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Analysis of a freshwater benthic community with special reference to the chironomidae. Hamilton, Andrew Lloyd

Abstract

The macroscopic bottom fauna of Marion Lake, British Columbia, was investigated from May, 1963 to September, 1964. The primary object was to document seasonal differences within and between specific populations and to interpret these difference in terms of the life histories of the species and their availability to a predator, rainbow trout. A detailed examination of the 51 species of Chironomidae known to occur in the lake has shown that the ecological characteristics of many of the closely related species are very different. Small species generally fed primarily on phytoplankton while the larger species ate more detritus and organic debris or other invertebrates. Predaceous species had more uniform distributions in the lake than did herbivores or detritus feeders. Most species of the subfamily Orthocladinae emerged in spring or fall and grew rapidly during the winter. The species of Chironominae and Tanypodinae usually emerged during the spring and summer and grew very little during the winter. Summer emerging Chironominae emerged later over deep water whereas the Tanypodinae emerged at much the same time above all depths. Larvae which underwent frequent vertical migrations had a higher mortality rate and were found more frequently in the stomachs of rainbow trout than larvae which rarely or never migrated. Many of the benthic organisms were not effectively utilized by rainbow trout. Organisms which numerically constituted approximately 1.5% of the benthic fauna accounted for more than 50% of the food items found in the trout stomachs. Large forms, such as the Odonata and Trichoptera and species which frequently moved off the bottom, formed the bulk of the food; small species and some of the species which were entirely benthic were rare or absent in the trout stomachs analyzed. This study has shown some of the advantages of working at the species level. Although studies at this level are tedious and often necessitate a time consuming taxonomic study, the additional information is likely to justify the extra effort. The results of ecological investigations that are not carried out at the species level ignore, or at best oversimplify, relationships that exist. Indeed, a comprehensive understanding of, for example, energy transfer within a community, is impossible without a detailed knowledge of the life histories of the species involved.

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