Life cycle, production and habitat selection of Notoperla fasciata and N. magnaspina (Plecoptera: Gripopterygidae) in a headwater Patagonian stream

We examined the life history, annual production, diet, habitat preferences and competition of two species of stonefl ies Notoperla fasciata and N. magnaspina in a Patagonian mountain headwater stream.Benthic samples and adult collections were taken monthly from July 2004 to June 2005.A habitat selection study was performed concurrently during high and low water periods in fi ve substrate types.Although both species showed long life cycles (N.fasciata: 20 months and N. magnaspina: 3 years) their life histories and temporal dynamics were different.Growth was rapid during summer and early autumn as a result of warmer temperatures but N. magnaspina had a shorter emergence period (November to January) than N. fasciata (January to April).N. fasciata was the dominant Notoperla species with a mean annual density 6 times higher and secondary production 4.5 higher than that of N. magnaspina.While boulders in riffl es and pools, and leaf-pack habitats supported signifi cantly more individuals of N. magnaspina in the low water period (ANOVA, p < 0.02) habitat preferences were not observed in the studied species (ANOVA, p > 0.26).N. fasciata dominated in the high water period and N. magnaspina during the low water period.Analysis of gut contents revealed that both species were herbivorous grazers, and consumed the same food types.The interspecifi c overlap in density, biomass and annual production among habitat types was high in the low water period (PS > 0.5).However, N. fasciata were smaller than N. magnaspina.The existence of different life history strategies and the temporal shift of main generations and density peaks were critical to allow species coexistence and to reduce competition.