Community ecology of fishes and aquatic insects in rainforests of the Ecuadorian Amazon

I studied fish and aquatic insect communities in rainforest habitats in the Napo River basin of the Ecuadorian Amazon. First, within clearwater stream and riverine habitats I studied aquatic insect community structure and population genetics of two water strider species. Secondly, within lowland blackwater habitats, I studied aquatic insect and fish community structure and seasonality. Alpha diversity was estimated by species accumulation curves, Simpson's diversity and evenness, and Rarefaction. Beta diversity was estimated non-metric multidimensional scaling ordination and Bray-Curtis hierarchical clustering. I collected 4,214 aquatic insect individuals representative of 49 families and 182 morphotypes in clearwater sites. Relative abundance and density were low, but family and morphotype richness and diversity were high. Community structure on the family and morphotype level was variable and dominated by Ephemeroptera and Trichoptera. A faunal turnover occurred along the altitudinal gradient with corresponding changes in substrate. Collecter-gatherers, collector-filterers, and predators were abundant. The population genetic structure between and among water strider populations of Potamobates williamsi and P. sumaco, estimated from the sequenced COI mitochondrial gene, revealed moderate genetic structure and low gene flow. The significant correlation of air and river distances with gene flow indicates isolation by distance. Aquatic insect and fish communities in lowland blackwater habitats were influenced by habitat type and seasonality. I collected 2,859 aquatic insect individuals, representative of 35 families and 85 morphotypes. Odonata, Hemiptera and Coleoptera were dominant. Predators dominated in all but two samples where collector-gatherers were dominant. I collected a total of 196 fish species, increasing the current number of species for the Napo River basin to approximately 563. Lagoon, river and forest stream fish communities were composed of common species found within several habitats, of characteristic species found throughout the year, and of seasonal species found only within transitional, wet or dry seasons. The steady rates of species accumulations per sample in clearwater aquatic insect and blackwater fish communities suggest that these communities are still under sampled. The variability in aquatic insect and fish communities highlights the importance of seasonality for adequately assessing aquatic diversity and for developing research and conservation programs encompassing whole river ecosystems.