Zandonà Eugenia, Sullam Karen E, Dalton Christopher M, El-Sabaawi Rana W, Kilham Susan S, Flecker Alexander S
Departamento de Ecologia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
Department of Biology, Drexel University, Philadelphia, PA, USA.
Sci Rep. 2024 Dec 30;14(1):31923. doi: 10.1038/s41598-024-83420-5.
Consumers vary in their excretion of nitrogen and phosphorus, altering nutrient cycles and ecosystem function. Traditional mass balance models that focus on dietary and tissue nutrients have poorly explained such variation in excretion. Here, we contrast diet and tissue nutrient models for nutrient excretion with predation risk, an often overlooked factor, using the Trinidadian guppy (Poecilia reticulata) as our model system. We surveyed guppies at 12 sites spread across two streams with parallel gradients in food quality and predation risk. At each site, we assessed guppy diet, tissue nitrogen (N), and phosphorus (P) content, and N and P excretion. Predation risk best explained guppy excretion, especially P: guppies excreted less in sites with a dominant predator, while traditional models for excretion rate based on diet quality and tissue nutrients failed to explain it. Guppy tissue N (but not P) most closely correlated with guppy diet quality, showing evidence for flexible homeostasis. Our work extends previous laboratory studies' results to natural streams and shows that predation risk alters feeding behavior and physiology, driving substantial variation in guppy nutrient, particularly P, excretion rates. We suggest that predation risk is an important factor determining nutrient excretion variation, warranting further attention. Our results also show that tissue nutrients and excretion nutrients are decoupled.
消费者在氮和磷的排泄方面存在差异，这改变了营养循环和生态系统功能。传统的质量平衡模型侧重于饮食和组织中的营养物质，对排泄方面的这种差异解释得很差。在这里，我们以特立尼达孔雀鱼（Poecilia reticulata）作为我们的模型系统，将用于营养排泄的饮食和组织营养模型与捕食风险（一个经常被忽视的因素）进行对比。我们在两条溪流中的12个地点对孔雀鱼进行了调查，这些地点在食物质量和捕食风险方面具有平行梯度。在每个地点，我们评估了孔雀鱼的饮食、组织氮（N）和磷（P）含量以及氮和磷的排泄情况。捕食风险最能解释孔雀鱼的排泄情况，尤其是磷：在有优势捕食者的地点，孔雀鱼排泄较少，而基于饮食质量和组织营养的传统排泄率模型无法解释这一点。孔雀鱼组织中的氮（而非磷）与孔雀鱼的饮食质量最密切相关，显示出灵活的内稳态证据。我们的工作将先前的实验室研究结果扩展到了自然溪流，并表明捕食风险会改变摄食行为和生理状态，导致孔雀鱼营养物质，特别是磷的排泄率出现显著差异。我们认为捕食风险是决定营养排泄差异的一个重要因素，值得进一步关注。我们的结果还表明组织营养和排泄营养是脱钩的。
