Here we present data on polyspecific associations for several social groups within our primary study grid. The focal subjects were two groups of Procolobus badius (bad1 and bad2) and two groups of Cercopithecus diana (dia1 and dia2). Association data on the Procolobus badius groups were collected between June 1996 and May 1998 while association data on the Cercopithecus diana groups were collected between April 1997 and May 1998. On most observation days we followed a focal group from 7:00 h to 17:30 h. Data on association behavior were collected at every one-hour interval and one hourly group scan represents a single data point. During each hourly scan, we recorded the number of species “in association” with the focal species. Groups of different species were considered associated when the distance between imaginary polygons connecting the most outermost members of each group was less than 25 m. Association rates were calculated by dividing the time each group was seen “in association” with another species by the total observation time. In late 1997 both Procolobus badius groups divided into subgroups, each of which had a preferred Cercopithecus diana association partner.

The study of primate behavior and ecology has been an ongoing area of research for over 50 years, building on the pioneering work of such people as C. R. Carpenter, Washburn and DeVore, C. R. L. Hall, J. J. Petter, and the Altmanns. There are relatively few of the 300 plus species of living primates that have not been the object of at least a survey; many have been studied for a complete year; and a few taxa have been the subject of long-term efforts lasting decades (e.g. Strier et al. 2006). Primatology has grown to become an integral part of anthropology or zoology in most parts of the world and a discipline that is the focus of numerous national and international organizations, more than half a dozen specialist journals and numerous book series.

Although year-long studies of a single species have long been the standard research protocol in primatology, some of the greatest advances in our understanding of primate behavioral ecology have come from coordinated studies of numerous species at a single site. Because all of the species are living in the same habitat with identical climatic and phonological variations, they enable a clearer insight into species-specific differences and similarities in adaptive strategies. The comparative, synecological studies of the primate assemblages such as those conducted at Makokou in Gabon, Morondava in Madagascar, Kibale Forest in Uganda, Kuala Lompat in Malaysia, Raleighvallen-Voltsberg in Suriname, and Manu in Peru stand out as milestones in the history of primatology and have disproportionately advanced our understanding of the relationship between behavior and ecology in primate evolution.

Introduction

Primates live in habitats in which food abundance and other resources fluctuate over time, usually on a seasonal basis, and space. This variation affects the lives of primates in many ways, from behavioral ecology to reproduction (see Chapters 3 and 11). In this chapter, we explore how environmental and behavioral seasonality affect sexual dimorphism.

Sexual dimorphism in body and canine size among primates generally is viewed as primarily a consequence of sexual selection operating through the mechanism of male–male competition for mates (Leutenegger & Kelly 1977; Clutton-Brock et al. 1977; Kay et al. 1988; Plavcan & van Schaik 1992, 1997; Ford 1994; Lindenfors & Tullberg 1998) and modified by female choice for male traits (Plavcan 2004). Sexual dimorphism can be affected by environmental seasonality in two independent ways (see Fig. 14.1): first through the indirect impact of seasonality on the potential for mate monopolization (Mitani et al. 1996a; Nunn 1999; Pereira et al. 2000), and second through the direct impact of seasonality on male and female body size (Albrecht 1978; Turner et al. 1997). In the first case, phenological or climatic seasonality brings about the simultaneous presence of multiple cycling females due to reproductive seasonality and also may favor larger female group size. These effects in turn should affect the number of males present in a group, and patterns of male–male competition and resulting reproductive skew – in other words, several aspects of social organization and the mating system, all of which are tied to sexual dimorphism.