The effects of global warming on the trophic structure and ecosystem functioning in tank-bromeliads

Abstract

The number of studies on the effects of climate change on biodiversity have increased over the past 10 years. However, only a few have attempted to empirically investigate the effects of global warming on the ecosystem and trophic structure of aquatic systems, especially in neotropical systems. In this study, we will investigate the effects of global warming combine with the effects of predator diversity on community structure (number and composition of species and functional groups) and ecosystem functioning of aquatic ecosystems (productivity, decomposition and nutrient cycling) in phytotelmatas from tank-bromeliads. Specifically we tested whether the increased temperature i) influences community structure and trophic composition (e.g., abundance and biomass of functional trophic groups, predator-prey ratio); ii) affects the productivity rate, detritus decomposition and nitrogenflux of phytotelmatas, iii) decreases the average body size of aquatic organisms, altering the trophic structure (e.g., predator-prey ratio biomass) and ecosystem responses. We also evaluate whether predators diversity counter balance the increased temperature effect on ecosystem functioning. We manipulate global warming by using heaters and thermostats with temperature control systems and digital monitoring. The heating was composed of three temperature levels: i) control (current temperature, ii) average projected for 2040 (increase to 2°C), iii) 2100 (4°C increase). We manipulated predator diversity as: 1) no predator (control), 2) low diversity (only one species of predator) 3) high diversity (three species of predators). Each block consisted of nine combinations of heating and predators, for a total of five blocks. We expect that warming will promote changes in the trophic structure and aquatic ecosystem functions, primarily affecting organisms of higher trophic levels.A possible cause of this pattern may be attribute to the difference in body size of predators and prey. The heating may beneficiate smaller body size of organisms, possibly by decreasing the concentration of dissolved O2, reducing the average body size of the community and changing consumer-resource relationships. Thus, there could be a change in the dynamics of trophic networks controlled by top-down relationships, increasing the magnitude of effects derived from detritivores. However, in communities with greater diversity of predators, the effects of warming may have a minor impact due to the high consumption of prey. Therefore, in such scenario, we expect cascading effect to be greater and the rates of decomposition and nutrient cycling lower.