A COMPARISON OF THE FOOD SOURCES OF STONEFLIES (PLECOPTERA) FROM AN OPEN-AND A CLOSED-CANOPY HEADWATER STREAM IN SOUTH AFRICA USING STABLE-ISOTOPE TECHNIQUES

Abstract

Summary The effects of different local food resources on the diets of some filipalpian stonefly nymphs (Aphanicerca spp.) were investigated. Animals from two headwater reaches, one primarily allochthonously driven and the other an open-canopied autochthonous-based system were compared. However, gut and stable carbon isotope analyses revealed no real differences in plecopteran diets between the systems, with leaf detritus being a major source of carbon, and algae contributing virtually nothing to their diets. δ15N analysis suggested that the animals obtained their nitrogen from sources other than leaf material itself, and it was hypothesized that this source was the microbial slime layer formed on decomposing leaves. It was concluded that the feeding behaviour of Plecoptera is consistent with that of shredders of leaf detritus, and as such they uphold River Continuum Concept predictions of large shredder populations being indicative of a predominance of coarse particles in headwater reaches. This study als...