Caribou are not evenly distributed across the landscape. Researchers explored methods to determine what factors influence habitat selection by caribou in Denali National Park and Preserve using more than 20 years of telemetry (caribou location) data. What they found was, in winter, over the long term, caribou chose easy access over their preferred food. They used windswept areas with low snow cover, but with less-preferred forage, more often than areas with deeper snow and their preferred forage, lichens. Within a winter, however, caribou did move to areas where the snow had subsided and lichens became more accessible.
Because wind and habitat type affects snow condition, landscape-scale maps were better predictors than limited field measurements. Generations of wildlife biologists have prioritized increased sample size of animal relocations over predictive map layers like habitat type, snow cover, and terrain. This research showed that better predictive maps with less caribou data produced more accurate maps of habitat selection than models with more caribou data and less predictive maps. The acquisition of high-quality predictive maps should be made more of a priority in the future.
Evaluating relocation extent versus covariate resolution in habitat selection models across spatiotemporal scales
Many habitat selection studies have focused on the importance of spatiotemporal scales and sample size, yet often hidden within is a trade-off between using more animal locations versus more predictive covariates. Few have evaluated the outcome of choosing between these two different paths even though the trade-off can have significant impacts on the conclusions drawn from habitat modeling. We evaluated the covariate resolution versus relocation trade-off across multiple spatiotemporal scales by building habitat selection models using a data-mining approach with 22 years of VHF collar data from the Denali Caribou Herd. We asked whether caribou selected winter habitat based on forage resources after accounting for snow depth. Habitat selection models at three temporal scales (decadal, inter-annual and intra-annual) provide correlative evidence of active selection for winter forage. Based on model performance and predicted occupancy, we found that acquiring appropriate covariate layers is critical and likely even more important than using more animal locations. Based on analyses that utilized more covariates, caribou predominantly selected high graminoid cover, their second most important winter food, over areas with high lichen cover, their primary winter food, at all spatial scales implying a need to balance food quality and accessibility. However, habitat selection differed between temporal scales. Two years in a row, caribou switched to flatter areas with higher lichen cover and low shrub cover while intra-annual variation in habitat selection showed caribou congregated in areas of higher lichen cover and lower snow depths as winter progressed. We conclude that large patches of tussock tundra are high-use areas for wintering caribou in Denali at decadal scales while lichen-rich areas were used at inter-annual and intra-annual temporal scales. Lower snow levels in the future may allow heavier use of lichen woodlands, but increased wildfire activity and shrub encroachment may counteract increased lichen availability in woodlands.
Nelson, P. R., K. Joly, C. A. Roland, and B. McCune. 2018. Evaluating relocation extent versus covariate resolution in habitat selection models across spatiotemporal scales. Ecological Infomatics DOI: 10.1016/j.ecoinf.2018.10.001
Last updated: October 20, 2018