Quantitative and qualitative traits of arthropod communties in the canopy strata

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Quantitative and qualitative traits of arthropod communties in the canopy strata were examined with the breeding ecology of great tits (Parus major) and varied tits (P.varius) inhabiting plantations of Japanese cedar (Cryptomeria japonica : CJ) and Japanese larch (Larix kaempfer : LK), each containing a small area of deciduous broad-leaved trees, in relation to the resource utilization patterns characterized by both availability of arboreal arthropods as nestling diets and diet selection in foraging microhabitats.1 Potential food availability for both Parus species in CJ and LK, and in a stand of deciduous broad-leaved trees for comparison, was evaluated with the biomass of arboreal arthopods estimated by the frass-trap method at each stand and a branch-clipping from sample trees. The total amount of frass was consistently larger in LK than in CJ. The branch-clipping data showed that the number of individuals and biomass of all arthropods was highest in deciduous broad-leaved trees and … More lowest in CJ.2 The composition of nestling diets differed between Parus species. The single-prey loader P.major preferred large prey, whereas the multiple-prey loader P.varius did small prey. The abundance and size distribution of arthropods greatly differed among foraging microhabitats. Both Parus species selectively used foraging microhabitats according to their prey-size preference.3 Breeding density and performance did not differ between CJ and LK, and were similar to those in otherforests in Japan. Fledgling success was relatively high, being about 90% for both species. The proportions of caterpillars in the diet were 26% in CJ and 47% in LK for P. major, but 73% and 84% for P.varius. The consumption of caterpillars by P.major in both plantations was much less than that in many other habitats. After caterpillars, the nestling diets consisted mainly of Orthoptera, which had almost the same energy content as caterpillars. A shift in diet between caterpillars and orthopterans in response to a change in their relative abundance suggests that even in conifer plantations with a potentially low abundance of insects, Parus species can attain a relatively high breeding success. Less