Wehr Nathaniel H, Moore Seth A, Isaac Edmund J, Kellner Kenneth F, Millspaugh Joshua J, Belant Jerrold L
Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI, USA.
Department of Biology and Environment, Grand Portage Band of Lake Superior Chippewa, Grand Portage, MN, USA.
Mov Ecol. 2024 Apr 26;12(1):33. doi: 10.1186/s40462-024-00466-w.
Prey are more vulnerable during migration due to decreased familiarity with their surroundings and spatially concentrated movements. Predators may respond to increased prey vulnerability by shifting their ranges to match prey. Moose (Alces alces) and white-tailed deer (Odocoileus virginianus) are primary gray wolf (Canis lupus) prey and important subsistence species for Indigenous communities. We hypothesized wolves would increase use of ungulate migration corridors during migrations and predicted wolf distributions would overlap primary available prey.
We examined seasonal gray wolf, moose, and white-tailed deer movements on and near the Grand Portage Indian Reservation, Minnesota, USA. We analyzed GPS collar data during 2012-2021 using Brownian bridge movement models (BBMM) in Migration Mapper and mechanistic range shift analysis (MRSA) to estimate individual- and population-level occurrence distributions and determine the status and timing of range shifts. We estimated proportional overlap of wolf distributions with moose and deer distributions and tested for differences among seasons, prey populations, and wolf sex and pack affiliations.
We identified a single migration corridor through which white-tailed deer synchronously departed in April and returned in October-November. Gray wolf distributions overlapped the deer migration corridor similarly year-round, but wolves altered within-range distributions seasonally corresponding to prey distributions. Seasonal wolf distributions had the greatest overlap with deer during fall migration (10 October-28 November) and greatest overlap with moose during summer (3 May-9 October).
Gray wolves did not increase their use of the white-tailed deer migration corridor but altered distributions within their territories in response to seasonal prey distributions. Greater overlap of wolves and white-tailed deer in fall may be due to greater predation success facilitated by asynchronous deer migration movements. Greater summer overlap between wolves and moose may be linked to moose calf vulnerability, American beaver (Castor canadensis) co-occurrence, and reduced deer abundance associated with migration. Our results suggest increases in predation pressure on deer in fall and moose in summer, which can inform Indigenous conservation efforts. We observed seasonal plasticity of wolf distributions suggestive of prey switching; that wolves did not exhibit migratory coupling was likely due to spatial constraints resulting from territoriality.
猎物在迁徙过程中由于对周围环境的熟悉度降低和空间上集中的移动而更加脆弱。捕食者可能会通过改变其活动范围以匹配猎物来应对猎物脆弱性的增加。驼鹿（Alces alces）和白尾鹿（Odocoileus virginianus）是灰狼（Canis lupus）的主要猎物，也是原住民社区重要的生计物种。我们假设狼在猎物迁徙期间会增加对有蹄类动物迁徙走廊的利用，并预测狼的分布会与主要的可获取猎物重叠。
我们研究了美国明尼苏达州大港湾印第安保留地及其附近灰狼、驼鹿和白尾鹿的季节性移动情况。我们在2012年至2021年期间使用迁移映射器中的布朗桥运动模型（BBMM）和机制性范围转移分析（MRSA）分析了GPS项圈数据，以估计个体和种群水平的出现分布，并确定范围转移的状态和时间。我们估计了狼的分布与驼鹿和鹿的分布的比例重叠，并测试了季节、猎物种群以及狼的性别和狼群归属之间的差异。
我们确定了一条单一的迁徙走廊，白尾鹿在4月同步离开并于10月至11月返回。灰狼的分布全年都类似地与鹿的迁徙走廊重叠，但狼在其活动范围内的分布会随着猎物分布季节性地改变。秋季迁徙期间（10月10日至11月28日）狼的季节性分布与鹿的重叠最大，夏季（5月3日至10月9日）与驼鹿的重叠最大。
灰狼并没有增加对白尾鹿迁徙走廊的利用，但会根据季节性猎物分布改变其领地内的分布。秋季狼与白尾鹿的重叠更大可能是由于鹿的异步迁徙运动促进了更高的捕食成功率。夏季狼与驼鹿的重叠更大可能与驼鹿幼崽的脆弱性、美洲河狸（Castor canadensis）的共存以及与迁徙相关的鹿数量减少有关。我们的结果表明秋季对鹿和夏季对驼鹿的捕食压力增加，这可为原住民保护工作提供参考。我们观察到狼分布的季节性可塑性表明存在猎物转换；狼没有表现出迁徙耦合可能是由于领地性导致的空间限制。
