| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 1993: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1992: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Research Abstract |
1. Three sets of differential equation models were constructed to describe the plant-herbivore interactions without or with the latter's natural enemy that are in turn free or not free from the secondary enemy. The modes of effects upon the average level of plant biomass and the overall system stability were then elucidated as for various basic parameters concerning the efficiency of herbivores, primary enemies, or secondary ones for finding or consuming the respective food organisms.
2. Community structures of insect herbivores were studied by regular field surveys on natural stands of a thistle, Cyrcium kagamontanum, in a forest and of several wilow species, Salix spp., on a riverside. In either case more than several tens of herbivore species were found stably coexisting in the stand. While generalist herbivores were far superior to specialists in the number of species, the reverse was true in their population density. The densities of individual herbivore populations were generally so low that there was no indication of the occurence of interspecific cometition. Meanwhile, analysis of food habits of Japanese 226 butterflies showed that their host plants are diversified to as many as 67 plant families. While 94 % of the individual species proved to be oligophagous confining the respective hosts within less than two plant families, a definite tendency to show habitat/host plant partitioning was commonly forund among closely related sympatric species.
3. To account for such a type of habitat segregation which the usual competition theory can not explain, two different factors, reproductive interference and anti-enemy escape strategy, were suggested to be working and their importance stressed.
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