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

The earth's major mountain ranges provide opportunities to assess the effec ts of altitude and land use on stream fauna, but many basic patterns are st ill undescribed. Macroinvertebrates were therefore sampled from rifle and m arginal habitats of 45 streams in three regions of the Ecuadorian Andes. As semblage structure and richness were assessed in relation to habitat charac ter, water chemistry and catchment land use. Land use varied from humid mon tane 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 plantation s. Water chemistry and stream habitat varied significantly between regions, altitudes and land use. Invertebrate assemblages were dominated by Baetida e, Leptophlebiidae, Tricorythidae, Elmidae, and Chironomidae, but ordinatio n revealed major variations in assemblage structure with altitude. Hydropsy chidae, Philopotamidae, Ptilodactyidae and Gomphidae were restricted to low er altitude whereas Scritidae and Gammaridae characterised higher altitude sites. Secondary variations in assemblage structure were correlated with ha bitat structure and metal concentrations (Al, Fe and Mn), and in turn were reflected in taxon richness. Classification revealed generally similar patt erns, but showed also potential effects on assemblage structure in the West ern Cordillera where humid montane forest had been cleared for agriculture. We conclude that, as in other mountain regions, major downslope patterns a re clear among aquatic invertebrates in the Ecuadorian Andes. However, from these data altitude affects assemblage composition more than richness. Dow nslope patterns might have been modified by human activity at the catchment scale, and also by local site attributes such as habitat structure and str eam chemistry. We erect three hypotheses about the effects of land use on A ndean rivers that will be testable through further work.