Niche partitioning is an important mechanism for allowing ecologically similar species to coexist, contributing to biodiversity and the functioning of ecological communities. Species partition niches by taking advantage of environmental heterogeneity. However, niche partitioning and species coexistence investigations often do not include intraspecific variation or individual differences like sex and body size even though these factors can have important ecological consequences. Such intrapopulation factors can reduce the number of individuals among species that overlap in resource use and potentially facilitate coexistence. Using stable isotopes (δ13C and δ15N), we quantified dietary differences among three ecologically similar, sympatric watersnake species: Nerodia erythrogaster, N. rhombifer and N. sipedon. Additionally for each species, we determined intraspecific dietary patterns and determined how those within-species patterns may contribute to dietary niche partitioning among species. Nerodia erythrogaster fed more on terrestrial prey, while N. rhombifer fed at higher trophic levels. Females across species fed at higher trophic levels than did males, and isotopic variance differed between the sexes in N. sipedon. Larger watersnakes foraged at higher trophic levels and fed more on terrestrial prey. Each watersnake species had a distinct diet that overlapped to some degree with the other species’ diets, but these diets varied both between sexes and among size groups within species. This inter- and intraspecific dietary variation can facilitate species coexistence by reducing the number of individuals from all species that use the same resources. Intraspecific variation can add important and nuanced layers to the evolution of species coexistence, and research on interspecific niche relationships needs to increasingly consider the effects of these intraspecific variations.

中文翻译：

---

生态相似蛇群落生态位划分的种内饮食变化

生态位划分是允许生态相似物种共存的重要机制，有助于生物多样性和生态群落的功能。物种通过利用环境异质性来划分生态位。然而，生态位划分和物种共存调查通常不包括种内变异或个体差异，如性别和体型，即使这些因素可能会产生重要的生态后果。这种种群内因素可以减少资源使用重叠的物种之间的个体数量，并可能促进共存。使用稳定同位素（δ13C 和 δ15N），我们量化了三种生态相似的同域水蛇物种之间的饮食差异：Nerodia erythrogaster、N. rhombifer 和 N. sipedon。此外，对于每个物种，我们确定了种内饮食模式，并确定了这些种内模式如何有助于物种之间的饮食生态位划分。Nerodia erythrogaster 以陆地猎物为食，而 N. rhombifer 以更高的营养水平为食。跨物种的雌性以比雄性更高的营养水平喂养，并且 N. sipedon 中的性别差异在性别之间存在差异。较大的水蛇在较高的营养水平上觅食，更多地以陆地猎物为食。每个水蛇物种都有独特的饮食，在某种程度上与其他物种的饮食重叠，但这些饮食在性别之间和物种内的大小组之间有所不同。这种种间和种内饮食变化可以通过减少使用相同资源的所有物种的个体数量来促进物种共存。