Table_1_Long-term dietary shifts in a generalist predator, the wolverine (Gulo gulo).docx

Over the last hundred years, many large carnivore species have suffered range contractions, population losses, and habitat alterations that may be influencing their dietary preferences. To identify shifting isotopic niches and reconstruct past and present diets from species of high conservation concern, stable isotope analysis (SIA) of δ13C and δ15N values of tissue from museum collections and ongoing non-invasive monitoring programs offers an effective approach. Here, we assessed the long-term alterations in the trophic structure of a generalist large carnivore over a time of population loss and recovery. Wolverine stable carbon (δ13C) and nitrogen (δ15N) isotopes were measured in hair samples collected from 44 individuals in Finland for the period 1905–2020, and potential dietary were quantified using isotopic niche metrics shifts in two study areas. We provide evidence of a long-term diet shift in Finnish wolverines, with a temporal depletion of hair’s δ13C (β = −0.016‰, R² = 0.46, p < 0.001). Correspondingly, there was a shift in the isotopic niches of the Historical population (before the year 2000) and Recent population (after 2000), with the niche overlap between the Historical and Recent periods being only 33% throughout Finland, and even lower in the two study areas (22% to 24%). The breadth of the isotopic niche, however, did not significantly differ between the two periods, suggesting that despite a change in diet composition, wolverines did not specialize more. The trophic level of wolverines in Finland was stable throughout the study period, with no significant change in δ15N with time (β = 0.0055‰, R² = 0.043, p = 0.17). In summary: A) the strong trophic resilience of this top predator was shown by the stability of its niche breadth and trophic level feeding regime during periods of population decline and recovery as well as during a period of major anthropogenic alterations in their environment; B) the use of SIA methods on historical and recent hairs provided a unique tool to unravel long-term changes in wolverine feeding strategies.

近百年来，诸多大型食肉动物类群均经历了分布范围缩减、种群数量下降以及生境改变，这些变化或对其食性偏好产生影响。为识别同位素生态位的动态变化，并重建受高度保护关注物种的古今食性，利用博物馆馆藏组织样品与当前非侵入式监测项目获取的材料开展δ¹³C与δ¹⁵N稳定同位素分析（Stable Isotope Analysis, SIA），是一种行之有效的研究手段。本研究针对经历种群下降与恢复阶段的广食性大型食肉动物，评估其营养结构的长期变化。我们对1905年至2020年间芬兰境内采集的44只狼獾（wolverine）毛发样品中的碳同位素δ¹³C与氮同位素δ¹⁵N进行了测定，并利用同位素生态位指标量化了两个研究区域内的食性转变。

研究结果表明，芬兰狼獾存在长期食性转变，其毛发δ¹³C值随时间呈显著耗竭趋势（β = −0.016‰，R² = 0.46，p < 0.001）。相应地，历史种群（2000年之前）与现代种群（2000年之后）的同位素生态位发生了分化：整个芬兰范围内，历史与现代时期的生态位重叠度仅为33%，在两个研究区域内该数值更低（22%至24%）。然而，两个时期的同位素生态位宽度并无显著差异，这表明尽管食性组成发生改变，狼獾并未出现食性特化。研究期间，芬兰狼獾的营养级保持稳定，δ¹⁵N值未随时间产生显著变化（β = 0.0055‰，R² = 0.043，p = 0.17）。

综上：
A）该顶级捕食者展现出强大的营养弹性——在种群下降、恢复以及生境遭受重大人为改造的时期，其生态位宽度与营养级摄食模式均保持稳定；
B）对历史与现代毛发样品开展稳定同位素分析，为揭示狼獾摄食策略的长期变化提供了独特的研究工具。