Five New World Primates: A Study in Comparative Ecology

by John Terborgh

Overview

Launching a new series, Monographs in Behavior and Ecology, this work is an intensive study of five species of New World monkeys—all omnivores with a diet of fruit and small prey. Notwithstanding their common diet, they differ widely in group size, social system, ranging patterns, and degree of territoriality.

Originally published in 1984.

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Product Details

ISBN-13:	9780691613024
Publisher:	Princeton University Press
Publication date:	07/14/2014
Series:	Monographs in Behavior and Ecology , #622
Pages:	276
Product dimensions:	6.00(w) x 9.20(h) x 0.80(d)

Read an Excerpt

Five New World Primates

A Study in Comparative Ecology

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By John Terborgh

PRINCETON UNIVERSITY PRESS

Copyright © 1983 Princeton University Press
All rights reserved.
ISBN: 978-0-691-08338-4

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CHAPTER 1

Introduction

Primates are ideally suited for ecological study. Their size and diurnal habits put them comfortably within the range of human sensory abilities. Unlike birds, they can be followed and observed continuously throughout the daily activity period. But most importantly, primates gradually come to accept an observer as part of the landscape, or as just another participant in a mixed species troop. One gets to know each individual as a separate and distinct personality, and is privileged to observe the normal daily round of activity at close range without perturbing the course of events. The feeling of intimacy that one gains from this is certainly one of the greatest pleasures in studying primates. It is hard to think of another group of animals with such outstanding advantages.

But no matter how compelling these advantages may be, one does not simply walk into a new locality, even one as ideal as Cocha Cashu, and start observing monkeys. There are only a handful of places in the world where intact primate communities have been studied. Each one of them has required a major preliminary investment on the part of the investigators. At the very least, trails must be built and surveyed, and study troops must be habituated to the observers. Usually it is desirable to learn something about the population structure of the local primate community, the population densities of the various species, the size and composition of groups, the extent of home ranges, the amount of home range overlap, etc. Such background statistics are obtained by conducting extensive surveys employing protocols quite distinct from those used in detailed observations on habituated focal groups. For evaluating interspecific relationships it is important, in addition, to determine what the animals are eating. This calls for enlisting the collaboration of a skilled professional botanist, for the identification of plant specimens from most tropical regions requires a level of erudition that is utterly beyond the capacity of even a dedicated amateur. Finally, to interpret seasonal changes in diet and behavior, it is necessary to obtain data on the phenology of food resources. Obviously, not all these requirements can be met at once.

Our efforts began quite modestly in the summer of 1974. The station then offered little more than shelter; there were only the rudiments of a trail system and thus no ready access to much of the surrounding terrain. We had to spend the first weeks cutting trails on compass course, and were often surprised when the vegetation abruptly changed as we encountered swamps, canebreaks, and other features of the complex mosaic of habitats (Fig. 1.1). With the core of the trail system cut and surveyed, we spent the rest of the 1974 field season conducting a census of the primate community. As none of us had had any previous experience with primates, this also served to familiarize ourselves with the animals', and just as importantly, to familiarize the animals with us.

In this preliminary experience we were struck by the fact that among the eleven species present, there were great differences in troop size, social systems, activity patterns, and territorial behavior. There was nothing particularly unexpected in this, except that the first-hand experience of seeing it for oneself drove home the realization of how marked the differences between the species actually are. Another behavioral characteristic of some of the species also unavoidably attracted our attention. It was the tendency, very strongly developed, to join in mixed troops. This was especially interesting to me because at the time I was engaged in a study of mixed flocks of birds. Extrapolating from the avian flock systems with which I was familiar, there were some similarities in the behavior of the monkeys, but also some puzzling differences.

There were five primate species that participated in mixed troops. AU of them fed on ripe fruit and devoted a considerable amount of time to searching for insects, and none of them was seen to eat leaves. They could thus all be classified as omnivores and be regarded as occupying the same trophic level. What was peculiar about them was that they displayed a wide range of group sizes, social systems, and territorial behaviors. Among birds, by and large, this is not the case. Species on the same trophic level that eat similar things tend to live in very much the same way. The monkeys violated this generality and therefore seemed paradoxical.

Two major issues thus forced themselves on our thinking. The first was, Why should a set of species which superficially seemed so similar in their feeding habits diverge so conspicuously in their social systems and use of space? The second was, What motivated the formation of mixed troops of primates when in some respects the circumstances were at odds with the better-understood avian situation? We were now convinced of the potential theoretical interest of a comparative study.

Returning in the summer of 1975, we set out for the first time to follow troops and to make systematic observations on the five species. We made many mistakes, including losing the focal group all too frequently, but we gained valuable experience. Most critically, we developed a protocol that permitted us to make maximum use of the limited time provided by an academic vacation. Following monkeys on a day-by-day basis is a very exhausting proposition. By working as a team (Janson, Moskovits, Russell, and Terborgh), we found that we could easily maintain contact with the study troops for longer than the five-day sample periods that are customary in primatology. The shifts gave everyone time to transcribe data, and to participate in other kinds of activities related to the project, such as mapping trails and servicing fruit traps. We also had time to ourselves, an important factor in maintaining morale through a long stint in the field. With some free time to look forward to each day, the routine never became oppressive. We were able to keep animals under observation continuously (except for brief interruptions when we lost troops) for practically the entire time of our residence at the station.

The following year I was given a sabbatical leave and at the same time received a grant from the National Science Foundation. These favorable circumstances provided the opportunity to carry out the main body of the study. In a 12-month period, starting in August 1976 and ending in August 1977, we logged over 2,700 contact hours with our study troops, for an average of about 540 hours per species. Here the advantage of working as a team is clear. It is common in studies conducted by single observers to limit troop following to 5 days per month. Over a year this mounts up to about 60 days of observation, a level we were able to match for several species. In place of short samples each month, we elected to conduct much longer samples (ca. 20 days) at less frequent intervals of about 3 months. This schedule permitted us to resolve the characteristic ranging patterns of each species, which in some cases are not discernible in five-day periods, as well as to compare the diets and ranging of each species within each of the four annual seasons: wet, dry, and the transitions between them.

While following the monkeys, we took four kinds of data: activity status of the troop, troop movements, use of resource trees, and timed samples of foraging activity. These provide basic information on time budgets, ranging behavior, diets, and foraging techniques. These ecological parameters were consciously emphasized to obtain the best possible picture of each species' interaction with its environment. Our approach necessarily relegated detail on behavioral interactions, vocalizations, etc. to a back-seat position. While this may prove frustrating to some readers, it is simply not possible to record everything about five species in a single year's study. Continuing research at Cocha Cashu will, over time, fill out the behavioral picture for the five species included in this study, and for others as well.

The comparative approach is followed throughout. Conclusions are drawn deductively or inferentially and are based on the analysis of differences between the species. The adaptive meaning of what a single species does (in the absence of a comparative context to provide a frame of reference) is very difficult to interpret. The common practice in primatology of studying one species at a time has provided a great deal of valuable information on many species, but such studies have often failed to generate incisive questions, much less answer them. The comparative approach provides the necessary perspective for framing the salient questions. For this reason I have organized the book not as a series of chapters on each of the species, but as a set of topical discussions in which differences between the species are analyzed and interpreted.

The presentation consists of eleven chapters. Following the present introduction are two additional preliminary chapters that describe, respectively, the vegetation and climate of the study site, and the primate community. The text then continues with a series of chapters that lay out the principal results. Activity budgets are taken up first because a consideration of how animals spend time provides insights into the priorities in their lives. The next two chapters, numbers five and six, offer data on the diets of the five species as represented, respectively, by the amount of time spent feeding on various kinds of plant materials, and by timed sequences of the actions employed in foraging for animal food. The seventh chapter presents data on ranging behavior. Large differences between the species in their responses to a seasonally fluctuating food supply are brought out particularly strongly in this chapter, though the theme is one that appears in nearly every section of the book. In Chapter 8 the problem of mixed species associations is addressed in the light of the two main types of associations at Cocha Cashu, those between Cebus spp. and Saimiri, and between the two species of Saguinus. The principal adaptational variables involved in structuring ecological relationships in the entire Cocha Cashu primate community are the subject of Chapter 9. Our findings are compared with those of other studies of sympatric primates in other parts of the world. In the tenth chapter I attempt to synthesize what has been learned previously, emphasizing results that bear on observed differences among the five species in the use of space, territorial behavior, and mean group size. The eleventh and final chapter is a brief epilog that offers suggestions on how tropical forests might be managed in the future to provide resources for both humans and primates.

CHAPTER 2

The Study Site: Its Climate and Vegetation

Here I describe the environmental setting at Cocha Cashu. The chapter opens with a cursory account of the several types of vegetation that enter into the local habitat mosaic. Most of these are seral stages in successional sequences initiated by changes in the course of the river. Climatic data are presented next. Even though complete records exist for only a single year, there is no doubt that the region typically experiences a sharp alternation between wet and dry periods. This has far reaching consequences in driving the annual cycle of flowering and fruiting in the vegetation. In the latter part of the chapter it is demonstrated that the productivity of fruit by the forest follows a seasonal cycle of large amplitude, a fact that has profound implications for animals that depend on fruit as their primary food resource.

Habitats at Cocha Cashu

Riparian Succession

Cocha Cashu and all the terrain that lies around it on every side are creations of the Rio Manu. The sinuous meanderings of the river transform the landscape with a nearly imperceptible, though relentless, regularity. At each bend the forest is undermined and carried away at a rate of 5–20 m a year, while on the opposite, inside shore, new land is laid down in the form of broad beaches. Later, as the beaches are invaded by plants, they become incorporated into an incremental series of levee-backwater units. Thus, to walk into the rank vegetation bordering a beach is to walk backward in time, toward progressively older terrain, and progressively older vegetation.

Fronting the beaches are even-aged stands of Tessaria sp. (Compositae), a fast growing willow-like tree that springs up each year from seed at the beginning of the dry season. After two or three years, the Tessaria is invaded by heavy 10 m tall stands of cañia brava (Gynerium sagittum, Gramineae), which advance up to a dozen meters a year by means of vigorous underground runners. At this stage the Tessaria declines rapidly, half or more of the trees dying each year, so that few individuals see even as much as a decade. The caña phase is more prolonged. It is during this period that many tree species become established, including the ones which dominate later stages in the succession. The fastest growing of these is a species of Cecropia (Moraceae), which, in about 5 years, succeeds in overtopping the caña. For a brief interval Cecropia forms a nearly closed canopy over the caña, but Cecropia, like Tessaria, is short-lived, and gaps soon appear in the canopy. These are promptly filled by a number of other species: Erythrina spp. (Leguminosae), Guarea sp. (Meliaceae), Casearia sp. (Flacourtiaceae), Sapium sp. (Euphorbiaceae), Ficus insipida (Moraceae), and Cedrela odorata (Meliaceae). The latter two of these outgrow the rest, eventually forming a closed canopy at a much higher level than the Cecropia (ca. 40 m vs. 15–18 m). Unlike the preceding stages, the Ficus-Cedrela forest is long lived, with individual trees commonly attaining diameters of 1–1 ½ m, and ages well in excess of 100 years. The understory at this stage is a 3–4 m tall jungle of "platanillos," broad-leafed monocotyledonous plants in the banana (Heliconia-Musaceae), ginger (Costus, Renealmia-Zingiberaceae), and marantad families (Calathea, Monotagma-Marantaceae). These are more shade tolerant than the caña brava and invade subsequent to the Cecropia phase as the over-topped caña goes into decline.

Large areas in the Manu basin adjacent to the river are occupied by successional vegetation. The interiors of meander loops are filled with it. Because of the great regularity with which plant species replace one another in the canopy, and because each stage reaches a greater absolute height than the previous one, the successional vegetation is strikingly zoned. As viewed from the vantage of a passing boat, one sees an orderly sequence of stands — Tessaria, Gynerium, Cecropia, mixed forest, and Ficus-Cedrela — each forming a nearly discrete band of greater or lesser width running parallel to the adjacent beach. Of these, the Ficus-Cedrela association occupies by far the largest area by virtue of its vastly greater longevity. Eventually, however, the Ficus and Cedrela trees begin to die off, one by one, and are replaced by an entirely different set of species which form a forest of considerably greater diversity. The succession continues, in other words, to even more advanced stages, but the details have not been studied.

Successional vegetation along the Rio Manu is exposed to periodic inundation during the rainy season. Flooding results in the deposition of a fresh layer of silt each year, rejuvenating the already high fertility of the alluvium, and gradually raising the elevation of the terrain to equal that of the highest water levels. Tree growth is extremely rapid. Young specimens of Ficus insipida, Ochroma pyramidalis and other species may increase in circumference as much as 100–200 mm, or up to 30%, in a single year. Trees of similar size in climax forest rarely achieve growth rates even one-tenth as great. Whatever the reasons for this contrast, it is evident that successional stands are highly productive. This fact is widely recognized by immigrant settlers and indigenous inhabitants alike, as their agricultural efforts are typically concentrated in the upper levels of the flood zone. The high productivity of this zone, coupled with the breathtaking value of its Cedrela timber, has encouraged an intensive selective exploitation of Ficus-Cedrela forest wherever it occurs in the Amazonian headwaters region. Little of it remains in natural condition outside the Manu park.

Lacustrine Succession

Over many millennia the Rio Manu has carved a 6–8 km wide meander belt into the local topography. Wherever it contacts the fringing hills, the river cuts into them, creating steep banks, and depositing fresh silt in place of the eroded sediments. By this process, the meander belt is gradually widened, but judging from the paucity of such contact points, the rate of widening today is extremely slow. The fringing hills, barely 20–30 m above the present river level, are themselves composed of sandy alluvium, probably the remnants of a previous outwash plain.

(Continues...)

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Excerpted from Five New World Primates by John Terborgh. Copyright © 1983 Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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Table of Contents

• FrontMatter, pg. i
• Contents, pg. vii
• Preface, pg. ix
• 1. Introduction, pg. 1
• 2. The Study Site: Its Climate and Vegetation, pg. 8
• 3. The Primate Community at Cocha Cashu, pg. 25
• 4. Activity Pattems, pg. 40
• 5. The Use of Plant Resources, pg. 59
• 6. Foraging for Prey, pg. 96
• 7. Rangin Patterns, pg. 129
• 8. Ecology of Mixed Troops, pg. 155
• 9. Ecological Relationships in the Manu Primate Community, pg. 190
• 10. Synthesis nad Conclusions, pg. 211
• Epilogue, pg. 235
• Literature Cited, pg. 238
• Author Index, pg. 253