When some rodent species with asymmetric interspecific relationships coexist sympatrically, subordinate species may change its foraging behavior, possibly to enhance its foraging efficiency. In Japanese forests, Apodemus speciosus and Apodemus argenteus inhabit the same area, where A. speciosus is larger in body size and thus likely superior in interspecific competition than A. argenteus. These two species can distinguish between sound chestnuts and insect-infested chestnuts with exit hole of moth larvae (hereinafter referred to as EH nuts), and tend to remove sound ones preferentially. Therefore, the foraging behavior of A. argenteus may change depending on whether A. speciosus is present or not. In this study, to verify this behavioral change, we conducted a series of field tests over three consecutive days using an arena (a plot of forest floor enclosed by walls).
Each day, three sound nuts and three EH nuts were placed on one feeding dish set up in the arena, with a sensor camera installed to record the mice's behavior at this dish. On DAY 1, one A. argenteus was introduced to the arena under solitary condition to survey the order in which the mice removed the nuts (removal order) and their behavioral patterns during this process (removal behavior). On DAY 2, one A. speciosus was added to the arena to investigate some direct interspecific interference. On DAY 3, A. speciosus was removed from the arenas, and A. argenteus was returned to solitary condition. The results of removal order and removal behavior were compared with those of the DAY 1.
Under solitary conditions, A. argenteus preferred sound nuts to EH nuts. They often examined these nuts before removing them. Under co-habitation conditions, A. speciosus exhibited unilaterally chasing behavior toward A. argenteus. When returned to solitary conditions, A. argenteus behaved in a similar manner observed on DAY 1.
Based on above findings, this presentation will discuss the foraging strategy of A. argenteus for chestnut, taking into account the presence or absence of A. speciosus.