| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
This study aimed at clarifying the effect of trophic cascade on the process chain in detrital food webs by using the system consisting spider-colembola-microorganism-litter-soil animals. I investigated direct and indirect effects of the predator Neriene brongersmai, a web spider abundant in the forest-floor of the Japanese cedar, on soil ecosystems by establishing field enclosures with and without this spider. Four a priori hypotheses that I had made are as follows,
1)Do spiders control the abundance of Colembola?
2)Do spiders indirectly increase the biomass of soil microorganisms?
3)Do spiders indirectly increase the rate of decomposition of litter?
4)Do spiders indirectly increase soil animals that are not directly eaten by spiders?
A land 1/2 year long experiment showed that the hypothesis 1 was supported, i.e., spiders suppressed collembolan abundance. Contrary to my expectation, the hypotheses 2 to 4 were not verified. I proposed several reasons for these negative effects, including 1)top-down effect by the spiders was not strong enough to cause trophic cascade, 2)biomass of micoorganisms had decreased in a short term by spider predation, but the rapid turnover rate made the long term biomass invariable. This study failed to demonstrate the linkage between trophic cascade and process chain, but the approaches used in this study appeared to be useful. In the future, it is necessary to conduct manipulation experiments to examine how functional group level effect is operating, and how diversity of species or guilds within a functional group influences processes linking food web and process chain.
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