Black flies are abundant benthic organisms in well-oxygenated running water and are considered effective bioindicators of water quality. Information on the ecology of these organisms at the species level is important, since up to now information has mainly been available on a family level. The aim of this study was to evaluate the composition of black flies and their relationships to a group of physical and chemical factors in four small rivers of the Eastern Hills around Bogotá, Colombia. These headwaters are protected by the Empresa de Acueducto y Alcantarillado de Bogotá. Black fly larvae and pupae were collected during four sampling periods during the dry season to the early rainy season of 2012. Multivariate methods were used to determine the presence of each species in relation to dissolved oxygen, nitrates, pH, temperature, and water velocity. PCA ordination revealed a physicochemical environment with a tendency towards a certain homogeneity in the fourrivers studied. The DCA ordination confirmed that in La Vieja River the G. ortizi complex dominated while S. muiscorum was dominant in the other three rivers. Similarly, according to the NMDS, the composition of black flies in Arzobispo and Chorro de Padilla rivers was similar, while that of El Delirio and La Vieja rivers were different, especially in this last river. The rivers hadlow species richness (four species and one species complex). Simulium muiscorum was negatively correlated with dissolved oxygen, temperature and current velocity while S. ignescens was associated with slightly more oxygenated waters and S. furcilatum with fastercurrents.The low species diversity and richness for the four rivers is consistent with previous report sof low Neotropical diversity of black flies. Results showed that simuliid species could possibly be good indicators of the environmental conditions of Eastern Hills rivers around Bogotá.

At least three strata of vegetational formations can be recognized in many mountainous ecosystems. For instance, the Andean Yungas exhibits: 1) upper fog grasslands, 2) intermediate montane forest, and 3) lower montane rain forest. The respective delimiters are the treeline and the inter‐forest line. We develop an approach to perform an optimal tripartition of mountainous ecosystems using elevational cutoffs per watershed. This pair of cutoffs allows us to transform heights of a given digital elevation map onto a universal adimensional scale. Normalized elevation facilitates worldwide comparisons and entails synthetic information (e.g., >0 means above treeline and < −1 below inter‐forest line). To test the reliability of delimiting elevation lines, we compare them against the hand‐drawn treeline and we assess the agreement with another tripartition of sampling points, but based on a different set of organisms (i.e., mayflies, an ancient group of insects that mimic ecological patterns found in many other aquatic taxa). The resulting delimiters of strata pass the test successfully. The upper delimiter fits the detailed treeline well. The lower delimiter segregates different types of mayflies on either side. Only the intermediate layer holds a distinctive set of co‐occurring mayfly species. We finally stress the relevance of the inter‐forest line to track the imprints of global change on community composition. Abstract in Spanish is available with online material.