Data from: Prey selection of Scandinavian wolves: single large or several small?

Research on large predator-prey interactions are often limited to the predators' primary prey, with the potential for prey switching in systems with multiple ungulate species rarely investigated. We evaluated wolf (Canis lupus) prey selection at two different spatial scales, i.e., inter- and intra-territorial, using data from 409 ungulate wolf-kills in an expanding wolf population in Scandinavia. This expansion includes a change from a one-prey into a two-prey system with variable densities of one large-sized ungulate; moose (Alces alces) and one small-sized ungulate; roe deer (Capreolus capreolus). Among wolf territories, the proportion of roe deer in wolf kills was related to both pack size and roe deer density, but not to moose density. Pairs of wolves killed a higher proportion of roe deer than did packs, and wolves switched to kill more roe deer as their density increased above a 1:1 ratio in relation to the availability of the two species. At the intra-territorial level, wolves again responded to changes in roe deer density in their prey selection whereas we found no effect of snow depth, time during winter, or other predator-related factors on the wolves' choice to kill moose or roe deer. Moose population density was only weakly related to intra-territorial prey selection. Our results show that the functional response of wolves on moose, the species hitherto considered as the main prey, was strongly dependent on the density of a smaller, alternative, ungulate prey. The impact of wolf predation on the prey species community is therefore likely to change with the composition of the multi-prey species community along with the geographical expansion of the wolf population.

针对大型捕食者-猎物相互作用的研究往往局限于捕食者的主要猎物，而针对多有蹄类物种系统中猎物转换现象的潜在可能性的相关研究则极少开展。本研究以斯堪的纳维亚半岛一个正在扩张的灰狼（Canis lupus）种群的409例狼猎杀有蹄类记录为数据来源，在领地间和领地内两种不同空间尺度上评估了灰狼的猎物选择偏好。该灰狼种群的扩张过程伴随着猎物系统从单猎物向双猎物系统的转变，涉及两种密度可变的有蹄类：一种为大型有蹄类驼鹿（Alces alces），另一种为小型有蹄类狍（Capreolus capreolus）。在不同灰狼领地之间，狼猎杀记录中狍的占比与狼群规模及狍的种群密度均存在相关性，但与驼鹿密度无关。成对活动的灰狼相较于完整狼群，猎杀的狍占比更高；且当两种猎物的可获得性比例达到1:1以上时，灰狼会转向猎杀更多的狍。在领地内部尺度上，灰狼的猎物选择同样会随狍的种群密度变化而改变；但研究未发现积雪深度、冬季时段或其他捕食者相关因素会对灰狼选择猎杀驼鹿还是狍产生影响。驼鹿的种群密度仅与领地内的猎物选择存在微弱相关性。本研究结果表明，此前被视为灰狼主要猎物的驼鹿，其对应的灰狼功能响应强烈依赖于另一种小型备选有蹄类猎物的种群密度。因此，随着灰狼种群的地理扩张，狼捕食对猎物群落的影响可能会随多猎物群落的组成结构发生变化。