Species richness and abundance, as well as trophic relationships, are affected by habitat configuration. Smaller habitat patches suffer greater external interference, being more susceptible to diversity loss and could also receive more trophic subsidies from outside or matrix, which can favour the maintenance of populations even in small patches. Natural mosaics of forest patches in a grassland matrix in southern Brazil are good places to analyse such a process. Our objective was to analyse the effect of habitat patching on trophic relationships based on the evaluation of two forest amphibian species (Physalaemus lisei and P. carrizorum) and compare those from habitat patches versus core/contiguous habitat. We compared isotopic carbon (δ¹³C) and nitrogen ratios (δ¹⁵N) in two anuran species as well the variation in their diet at different forest patch sizes. We chose carbon isotopes since they act as a proxy for inferences on the original habitat from which the matter flows towards the anurans, while nitrogen reveals their tropic level. Our results revealed that trophic sources for these amphibians derives predominantly from primary forest productivity. However, Physalaemus lisei δ¹³C values indicated that the contribution of grassland trophic sources in the diet was higher in frogs from forests patches (<100 ha) than in those from core forest habitat. In smaller patches, P. lisei consumed predominantly ants, which was the most abundant prey on habitat. On the other hand, in the core forest, where isopods were the most abundant prey, most of its consumption was beetles, spiders and ants. In contrast, P. carrizorum showed no significant changes in isotopic ratios or diet across habitats. Isotopic data suggested that both species occupied lower trophic levels in smaller forests than in core forests. Our data showed a tendency towards the increase of grassland contribution and decrease of amphibian trophic position in patched habitats in comparison to continuous habitat.

中文翻译：

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大西洋森林斑块和核心森林中两种两栖动物的营养生态学：饮食和同位素方法

物种丰富度和丰度以及营养关系受到栖息地配置的影响。较小的栖息地斑块受到更大的外部干扰，更容易受到多样性丧失的影响，并且还可以从外部或基质中获得更多的营养补贴，即使在小斑块中也有利于维持种群。巴西南部草原基质中森林斑块的天然马赛克是分析这一过程的好地方。我们的目标是基于对两种森林两栖动物物种（ Physalaemus lisei和P. carrizorum ）的评估，分析栖息地修补对营养关系的影响，并将栖息地斑块与核心/连续栖息地进行比较。我们比较了同位素碳 ( δ¹³ C）和氮比（δ ¹⁵ N）在两种无尾蜥物种中，以及它们在不同森林斑块大小下的饮食变化。我们选择碳同位素是因为它们可以作为推断物质流向无尾目动物的原始栖息地的代理，而氮则揭示了它们的热带水平。我们的研究结果表明，这些两栖动物的营养来源主要来自原始森林生产力。然而，Physalaemus lisei δ ¹³ C 值表明，来自森林斑块（<100 公顷）的青蛙中草原营养源在饮食中的贡献高于来自核心森林栖息地的青蛙。在较小的斑块中，P. lisei主要以蚂蚁为食，蚂蚁是栖息地中最丰富的猎物。另一方面，在等足类动物是最丰富的猎物的核心森林中，它的大部分消耗是甲虫、蜘蛛和蚂蚁。相比之下，P。 carrizorum显示不同栖息地的同位素比率或饮食没有显着变化。同位素数据表明，这两个物种在较小的森林中的营养水平低于核心森林。我们的数据显示，与连续栖息地相比，补丁栖息地的草地贡献增加和两栖动物营养位置减少的趋势。