Print PageWe are losing species at a fast rate worldwide, while continuing to be ignorant about the full consequences of extinctions for ecosystems and their functioning. Previous studies have largely studied these consequences at single trophic levels. However, species loss can cascade through food webs and might ultimately affect functions at other trophic levels. Bromeliads are an ideal study system for these kinds of questions. These tropical plants form natural mesocosms by accumulating water between their leaves and hosting simple food webs of aquatic insects. The bromeliad benefits from nutrients becoming available through decomposition processes enhanced by the insects. We used bromeliads in Costa Rican rainforests and experimentally manipulated species richness at low (resource) and high (predator) trophic levels of the contained food web simultaneously. We then examined the bottom-up and top-down effects of species richness on the intermediate trophic level: a standardized community of detritivores. Furthermore, we assessed ecosystem functioning at this level by measuring decomposition rates, nutrient flow to the bromeliad using isotope-labeled resources and ultimately, growth of the bromeliad.
Results/Conclusions
Preliminary analyses suggest that both predator and resource richness had a small positive effect on ecosystem functioning in terms of decomposition rates in the system. Detritivore abundance and bromeliad growth were higher in the presence of two predator species as compared with the average predator “monoculture”. However, we did not find strong interactive effects between species loss at low and high levels of the food web. We conclude from our preliminary results that species richness can have both bottom-up and top-down effects on other trophic levels and their functions. These cross-level processes should be taken into account when assessing the consequences of species loss on ecosystem functioning in interconnected food webs.
