The availability of resources such as water, sunlight and nutrients, is a key determinant of the structure and functioning of ecosystems. Even though many aspects of global change increase the temporal variability of resource supply, the implications for ecosystems of these reductions in resource stability remain largely unknown. We established an experiment in outdoor freshwater mesocosms to investigate whether the destabilization of resource supply alters ecosystem multifunctionality. In addition, because predators often exert strong top-down control on ecosystems, we examined whether their presence can buffer ecosystems against the effects of enhanced resource variability. We enriched mesocosms in three distinct ways by adding nutrient pulses in contrasting regimes, each with different temporal stability, with the presence of fish predators also incorporated in a full-factorial experimental design. The overall frequency and total mass of nutrient subsidies were, however, identical across all enriched treatments.
Results/Conclusions
We found that the efficiency of nutrient cycling varied significantly among the different enrichment regimes, being lowest in the regime with the most temporally stable resource supply, whereas conversely the stability of ecosystem respiration was enhanced by resource variability. Further, the presence of fish predators buffered some, but not all, ecosystem functions against increased variability in resource supply. Our results demonstrate that the stability of resource availability regulates ecosystem multifunctionality and that this effect can be moderated at least in part by food web structure. We conclude that widespread reductions in resource stability are likely altering ecosystem functioning throughout the globe in many previously unanticipated and largely unpredictable ways.