Responses to nitrate pollution, warming and density in common frog tadpoles (Rana temporaria)

Amphibians face a variety of anthropogenic environmental perturbations that could act alone or in combination to influence population size. We investigated interactive effects of warming conditions, a moderate pulse of nitrogen pollution, and conspecific density on larvae of the common frog, Rana temporaria. The 16-day experiment had a 2 × 2 × 2 factorial design implemented in 80-l outdoor mesocosms. High density and warm temperature both resulted in reduced activity and visibility; tadpoles grew and developed more quickly at low density and high temperature. The high-nitrogen treatment did not influence behavior, growth, or development rate. We attribute this to several realistic features of our study, including a pulsed treatment application and natural denitrification within the mesocosms. There was only a single interaction among the three factors: higher temperature exacerbated density-dependence in growth rate. These results illustrate that climate warming may benefit temperate amphibians, although the benefits may be counteracted by enhanced larval crowding.两栖动物面临多种人为环境扰动，这些扰动可单独或联合作用，对其种群规模产生影响。本研究以普通蛙（Rana temporaria）的幼体为研究对象，探究了增温环境、中等强度氮污染脉冲以及同种个体密度三者的交互效应。实验为期16天，采用2×2×2析因设计，在80升的室外中型实验生态系统（mesocosms）中开展。研究结果显示，高密度与高温均会降低蝌蚪的活动能力与可见性；在低密度且高温条件下，蝌蚪的生长与发育速度更快。高氮处理未对蝌蚪的行为、生长及发育速率产生影响。我们将这一结果归因于本实验的几项现实设置特征，包括脉冲式施氮处理以及中型实验生态系统内的自然反硝化作用。三个实验因素间仅存在一种交互作用：高温会加剧生长速率的密度制约效应。本研究结果表明，气候变暖可能对温带两栖动物带来益处，但该益处可能会因幼体拥挤程度加剧而被抵消。