Global Wildlife Conservation Center, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, New York, 13210, USA.
Michigan Natural Features Inventory, P.O. Box 13036, Lansing, Michigan, 48901, USA.
Ecology. 2021 Nov;102(11):e03494. doi: 10.1002/ecy.3494. Epub 2021 Aug 20.
Trophic cascades reportedly structure ecological communities through indirect species interactions. Though the predator-herbivore-autotroph relationship has received much attention, mechanistic evidence supporting intraguild trophic cascades is rare. We established 348 remote camera sites (1 August-5 September 2019) across seven study areas of varying wolf (Canis lupus) density including one study area where wolves were absent in northern Michigan, USA. Using multi-species occupancy modeling at species-relevant spatial scales, we evaluated the hypothesis that increased wolf occurrence suppresses coyote (C. latrans) occurrence with corresponding increased red fox (Vulpes vulpes) occurrence mediated by land cover edge density, human presence, and temporal partitioning. Remote cameras recorded >600,000 images and included 6,370, 10,137, and 4,876 detections of wolves, coyotes, and foxes, respectively. Fox occupancy probability was more than three times as high (0.29) at camera sites where wolves were present, relative to sites wolves were absent (0.09). Pairwise species interactions supported expected size-based dominance patterns among canids and insignificant effects were directionally consistent with reported reduced strength of top-down effects in peripheral wolf range. Increased edge density also increased co-occurrence of coyote and wolves, likely a function of increased prey availability and refugia for coyotes. Though foxes occurred in spatial proximity to wolves, competition was limited by greater temporal partitioning than observed between coyotes and foxes that were spatially segregated. Collectively, our results provide marginal support for the reported trophic cascade among wolves, coyotes, and foxes wherein top-down effects may be reduced near the edge of current wolf distributions. As predators continue to recolonize portions of their historic range, knowledge of the effects on intraguild predators has implications for species management and predicting prey population responses.
据报道，营养级联通过间接物种相互作用来构建生态群落。尽管捕食者-食草动物-自养生物关系受到了广泛关注，但支持同营养级级联的机制证据却很少。我们在美国密歇根州北部的一个没有狼的研究区域设立了 348 个远程摄像头站点（2019 年 8 月 1 日至 9 月 5 日），这些站点跨越了 7 个不同狼密度的研究区域。我们使用与物种相关的空间尺度上的多物种占有模型，评估了以下假设：增加狼的出现会通过土地覆盖边缘密度、人类存在和时间分区来抑制郊狼的出现，从而导致红狐的出现相应增加。远程摄像机记录了超过 60 万张图像，其中包括狼、郊狼和狐狸的 6370、10137 和 4876 次检测。在有狼出现的摄像机站点，狐狸的占有概率（0.29）是狼不存在的摄像机站点（0.09）的三倍多。种间相互作用支持了犬科动物之间基于体型的优势模式，并且方向上与报道的在狼分布范围的外围减少顶级捕食者效应的强度一致。边缘密度的增加也增加了郊狼和狼的共同出现，这可能是由于猎物的可用性增加和郊狼的避难所增加所致。尽管狐狸与狼在空间上接近，但竞争受到的限制比在空间上分开的郊狼和狐狸之间的竞争要小，这主要是由于它们在时间上的分区更大。总的来说，我们的研究结果对狼、郊狼和狐狸之间的报告营养级联提供了有限的支持，其中顶级捕食者的影响在当前狼分布范围的边缘可能会减弱。随着捕食者继续在其历史分布范围的部分地区重新定居，了解它们对同营养级捕食者的影响对于物种管理和预测猎物种群的反应具有重要意义。
