The return of large carnivores: Using hunter observation data to understand the role of predators on ungulate populations

Coexisting with large carnivores based on the Volterra principle

Coexistence with large carnivores represents one of the world's highest profile conservation challenges. Ecologists have identified ecological benefits derived from large carnivores (and large herbivores), yet livestock depredation, perceived competition for shared game, risks to pets and humans, and social conflicts often lead to demands for reduction of predator numbers from a range of stakeholder groups. Nearly 100 years ago, Vito Volterra predicted that increased mortality on both prey and predators results in increased abundance of prey and decreased abundance of predators. This principle appears to be robust and often consistent with the objectives of wildlife management. Although seldom recognized, and rarely tested in the field, the Volterra principle is a fundamental outcome of ecological theory with important implications for conservation.

Quantifying large carnivore predation relative to human harvest on moose in an intensively managed boreal ecosystem

The return of large carnivores to areas with strong anthropogenic impact often results in conflicts among different interest groups. One cause of conflict is that large carnivores compete with humans for wild game species. In Scandinavia, the recolonization of wolves (Canis lupus) and brown bears (Ursus arctos) has important ramifications for the harvest of an ungulate species with high economic and recreational value, the moose. We estimated wolf and brown bear predation rates on moose (Alces alces) relative to harvest, natural causes of death, and vehicle collisions within 20 wolf territories. We used data on multi-season kill rates of wolves and brown bears on moose combined with wolf territory sizes and estimates of the population density of brown bears and moose. Wolf predation rate on moose was not related to the density of moose, wolf pack size, nor kill rate but was positively related to wolf density and strongly negatively related to the abundance of moose within wolf territories. Estimated annual wolf and brown bear predation rates averaged 8.6% (range 2.8%-16.9%) and 2.3% (range 0%-12.7%) respectively, among wolf territories, whereas estimated annual harvest rates averaged 17.5% (range 8.1%-33.1%). In wolf territories with relatively high bear densities, the combined predation rates from wolves and brown bears exceeded harvest rates. Across wolf territories, harvest rates were not related to wolf predation rates or to the combined predation rates from wolves and brown bears, indicating that large carnivore predation and harvest were not compensatory to each other at this spatial level. The recolonization of these large carnivores in the Scandinavian boreal forest ecosystem may have small to significant consequences for the sustainable management of moose populations depending on the local conditions of both wolves, brown bears, and moose. Comparison of annual mortality rates for moose in our study in Scandinavia with corresponding data from areas with lower anthropogenic impact (Alaska) shows lower total mortality rates in Scandinavia. This likely results from a different age and sex composition of moose killed by wolves and brown bears versus harvest, in combination with a significant difference in the relative importance of these mortality factors between areas.

Human Footprint and Forest Disturbance Reduce Space Use of Brown Bears (Ursus arctos) Across Europe

Three-quarters of the planet's land surface has been altered by humans, with consequences for animal ecology, movements and related ecosystem functioning. Species often occupy wide geographical ranges with contrasting human disturbance and environmental conditions, yet, limited data availability across species' ranges has constrained our understanding of how human pressure and resource availability jointly shape intraspecific variation of animal space use. Leveraging a unique dataset of 758 annual GPS movement trajectories from 375 brown bears (Ursus arctos) across the species' range in Europe, we investigated the effects of human pressure (i.e., human footprint index), resource availability and predictability, forest cover and disturbance, and area-based conservation measures on brown bear space use. We quantified space use at different spatiotemporal scales during the growing season (May-September): home range size; representing general space requirements, 10-day long-distance displacement distances, and routine 1-day displacement distances. We found large intraspecific variation in brown bear space use across all scales, which was profoundly affected by human footprint index, vegetation productivity, and recent forest disturbances creating opportunity for resource pulses. Bears occupied smaller home ranges and moved less in more anthropized landscapes and in areas with higher resource availability and predictability. Forest disturbances reduced space use while contiguous forest cover promoted longer daily movements. The amount of strictly protected and roadless areas within bear home ranges was too small to affect space use. Anthropized landscapes may hinder the expansion of small and isolated populations, such as the Apennine and Pyrenean, and obstruct population connectivity, for example between the Dinaric Pindos population and the Alpine or Carpathian population. Our findings call for actions to maintain bear movements across landscapes with high human footprint, for example by maintaining forest integrity, to support viable bear populations and their ecosystem functions.

Habitat Selection by Brown Bears with Varying Levels of Predation Rates on Ungulate Neonates

In northern Eurasia, large carnivores overlap with semi-domestic reindeer (Rangifer tarandus) and moose (Alces alces). In Scandinavia, previous studies have quantified brown bear (Ursus arctos) spring predation on neonates of reindeer (mostly in May) and moose (mostly in June). We explored if habitat selection by brown bears changed following resource pulses and whether these changes are more pronounced on those individuals characterised by higher predatory behaviour. Fifteen brown bears in northern Sweden (2010–2012) were fitted with GPS proximity collars, and 2585 female reindeers were collared with UHF transmitters. Clusters of bear positions were visited to investigate moose and reindeer predation. Bear kill rates and home ranges were calculated to examine bear movements and predatory behaviour. Bear habitat selection was modelled using resource selection functions over four periods (pre-calving, reindeer calving, moose calving, and post-calving). Coefficients of selection for areas closer to different land cover classes across periods were compared, examining the interactions between different degrees of predatory behaviour (i.e., high and low). Bear habitat selection differed throughout the periods and between low and high predatory bears. Differences among individuals’ predatory behaviour are reflected in the selection of habitat types, providing empirical evidence that different levels of specialization in foraging behaviour helps to explain individual variation in bear habitat selection.