Alien war: ectoparasite load, diet and temporal niche partitioning in a multi-species assembly of small rodents

Interspecific interactions shape the structure of animal communities, and they rely on a number of multifactorial mechanisms, including e.g. activity rhythms, ectoparasite prevalence, predation pressure and food habits. Despite this, no study has analysed multispecies interactions by combining such a high number of aspects, mostly because the experimental manipulation of studied populations is rarely possible. In our work, we assessed several aspects of interspecific interactions in a rodent assembly composed by three species, by examining diet and temporal- niche partitioning, as well as relevant ectoparasite load and predation pressure, in a natural environment. We analysed stomach contents and ectoparasite load of 78 individuals belonging to all the species, whereas activity rhythms were measured with camera trapping (2200 night-traps, throughout 1 year). Our findings showed that the largest-sized species, i.e. the brown rat Rattus norvegicus was the strongest competitor and may affect diet, temporal behaviour and susceptibility to parasites of smaller-sized ones, i.e. the black rat Rattus rattus and the house mouse Mus domesticus. Larger-sized species showed a broader trophic niche with respect to smaller-sized ones, whereas the smallest species seemed to avoid the largest ones by shifting its temporal activity when the latter was mostly inactive. Larger-sized species may also act as potential predators towards smaller ones, which are also more vulnerable to ectoparasite infestation and to the predation by the only raptor bird present in the study area, the barn owl Tyto alba. We therefore highlight the importance to carry out community-wide studies, to understand interspecific intraguild relationships.