Food-web structure in Chilean rivers

The analysis of food-webs is fundamental to understand how an ecosystem works and functions. In rivers and streams, many food-web studies have demonstrated the preponderance of allochthonous matter as food source. However, recent research shows that some stream food-webs depend on autochthonous matter.
The current investigation was the first assessing food-webs in Chilean rivers, including three temperate, neotropical rivers located in the Andes (Coilaco, Guampoe and Trancura) of southern Chile. The gut contents of invertebrates (4251 individuals) were examined to analyse the feeding interactions and their differences among those rivers. The food-webs were dominated by herbivorous invertebrates (50 - 73%) supported by a species-rich algal diet dominated by diatoms (basal species). In contrast to other stream systems, these Chilean rivers are characterized by having few omnivore and predatory species. The size of the food-webs varied between 93 and 131 species, but the number of top species (those that are not preyed upon) was distinctly lower than intermediate and basal species. These food-webs display significant seasonal changes in food preference among the river systems investigated.