Significance of developmental stages in the coexistence of three species of Mononchoidea (Nematoda) in a pasture soil

Summary

Populations of each developmental stage of three mononchid species (Clarkus, Cobbonchus, Iotonchus) under grazed pasture were estimated in the presence and absence of the earthworm Aporrectodea caliginosa. All stages of all species had signs of prey in their gut. Introduction of earthworms changed the abundance of the species from 158000, 84000 and 2400/m² to 43 000, 5000 and 41300/m², but total biomass remained relatively unchanged at 288000 μg/m². The larger Iotonchus was more abundant in the soil with earthworms and improved texture. The length ratios between the stages of the three species are 1.225, 1.235 and 1.395, with the overall mean of 1.285 close to the value for the Dyar-Hutchinson rule. Other analyses of population separation are made. Given the unequal abundance of the various stages, the species successfully coexist and exploit a wide resource. Predation by such nematodes on bacterial-feeding nematodes may influence bacterial grazing and thus nutrient cycling.