Reproduction Activity of an Epigeic Earthworm Species (Dendrobaena octaedra) as Affected by a Complex of Environmental Factors

Lumbricid earthworms as ecosystem engineers are of a profound significance for the functioning of detrital food webs; hence, their responses to effects of soil environment need to be investigated for a better understanding of their activities. However, despite the ample knowledge on the effects of various soil parameters, studies on their combined effects on earthworm performance are rare. In the present study reproduction activity of an epigeic species, Dendrobaena octaedra, was experimentally assessed as affected by a combination of several parameters of soil environment (namely, temperature and moisture constant and fluctuating regimes, amount of leaf-litter food resource and presence of conspecifics), in the gradients of their intensity in the nature. Temperature regime most significantly explained the rates of offspring production in D. octaedra. The range of daily temperature fluctuations around the reproductive optimum (15°C) was the major factor determining the variation of earthworm fecundity and biomass loss, apparently promoting a reallocation of available resources between self-maintenance and reproduction effort. In contrast, changes in moisture from constantly moist litter to fluctuations between wet—relatively dry litter did not prove significant suggesting a considerable tolerance of D. octaedra reproduction activity to variations in moisture regime. Amount of litter—food and shelter of earthworms showed a subordinate significance. A second important factor was intraspecific competition strongly negatively affecting reproduction rates in D. octaedra. Possible consequences of these effects for carbon budget of earthworm individuals and dynamics of field populations are discussed.