Food web structure including grazing and detritus food chains: case studies in forests and farm ponds.

本研究的目的是阐明碎屑注入放牧食物网的重要性，这是迄今为止没有得到很好的研究。我们估计输入的生物体或能量从碎石放牧链在两个不同的系统，森林和农场池塘。森林：我们估计在何种程度上，蜘蛛网，主要的陆地通才捕食者，依赖于生物碎屑食物链。在草原生境中，夏季对放牧链的依赖性变高，而在森林生境中，对碎屑链的依赖性一直很高，且随季节变化不大。然而，即使在同一生境中，这种依赖性也会因网的结构和网的位置而异。我们还通过野外实验研究了网蜘蛛的种群密度和物种丰富度是否通过从地下输入猎物来维持。我们在地面上建立了有和没有床单的蜘蛛围栏，以观察从地面出现的昆虫的拦截效果。因此，无论是数量的个人和数量的物种更丰富的围隔没有一个表在地面上。由于大量的飞行昆虫是较高的外壳没有一个表在地面上，看来，碎屑注入有显着影响的维持通才捕食者在地面上。通过稳定同位素分析，我们估计了农场池塘的食物网结构。我们从农场池塘中收集了各种生物和碎屑，包括小龙虾、昆虫、鱼类、浮游生物和垃圾。在大部分被森林包围的池塘中，小龙虾在很大程度上依赖于凋落物和DOM，但在附近没有森林的池塘中，初级生产者对小龙虾很重要。此外，池塘具有低同位素比的凋落物显示出较低的整体同位素比的食物网水平。这些结果表明，凋落物似乎是能量和养分循环的基础。

The aim of this study is to clarify the importance of detrital infusion into grazing food webs, which was not well studied so far. We estimated input of organisms or energy from detritus to grazing chains in two different systems, forests and farm ponds.1. Forests:We estimated the extent to which web spiders, major terrestrial generalist predators, depend on organisms from detritus food chain. In a grassland habitat, dependency on grazing chain became higher in summer, but in a forest, the dependency on detritus chain was consistently high and did not change greatly with seasons. However, the dependency varied with web structure and web placement even in the same habitat. We also examined whether population density and species richness of web spiders are sustained by input of prey from underground by field experiments. We established spider enclosures with and without a sheet on the ground to see the effects of interception of insects emerging from the ground. As a result, both number of individuals and number of species were more abundant in enclosures without a sheet on the ground. Because abundance of flying insects was higher in enclosures without a sheet on the ground, it appears that detrital infusion has a significant impact on the maintenance of generalist predators aboveground.2. Farm pondsWe estimated food web structure in farm ponds by using stable isotope analysis. We collected various organisms and detritus from farm ponds, including crayfish, insects, fish, plankton, and litter. In ponds surrounded mostly by forests, crayfish depended heavily on litter and DOM, but in ponds with no forests nearby, primary producers were important for crayfish. Moreover, ponds having litter with a low isotope ratio showed a low overall isotope ratio for the food web level. These results suggest that litter seems to be the basis for energy and nutrient cycling.