Competition and Chironomid Distribution Patterns in a Newly Flooded Lake

Abstract

The investigation on the early colonization of a new lake ecosystem has shown that interactions between the larvae of invading midges are important in affecting their distribution patterns. Laboratory evidence is presented to support field observations which suggest that the distribution of a major species, Tanytarsus gregarius (Kieffer), was the outcome of competition with final instar Chironomus plumosus L. larvae. The activities of C. plumosus cause T. gregarius larvae to disperse towards the lake margins where encounters with C. plumosus larvae are less frequent. This is a response encouraged by an inherent positive phototaxis on the part of T. gregarius which is not shared by C. plumosus. In addition, the thin layers of sediment found at the periphery make the shore an unsuitable situation for C. plumosus. The size of competing larvae, rather than the species, is shown to be critical in determining the outcome of competition for space. Since C. plumosus are 362 .+-. 24% longer than the largest T. gregarius larvae, competition is invariably won by C. plumosus.