Den selection criteria

Climate warming is favoring the expansion of non-native species onto the Arctic tundra, where they may compete over resources with native species. In the harsh tundra conditions, sympatric red foxes (Vulpes vulpes) and Arctic foxes (Vulpes lagopus) may compete over denning sites, which are important for their reproduction and survival. We studied den selection by red and Arctic foxes in spring and summer, and their possible competition over this resource in an ecotone near Churchill, Manitoba, on the west coast of Hudson Bay, by examining patterns of den occupancy related to den characteristics and spacing patterns between neighbors. Based on 11 years of occupancy data for 42 tundra dens, we determined that red and Arctic foxes favored dens based on shelter quality in both spring and summer, rather than proximity of specific habitats (and thus specific prey). Mechanisms of den selection differed between species, which may promote co-existence, and areas of high den density were avoided by red foxes and preferred by Arctic foxes. We did not find evidence of exclusion of Arctic foxes by red foxes: spacing patterns showed that foxes spaced themselves based on their need for space, territoriality and food availability but not interference. In the current abiotic Arctic conditions, taiga species settling on the tundra could coexist with tundra endemics, at given density thresholds of both competitors. As Arctic conditions may become milder, an increase in newcomer abundance could disrupt the current balance that favors species coexistence. This study was carried out in and around Wapusk National Park, on the western edge of Hudson Bay near Churchill, Manitoba, Canada (58°45’ N; 94°10’ W), where red foxes have settled in tundra dens to reproduce exhibiting a continuous presence since 2010.气候变暖正推动外来物种向北极苔原扩张，这些外来物种可能与本地物种争夺资源。在严苛的苔原环境中，同域分布的赤狐（Vulpes vulpes）与北极狐（Vulpes lagopus）可能会争夺巢穴位点——这类位点对二者的繁殖与生存均至关重要。本研究于哈德逊湾西岸马尼托巴省丘吉尔市附近的一处生态交错带中，通过分析与巢穴特征、邻体间距模式相关的巢穴占用规律，探究了春夏季赤狐与北极狐的巢穴选择偏好，以及二者对该资源的潜在竞争关系。基于42个苔原巢穴的11年占用数据，本研究发现：赤狐与北极狐在春夏季均会依据巢穴的遮蔽质量选择位点，而非特定生境的远近（进而影响猎物可得性）。二者的巢穴选择机制存在差异，这或有助于物种共存；同时，赤狐会回避高密度巢穴区域，而北极狐则偏好此类区域。本研究未发现赤狐排挤北极狐的证据：邻体间距模式显示，狐狸的空间分布仅受自身空间需求、领域性与食物可获得性的影响，而非种间干扰。在当前北极非生物环境条件下，定居于苔原的泰加林（taiga）物种可与苔原特有物种实现共存，前提是两类竞争者的种群密度处于特定阈值范围内。随着北极环境逐渐趋于温和，外来物种种群数量的增长可能会打破当前有利于物种共存的平衡状态。 本研究的开展区域为加拿大马尼托巴省丘吉尔市附近、哈德逊湾西岸的瓦普斯克国家公园（Wapusk National Park）及其周边区域（北纬58°45′，西经94°10′），自2010年起，赤狐便在此处的苔原巢穴中定居繁殖，且种群持续存在至今。