Aquatic Insect Colonization in Streams within Early, Mid, and Mature Successional Tropical Forests

The dynamics of leaf litter decomposition in neotropical streams has emerged as a major research focus over the last two decades. These studies have demonstrated that leaf litter breakdown rates are influenced by anthropogenic disturbance, microbial activity and the physical and chemical properties of the stream itself. Understanding leaf litter breakdown may help illuminate how energy flows through stream ecosystems (Benfield 2006). However it is still unclear how aquatic insect communities alter leaf litter breakdown in a tropical stream and the colonization rates of insect assemblages on these leaf packs.  I investigated how aquatic insect assemblages were correlated with insect abundance and biodiversity in tropical premontane forest between three streams at the Las Cruses Biological Station in Costa Rica.  These streams were chosen to represent different levels of anthropogenic disturbance (i.e., primary forest, secondary forest, and abandoned pasture).  Bags containing Miconia leaf packs were placed in these streams and the taxonomic diversity of insects on these packs was monitored over the course of several weeks.  Estimates of leaf loss over time were also calculated based upon the remaining leaf material in the bags.  Our results suggest that insect diversity in leaf packs was greatest in leaf litter from primary and abandoned pasture sites and low in secondary forest.  These patterns were likely due to differences in the physical and chemical characteristics of the streams and provide useful insight into ecosystem function of streams embedded within different levels of terrestrial disturbance.