ECOLOGY OF INVERTEBRATE PREDATORS IN A COASTAL-PLAIN STREAM

1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand-bottomed, headwater stream in Virginia, U.S.A. 2. Annual mean density and biomass of predators in debris dams were 3897 individuals m-2 and 2.5 g dry mass m-2, respectively, but only 711 individuals m-2 and 0.2 g m-2 on the sediment. Predator production was 8.36 g M-2 yr-1 in debris dams compared to 1.52 g m-2 yr-1 on the sediment. Annual predator production, weighted by habitat availability, was 1.73 g m-2 yr-1. 3. The predominant taxa in terms of production were the chironomids Thienemannimyia spp. complex, Ablabesmyia parajanta, Zavrelimyia sp., and the odonate Cordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild. 4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 g m-2 yr-1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the channel surface of the stream.