2012年后新成立研究组知识库

Changes in the strength of trophic cascades over time have been associated with dramatic shifts in community structure and function. However, the pattern, process, and potential underlying mechanism of temporal variation in trophic cascades remains relatively unexplored. A top-down trophic cascade has been documented for the effects of predacious weaver ants Oecophylla smaragdina on the success of fig tree Ficus racemosa seed production. Ants cause high mortality of non-pollinating fig wasps Sycophaga mayri that parasitize fruits, leading to greater success for the pollinating fig wasp-fig tree mutualists. Here, using a design in which pairs of branches were selected on a tree, and ants were excluded from one of each pair, we quantified the magnitude of the trophic cascade in the cool-dry, hot-dry and rainy (hot-wet) seasons in Xishuangbanna, southwest China. We also recorded the daily behavioral dynamics of ants and fig wasps in different seasons and analyzed the correlation between behavioral, activity and trophic cascade strength. We found that the strength of the trophic cascade was strong in the hot-dry season, diminished in the rainy season and disappeared in the cool-dry season in this system. The strength of species interactions between ants and non-pollinating fig wasps, is positively correlated with trophic cascade strength, indicating that trophic cascade strength is determined by a top-down process when the community is well established. Moreover, because pollinating fig wasps, Ceratosolen fusciceps, play a central role in the establishment of fig wasp communities, when C. fusciceps wasps are absent, the community quickly disassembles as is the case in the cool-dry season. In summary, the strength of the trophic cascade is triggered by top-down processes, however, the occurrence of the trophic cascade is determined by a keystone species that plays a central role in assembly of the community.