Effects of warming on structure of aquatic communities in tropical bromeliad microecosystems

Freshwaters are among the most vulnerable ecosystems to climate warming, with projected temperature increases over the coming decades leading to significant losses of aquatic biodiversity. Experimental studies that directly warm entire natural ecosystems in the tropics are needed, for understanding the disturbances in aquatic communities. Therefore, we conducted an experiment to test the impacts of predicted future warming on density, alpha diversity, and beta diversity of freshwater aquatic communities, inhabiting natural microecosystems – Neotropical tank bromeliads. Aquatic communities within the tank bromeliads were experimentally exposed to warming, temperatures ranging from 23.58 to 31.72°C. Linear regression analysis was used to test the impacts of warming. Next, distance-based redundancy analysis was performed to assess how warming might alter total beta diversity and its components. This experiment was conducted across a gradient of habitat size (bromeliad water volume) and availability of detrital basal resources. A combination of the highest detritus biomass and higher experimental temperatures resulted in the greatest density of flagellates. However, the density of flagellates declined in bromeliads with higher water volume and lower detritus biomass. Moreover, the combination of the highest water volume and high temperature reduced density of copepods. Finally, warming changed microfauna species composition, mostly through species substitution (βrepl component of total beta-diversity). These findings indicate that warming strongly structures freshwater communities by reducing or increasing densities of different aquatic community groups. It also enhances beta-diversity, and many of these effects are modulated by habitat size or detrital resources. Methods Further methodological details on data collection can be found within the published paper and its supplementary material.