Context-dependent responses of food-hoarding to competitors in Apodemus peninsulae: implications for coexistence among asymmetrical species.

Superior species may have distinct advantages over subordinates within asymmetrical interactions among sympatric animals. However, exactly how the subordinate species coexists with superior species is unknown. In the forests west of Beijing City, intense asymmetrical interactions of food competition exist among granivorous rodents (e.g. Apodemus peninsulae, Niviventer confucianus, Sciurotamias davidianus and Tscherskia triton) that have broadly overlapping habitats and diets but have varied body size (range 15-300 g), hoarding habits (scatter vs larder) and/or daily rhythm (diurnal vs nocturnal). The smallest rodent, A. peninsulae, which typically faces high competitive pressure from larger rodents, is an ideal model to explore how subordinate species coexist with superior species. Under semi-natural enclosure conditions, we tested responses of seed-hoarding behavior in A. peninsulae to intraspecific and interspecific competitors in the situations of pre-competition (without competitor), competition (with competitor) and post-competition (competitor removed). The results showed that for A. peninsulae, the intensity of larder-hoarding increased and the intensity of scatter-hoarding declined in the presence of intraspecifics and S. davidianus, whereas A. peninsulae ceased foraging and hoarding in the presence of N. confucianus and T. triton. A. peninsulae reduced intensity of hoarding outside the nest and moved more seeds into the nest for larder-hoarding under competition from intraspecific individuals and S. davidianus. In most cases, the experimental animals could recover to their original state of pre-competition when competitors were removed. These results suggest that subordinate species contextually regulate their food-hoarding strategies according to different competitors, promoting species coexistence among sympatric animals that have asymmetrical food competition.