Direct and indirect competition negatively affect the foraging activity of a neotropical shredder

Although competition for resources is a biotic interaction with fundamental impacts on the structure of aquatic ecosystems, the role of this interaction in allochthonous matter dynamics in streams is still poorly studied or understood. Allochthonous litter that accumulates on stream beds is the main energy input in these ecosystems, being used by invertebrate shredders for shelter and food. Herein, we evaluate the effect of direct and indirect competition on the consumption of senescent Inga uruguensis leaves by Phylloicus sp. larvae. The effect of competition was measured by two treatments and one control: direct competition (two free larvae in a 4-L volume microcosm), indirect competition (two larvae separated by 0.05-mm mesh in a 4-L volume microcosm), and competition-free control (one larva in a 2-L volume microcosm). Both direct (33.46 ± 9.32 mg mg −1 ;16 ± 8%) and indirect (20.85 ± 5.26 mg mg −1 ; 16 ± 15%) competitions decreased the feeding activity of Phylloicus sp. larvae relative to the competition-free control (74.71 ± 9.25 mg mg −1 ; 37 ± 16%). In this sense, regardless of the type of competition, the presence of a congeneric competitor in the system negatively affects leaf fragmentation rates.