The Makapansgat Valley is located in Limpopo Province, South Africa (Figure 7.1), and is the northernmost of the South African australopithecine fossil sites. Hominin fossils were first recovered there in 1947, but the history and significance of the valley dates to the nineteenth century. The name of the site and valley derives from the Historic, or Gwasa, Cave at the head of the valley, which was the location of a siege in 1854 (Naidoo, 1987; Esterhuysen et al., 2008) on local Ndebele tribespeople by a Boer Commando in retaliation for two massacres – themselves retaliation for raids for ivory and slave labor by the Boer on Ndebele villages. The chief was Mokopane, and the cave became known as “Makapan’s Cave” or -gat in Afrikaans.

Fossiliferous sediments of the Hadar Formation (Afar, Ethiopia) are preserved in the Hadar, Dikika, Gona, and Ledi-Geraru research areas, and have produced the most informative record of the mid-Pliocene hominin Australopithecus afarensis. Hundreds of specimens of A. afarensis have been recovered from the Hadar site, including a partial skeleton (A.L. 288–1), two nearly complete adult skulls (A.L. 444–2; A.L. 822–1), and a dense accumulation of hominin individuals of various ages (A.L. 333; Johanson et al., 1978b; Kimbel et al., 1994; Kimbel and Delezene, 2009). Across the Awash River at Dikika, a juvenile hominin skeleton (DIK-1–1) was recovered and possible evidence of hominin carnivory ~3.4 Ma based on cut-marked bone was reported from Hadar Formation sediments (Alemseged et al., 2006; McPherron et al., 2010; Thompson et al., 2015). Thus, the outcrops of the Hadar Formation, particularly those at Hadar, have been tremendously important in interpreting Pliocene hominin evolution in eastern Africa.

Introduction

Climatic and subsequent habitat change has often been invoked as a driving force of evolutionary change in hominins, mammals, and other taxa (Vrba 1988a, 1988b, 1992, 1995; Bromage & Schrenk 1999; Potts 1998; Bobe & Eck 2001; Janis et al. 2002). Global climatic change in the mid Pliocene Epoch has been suggested as a cause for hominin speciation events (Vrba 1995) and is correlated with changes in dentition and jaw morphology of two hominin lineages (Teaford & Ungar 2000). Climatic change also influences seasonality, such that drying trends, for example, likely instigate short wet seasons, while the reverse is also true. Although Foley (1987) indicated that seasonal differences were likely important in determining hominin foraging effort, and Blumenschine (1987) posited a dry-season scavenging niche for Pleistocene hominids, little attention has been given to how seasonal changes over time might contribute to differences among hominin behavioral adaptations. Seasonal changes refer to changes in the lengths of regular four-season patterns in temperate climates or wet and dry seasonal differences in the tropics over geological time.

Evolutionary changes in fossil hominins are detected through changes in morphology that represent different behavioral adaptations. Fossil hominin diets are inferred from comparisons with extant primates in features such as tooth size (Hylander 1975; Kay 1984; Ungar & Grine 1991), molar shearing crests (Kay 1984), dental microwear (Grine 1981; Teaford 1988; Ungar 1998), biomechanics (Hylander 1988; Daegling & Grine 1991), and isotopic signatures (Sponheimer & Lee-Thorp 1999; van der Merwe et al. 2003).

Introduction

Over four decades, Charles Oxnard has been a relentless pioneer in expanding the quantitative horizons of research in primate and human evolution. His many works using multivariate analyses to elucidate and amplify our understanding of the primate shoulder, the primate foot, primate locomotion, prosimians, primate limb proportions, and the relationships of early hominids are well known and widely cited (Ashton et al., 1965, 1975, 1976; Oxnard, 1981, 1984). Less widely cited are his efforts with Robin Crompton and Susan Lieberman to use many of the same quantitative techniques to examine broad patterns in primate behavior and ecology (Crompton et al., 1987; Oxnard et al., 1990). In recent years we have made several efforts to redress this oversight (Fleagle and Reed, 1996, 1999a; Reed, 1999), and it seems particularly appropriate to provide here a general summary of that work. Charles Oxnard is more than a gifted quantitative biologist; he is also a person who delights in reducing the seemingly insurmountable complexity of nature to simple and often esthetically pleasing patterns. Yet, at the same time, he has always been keen to push his analyses one more step and demonstrate that a dataset may yield very different patterns when viewed from a slightly different perspective. Accordingly, in the spirit of Charles's work we will concentrate on some of the broader patterns that emerge from our studies of primate communities when we look at the same dataset from a slightly different perspective.

INTRODUCTION

As many studies in this volume and elsewhere have noted, there are persistent differences in the ecological characteristics of the individual species assemblages found on different continents (Terborgh & van Schaik, 1987; Fleagle & Reed, 1996; Kappeler & Heymann, 1996). For example, the primates of the Neotropics tend to be smaller and less ecologically diverse than those of other continents, while Madagascar has a larger number of folivores than other biogeographical areas. It seems almost certain that the differences between the primate assemblages of different biogeographical regions are the result of many causal factors and their interactions, including differences in productivity, in the composition of the plant communities, in climate and soil, and in the potential for competition with other groups of vertebrates. These factors are examined in other chapters of this volume.

However, the primate assemblages we see today are not simply epiphenomena of present ecological conditions. Rather, they are also the product of evolutionary and ecological processes that have been ongoing for millions of years. Environments are not stable today, and they never have been; they are constantly changing. The temporal scale of environmental change ranges from decades and centuries for human-induced activities of habitat destruction such as logging, land clearing, hunting, or introduction of exotic species (Struhsaker, chapter 17, this volume) and also for natural epidemics. Global climatic cycles seem to have periodicities ranging from a few years, such as the El Niño phenomena to tens of thousands of years for the glacial cycles that have dominated the past two million years (Tutin & White, chapter 13, this volume; Potts, 1994).

INTRODUCTION

The studies of primate communities that have compared primate species' ecological characteristics have found major differences among Africa, the Neotropics, Asia, and Madagascar (Raemaekers et al., 1980; Bourlière, 1985; Terborgh & van Schaik, 1987; Gautier-Hion, 1988; Ganzhorn, 1988, 1992; this volume; Terborgh, 1990; Fleagle & Reed, 1996; Kappeler & Heymann, 1996; McGraw, 1998). These studies have also shown ecological patterns within the same continental areas. However, most of these previous studies compare ecological differences among primate communities on different continents with attributes of individual species, i.e., contrasts in size, diet, and locomotor adaptations among individual species within communities. The unit of analysis is the species. Using these data, Fleagle & Reed (1996) showed that overall ecological space represented by ecological data occupied by primate species in communities were quite similar within continental areas, and were different between them. Thus, each primate species within each community held a particular position in ecological space (Hutchinson, 1978).

However, primates, for the most part, do not live individually. The density of primates, as well as diversity, presumably affects the size and shape of the ecological space that each community holds. For example, mammalian population density has been directly related to the size of an animal such that as animals get larger their population densities usually decrease (Fa & Purvis, 1997). It has been suggested that the scaling of this phenomenon is approximately the same for all mammalian herbivores (Damuth, 1981). Peters (1983) proposes that one of the most important reasons that population density falls with increasing body size is the constraint of food supply.

Following upon the chapters in the first section of this volume, which provided geographically restricted overviews of a single biogeographical region, the chapters in this section have provided broad comparisons between the primates of different regions. Fleagle & Reed (chapter 6) review the fossil record of primate evolution over the past 60 million years and examine the relationship between quantitative measures of ecological distance and phylogenetic divergence times within and between communities in the four major geographical regions. Their results indicate that the rate of ecological divergence between pairs of taxa is constant for primates of all regions, but that the strength of the correlation varies depending upon the biogeographical history of the region. They find a major distinction between the extant faunas of Africa and Asia, which contain elements from many different radiations from the past 60 million years and show a high correlation between divergence time and ecological distance, and the faunas of South America and Madagascar that are the result of more temporally restricted explosive radiations.

In contrast to most of the chapters in this volume which compare communities in terms of the component species, Reed's chapter 7 compares modern communities in the four geographical areas from the perspective of how much primate biomass is supported by different types of resources. Comparing the body masses of primates in different regions, she finds Asian communities stand out in having a very restricted size range compared with primates of the other regions.

Ganzhorn (chapter 8) compares patterns of body mass among the primate communities of different biogeographical regions to examine the extent to which there is evidence for competition among primate species within communities.

The chapters in this section have provided a series of geographically focused reviews of the diversity of ecological communities in the four major biogeographical regions currently inhabited by non-human primates – Africa, Asia, Madagascar, and the neotropics of South and Central America. The comparative data that are available for these different regions are by no means uniform. As a result, these chapters not only offer an opportunity to compare the similarities and differences in the primate communities of these different regions, but also highlight the gaps in our current knowledge. Despite differences in the scope and focus of the different chapters, several general themes emerge in the intraregional studies found in this section.

In all of the chapters, the authors emphasized that there are very few primate communities in the world today that have not been affected in some way by human activity (see also Tutin & White, chapter 13, Peres, chapter 15 and Struhsaker, chapter 17, this volume). In addition, it is important to keep in mind that many of the sites where primates have been most thoroughly studied have often been chosen precisely because they have extremely high numbers of species and often easy access from roads. As a result all comparisons either within regions or between them need to make some attempt to take these factors into consideration.

The chapters in the preceding section have reviewed evidence that the present structure of primate communities is affected by resource abundance (Janson & Chapman, chapter 14, Peres, chapter 15), food quality and digestive strategies (Janson & Chapman), seasonality (Janson & Chapman; Tutin & White, chapter 13), disease (Tutin & White), contemporary hunting (Peres), recent land-use history (Tutin & White), climatic change in the recent past and the Pleistocene (Tutin & White; Eeley & Lawes, chapter 12), and regional species source pools (Eeley & Lawes; Peres). Despite the diversity of these themes, they fall into two broad contrasts which we shall use to review the preceding results: (1) local vs. regional explanations of primate community structure; and (2) equilibrial vs. nonequilibrial views of community structure.

LOCAL VS. REGIONAL DETERMINANTS OF PRIMATE COMMUNITY STRUCTURE

There is a tension between explanations that rely on local versus regional ecological factors to explain local site diversity. Local factors include resource abundance and quality, seasonality, competition and contemporary hunting. Regional analysis focuses on regional source pools of species – a local site cannot have a primate species that is not in the regional source pool. This distinction is essentially parallel to that between alpha-and gamma-diversity in community ecology. Alpha-diversity reflects the number of coexisting species in a single site, whereas gamma-diversity includes additional species that may replace each other in separate areas of similar habitat only because of geographical isolation. Proponents of local factors find support in the fact that primate population densities predictably increase in areas of greater soil fertility (Peres), high food quality (Janson & Chapman), and low hunting pressure (Peres).

During the last four decades, the primates of Africa, Asia, Madagascar and South America have been the subject of hundreds of field studies involving millions of hours of observation. Despite this remarkable effort, there have been only a handful of attempts to undertake broad comparisons of the primate faunas in different biogeographical regions in order to document and understand their similarities and differences. This volume is an effort to make a start in addressing that major gap in our understanding of primate evolution. By bringing together a group of researchers with many decades of combined experience in all the major regions of the world inhabited by primates today, we hoped to summarize our current understanding of the factors determining primate community biology, highlight the many lacunae in our knowledge, and provide a baseline for future research in the area.

Like many projects of this nature, this one has a long history and has only been possible through the efforts and generosity of many people and organizations, especially the citizens and governments of countries inhabited by non-human primates today who have permitted and supported the research by primate field workers that ultimately formed the basis of the studies summarized here. The Wenner–Gren Foundation provided funds, and the Department of Anthropology at the University of Wisconsin provided the space, for a workshop on “Primate Communities” in 1996 that enabled many of the authors to discuss this topic face-to-face over three intense days in Madison, Wisconsin. We especially thank Dr Sydel Silverman, President of the Wenner–Gren Foundation, and Drs Karen Strier and Margaret Schoeninger for their support of the workshop. Joan Kelly was indispensable in organizing the workshop.

The goal of this volume was to bring together the efforts of scientists with research interests and experience from many parts of the world to provide a comparative perspective of the primate communities or assemblages from different biogeographical regions. The preceding chapters have taken a wide range of approaches to the study of communities including: (1) broad surveys and analyses of the diversity of communities within individual regions; (2) detailed examinations of the factors that underlie community differences at both a microecological level and a macroecological level; (3) comparative study of the relationship between primate diversity and that of other aspects of the fauna and of the flora; and (4) attempts to put extant communities in a temporal perspective through examination of the history of individual and regional faunas and habitats, as well as attempts to predict changes that primate communities are likely to undergo in the coming years if present patterns of extinction continue.

COMMUNITY DIFFERENCES

In general, most authors seemed to find the differences among communities far more impressive than the overall similarities among communities. The chapters by Kappeler, Reed, and Ganzhorn (chapters 9, 7 and 8 respectively) found significant differences in the body size distributions of primates from different regions both at a regional level and for individual communities. Fleagle & Reed's chapter 6 (see also Fleagle & Reed, 1996) documented differences in the ecological space occupied by individual communities of primates of different regions. Recently, Jernvall & Wright (1998) obtained very similar results using the same technique on a different data set for the primates of entire biogeographic regions.