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Keywords:

  • connectance;
  • food chain length;
  • gut content analysis;
  • invertebrate;
  • stream algae

Abstract

Food web analyses have been fundamental in understanding community organization and ecosystem functioning. To date, a number of studies demonstrate that stream food webs depend to a large extent on allochthonous detritus, but there are more recent studies that show a high degree of autochthony. Our food-web study was carried out in three Andean rivers (Coilaco, Guampoe and Trancura) within the catchment area of Toltén River in southern Chile. Based on the analyses of 4251 invertebrate gut contents, we found that these Andean stream food webs are dominated by herbivores (range: 50–73% of all species) supported by a species-rich algal (basal) component, and characterized by a low proportion of omnivores (range: 8–27% of all species) and predatory species (range: 10–24%). Significant differences in the number of feeding links of the herbivores Meridialis diguillina and Antarctoperla michaelseni and the omnivore Smicridea chilensis were found between seasons. The spring herbivore Aubertoperla sp. showed significant differences between rivers. S. chilensis fed on 50 different prey items as compared with the herbivores whose maximum number of links ranged between 37 and 40. Web sizes ranged between 93 and 131 species and the proportion of top species was distinctly lower than those of basal (up to 0.651 in Coilaco River) and intermediate species. Direct connectance (links per species2) values were low and similar among rivers (range: 0.051–0.074), whereas mean food chain length ranged between 2.23 and 2.90. The distributions of web property values from the Andean rivers differed from those previously published. In contrast to previous predictions, mean food chain length in these Andean streams displayed a scale-invariant pattern across different web sizes, but it was significantly related to the proportion of intermediate species.