Community-wide mesocarnivore response to partial ungulate migration

Mesocarnivores increase in number and geographic range in human-disturbed ecosystems with cascading negative impact on biodiversity. To mitigate such impacts it is essential to identify the proximate causes of such mesocarnivore releases. Here we assess to what extent increased partial migration in semi-domesticated tundra reindeer induce a response in boreal and arctic mesocarnivores. We used a large-scale and multi-year quasi-experimental study design with camera traps deployed on coastal tundra peninsulas in northern Norway to estimate area occupancy of the whole carnivore community. These peninsulas represent summer pastures for separate semi-domestic reindeer herds that, owing to different degrees of partial migration, now display spatially and temporally variable densities of year-round resident reindeer. We estimated resident reindeer density by means of aerial surveys. Area occupancy of all the recorded carnivore species increased strongly when resident reindeer densities exceeded 1.5 deer km-2. Most of the increasing carnivore species were typical boreal forest species, implying range expansions into tundra when provided with stable food resources (prey and carrion) in terms of resident reindeer. Synthesis and applications. We found that boreal mesocarnivores, known to negatively impact the productivity of reindeer and arctic wildlife of conservation concern, steeply increased in tundra areas with many year-round resident reindeer due to increased partial migration. To avoid such negative impacts, actions should be taken to minimize residency in tundra reindeer.

中型食肉动物（Mesocarnivores）在受人类干扰的生态系统中，种群数量与地理分布范围均会扩张，进而对生物多样性造成级联负面影响。为缓解此类负面影响，明确这类中型食肉动物种群释放的近因至关重要。本研究旨在探究半驯化苔原驯鹿（semi-domesticated tundra reindeer）的部分迁徙（partial migration）比例提升，会在多大程度上引发北方与北极中型食肉动物的种群响应。本研究采用大规模多年准实验研究设计，在挪威北部的沿海苔原半岛布设红外相机陷阱（camera traps），以估算整个食肉动物群落的区域占用率（area occupancy）。这些半岛是多个独立半驯化驯鹿群的夏季牧场；由于部分迁徙程度存在差异，这些驯鹿群的全年居留驯鹿密度呈现出空间与时间上的异质性波动。研究人员通过航空调查（aerial surveys）估算了居留驯鹿的种群密度。当居留驯鹿密度超过1.5头·km⁻²时，所有记录到的食肉动物物种的区域占用率均显著上升。种群数量上升的食肉动物大多为典型的北方森林物种，这意味着当居留驯鹿提供了稳定的食物资源（猎物与腐肉）时，这些物种会向苔原地区扩张分布范围。综合与应用：本研究发现，已知会对驯鹿种群生产力以及受保护关注的北极野生动物造成负面影响的北方中型食肉动物，由于部分迁徙比例提升，在居留驯鹿数量较多的苔原地区种群数量急剧上升。为避免此类负面影响，应采取措施降低苔原驯鹿的居留比例。