2種のタマゴヤドリコバチにみられる種間競争について(第2報) : 寄主の分布様式のちがいは競争結果にどのような影響を与えるか

抄録

SASABA, Takafumi (Kyoto Univ., Kyoto) Interspecific competition between two species of Trichogrammatidae. 2nd report. How are the competition outcomes influenced by the difference of host's distribution. Jap. J. Ecol. 15,189-193 (1965). There are two different views in the study on the interspecific competition between the species which have similar ecological needs. One of these is the analysis of the mechanism involved in the many different processes of competition during the whole life (BAKKER 1961,etc.), while another is emphasizing the final result of competition mainly from the mathematical treatment (NEYMAN et al. 1955,etc.) In the previous report the author stated the importance of the analysing research for progressing the study on the interspecific competition using two species of parasites (Trichogramma japonicum ASHMEAD and T. minutum RILEY)(SASABA 1964). In this paper an attempt is made to discuss on the same problem based upon another experimental result, comparing with those of the previous report. Although, in the previous report the host (eggs of Cadra cautella WALKER) was distributed in the containers (container A : 8cm in diameter, 3.5cm in height, and 126cm^3 in volume ; container B : 19cm in diameter, 5cm in height, and 2550 cm^3 in volume). In this experiment the host is distributed in a mass within an area of 3cm in diameter at the center of the container B. The ratio of number of wasps to the number of hosts at the start of the experiment varied with changing of the number of wasps (Experiment I) and the number of hosts (Experiment II). Though the outcome of competition is not simple, a clear tendency in the result is observed as had been observed in the previous report. T. minutum in this experiment had more opportunities to remain as a population than in the experiment of the previous report. Considering with the previous report in the present study, the low density of wasps, the wide area of rearing space, large number of hosts, and clumped distribution of the host take advantage of the outcome of T. minutum. While the result is vice versa under the reverse conditions. It can be said that the competition for the host finding in the adult wasp is the main factor under the former condition, and on the other hand the competition for food in the larval stage of the wasp is main one under the latter condition. The difference of ecological characters between the two species of parasitic wasps plays an important role on the competition processes and outcome, but the competition processes are varied with the different enviromental conditions. Thus, for clarifying the complex mechanism or competition, it is important to find the difference in the ecological characters between the two species. It is necessary to discuss the problem from the analytical standpoint of the process of competition rather than from the mathematical treatment of outcome in competition.