Do disturbance and periphyton productivity affect stream invertebrate traits?

Abstract

Disturbance in lotic ecosystems strongly influences which animals can survive and how those ecosystems function. Flow disturbances physically remove animals and periphyton, but it is unclear whether physical removal of individuals or the loss of food is the principal driver of effects of flow disturbances on invertebrate communities. Invertebrates possess traits that help them withstand high flows or recolonize rapidly after floods. At light-limited, closed-canopy sites, periphyton biomass should be unaffected by disturbances, so disturbance should affect invertebrate community trait composition by direct removal of animals. At open-canopy sites, disturbance should affect trait composition by both removing individuals and reducing periphyton food resources. We investigated whether a trait-based approach could elucidate drivers of effects of flow disturbance on benthic invertebrate communities and better identify potential mechanistic linkages. We sampled 10 autotrophic streams that differed in substrate-disturbance regime and varied from 100 to 0% canopy cover. We sampled 2 sites per stream, 1 in forest (closed-canopy) and 1 downstream in low-intensity agricultural grassland (open-canopy). Regardless of canopy, in streams with greater substrate disturbance, the proportion of individuals that respired with a plastron increased and proportions of individuals having 2 aquatic life stages or that were filter-feeders decreased. At open-canopy sites, the proportion of collector–gatherers with flattened bodies increased with increased substrate disturbance and decreased periphyton biomass, and the proportion of taxa having high body flexibility and 2 aquatic life stages increased with decreased substrate disturbance and increased periphyton biomass. Trait composition of these mountain stream invertebrate communities is strongly influenced by physical removal via substrate movement and by reduced periphyton resources.