Factors affecting the spatiotemporal distribution of moose, with a special emphasis on supplementary feeding
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Large herbivores constitute an important natural resource and are actively managed to meet economic, conservation and environmental objectives. To alleviate the potential of resource limitation and damage to commercially important habitats in areas with high population densities, the provisioning of artificial or supplementary forage has become a popular wildlife management intervention throughout Europe and North America. However, the usefulness of supplementary feeding is equivocal and little is known about how it affects spatiotemporal distribution patterns of large herbivores. The main aim of this thesis is to quantify the effect of supplementary feeding on the spatiotemporal distribution of moose (Alces alces L. 1758) living in southern Norway. I used locations of free-ranging GPS (global positioning system) collared moose (N = 26 in summer and N = 32 in winter) with access to supplementary feeding stations to estimate habitat selection and home range size as a function of feeding status (i.e. feeding station users vs. non-users), variation in browse quantity and quality, and also in terms of local climate and individual characteristics. To evaluate fine-scale distribution patterns and foraging decisions around supplementary feeding stations I employed 2 independent datasets (GPS data and browsing estimates) from two study areas (in Telemark and Hedmark counties) that differ in the length of their feeding history. I apply central-place foraging theory to explain the observed patterns. My results indicate that supplementary feeding affects the spatiotemporal distribution of moose only at intermediate to fine spatial scales during winter, with feeding station users behaving as central-place foragers. However, feeding station users did not differ in their large-scale habitat selection patterns or home range size compared to non-users. Instead, moose habitat selection was driven by a scale-dependent trade-off between browse quantity (landscape-scale) and browse quality (within-home rangescale). Moreover, depletion of high quality browse during winter lead moose to increase selection for lower quality browse within their home range. Variation in home range size was affected by several extrinsic (i.e. climate and natural browse) and intrinsic variables (i.e. individual characteristics) and their effects varied between and within spatiotemporal scales. After 6 years of feeding, moose that used feeding stations selected for commercially valuable browse (i.e. Scots pine) within their home range to the same extent as non-users, which questions the effectiveness of winter feeding in reducing browsing pressure over large spatial scales. In addition, as the time scale of feeding increased from 5-10 to 15-20 years, browsing pressure on commercially valuable browse (i.e. Scots pine and Norway spruce) was amplified at a fine spatial scale. At the same time, resource depletion in the vicinity of feeding stations lead moose to forage at increasing distances from feeding stations and browsing damage occurred at least up to 1 km from feeding stations. These findings suggest that when supplementary feeding is practised over longer time scales (more than 20 years) there is the potential for a trade off to occur between the energetic cost of returning to the central-place (i.e. feeding station) and the energetic benefits it provides. Evaluating management actions is important to determine whether the objectives and desired effects are realized. I have shown how supplementary feeding can affect the spatiotemporal distribution of moose and how subsequent browsing pressure around feeding stations can change over time. However, there are a variety of direct and indirect effects that follow the provisioning of supplementary forage that have not yet been adequately assessed. A holistic evaluation of the effectiveness of supplementary feeding as a wildlife management tool is required and needs to consider all the associated benefits and costs, especially considering long-term developments and potential ecosystem-level effects.
Doktorgradsavhandling ved Universitetet i Oslo ved det matematisk- naturvitenskapelige fakultet, nr 1016.