Wolves adapt territory size, not pack size to local habitat quality

Abstract

Summary1. Although local variation in territorial predator density is often correlated with habitat quality, the causal mechanism underlying this frequently observed association is poorly understood and could stem from facultative adjustment in either group size or territory size. 2. To test between these alternative hypotheses, we used a novel statistical framework to construct a winter population-level utilization distribution for wolves (Canis lupus) in northern Ontario, which we then linked to a suite of environmental variables to determine factors influencing wolf space use. Next, we compared habitat quality metrics emerging from this analysis as well as an independent measure of prey abundance, with pack size and territory size to investigate which hypothesis was most supported by the data. 3. We show that wolf space use patterns were concentrated near deciduous, mixed deciduous/ coniferous and disturbed forest stands favoured by moose (Alces alces), the predominant prey species in the diet of wolves in northern Ontario, and in proximity to linear corridors, including shorelines and road networks remaining from commercial forestry activities. 4. We then demonstrate that landscape metrics of wolf habitat quality -projected wolf use, probability of moose occupancy and proportion of preferred land cover classes -were inversely related to territory size but unrelated to pack size. 5. These results suggest that wolves in boreal ecosystems alter territory size, but not pack size, in response to local variation in habitat quality. This could be an adaptive strategy to balance trade-offs between territorial defence costs and energetic gains due to resource acquisition. That pack size was not responsive to habitat quality suggests that variation in group size is influenced by other factors such as intraspecific competition between wolf packs.

Selection for forage and avoidance of risk by woodland caribou (Rangifer tarandus caribou) at coarse and local scales

“…Considerable effort has gone into ensuring that our models are satisfactory (for more information, see Kittle et al [2015] and Avgar et al [2015]). Importantly, the use of biomass and wolf density as variables for this study allowed us to directly assess and interpret caribou's responses to forage and risk across a broad landscape.…”

“…The managed half of the landscape (located near v www.esajournals.org the Nakina township) is characterized by younger forest stands dominated by mixedwood and deciduous species that have largely regenerated from anthropogenic disturbance, whereas the northwestern half of the study area (located near the Pickle Lake township) is characterized by older stands of coniferous species that have regenerated from natural disturbance. The southeastern part of the study area has lower lichen density (Avgar et al 2015), but higher densities of both moose and wolves (Kittle et al 2015, Street et al 2015. Because of extensive logging activity, the southeastern part of the study also has higher road density (LIO; https://www.javacoeapp.lrc.…”

“…Four wolf density kernels were calculated for winter (a different kernel for each winter between the winters of 2009-2010 and 2012-2013) using data from 32 packs, and three kernels were calculated for summer (2010)(2011)(2012) using data from 34 packs (Kittle et al 2015). Local wolf density (log transformed) was related to temporally-matched landscape characteristics for each season.…”

“…Using encounter likelihoods as a proxy for risk has both advantages (measurability) and disadvantages (it does not account for ability of prey to modify their actual chances of mortality, given an encounter, through defensive investment). For more details, see Kittle et al (2015) and Avgar et al (2015).…”

“…Despite the fact that moose (Alces alces) predominate in their diet, wolves (Canis lupus) nonetheless often have a strong impact on woodland caribou populations (Seip et al 1991, Bergerud et al 1994, Festa-Bianchet et al 2011. Wolves tend to spend most of their time in early successional forests, presumably because these are the habitats preferred by moose, their primary prey (Cumming et al 1996, Kittle et al 2015. Because forage abundance and wolf predation risk play important roles in caribou survival and reproduction (Gustine et al 2006), caribou have a clear opportunity to select habitats that improve fitness either through increased access to forage or reduced risk of predation as caribou move across heterogeneous boreal landscapes.…”