Snakes are a useful model for ecological studies because they are gape-limited predators that may undergo ontogenetic changes in diet. We analyzed carbon and nitrogen stable isotope ratios to estimate percent contributions of different prey to snake biomass, trophic positions and isotopic niche width of juveniles and adults of the snake Thamnodynastes hypoconia. We also estimated the isotopic niche overlap between the two age categories. During eight intervals over a two-year period, we collected samples of whole blood and scales at a site in southern Brazil. Isotopic ratios of carbon and nitrogen did not differ between juveniles and adults for either tissue type, nor did mean trophic positions of juveniles and adults differ. The percent contribution of prey categories to snake biomass differed to a limited extent between the two years, with Hylidae being the most important anuran group assimilated during the first year and Leptodactylidae during the second year, for both ages. The isotopic niche occupied by adult snakes was slightly larger than that of juveniles when the analysis was based on data from whole blood samples, as expected because snakes are gape-limited. We found a reverse pattern when the analysis was based on scales, which may indicate that adult snakes have a smaller niche over the long term as they become selective foragers in certain prey. Isotopic overlap between juveniles and adults occurred during the two years, but it was bigger during the second year. We infer that, despite differences in gape size, juvenile and adult snakes in the study area exploit similar prey, with the degree of trophic similarity varying interannually.

中文翻译：

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稳定同位素告诉我们关于巴西南部 Thamnodynastes hypoconia (Serpentes: Dipsadidae) 的营养生态学什么？

蛇是生态研究的有用模型，因为它们是张口受限的捕食者，可能会在饮食中发生个体遗传变化。我们分析了碳和氮稳定同位素比率，以估计不同猎物对蛇类生物量、营养位置和同位素生态位宽度的贡献百分比。我们还估计了两个年龄类别之间的同位素生态位重叠。在两年期间的八次间隔中，我们在巴西南部的一个地点收集了全血和鳞片样本。对于两种组织类型，碳和氮的同位素比率在幼鱼和成鱼之间没有差异，幼鱼和成鱼的平均营养位置也没有差异。猎物类别对蛇生物量的百分比贡献在两年之间有所不同，对于这两个年龄段，Hylidae 是第一年同化的最重要的无尾类群，第二年是 Leptodactylidae。当分析基于全血样本的数据时，成年蛇占据的同位素生态位略大于幼蛇，正如预期的那样，因为蛇是张口受限的。当基于尺度进行分析时，我们发现了一种相反的模式，这可能表明成年蛇在长期内具有较小的生态位，因为它们成为某些猎物的选择性觅食者。幼鱼和成鱼之间的同位素重叠发生在两年内，但在第二年更大。我们推断，尽管研究区域的幼蛇和成年蛇的张口大小存在差异，但它们利用相似的猎物，营养相似程度每年都会有所不同。