The invertebrate community which colonised litter bags was dominated by taxa of mayflies (mainly Leptohy-phidae), caddisflies and Chironomidae. Most of the variation in colonist densities and species composition was explained by leaf type and time of exposure. Colonisation on Sloanea medusula increased slowly within exposure time and showed the lowest population density. Peaks of macrozoobenthos colonisation (total individuals and abundance of major taxa) occurred between 10 and 20 days of exposure on A. Leaf material of 4 common tree species, Acalypha diversifolia (Euphorbiaceae), Cecropia obtusifolia (Cecropi-aceae), Tetrathylacium macrophyllum (Flacourtiaceae) and Sloanea medusula (Elaeocarpaceae) were exposed in the stream. In view of various defence mechanisms against herbivory (polyphenols – especially tannins) of plants in tropical rainforests, leaf decay rates and macroinvertebrate colonisation of 4 plant species, representing a range of life history and defence strategies, were investigat-ed using litter bags. Leaf litter decomposition in tropical lotic systems has received less attention than in streams in the temperate region. Shredders, such as Leptoceridae and Calamoceratidae were rare. In terms of species numbers, representing the differ-ent trophic guilds, the fauna is mostly made up of collector-gatherers (53%), followed by predators (16.5%) and filter-feeders (14.5%). The macrozoobenthos of pools was dominated by Diptera (36%) and Ephemeroptera (31.9%), including the family of Caenidae (11%) which were not found at riffle sites. These two fami-lies were not present at pool sites. Collector-filterers were mainly represented by Philopotamidae and Hydropsychidae (Trichoptera). At riffle sites, Ephemeroptera was the dominant insect order (37%), followed by Coleoptera and Diptera. The taxonomic composition of stream benthic fauna and its trophic structure (functional feeding group -FFG) within rif-fle and pool sites were distinguished. The Quebrada Negra, a first order tropical lowland stream within the Piedras Blancas National Park, Costa Rica, is a heterogeneous environment with a high diversity of habitats where environmental characteristics vary drastically over small dis-tances.
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