The Role of Feral House Mice in Ecosystem Functioning on Marion Island

Abstract

The chief prey of feral house mice on Marion Island is larvae of the flightless moth Pringleophaga marioni Viette (Tineidae), which constitute about 50% of their diet throughout the year. The litter-dwelling, detritivorous larvae take more than 2 years to mature, during which time they process (i.e. fragment, ingest and excrete) large quantities of litter. At an annual mean biomass of 9.3 kg ha−1, and an individual consumption rate of approximately 0.6 × their own mass in litter daily, P. marioni larvae are estimated to process at least 1500 t of litter annually on Marion Island’s vegetated coastal plain (all results expressed as dry mass). The larvae facilitate the release of nutrients from plant litter through their feeding activity and the resultant enhancement of microbial decay. Mice remove daily 65 g ha−1 or 0.7% of the standing crop of P. marioni larvae on the island’s coastal plain. The indirect effect of mouse predation, through the removal of a large proportion of decomposer biomass and subsequent impediment of nutrient mineralization, has implications for the functioning of the decomposer subsystem of the Island’s terrestrial ecosystem. Since mice and their prey appear to be in dynamic or even stable equilibrium, the direct impact of mice through predation may be eclipsed by these indirect detrimental effects to nutrient cycling.