Cascading effects of spiders on a forest-floor food web in the face of environmental change

Abstract Spiders have cascading effects on forest-floor food webs and ecosystem processes by depressing soil fauna densities and altering species composition. However, it remains unclear how spiders with different foraging strategies influence cascading effects on decomposition. In addition, prolonged droughts would likely have important consequences for trophic interactions in detritus-based food webs. In the present study, we evaluated how interactions between spider predation and drought affect litter decomposition in a tropical forest floor. We manipulated densities of dominant spiders with actively hunting or sit-and-wait foraging strategies in microcosms which mimicked the tropical-forest floor. We found a positive trophic cascade on litter decomposition rates triggered by actively hunting spiders under ambient and reduced moisture. However, sit-and-wait spiders showed no cascading effects on litter decomposition under ambient and drought conditions. Our findings suggest that trophic interactions in detritus-based food webs should be considered to better understand litter decomposition in the face of environmental change.