Macroinvertebrate distribution in Ecuadorian hill streams: the effects of altitude and land use

Abstract

The earth's major mountain ranges provide opportunities to assess the effects of altitude and land use on stream fauna, but many basic patterns are still undescribed. Macroinvertebrates were therefore sampled from rifle and marginal habitats of 45 streams in three regions of the Ecuadorian Andes. Assemblage structure and richness were assessed in relation to habitat character, water chemistry and catchment land use. Land use varied from humid montane forest in the Western and Eastern Cordillera to transition forest and Paramo in the Central Valley. However, c. 30 % of sites in each region were located in managed catchments of cleared forest, pasture or crop plantations. Water chemistry and stream habitat varied significantly between regions, altitudes and land use. Invertebrate assemblages were dominated by Baetidae, Leptophlebiidae, Tricorythidae, Elmidae, and Chironomidae, but ordination revealed major variations in assemblage structure with altitude. Hydropsychidae, Philopotamidae, Ptilodactyidae and Gomphidae were restricted to lower altitude whereas Scritidae and Gammaridae characterised higher altitude sites. Secondary variations in assemblage structure were correlated with habitat structure and metal concentrations (Al, Fe and Mn), and in turn were reflected in taxon richness. Classification revealed generally similar patterns, but showed also potential effects on assemblage structure in the Western Cordillera where humid montane forest had been cleared for agriculture. We conclude that, as in other mountain regions, major downslope patterns are clear among aquatic invertebrates in the Ecuadorian Andes. However, from these data altitude affects assemblage composition more than richness. Downslope patterns might have been modified by human activity at the catchment scale, and also by local site attributes such as habitat structure and stream chemistry. We erect three hypotheses about the effects of land use on Andean rivers that will be testable through further work.