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Aim:We aimed to understand how aquatic insect larvae communities associated with bromeliad phytotelmata are affected by plant architecture, predators and resources (local factors), and by geographical distance (regional factors) in two different plant phenological phases. Bromeliad flowering results in plant structural changes, which favours insect dispersal. Considering that local and regional factors may affect the community of aquatic insect larvae, we expected that composition, beta diversity and the importance of those factors would differ in the vegetative growth and flowering phases. Methods: We performed six samplings of the bromeliad associated fauna in 2010, three during the first semester -vegetative growth phase -and three during the second semester -flowering phase. In each sampling, we collected 12 plants along the rocky walls with similar location distribution, with a total of 72 bromeliads studied. Results: Although beta diversity (PERMDISP) did not differ between vegetative growth and flowering, NMDS followed by ANOSIM showed that composition was significantly different in the distinct phenological phases. IndVal results showed that three Diptera morphospecies were discriminant of the vegetative growth phase. In addition, pRDA revealed differences in the relative contribution of local and regional factors to explain insect larvae community structure. During the flowering phase, local factors predominated, while during vegetative growth, regional factors were more important. Conclusion: Differences in dispersal rates between the two phenological phases, likely due to adult insect pollination and further oviposition, influenced community structuring. Therefore, flowering events account for differences not only in the composition, but also in community structuring of aquatic insect larvae inhabiting the phytotelmata of Aechmea distichantha Lem. (Bromeliaceae).

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Despite the key role of biotic interactions in structuring ecological communities, their influence is often overlooked in predictions of how communities respond to environmental change. Here, we present an experiment that tests hypotheses based on metacommunity theory about how abiotic responses, biotic interactions, and dispersal jointly determine the response of ecological communities to environmental perturbations. We established experimental zooplankton metacommunities across spatial temperature gradients, connected by three levels of dispersal, that experienced natural temporal variation in ambient temperature. Prior to a mid-summer heatwave, community composition varied across the spatial temperature gradients. The heatwave homogenized the metacommunities and when conditions cooled, communities diverged into multiple compositional states that were not associated with temperature. These states appear to have been driven by biotic interactions that prevented the reestablishment of the pre-heatwave thermal compositional gradients. This highlights how biotic interactions can prevent metacommunities from tracking temperature changes via dispersal-facilitated species sorting.