The feeding behaviour of some common lotic insect species in two streams of differing detrital content

The trophic relationships of the benthic invertebrates at two places of differing detrital content in an oligotrophic stream system were examined during a 12 month period. The sites are described and their detrital contents and other abiotic features compared. The faunal list at each site is fairly similar but certain species are more common at or restricted to one or other site. The reasons for this are briefly discussed. The predators and omnivores are in two groups: the first feed only on certain prey and are thus limited by the distribution of their prey. The others consume a wide range of prey and have wider distributions. The predator species are non‐selective in their choice of prey which are devoured in an intensity which cannot however be related to their density in the benthos. In poorer trophic conditions predators adapt by consuming a greater quantity of algae and detritus; cannibalism and interpredator‐predation occur. The prey species are more intensely consumed under poor trophic conditions. The ecology of two species of predatory Plecoptera is examined and the results indicate that competition probably occurs between them.