Spatial processes and diversity in host-parasite systems

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M.Shimada studied dynamical properties of 1 host-2parasitoid experimental systems, using a bruchid host, a pteromalid wasp (A.c.) and a braconid one (H.p.). Though the populations first oscillated mildly in the host-A.c.system, after adding H.p., the host and A.c.increased gradually the amplitude of population fluctuations and, finally, the two populations fluctuated quite large and emergence of chaos was detected by LENNS and RSM in the 3 species system. The two wasps parasitize from the fourth instar larva to the pupa, though H.p.prefers a slightly younger host stages than A.c.. The attacking rate of A.c.depends strongly on host density per bean but not for H.p.. In larval competition between the two parasitoids, the first attacker is likely to be more advantageous irrespective of the species. Shimada, M.Tuda, and H.C.J.Godfray constructed models by two approaches : a top-down time-series model and a bottom-up stage-structured model with niche separation. We examined which factor (s) … More and process (es) change the host and A.c.populations from stable to chaotic dynamics in the 3 species system with H.p..In addition, Shimada studied community structure of legume-bruchid systems in the New World ; Hawaii, Arizona and Mexico. Collecting drying matured legume seed pods, he investigated emergent bruchid species and the relative abundances. Based on the data, he constructed trees of niche similarities among bruchids in three districts. They showed more complicated branching in Arizona and Mexico because of one-to-multiple correspondence between legumes and bruchids. The results suggest host-shift through adaptation may be comparable enough to, or much stronger than, phylogenetic constraint.Y.Iwasa studied evolutionary gemes in host plant-herbivore interactions and, with Tuda, evolutionary changes in local population capacity and population dynamics, based on ESS.Godfray and M.P.Hassell further studied host-parasite dynamics and coevolution with metapopulation structures.All the studies concerning the international joint project are discovering important effects of spatial processes on ecological and genetic diversities in host-parasite systems. Less