Long-term density fluctuations and microhabitat use of sympatric Apodemus flavicollis and Myodes glareolus in central Italy

The role and importance of interspecific competition for rodent communities have been much debated issues, with some early authors suggesting that these are important, and several recent articles suggesting the contrary. In this paper, we studied, for 14 years at a mountainous locality in central Italy, the coexistence dynamics of a two-species system (Apodemus flavicollis, Myodes glareolus) within a 1.44 ha trapping grid, by Capture-Mark-Recapture. Overall, we captured over 1000 rodents during the study period, with annual abundance ranging 2-7 individuals × ha-1. However, the density of the two species varied substantially across years and between sectors of the study plot. Thus, the distributions of the two species on the scale of the study grid were not related to one another. Density of a given species did not affect the percentage of lactating females in either A. flavicollis or M. glareolus. Individual traps differed in their rate of capture such that about 40% of traps were associated more with a particular species. Considering the spatial distribution of traps, we determined that three areas were associated with high probability of capture for only one of the two study species, two of these areas being associated to A. flavicollis and one to M. glareolus. Our analyses suggest that interspecific competition may be present at the local micro-scale, as explained by the fact that in the great majority of the cases in which a given trap was highly successful in capturing one species, it was also very unsuccessful in capturing the other species. However, manipulation experiments are needed to confirm that suggestion.