Individual diet specialization (IS) has important community- and population-level implications and its ecological drivers are actively investigated. Here, to test the hypothesis that local environmental conditions may influence IS in wild populations, we analyzed the stomach contents of 395 individuals from eight populations of five allopatric species of European cave salamanders (genus Hydromantes). We assessed whether their degree of individual diet specialization i) scaled positively with the respective niche widths, in agreement with Van Valen's niche variation hypothesis (NVH), and ii) could be predicted by satellite-derived climatic and vegetation characteristics of the sites where the populations live. Consistent with the NVH, the degree of individual diet specialization increased with the populations' total niche width. Furthermore, two variables describing local non-arboreal vegetation cover and habitat heterogeneity successfully predicted the variation in individual specialization across the eight populations. Climatic factors had a generally low predictive power, with individual specialization in low- and high-elevation populations showing contrasting patterns of co-variation with air temperature in the warmest quarter of the year. However, independently from elevation, specialization peaked under conditions of high non-arboreal vegetation cover and high precipitation regimes. We discussed the results against two mutually non-exclusive scenarios hypothesizing different mechanisms linking environmental factors to salamanders' trophic strategy at an individual and population level. We concluded that satellite-derived climatic and vegetation variables, to date generally adopted to model Grinnellian niches, might also be useful in predicting spatial variations in dietary habits of populations, i.e. their Eltonian niches.

中文翻译：

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个体饮食专业化的种间和种群间变异：环境因素是否起作用？

个人饮食专业化 (IS) 具有重要的社区和人口水平影响，并且正在积极研究其生态驱动因素。在这里，为了检验当地环境条件可能影响野生种群中 IS 的假设，我们分析了来自欧洲洞穴蝾螈（Hydromantes 属）的 5 个异域物种的 8 个种群的 395 只个体的胃内容物。我们评估了他们的个体饮食专业化程度 i) 是否与各自的生态位宽度成正比，与 Van Valen 的生态位变异假设 (NVH) 一致，并且 ii) 可以通过卫星衍生的气候和植被特征预测人口居住。与 NVH 一致，个体饮食专业化程度随着种群的总生态位宽度而增加。此外，描述当地非树栖植被覆盖和栖息地异质性的两个变量成功地预测了八个种群的个体专业化的变化。气候因素的预测能力普遍较低，低海拔和高海拔人群的个体专业化在一年中最温暖的季度表现出与气温的对比模式。然而，独立于海拔，专业化在高非树栖植被覆盖和高降水状况的条件下达到顶峰。我们针对两种互不排斥的情景讨论了结果，假设不同的机制将环境因素与个体和种群水平的蝾螈的营养策略联系起来。我们得出结论，卫星衍生的气候和植被变量，