Bottom-up meets top-down: Leaf litter inputs influence predator-prey interactions in wetlands, 2011.

While the common conceptual role of resource subsidies is one of bottom-up nutrient and energy supply, inputs can also alter the structural complexity of environments. This can further impact resource flow by providing refuge for prey and decreasing predation rates. However, the direct influence of different organic subsidies on predator–prey dynamics is rarely examined. In forested wetlands, leaf litter inputs are a dominant energy and nutrient resource and they can also increase benthic surface cover and decrease water clarity, which may provide refugia for prey and subsequently reduce predation rates. In outdoor mesocosms, we investigated how inputs of leaf litter that alter benthic surface cover and water clarity influence the mortality and growth of gray treefrog tadpoles (Hyla versicolor) in the presence of free-swimming adult newts (Notophthalmus viridiscens), which are visual predators. To manipulate surface cover, we added either oak (Quercus spp.) or red pine (Pinus resinosa) litter and crossed these treatments with three levels of red maple (Acer rubrum) litter leachate to manipulate water clarity. In contrast to our predictions, benthic surface cover had no effect on tadpole survival while darkening the water caused lower survival. In addition, individual tadpole mass was lowest in the high maple leachate treatments, suggesting an interaction between bottom-up effects of leaf litter and topdown effects of predation risk that altered mortality and growth of tadpoles. Our results indicate that realistic changes in forest tree composition, which cause concomitant changes in litter inputs to wetlands, can substantially alter community interactions.

尽管资源补贴的常见概念性作用为自下而上的营养与能量供给，但其输入亦可改变环境的结构复杂性。该效应可通过为猎物提供庇护、降低捕食率，进一步影响资源流动。然而，不同有机补贴对捕食者-猎物动态的直接影响却鲜有研究。
在森林湿地中，落叶凋落物输入是主要的能量与营养资源，同时还可增加底栖表面覆盖度、降低水体透明度，这或可为猎物提供庇护，进而降低捕食率。
本研究在室外中型实验生态系统（mesocosms）中，探究了可改变底栖表面覆盖度与水体透明度的落叶凋落物输入，对自由活动的视觉捕食者——成年蝾螈（Notophthalmus viridiscens）存在时，灰树蛙蝌蚪（Hyla versicolor）的死亡率与生长的影响。
为调控底栖表面覆盖度，我们添加了栎属（Quercus spp.）枯落物或红松（Pinus resinosa）枯落物，并将这些处理与三个浓度梯度的红枫（Acer rubrum）枯落物沥出液处理交叉组合，以调控水体透明度。
与实验预期相反，底栖表面覆盖度对蝌蚪存活率无显著影响，而水体变暗则导致存活率降低。此外，在高浓度红枫沥出液处理组中，蝌蚪个体体重最低，这表明凋落物的自下而上效应与捕食风险的自上而下效应之间存在交互作用，进而改变了蝌蚪的死亡率与生长情况。
本研究结果表明，林木组成的现实性变化（其会伴随湿地凋落物输入的改变）可显著改变群落相互作用。