Inter- and intraspecific interactions in lumbricid earthworms: Their role for earthworm performance and ecosystem functioning

SummaryEarthworm species differentially affect organic matter and energy transformations, and interrelationships among soil food web components. Hence, knowledge of earthworm species associations and their interactions is important not only for an understanding of the functioning of soil systems and predicting the consequences of invasions of peregrine earthworms for native earthworm fauna, soil food web structure and functioning, but also for the structure and functioning of the aboveground food web. Over 60 studies investigating a total of 19 species and about 20 response variables were studied to summarize the scattered information on inter- and intraspecific interactions in lumbricids. Information on interactions between species is restricted to species pairs, while there is no data on species interactions within more complex associations. For further analysis, interactions were classified into positive and negative (i.e., those enhancing or decreasing the fitness of a given species). Based on this approach, “interactive portraits” (combinations of responses and effects) for six widespread species and for major ecological groups of earthworms were composed. Species and group characteristics were confirmed by meta-analysis. In multispecies communities, species strongly react to species composition and community structure with the mechanisms of species interactions likely being context-specific. Interactions between both species and ecological groups strongly affect soil biota and soil processes, with synergistic and neutralizing effects being most important. At the species level, lumbricids are among the few groups of soil invertebrates where density-dependent regulation of populations appears to be prevalent. These conclusions have important implications for the role of earthworms acting as ecosystem engineers in terrestrial systems.