Competition and the Structure of a Benthic Stream Community

Abstract

The mechanisms structuring benthic stream communities composed largely of highly mobile taxa are poorly known. I studied the role of competition in structuring the benthic community of hard substrates in a coldwater stream dominated by mobile insects that grazed upon periphyton and by relatively sessile filter-feeding insects. I expected competitive interactions among periphyton grazers to be significant and chronic because the community was not subject to frequent flow-related disturbances and grazer densities were high despite consistently low periphyton availability. Laboratory and field experiments were performed to determine: (1) the potential for, and relative strengths of, competition within and between two common, widely distributed grazers, the caddisfly Glossosoma nigrior and the mayfly Baetis tricaudatus, (2) the role of Glossosoma in affecting the organization of the community, and (3) the mechanisms of competition.Strong intraspecific effects on Baetis survivorship were observed in laboratory enclosures within the range of natural densities, but interspecific effects were not detected. Glossosoma survivorship was not affected by competition with itself or with Baetis. Individuals of both species experienced significant intra-and interspecific effects on growth, but the relative strengths of these effects differed between species. The effects of Baetis on Glossosoma growth were stronger than the effects of Glossosoma on itself. In contrast, Baetis growth was much less affected by the presence of Glossosoma than by conspecifics. Both species strongly depressed periphyton abundance, indicating that observed competitive effects resulted, in part, from exploitation.Exclusion of Glossosoma from habitats in the field resulted in a marked increase in periphyton biomass throughout a 1 0-mo study in which the movements of other taxa were not restricted. Most periphyton grazers responded to this increase in resource availability with increased densities in the Glossosoma exclusion treatment relative to the control. The size distributions of several chironomid grazers suggested that larval growth rates were greater in the absence of Glossosoma than with Glossosoma present. The larvae of two relatively small-bodied filter-feeders (Simulium, Rheotanytarsus) responded positively to the removal of Glossosoma, but larger bodied species (Hydropsyche, Brachycentrus) were not affected. There was not strong evidence for seasonal variation in the intensity of competition.Effects of Glossosoma on filter-feeders appeared to result from a form of interference competition, but there was no evidence for the operation of interference among grazers. Glossosoma had no effect on the colonization of habitats by grazers, and the feeding rates of Baetis and Glossosoma were not affected by the presence of conspecifics or heterospecifics.Contrasting patterns in periphyton abundance between the laboratory and field experiments suggest that, when their movements are unrestricted, Baetis departs periphyton patches at higher food densities...

Biological barriers to restoration: testing the biotic resistance hypothesis in an upland stream recovering from acidification

“…Many studies have shown that stream invertebrates, including mayflies and stoneflies, reduce algal standing crop and compete for these resources in small streams (e.g. Kohler, 1992;Ledger & Hildrew, 2000b), but we found no evidence for resource depression by either species in this experiment. Weak grazing pressure can be explained by low numerical abundance of consumers, poor match between consumer mouthparts and resource structure, and rates of algal primary production that counteract consumptive losses (e.g.…”

“…Ledger & Hildrew, 2000a, b) and mayflies (e.g. Kohler, 1992) characteristic of upland streams, but the extent to which competition occurs between these groups has not been tested within the context of acidification. Specifically, we assessed the degree of resource overlap between Leuctra inermis and Baetis rhodani and, using a field experiment, tested the hypothesis that the growth rate of a recolonist, Baetis, could be affected by Leuctra, its putative competitor.…”

Environmental factors – spatial and temporal variation of chironomid communities in oceanic island streams (Azores archipelago)

“…The percentage of variance in chironomids assemblages explained only by hydromorphological variables in our study was considerable (30.8%) and similar to the percentage of variation explained by physicochemical variables (27.7%). The relatively high percentage of unexplained variation (41.5%) in our study is typical of noisy data sets with many 0 values (Borcard et al, 1992), and could be result of abiotic and biotic factors not considered in this study, such as species' interactions (Kohler, 1992), food availability (Peeters et al, 2004), reproduction, competition and predation (MacNeil et al, 1999).…”

Spatial and temporal organization of aquatic insects assemblages in the longitudinal gradient of a tropical river

“…Several factors have been considered as decisive in structuring macroinvertebrate assemblages in streams: substrate (Reice, 1980;Rae, 1985), allochthonous matter (Cummins & Klug, 1979), temperature (Vannote & Sweeney, 1980;Ward & Stanford, 1982), flow (Rabeni & Minshall, 1977;Dudgeon, 1993a), disturbance (Siegfried & Knight, 1977;Death & Winterbourn, 1995), and biotic interactions (Kohler, 1992).…”