Interspecific Interactions and Selective Feeding by Tubificid Oligochaetes1

Improved values of respiration and growth have been determined for three tubificid species. Maintaining the same individuals in mixed species culture before or after maintaining them separately lowered respiration by about a third, whereas lowering the population density of a single species had no such effect. The presence of Peloscolex multisetosus increased the weight gain of Tubifex tubifex and Limnodrilus hoffmeisteri by a factor of 2–3 times that in pure culture in a 6‐month period, although the first species seemed to remain unaffected. More energy was used for growth plus respiration when the three species were mixed than when maintained in pure culture. Attempts to measure ingestion and egestion were handicapped by failure to demonstrate a reduction in percent organic matter, percent nitrogen, or caloric content in feces as opposed to the mud presented as food; this indicates selective feeding. Further, variation in defecation rate was noted, which complicates the measurement of material cycling. The study suggests that the attempt to recreate energy or material budgets for communities from laboratory studies of isolated components is less promising than the attempt to study communities in situ.