Invertebrate Drift From Predator‐Prey Associations

Abstract

Laboratory experiments evaluated the effect of a predator, Acroneuria abnormis (Plecoptera), on the drift of two prey taxa, Taeniopteryx spp. (Plecoptera) and Stenacron interpunctatum (Ephemeroptera), from substratum patches in artificial stream channels. Drift of Taeniopteryx spp. increased significantly as its own density and the predator's density increased, but a predator density threshold was required to boost drift of the prey substantially. Drift of S. interpunctatum increased as its own density increased but was not significantly affected by the predator's density. Consumption of Taeniopteryx spp. by A. abnormis increased as the former's density increased but was not significantly affected by the predator's density. More S. interpunctatum were consumed as densities of the predator and prey increased. Both prey taxa occupied interstitial refuges in the substratum patches but Taeniopteryx spp. occupied them more successfully. Some Taeniopteryx spp. may have actively deserted the substratum patches in the presence of the predator. Drift of Taeniopteryx spp. alone was judged density independent at a current velocity of 12.5 cm/s but density dependent at 25.0 cm/s. Drift of S. interpunctatum alone (at 8.0 cm/s) was density independent. At 25.0 cm/s, drift of A. abnormis alone was density dependent, but insufficient drift of this taxon occurred at a lower velocity (8.0 cm/s) to allow such a determination. Predator satiation did not occur in these experiments. Occupation of interstitial refuges and drift by the prey combined to reduce the predator—prey encounter rate. Drift of the predator was not significantly affected by prey density.