Seasonal Production Dynamics in a Guild of Periphyton‐Grazing Insects in a Southern Appalachian Stream

Temporal partitioning has been found to be a predominant mode of ecological segregation among groups of systematically related stream insects. We extended this concept to a functionally similar but systematically diverse group of species. The life cycles and secondary production of six species of periphyton—grazing insects (scrapers) were studied in a fourth—order unshaded stream reach in the southern Appalachian Mountains. Total annual production (as ash—free dry mass) calculated with the instantaneous—growth rate method was 1195 mg/m 2 . The size—frequency estimates was 6.4% lower. Annual production (AFDM) by species ranged from 612 mg/m 2 for Glossosoma nigrior to 10 mg/m 2 for Goera fuscula. The production peaks of the six species occurred at separate points in the year, with very little overlap between species. Comparison with a neutral model indicated that production peaks were significantly more regularly spaced (P <.1) than would be expected by chance alone. Temporal overlap between species was calculated using density, biomass, and production. Overlaps based on density and biomass were similar (means of .173 and .171, respectively). Mean overlap based on production was significantly lower (.124). The patterns of temporal organization observed in this group of species were linked with specialized life histories. Five of the six species were univoltine, with periods of larval development (cohort production intervals [CPI] ranging from 44 to 215 d. The shortest CPIs were associated with species that diapaused in the egg (Agapetus sp.) or larval (Neophylax consimilis) stages. Summer production was dominated by G. nigrior, which had a bivoltine life cycle. Production by the spring—summer cohort of G. nigrior was 4.5 ° the production of the winter cohort. Glossosoma's bivoltinism apparently provides it with the life history flexibility to utilize the high summer periphyton production permitted by the lack of canopy cover at the study site. Seasonal production by the six species was distributed 18% in winter (January—March), 36% in spring, 38% in summer, and 8% in autumn. The seasonal distribution of grazer secondary production correlates well with previously reported seasonal dynamics of periphyton production.