2種のタマゴヤドリコパチにみられる種間競争について

抄録

Until recently, the interspecific competition between the species occupying the similar ecological niche has been fully studied in an experimental way, based upon the theoretical postulate of LOTKA or VOLTERRA. Among these, such works as CROMBIE's (1947) or PARK's (1954) seem to be most extensive and classical. In this paper, the interspecific competition was studied experimentally using two species of parasitic wasp Trichogrammatidae with 170 replications under the constant condition of temperature and relative humidity. Two species of parasitic wasps, Trichogramma japonicum ASHMEAD and T. minutum RILEY, were reared on the eggs of the almond moth, Cadra cautella WALKER, propagated on rice bran. And they competed changing the initial number of wasps, the ratio of the initial number of wasps, the area of rearing space and the number of hosts. Counts of wasps were made in every generation at regular intervals(10 days). The population of each single species grew and attained a steady state under the given experimental condition where 100 eggs of the host species were supplied in each parasite generation (Fig.1). The amplitude of population fluctuation of T. minutum was greater than T. japonicum. It may be caused by the difference of the ecological charactors between the two species. When each species competed with one another, one species was depressed and became completely extinct or both became extinct after several generations. As GAUSE's principle, the coexistence of these two competing species should not occur. However, the results were not always uni-directional and adverse results were obtained, even under the same environmental conditions. These results are nearly the same as that of PARK et al.(1955) in Tribolium. Thus the treatment from the probability theory seems to be adequate to analyze these results. But, generally speaking, the following definite tendency was found. T. japonicum had much opportunities to become the victor, when the two species competed with each other under the condition of narrow area of rearing space and high density of initialy introduced wasps. While the results were vice versa under the condition of wide area and low density of wasps. So, it is possible to consider that the competition process became different by varying the density of parasitic wasp. And these suggest that the difference of ecological characters between two species affected the competition processes and outcomes. Therefore, it is important to clarify the difference of ecological characters between the two species in order to analyze the mechanism of competition.