Scale-dependent ecology of an endangered woodland caribou (Rangifer tarandus caribou) ecotype: Individual foraging decisions to remaining distribution.
Serrouya, Robert*,1, McLellan, Bruce2, Apps, Clayton3, Wittmer, Heiko4, 1 Consultant, South Slocan, British Columbia, Canada2 British Columbia Ministry of Forests, Revelstoke, British Columbia, Canada3 Aspen Wildlife Research Inc., Calgary, Alberta, Canada4 University of California, Berkeley, California, USA
ABSTRACT- Mountain caribou are an endangered ecotype of woodland caribou that live in high-precipitation, mountainous ecosystems of SE British Columbia and N Idaho. The number of these animals is in decline and they are currently fragmented into 18 subpopulations. This ecotype relies on old conifer forests for several life-history requirements including an abundance of their primary winter food, arboreal lichen, and a scarcity of other ungulates and their predators. These old forests have high timber value and understanding the ecology of mountain caribou at a variety of spatial scales is required to develop guidelines that can be implemented at a corresponding variety of scales. At the scale of their entire distribution, we investigated factors that differentiate where mountain caribou persist relative to where they have been extirpated, and determined that the extent of wet and very wet climatic conditions, the distribution of old (>140 yr) forests and remoteness from human presence were among the most important. By comparing among subpopulations, we also found a negative relationship between the amount of early to mid-seral vegetation (a possible surrogate for other ungulates and associated predators), and adult female survival. At 4 finer scales, the analysis of radio-telemetry and GIS basemaps revealed that habitat selection varied seasonally but, old stands, gentle terrain, and seasonally drier ecosystems were selected. At the finest scales we examined factors that were not distinguishable from remotely sensed GIS maps by asking the question: are all old forests in a given ecosystem of equal quality to mountain caribou? This question addresses how to allocate limited amounts of old-forest retention areas. We determined that variability of caribou use among old stands was explained by the abundance of fallen trees, standing live and dead trees, and lichen litterfall. These attributes facilitate access to arboreal lichen but some of them are common in diseased stands that are often subject to salvage logging. Broad-scale factors related to the distribution of predators and human use and fine-scale factors that influence foraging decisions clearly need to be addressed in concert to conserve mountain caribou.
Key words: Rangifer tarandus caribou, fragmentation, demography, endangered
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