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

这项研究的目的是阐明碎屑注入放牧食物网的重要性，这一点到目前为止还没有得到很好的研究。我们估计了两个不同系统--森林和农场池塘--中从碎屑到放牧链的有机体或能量的输入。森林：我们估计了网络蜘蛛--主要的陆地多面手捕食者--对碎屑食物链有机体的依赖程度。在草原生境中，夏季对放牧链的依赖程度较高，而在森林中，对碎屑链的依赖程度一直较高，且随季节变化不大。然而，即使在相同的生境中，这种依赖也会随着网状结构和网状位置的不同而不同。我们还通过野外实验检验了蜘蛛的种群密度和物种丰富度是否依赖地下猎物的输入来维持。我们建立了蜘蛛围栏，在地上有床单和没有床单，以观察拦截从地面出现的昆虫的效果。因此，在没有地面覆盖的围栏中，个体数量和物种数量都更加丰富。由于地面上没有床单的围栏中飞行昆虫的数量更多，因此碎屑输液似乎对地上多面手捕食者的维持有重大影响。农场池塘我们利用稳定同位素分析估算了农场池塘的食物网络结构。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、浮游生物和垃圾。在主要被森林包围的池塘里，小龙虾严重依赖垃圾和DOM，但在附近没有森林的池塘里，初级生产者对小龙虾很重要。此外，具有低同位素比率的枯枝落叶的池塘显示出食物网水平的整体同位素比率较低。这些结果表明，凋落物似乎是能量和营养循环的基础。

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.