INTRODUCTION

Primates comprise the most intensively investigated mammalian order, with the vast majority of genera having been subjected to at least one single-species ecological study. It is thus paradoxical that primates still remain so poorly studied at the level of species assemblages, from the perspective of either synecological studies restricted to a single site (Terborgh, 1983; Peres, 1993a) or comparisons of multiple sites within or between continents (Bourlière, 1985; Waser, 1986; Peres, 1997a). As a consequence, many questions related to the determinants of local species richness and community assembly rules are yet to be addressed to primates (but see Cowlishaw & Hacker, 1997; Ganzhorn, 1997). This volume, therefore, goes some way towards a timely paradigm shift from the traditional emphasis on behavioral studies of primate groups and individuals to macroecological studies of populations and communities.

In this chapter we present a large-scale analysis of the structure of New World primate communities from the northern tropical forest frontier of southern Mexico to the subtropics of northern Argentina and southernmost Brazil (Appendix 3.1). Our primary goal is to examine the biogeographic determinants of species assemblages at a spatial scale covering the entire platyrrhine primate radiation. We investigate the effects of latitudinal gradients, forest types, extent of forest cover, and amount of rainfall on the central question in mainstream community ecology of how many species can coexist within a given area. Despite the nearly universal pattern of higher species diversity at lower latitudinal regions (Schall & Pianka, 1978; Brown & Gibson, 1983; Stevens, 1989; Pagel et al., 1991; Ruggerio, 1994; Eeley & Lawes, this volume), this relationship has been largely tested using widely distributed taxa occurring in both tropical and temperate habitats.