A community Analysis of the Benthic Insect Fauna of an Abandoned Beaver Pond

Abstract

Over the past decade the importance of allochthonous organic matter as an energy source in aquatic system has received increasing attention. Data are available for streams (Nelson & Scott 1962; Minshall 1967; Kaushik & Hynes 1971), lakes (Wetzel et al. 1972) and rivers (Berrie 1972), but ponds have received little attention. Allochthonous detritus type (Woodall & Wallace 1972), distribution (Egglishaw 1964) and possibly particle size (Cummins & Lauff 1969) have been shown to influence the distribution and hence faunal composition of stream insect communities. Beaver ponds are a characteristic feature of the forested foothill areas of the Rocky Mountains of North America. They are formed by the damming of streams, and at time of formation there is an input of allochthonous material into the pond equal to the standing crop of vegetation plus leaf litter on the flooded area. Furthermore, after being abandoned by beavers, seral succession proceeds and hydrophytes such as Salix sp. colonize the pond margins and ensure a continued input of plant detritus. The objectives of this study were to examine the feeding biology, distribution relative to substrate type and adult phenology of the benthic insect communities associated with a shallow abandoned beaver pond and to assess the importance of allochthonous detritus as a food source for these insects. The insect fauna of such ponds (Appendix 1) differs markedly from that of streams, rivers and lakes (see Hynes 1970), larvae of the Diptera, especially Tipulidae, are the major faunal component: the Chironomidae are poorly represented. Unfortunately, the larval systematics of the Diptera are poorly known and this creates problems.