (Volkman et al., 1980), their winter habitat preferences are radically different. Adélies are obligate inhabitants of the pack ice, whereas Chinstraps are ice-intolerant, preferring to remain in close association with open water (Fraser et al., 1992; Ainley et al., 1994). The quality and availability of winter habitat is an essential determinant of survival and therefore a key factor regulating seabird populations (Birkhead and Furness, 1984). Adélie penguins have decreased by 22% whereas Chinstrap penguins have increased by more than 400% over the past 25 years (Fraser and Patterson, 1997; Smith et al., 1999). This pattern supports the hypothesis that the increasing availability of open water as a result of warmer winters is favoring the survival of Chinstraps over the ice-dependent Adélies (see Fraser et al., 1992).
Other reports in this collection