Effects of Density and Microdetritus Enrichment on the Growth of Chironomid Larvae in a Small Pond

Densities, species-ratios, and food regimes of chironomid larvae were manipulated in enclosures placed in a small prairie pond, and effects of these treatments on the growth rates of larvae of Chironomus riparius and Glyptotendipes paripes were measured. These two species have tubiculous microphagous larvae that make up the majority of the benthos of the study pond. Intraspecific density effects strongly reduced growth rates for both species; however, interspecific effects were weak and sometimes not statistically significant. Chironomus riparius responded to the addition of sedimented microdetritus with a substantial increase in its growth rate, whereas G. paripes showed no response. The results indicate that the larvae of the two species can coexist stably at densities high enough to result in substantial intraspecies competition, and that differences associated with their mode of feeding contribute to resource partitioning. A sharp reduction in chironomid larval densities resulting from poor weather during the emergence period showed that the abiotic environment can override density effects in determining year-to-year abundance of these larvae.