ESTIMATION OF EARTHWORM COCOON DEVELOPMENT TIME AND ITS USE IN STUDIES OF IN-SITU REPRODUCTION RATES

Data from the literature on development rates of earthworm cocoons wer e used to predict the time of hatching of cocoons incubated in the fie ld. The numerical integration of a deterministic equation with the inc orporation of individual variation in development rate made it possibl e to predict the hatching lime distribution of a sample of cocoons pro duced over one week with good precision. This was shown for three spec ies of earthworms, Aporrectodea caliginosa, Allolobophora chlorotica, and Dendrobaena octaedra. By reversing the direction of time, the same algorithm finds the probability distribution for the expected product ion time of a cocoon, whose time of hatching is known. It is suggested that the method can be applied to cocoons sampled from soil cores and incubated in the laboratory. Thus, the most probable production time for each cocoon can be determined with its confidence interval; subseq uently, the number of cocoons produced per square meter during a given time interval can be calculated. If the density of adult earthworms i s known for the same time interval, the reproductive rate (based on su rviving cocoons) can be estimated. (C) 1997 Elsevier Science B.V.