Is Predaceous Stonefly Behavior Affected by Competition?

Abstract

Behavioral experiments were carried out in flow—through observation boxes in New York and Colorado streams to determine whether interactions between pairs of predaceous stoneflies were characterized by exploitative or interference competition and to determine the effect of prey density on such interactions. The presence of a competitor generally reduced the number of attacks and the time that predaceous stoneflies spent eating mayflies (Baetidae). Coexisting perlids (Acroneuria carolinensis and Agnetina capitata) in the New York stream and perlodids (Megarcys signata and Kogotus modestus) in the Colorado stream had mutual negative effects on each other's foraging behavior despite significant size differences between species (first larger athan second). A larger omnivorous stonefly (Pteronarcella badia, Pteronarcydae) also suppressed the feeding behavior of Megarcys, but a reciporcal effect was not observed. Most competitive encountes resulted in submissive or evasive behavior by one or both stoneflies ultimately leading to avoidance of further contact. Some stoneflies, however, were occassionally aggressive, either toward consecifics (Kogotus) or toward a smaller species or predator (Megarcys toward Kogotus). This behavior is consistent with the hypothesis that interference is a mechanism of competition among these stoneflies. The frequency of aggressive interactions increased for all stoneflies when prey density increased from 0 to 15 individuals per box but declined at 30 prey individuals per box. This observation suggests that the level of aggression is variable with availability of a food resource. As prey density increased, behavior associated wth predator—prey interactions (attacks, feeding) increased for some stoneflies, and other activities (dispersal, cleaning, stationary behavior) decreased, generally increasing the predator's probability of finding and consuming prey. Large species of stoneflies had shorter prey handling times than small species, and all stoneflies had very low rates of capture (successful captures 10—25% of total attacks. We postulate that direct interference competition from other stoneflies and predator—mediated dispersal of prey (unstable prey patches) reduce the benefit of aggregating in regions of high prey density.

Stream flow and predation effects on the spatial dynamics of benthic invertebrates

“…This probably reflects a functional response of predators to prey density. There was, however, no evidence of cannibalism or aggressive interference among caddis when prey were scarce, as has been suggested previously for P. conspersa demonstrated in some other lotic insects (Peckarsky & Penton, 1985;Hart, 1986;Hart & Latta, 1986). Relatively high consumption rates in some cages may be related to the heavy rain and subsequent spates that increased prey colonization.…”

The diet of two species of Isoperla (Plecoptera: Perlodidae) in relation to season, site, and sympatry

“…In other predatory stoneflies further indications of competition have been reported. Those included aggressive interactions (Peckarsky & Penton, 1985), territoriality (Sjostriim, 1985) and density-dependent predation rates (Walde & Davies, 1984, 1987Malmqvist, in press). …”

Multiple predator effects result in risk reduction for prey across multiple prey densities

“…Specifically, the risk reduction may have been caused by interference between predators or the presence of prey defenses that made one or both predators less effective in the presence of the other predator. Aquatic predators are known to interfere with each other (Peckarsky and Penton 1985;Soluk and Collins 1988a, b;Peckarsky 1991;Soluk 1993) primarily because of food resource limitation and the risk of intraguild predation (Peckarsky 1991;Soluk 1993). Although intraguild predation did not occur in the experiment, the fear of intraguild predation may still have influenced the predators.…”

“…This figure could be expanded to determine the outcome when risk enhancement is present and when the lines are non-linear between predatory stoneflies that only affected their feeding rates at intermediate prey densities and not at either high or low prey densities. Aggressive responses between stonefly species also increased at intermediate prey densities and decreased at the highest prey densities (Peckarsky and Penton 1985). One reason why the intensity of interspecific interactions between predators could change with prey density is that the likelihood of the predators' becoming satiated will often be a function of prey density.…”