昆虫均为完全或不完全变态发育, 其幼虫和成虫阶段往往有着不同的资源需求。研究昆虫在幼虫和成虫阶段的生态位和适合度, 有助于提升我们对昆虫物种共存和群落构建的认识。黑腹果蝇(Drosophila melanogaster)和伊米果蝇(D. immigrans)是全球广布的两种果蝇, 它们常常发生在相同的季节, 且均在腐烂的水果上产卵, 幼虫寄生在其中完成生长发育。本研究通过转瓶实验评估了这两种果蝇在连续竞争过程中的内禀增长率和种内与种间竞争系数, 并进一步检验了它们的成虫对产卵场所, 以及幼虫对食物的竞争强度, 据此计算了两个物种在成虫和幼虫阶段的生态位分化与适合度差异, 在当代物种共存理论的框架下分析了影响两种果蝇共存的关键因素。结果表明, 连续饲养过程中, 黑腹果蝇表现出更高的适合度, 大概率会竞争排斥掉伊米果蝇。具体而言, 两种果蝇在幼虫和成虫期均有极大的生态位重叠, 虽然伊米果蝇成虫对产卵场所有着更高的利用率, 黑腹果蝇的幼虫在生长发育阶段对饲料有着更高的利用率, 但两种果蝇在成虫、幼虫阶段竞争的结果更多地取决于谁先占据资源。本研究表明昆虫在不同发育阶段对资源利用率的变化会在一定程度上影响它们共存的可能性。

Aims: Metamorphosis is a common character of insect development, wherein larval and adult insects exhibit significant differences in their resource requirement and utilization efficiency. Exploring the variations in niche and fitness difference in different development stages among competing insects can enhance our comprehension of insect species coexistence and community formation. Drosophila melanogaster and D. immigrans, two widely distributed Drosophila species, cohabit during the same season and both feed on decaying fruit. This study aims to explore the shift in ontogenetic niche and fitness difference between these two Drosophila flies, thereby undercovering the underlying mechanisms that facilitate their coexistence.
Methods: We set up microcosm experiments to estimate the inter- and intra-species competition coefficients, and the niche overlap and fitness difference of two Drosophila species. We then investigated the resource competition between adult flies for oviposition sites and between larval flies for food resources. Ultimately, we analyzed the probability of coexistence between the flies in their larval and adult stages using modern coexistence theory.
Results: The results showed that D. melanogaster exhibited greater fitness than D. immigrans and possessed a higher probability of winning in competition. Furthermore, adult D. immigrans demonstrated superiority in competing for oviposition sites compared to D. melanogaster, while larval D. melanogaster displayed higher nutrient efficiency than D. immigrans. However, there is significant overlap in the resources required by both species during their adult and larval stages. The competition outcomes in both larval and adult stages were predominantly determined by the sequence of resource access.
Conclusions: According to our competition experiments involving two Drosophila species, we have made an intriguing observation: two species can exhibit excellent competitive abilities during different developmental stages, seemingly enhancing the coexistence of these species. However, the presence of substantial niche overlap, leading to priority effects among the competing pairs, ultimately prevents their coexistence. Furthermore, the diverse competition strategies employed by the two Drosophila species offer an explanation for the victor in cases involving priority effects. Consequently, our findings provide valuable insights into the significance of developmental stages and phenotypic plasticity in species coexistence.