Effects of deforestation on macroinvertebrate diversity and assemblage structure in Ecuadorian Amazon streams

Abstract

The effects of deforestation on stream macroinvertebrate faunas were studied at twelve sites located in an area of fragmented rainforest in the Ecuadorian Amazon. The most pronounced changes in habitat characteristics with reduced riparian canopy cover were a reduced amount of litter detritus on the streambed and an increased periphyton biomass. Alpha diversity decreased with the degree of deforestation. Beta diversity was also lower in deforested than forested sites, indicating that macroinvertebrate composition among the forested sites were more heterogeneous than among the deforested sites. Total macroinvertebrate density increased with decreasing canopy cover, and with increasing periphyton biomass. The relative density of Ptilodactylidae, Tanypodinae, Euthyplociidae, Libellulidae and Megapodagrionidae were positively related with either canopy cover or litter detritus. A marked effect on the trophic structure of the macroinvertebrate fauna was found. The relative density of collectors decreased with canopy cover and the amount of litter detritus, while the relative density of predators increased. Shredder abundance was low and unrelated with canopy cover. Temporal variability in the macroinvertebrate data were greater in the deforested sites than in the forested sites. Using two-way indicator species analysis (TWINSPAN) and principal components analysis (PCA) riparian canopy cover was found important structuring the macroinvertebrate assemblages. Litter detritus associated with particulate organic material was the main variable related with the PCA ordination axes.