Interannual Variation in Nut Abundance Is Related to Agonistic Interactions of Foraging Female Japanese Macaques (Macaca fuscata)

Abstract

The importance of dominance status to foraging and ultimately survival or reproductive success in wild primates is known; however, few studies have addressed these variables simultaneously. We investigated foraging and social behavior among 17 adult female Japanese macaques (Macaca fuscata) on Kinkazan Island, northern Japan, from September to November in 2 consecutive years (2004 and 2005) to determine whether interannual variation in food availability was related to variation in agonistic interactions over food resources and the feeding behavior of individuals of different dominance rank. We compared energy obtained with daily energy requirements and also examined the effect of variation in feeding behavior on female survival and reproductive success. Fruiting conditions differed considerably between the 2 yr: of four nut-producing species, the nuts of only Torreya nucifera fruited in 2004, whereas all four species, particularly Fagus crenata, produced nuts in abundance in 2005. The abundance and average crown size of trees of Torreya nucifera were smaller than those of Fagus crenata, and there was a higher frequency of agonistic interactions during 2004, when dominant, but not subordinate, individuals were able to satisfy daily energy requirements from nut feeding alone through longer nut feeding bouts. In contrast, all macaques, regardless of their dominance rank, were able to satisfy their energy requirements by feeding on nuts in 2005. Subordinate macaques appeared to counter their disadvantage in 2004 by moving and searching for food more and maintaining larger interindividual distances. Several lower-ranking females died during the food-scarce season of 2004, and only one dominant female gave birth the following birth season. In contrast, none of the adult females died during the food-scarce season of 2005, and 12 females gave birth the following birth season. These findings suggest that an interaction between dominance rank and interannual variation in food availability are related to macaque behavior, survival, and reproduction.