A Simulation Model of Earthworm Invasions: 

The Impacts on Soil Nutrient Dynamics

Huang, C.-Y. and Hendrix, P. F.

Institute of Ecology, University of Georgia, Athens, USA

Recently, “species invasion” has become an important issue, because invasive species could completely change ecosystem structures and functions. Peregrine earthworm species have been introduced mostly by human activities (e.g., horticultural plant imports, habitat disturbance, and land-use changes) and distributions of these exotic earthworms now appear to overlap the range of native earthworms in many regions. Previous references indicated that native earthworm species have already disappeared in several areas that are now colonized by exotic species. Hence, the invasion of exotic earthworms could alter native earthworm communities and have an impact on nutrient cycling.

A simulation model has been developed to evaluate the potential impacts of earthworm invasions on nutrient cycles by considering three combinations of earthworm community structure: native earthworms only; exotic earthworms only; and native and exotic earthworms coexisting. This model also takes account of feeding and casting activities of the earthworms. Responses of several variables, including litter/soil organic matter, microbial biomass and earthworm population, have been evaluated. Preliminary results show that exotic earthworms induce slightly higher microbial biomass carbon and activities after one-year simulation time. However, this effect on microbes is suppressed when exotic and native earthworms coexist. For wider application in terrestrial ecosystems, more experimental data will be applied to calibrate and validate the model.