Effects of resource competition and apparent competition on community structure and distributions of drosophilids

研究了果蝇物种之间的竞争相互作用，以了解果蝇群落是如何构成的，以及它们的分布边界是如何确定的，特别是在低纬度地区。有两种类型的竞争相互作用，资源竞争和由较高营养水平的生物(如捕食者)介导的表观竞争。通过室内资源竞争实验表明，果蝇种内竞争较强，种间竞争较弱。实地研究的结果与这一结果并不矛盾。因此，资源竞争对群落结构或分布的影响似乎很弱。另一方面，耐寒物种可能容易受到捕食者或寄生蜂的攻击，因为它们的活动减少，发育周期延长，因此它们可能由于与寒冷敏感物种的明显竞争而被排除在温暖地区之外。然而，关于果蝇之间的明显竞争的信息很少。在此基础上，对可能参与表观竞争的寄生蜂的种类组成、分布和寄主关联性进行了研究。因此，所有的寄生蜂都能够寄生在一些寄主物种上。因此，它们可以调节寄主果蝇物种之间的相互作用。然而，在温带地区，寄生率并不高，有一段时间没有寄生，这表明明显的竞争很弱。然而，在亚热带和热带地区，存在明显的竞争相当激烈的可能性。在这个问题上还需要进一步研究。

Competitive interactions between drosophilid species are investigated to understand how drosophilid communities are structured and how the boundary of their distributions, especially at lower latitudes are determined. There are two types of competitive interactions, resource competition and apparent competition mediated by organisms of higher trophic level, such as predators. By laboratory experiments on resource competition, it was suggested that intraspecific competition was rather strong in drosophilid species, but interspecific competition was not so strong. The results of field studies did not contradict with this result. Thus, the effects of resource competition on community structure or distribution seem to be weak. On the other hand, cold-tolerant species are expected to be vulnerable to predators or parasitoids, since their locomotor activity is reduced and their developmental period was prolonged, and therefore they may be excluded from warmer regions due to apparent competition with cold-susceptible species. However, little information is available for apparent competition of drosophilids. Then, the species composition, distribution and host association was studied for parasitoids that are assumed to mediate apparent competition. As a result, all parasitoids were able to parasitize a number of host species. Thus, they could mediate interactions between host drosophilid species. In temperate areas, however, the rate of parasitism was not high and there were a period free from parasitism, suggesting that apparent competition was weak. However, there is a possibility that apparent competition is rather severe in subtropical and tropical areas. Further study is needed on this topic.