Estación Biológica de Doñana, CSIC, Avda. Americo Vespucio s/n, Sevilla, Spain.
Oecologia. 2013 Sep;173(1):95-105. doi: 10.1007/s00442-012-2428-3. Epub 2012 Aug 23.
Amphibian larvae constitute a large fraction of the biomass of wetlands and play important roles in their energy flux and nutrient cycling. Interactions with predators and competitors affect their abundance but also their foraging behaviour, potentially leading to non-consumptive cascading effects on the whole trophic web. We experimentally tested for plastic changes in larval trophic ecology of two anuran species in response to competitors and the non-lethal presence of native and non-native predators, using stable isotope analysis. We hypothesized that tadpoles would alter their diet in the presence of competitors and native predators, and to a lesser extent or not at all in the presence of non-native predators. First, we conducted a controlled diet experiment to estimate tadpole turnover rates and discrimination factors using Pelobates cultripes and Bufo calamita. Turnover rates yielded a half-life of 15-20 days (attaining a quasi-isotopic equilibrium after 2 months), whereas discrimination factors for natural controlled diets resulted in different isotopic values essential for calibration. Second, we did an experiment with P. cultripes and Rana perezi (=Pelophylax perezi) where we manipulated the presence/absence of predators and heterospecific tadpoles using microcosms in the laboratory. We detected a significant shift in trophic status of both amphibian species in the presence of non-native crayfish: the δ(15)N values and macrophyte consumption of tadpoles increased, whereas their detritus consumption decreased. This suggests that tadpoles could have perceived crayfish as a predatory risk or that crayfish acted as competitors for algae and zooplankton. No dietary changes were observed in the presence of native dragonflies or when both tadpole species co-occurred. Stable isotopic analysis is an efficient way to assess variation in tadpoles' tropic status and hence understand their role in freshwater ecosystems. Here we provide baseline isotopic information for future trophic studies and show evidence for plastic changes in tadpoles' use of food resources under different ecological scenarios.
两栖动物幼虫构成湿地生物量的很大一部分，并在湿地能量流动和养分循环中发挥重要作用。与捕食者和竞争者的相互作用不仅会影响它们的丰度，还会影响它们的觅食行为，从而对整个营养级联产生非消耗性的级联效应。我们使用稳定同位素分析方法，实验测试了两种蛙类幼虫在面对竞争者和本地及非本地捕食者的非致命存在时，其营养生态的可塑性变化。我们假设，在存在竞争者和本地捕食者的情况下，蝌蚪会改变其饮食，而在存在非本地捕食者的情况下，改变程度较小或根本不会改变。首先，我们进行了受控饮食实验，使用 Pelobates cultripes 和 Bufo calamita 估计蝌蚪的周转率和辨别因子。周转率得出的半衰期为 15-20 天（在 2 个月后达到准同位素平衡），而天然对照饮食的辨别因子得出了不同的同位素值，这些值对于校准至关重要。其次，我们在实验室的微生境中，通过操纵捕食者和异源蝌蚪的存在/不存在，对 P. cultripes 和 Rana perezi（=Pelophylax perezi）进行了实验。我们发现，非本地小龙虾的存在会导致两种两栖动物的营养状况发生显著变化：蝌蚪的δ(15)N 值和大型植物的消耗量增加，而其碎屑的消耗量减少。这表明，蝌蚪可能将小龙虾视为捕食风险，或者小龙虾可能将藻类和浮游动物视为竞争对象。当存在本地蜻蜓或两种蝌蚪共存时，未观察到饮食变化。稳定同位素分析是评估蝌蚪营养状况变化的有效方法，从而可以了解它们在淡水生态系统中的作用。在这里，我们为未来的营养研究提供了基线同位素信息，并为在不同生态情景下，蝌蚪对食物资源的利用发生可塑性变化提供了证据。
