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.针对大型捕食者与猎物间相互作用的研究往往局限于捕食者的主要猎物，针对多有蹄类（ungulate）物种系统中猎物转换现象的相关探讨则极为罕见。本研究以斯堪的纳维亚半岛种群扩张中的灰狼（Canis lupus）为研究对象，依托该区域409例灰狼捕食有蹄类的致死记录，在领地间与领地内两个不同空间尺度上评估了灰狼的猎物选择偏好。此次种群扩张使得该研究系统从单一猎物系统转变为双猎物系统，包含两种密度存在波动的有蹄类：一种为大型有蹄类驼鹿（Alces alces），另一种为小型有蹄类狍（Capreolus capreolus）。在不同灰狼领地间，狍在灰狼捕食致死记录中的占比与狼群规模、狍种群密度均显著相关，但与驼鹿密度无关。成对灰狼相较于多成员狼群，捕食狍的比例更高；当两种猎物的可获得性比例高于1:1时，灰狼会更多转向捕食狍。在领地内部尺度上，灰狼的猎物选择同样会随狍种群密度的变化做出响应，但未发现积雪深度、冬季时段或其他与捕食者相关的因素对灰狼选择捕食驼鹿或狍产生显著影响。驼鹿种群密度仅与领地内猎物选择存在微弱关联。本研究结果显示，灰狼对其此前被视为主猎物种的驼鹿的功能响应（functional response），在很大程度上取决于体型更小的替代性有蹄类猎物的种群密度。因此，灰狼捕食对猎物群落的影响，很可能会随着多猎物物种群落的组成变化，以及灰狼种群的地理扩张而发生改变。