18.104.22.168.1. Shifts in animal ranges and abundances
Ranges and abundances of prehistoric animals are known to have changed significantly
over time (Goodfriend and Mitterer, 1988; Baroni and Orombelli, 1994; Coope,
1995). Currently, many species are undergoing range changes because of habitat
conversion, land degradation (e.g., grazing, changes in fire regime), climate
change, or a combination of factors. Possible climatically associated shifts
in animal ranges and densities have been noted on three continents (Antarctica,
Europe, and North America) and within each major taxonomic group of animals
(see Table 5-3).
Invertebrates: Insect dispersal to favorable areas to make effective use of
microclimatic differences is a common response to changing climate (e.g., Fielding
et al., 1999). The ranges of butterflies in Europe and North America have been
found to shift poleward and upward in elevation as temperatures have increased
(Pollard, 1979; Parmesan, 1996; Ellis et al., 1997; Parmesan et al., 1999).
Warming and changed rainfall patterns also may alter host plant-insect relations,
through community or physiological responses (e.g., host plant food quality)
(Masters et al., 1998).
Amphibians and Reptiles: Amphibians may be especially susceptible to climatic
change because they have moist, permeable skin and eggs and often use more than
one habitat type and food type in their lifetimes (Lips, 1998). Many amphibious
species appear to be declining, although the exact causes (e.g., climate change,
fungus, UV radiation, or other stresses) are difficult to determine (Laurance,
1996; Berger et al., 1998; Houlahan et al., 2000). Disappearance of the golden
toad (Bufo periglenes) and the harlequin frog (Atelopus varius) from Costa Rica's
Monteverde Cloud Forest Reserve appear to be linked to extremely dry weather
associated with the 1986-1987 ENSO event (Pounds and Crump, 1994). Correlation
between warming, reduced frequency of dry-season mist, and the timing of population
crashes of four other frog species and two lizard species from the same cloud
forest also has been found (Pounds et al., 1999).
Birds: Bird ranges reportedly have moved poleward in Antarctica (Emslie et
al., 1998), North America (Price, 2000), Europe (Prop et al., 1998), and Australia
(Severnty, 1977). For example, the spring range of Barnacle Geese (Branta leucopsis)
has moved north along the Norwegian coast, correlated with a significant increase
in the number of April and May days with temperatures above 6°C (Prop et
al., 1998). The elevational range of some Costa Rican tropical cloud forest
birds also apparently are shifting (Pounds et al., 1999).
Mammals: Changes in mammal abundance can occur through changes in food resources
caused by climate-linked changes or changes in exposure to disease vectors.
For example, the Australian quokka (Setonix brachyurus) differs in susceptibility
to Salmonella infections depending on climatic environmental conditions (Hart
et al., 1985).