INFLUENCE OF POPULATION-DENSITIES ON GROWTH AND REPRODUCTION OF THE EARTHWORM EISENIA-ANDREI ON PIG MANURE

The development of groups of 3, 6 or 12 individuals of the earthworm Eisenia andrei fed with fresh solid pig manure was studied in 1 litre vol. The resulting populations were described in numbers and biomasses by cocoon production, different size classes and fertility stage during a period of 230 days. The total number of clitellate worms and cocoon production reached their summit after ca 175 days, with worms from the F1 generation becoming clitellate for a period of < 60 days, which is a very short period compared to a clitellate period of at least 150 days for the parental generation. Cocoon production and net recruitment had nearly ceased at the end of the period. The group of 12 individuals initially showed a more restrained development than the smaller groups as the F1 generation peak was much more pronounced than the F2 generation peak was. The growth of the total number of worms in the largest group was evolving lineary, while the less dense groups were growing more unrestrained, sigmoidally. All of the monitored groups of worms in the limited volume seemed to approach a high constant density with a homogeneous population composed of nonfertile worms > 100 mg, originating from both smaller slow-growing worms and degenerating clitellate worms. The relative growth was related to time in an exponential decreasing way and the conversion ratio was decreasing from 10 to 4% during the growth period. At the peak of the first generation the worms were ingesting about their own weight every day, but soon they were only ingesting their own weight once every week.