Combined effects of temperature and litter quality and functional diversity on the structure and functioning of natural freshwater microecosystemss

Abstract

Ecosystems are currently suffering from global climate change impacts and unprecedented shifts in species richness and composition. The temperature increase expected by the year 2100 is 4°C above pre-industrial levels and, simultaneously, land use change threatens the biodiversity of surrounding ecosystems. These stressors interfere with everything from trophic structure to the dynamics of energy flux of all ecosystems on the planet. However, tropical freshwater ecosystems are more vulnerable due to the limited ability of organisms to disperse and the dependence on climate to maintain temperature and water availability in these environments. Moreover, ectothermic organisms are exposed to the ambient temperature and abrupt climate changes interfere in their metabolism with consequences for trophic interactions and, therefore, for energy transfer in these systems. Despite this, we know little about the effects that emerge from the combination of both stressors. This is a necessary approach, since temperature and environmental complexity are altered concomitantly in nature. To identify interactive effects generated on ecosystem structure and functioning we need studies capable of integrating biotic and abiotic variables. Aiming to fill these knowledge gaps, our project will evaluate the effects of different leaf resource profiles - quality and functional diversity - and increased ambient temperature on aquatic insect communities. Specifically, we will evaluate how trophic structure and energy transfer dynamics in aquatic bromeliad communities change when exposed to 4°C temperature increase and gradients of litter quality and functional diversity. We predict that increased temperature may make top predators more vulnerable and consequently alter networks of consumer-resource interactions and decrease energy flow between trophic levels. High quality resources have the potential to buffer negative temperature effects through the bottom-up pathway by providing nutrients necessary for metabolism (nitrogen and phosphorus). Meanwhile, litter with high functional diversity promotes complementary nutrient use and facilitation, which can also buffer temperature effects. Our study seeks to contrast these two leaf litter profiles to identify the contribution of functional diversity in relation to resource quality to trophic dynamics and energy transfer under a global warming scenario. In addition we will also assess the equivalence between ecosystem structure and dynamics, often used as a proxy in studies of complex networks and energy flows. This approach allows future conservation efforts of tropical aquatic systems to have a quality theoretical basis to act effectively during global climate change.