Intraguild interactions and abiotic conditions mediate occupancy of mammalian carnivores: co-occurrence of coyotes-fishers-martens

The widespread eradication of large carnivores and subsequent expansion of top mesopredators have the potential to impact species and community interactions with ecosystem-wide implications. An example of these trophic dynamics is the widespread establishment of coyotes following the extirpation of wolves and mountain lions in eastern North America. Here, we examined the occupancy of three carnivores in northern New York considering both environmental/habitat factors and interspecific interactions. We estimated the co-occurrence of coyotes, fishers, and martens from a landscape-scale winter camera trap survey repeatedly annually for three years. Martens occurred independently of both coyotes and fishers, while fishers and coyotes displayed positive intraguild interactions that were constant across the landscape. Both marten and fisher first-order occupancy was driven by a combination of biotic and abiotic factors, with both species displaying positive associations with forest cover but antithetical responses to average snow depth. The integral and antithetical role of snow depth in driving the occurrence of martens (positive) and fishers (negative) in the landscape indicates that future climatic warming could reduce the availability of current spatial refuges for martens created by severe winter conditions. Climate-driven alterations to established competitive interactions and co-existence patterns between marten and fishers have critical implications for the species' survival and conservation. We provide correlational evidence consistent with the potential for positive top-down effects of dominant mesocarnivores on subordinate species, with fisher occupancy increasing conditional on the presence of coyotes across the landscape. These findings align with the hypothesis that under certain conditions, coyotes may facilitate certain subordinate carnivores. The evidence produced here is consistent with hypotheses on the dynamic nature of trophic niches. We demonstrate the need to consider the interplay between climate, habitat, and interspecific interactions to understand wildlife occupancy patterns and inform wildlife management in a rapidly changing world.

大型食肉动物的大范围灭绝以及随后的顶级中型食肉动物（mesopredator）种群扩张，可能会对物种种间互作与群落动态产生影响，并波及整个生态系统。北美东部狼与美洲狮局部灭绝后郊狼的广泛定殖，便是这类营养级动态（trophic dynamics）的典型案例。本研究针对纽约州北部的三种食肉动物展开调查，同时纳入环境/栖息地因子与种间互作的影响考量。研究基于为期三年、每年重复开展的景观尺度冬季红外相机（camera trap）调查数据集，估算了郊狼、渔貂（fisher）与美洲貂（marten）的物种共现性（co-occurrence）。结果表明，美洲貂的占用情况与郊狼、渔貂均无关联；而渔貂与郊狼则呈现出全景观范围内稳定的正同营养级互作（intraguild interactions）。美洲貂与渔貂的一级占用率（first-order occupancy）均由生物因子与非生物因子共同驱动：二者均与森林覆盖率呈正相关，但对平均积雪深度的响应却截然相反。积雪深度在调控美洲貂（正向关联）与渔貂（负向关联）的景观分布中发挥着不可或缺却截然相反的作用，这表明未来气候变暖可能会削减由严酷冬季条件为美洲貂提供的现有空间避难所（spatial refuges）。气候驱动的美洲貂与渔貂间既有竞争互作及共存模式的改变，对这两个物种的生存与保护具有关键意义。本研究提供的相关证据，支持优势中型食肉动物对从属物种存在正向下行效应（top-down effects）的假说：全景观范围内，渔貂的占用率会在郊狼存在的条件下显著升高。上述研究结果与“特定条件下郊狼可促进某些从属食肉动物种群存续”的假说相符。本研究得到的证据也契合营养生态位（trophic niches）具有动态性的相关科学假说。本研究表明，在快速变化的当今世界，若要精准解析野生动物的占用模式并为野生动物管理提供科学依据，必须综合考量气候、栖息地与种间互作之间的复杂相互作用。