Predatory invertebrates indirectly impact leaf-litter breakdown by different foragers in temporary wetlands

Abstract

Temporary wetlands constitute a reservoir of fauna, many of which are endemic species well adapted to the typical dry?flooded cycle. The degradation of organic matter (both autochthonous and allochthonous) is an important process in temporary wetlands. Wetland animals like caddisfly and anuran larvae participate directly and indirectly in litter breakdown. Both groups also experience predation by invertebrates and vertebrates, which could alter the dynamics of litter breakdown. We used mesocosms to experimentally study the roles of caddisfly and tadpoles in leaf litter breakdown in the presence of a caged predator. We investigated how the presence of different types of forager (larvae of the caddisfly Verger lutzi and Batrachyla taeniata tadpoles) impacts leaf litter breakdown and also whether the presence of a caged belostomatid predator affected this process. Additionally, we investigated the behavioral response of B. taeniata tadpoles and V. lutzi larvae to predation risk cues from belostomatids previously fed on tadpoles or caddisflies. Our results indicated that only caddisfly larvae have a significant impact on litter breakdown. Predation risk did not influence the process, caddisfly larvae exposed to a caged predator reached the pupal stage more quickly than larvae that were not thus exposed, and tadpoles significantly reduced their activity in response to predation risk cues. None of the life history parameters of B. taeniata were affected by the predator, but tadpoles accelerated their development in warmer water. Our study is the first in South America to analyze the interactions between a common assemblage of tadpoles and caddisfly larvae and their impact on leaf litter breakdown when they experience predation risk. The model used here contributes to our understanding of ecosystem processes such as leaf litter breakdown and the impact of different biotic and abiotic variables when foragers co-occur in the food webs of temporary aquatic systems.