| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2001: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2000: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
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 ponds
We 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.
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