Parasitized but undeterred: how mice disperse seeds while coping with ectoparasites

Abstract

Ectoparasites are known to induce behavioural changes in their hosts, yet their downstream effects on other ecological interactions are less well understood. We examined the influence of ectoparasites on a key process in forest ecosystems: seed dispersal by their granivorous hosts. In a controlled field experiment, we manipulated ectoparasite loads on wild yellow-necked mice, Apodemus flavicollis, and monitored changes in various aspects of acorn, Quercus robur, dispersal: removal, recovery, consumption, caching and dispersal distance. Contrary to the hypothesis that ectoparasite-infested mice would change seed-handling behaviours due to increased foraging costs, our results demonstrated minimal impacts of ectoparasites on these behaviours. Initially, we observed marginally lower removal rates of acorns and shorter dispersal distances in the ectoparasite-reduced populations, which later aligned with the control groups. No significant differences were found in the probability of acorn recovery, modes of consumption or caching behaviours between the control and treated groups. Thus, the anticipated parasite-induced trophic cascade did not occur. These patterns suggest that yellow-necked mice exhibit behavioural tolerance of infestation, and their ecological role as seed dispersers remains unchanged despite ectoparasite infestation. Our findings challenge the assumptions regarding the severity of ectoparasitic impacts on host foraging behaviour.