Long term populaton fluctuations and winter foraging ecology of arctic tundra caribou
Ferguson, Michael Arthur Darrell
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Caribou (Rangifer tarandus ') populations residing on Arctic tundra can be affected by both density-independent climatic events and density-dependent grazing impacts which may accumulate over several decades. Recovery of overgrazed how can require several decades. Indigenous peoples (Homo sapiens) possess knowledge about caribou, dating back generations and covering extensive areas. Researchers and management agencies may benefit from such knowledge of long-term changes in populations of caribou and ecological processes that may cause such changes. During 1983-94, I developed a method to collect and analyse Inuit knowledge about a caribou population on southern Baffin Island. Based on comparisons with other information, I retained the accuracy and precision inherent in Inuit oral traditions. During 1982-94, I also conducted aerial surveys and satellite telemetry to scientifically examine population changes that were both predicted and observed by Inuit within two winter ranges on Foxe (FP) and Meta Incognita (MIP) peninsulas. In April 1992, I studied the physical condition, forage selection and foraging ecology of caribou in these two winter ranges. Caribou distributions were extensive, and abundance was high, in most coastal areas from c. 1900 until the 1920s. Subsequently, caribou distributions contracted, and abundance declined about 9% annually, until the 1940s. From the 1950s until the mid-1980s, distribution expanded and abundance increased about 8%. Increases in caribou abundance followed phases of winter range expansion, range drift and finally range shift. When abundance was low, caribou frequently and unpredictably shifted their winter ranges. Population fluctuations of South Baffin caribou are cyclic, each cycle occurring over the lifetime of an Inuit elder. The population essentially abandoned its main wintering area on FP during the late 1980s, emigrating to MIP. Caribou density on FP dropped from 6.2 in 1984 to 0.3-km-2 in 1992. FP caribou began emigrating during winter 1988-89. Caribou density on MIP increased from 0.2 in 1982 to 5.0-km-2 in 1992. In April 1992, caribou on MIP were in better physical condition than those on FP. Fecundity and recruitment were lower on FP. Nevertheless, MIP caribou were in poorer condition than expected. Caribou on FP dug feeding craters in shallower, softer snow. Biomasses of most fruticose lichens were greater within foraging sites on MIP than on FP. 'D integrifolia' was the only plant class that bad higher biomass on FP than on MIP Cladina'/'Cladonia' spp., 'Sphaerophorms fragilis', and 'Cetraria nivalis' were eaten less frequently by FP caribou than by MIP caribou. Proportions of fruticose lichens in caribou rumens on both peninsulas were similar to those on other overgrazed tundra winter ranges. Overgrazing on FP reduced important forage resources on accessible sites, but plant associations were not fundamentally different. Caribou on FP were probably impacted largely by cumulative density-dependent overgrazing. Although grazing had affected forage resources on MIP, physical condition of caribou had not yet deteriorated. Even predation and harvesting of caribou, cumulative overgrazing on winter ranges can eventually compromise physical condition and productivity of Arctic tundra caribou. Other synergistic ecological processes may then influence Arctic tundra populations unable to emigrate to better range. Some ecologists may have ignored influences of long-term cumulative overgrazing either because of apparent dominance of short-term processes (e.g., climatic events) or because they lack adequate historical information.