TABLE OF CONTENTS
Acknowledgments
PART 1. INTRODUCTION
Introduction - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0001
[gorillas, socioecology, primates, tropics, conservation, survival, mating, gorilla society, strategies]
Socioecology is the study of how individuals' evolved survival, mating, and rearing strategies interact with the physical and social environments to produce the sort of society that we see. Primates, which live mostly in the tropics, are useful subjects of study in socioecology because they are so relatively well known, and their societies are so varied. Gorillas are an interesting primate because, being the largest bodied, they are an extreme, and extremes are always a good means of testing generalities. This book provides an easy introduction to modern thinking about socioecology in general and primate socioecology in particular by presenting the equivalent of a worked example of how socioecologists attempt to explain the nature of an animal's society. It explores the different survival, mating, and rearing strategies of the two sexes, as well as the socioecology of their strategies. The book offers suggestions for future research in gorilla and primate socioecology, assesses the future of gorillas as a species, and examines the relevance of gorilla socioecology to conservation. (pages 3 - 16)
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Primate Socioecology: A Brief Introduction - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0002
[primates, socioecology, competition, infanticide, cooperation, body size, anti-predation, heterosexual groups, males, females]
This chapter presents a summary of what is known about the current state of vertebrate socioecology. First, primates have a great variety of societies, which socioecological theory ties to the contrasting survival, mating, and rearing strategies of the two sexes. Second, different distributions of food and different foods correlate with different forms and intensities of competition, different costs and benefits of grouping, and different payoffs of using cooperation with others in competition. Third, body size affects anti-predation strategies. Fourth, in mammalian species in which females are in more or less large groups (often, large-bodied species feeding on poor resources), males compete intensively for the rich, clumped resource of females, and evolve extra-large body size. Fifth, primates are an unusual mammal in the proportion of species that live in more or less stable heterosexual groups. Sixth, infanticide by non-father males is seen in primate societies in which usually only one male mates with a number of females, and lactation is of far longer duration than gestation. Seventh, females have some counterstrategies to infanticide. (pages 17 - 62)
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PART 2. GORILLAS, ECOLOGY, AND SOCIETY
Introducing Gorillas: Some Background - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0003
[gorillas, biology, Pan, Pongo, socioecology, geographical distribution, Africa, taxonomy, life history, reproduction]
This chapter presents some background information on gorilla biology that is fundamental to an understanding of the species' socioecology, including their geographical distribution, taxonomy, life history and reproduction, body size and sexual dimorphism, maturation and reproduction, mortality, and life span. Gorillas live only in Africa. They are in the taxonomic family Hominidae, along with humans and all the other great apes (the orangutan and both species of chimpanzee), and in the subfamily Homininae, which does not include the orangutan. Our knowledge of wild gorillas comes mainly from twelve study sites, eight in west-central Africa and four in eastern Africa. Gorillas are by far the largest of the primates, and one of the most sexually dimorphic, with males weighing in at 160 kilograms—about twice the size of females. Despite their relatively large body size, gorillas have fast life histories compared to Pan and Pongo. (pages 65 - 90)
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Gorilla Ecology and Society: A Brief Description - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0004
[gorillas, gorilla society, ecology, social cohesion, Pan, Pongo, diets, foraging, body size, population density]
Gorilla society is based on cohesive groups usually containing one adult male, several breeding females, and their offspring, and is characterized by long-term association between males and females, sometimes lasting for years. Both sexes normally leave the group of their birth. Gorillas prefer fruit to foliage. Their large body size, however, enables them to survive on more abundant, but lower-quality food such as pith, leaves, and woody stems, when preferred fruit is unavailable. This dietary flexibility helps to explain variation across gorilla populations in diet, ranging behavior, and some aspects of social cohesion. The striking differences between all the great apes in the nature of their societies are closely tied to their contrasting diets, and to related variation in how they find food, that is, their foraging strategies. This chapter, which provides a brief description of gorilla ecology and society in comparison with Pan and Pongo, looks at body size and diet, general habitat and food preferences, variation in foraging effort, home-range size, group cohesion, and population density. (pages 91 - 144)
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PART 3. FEMALE STRATEGIES AND GORILLA SOCIETY
Female Strategies and Society: Food and Grouping - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0005
[gorilla females, food, Pan, Pongo, cooperation, competition, emigration, grouping, foliage]
Gorilla females, unlike Pan or Pongo females, always live in more or less stable groups with a male. Group-living entails increased competition for resources, yet can also offer the benefit of cooperating with others, especially kin, in competition for those resources. If gorilla females group, do they compete less than Pan or Pongo females, or cooperate more? In many respects, gorilla females act much like other group-living primates. They compete over food to such an extent that dominance hierarchies are sometimes evident—in which case why do they live in groups? And they cooperate in that competition, doing so with kin more than with non-kin—in which case why do they emigrate? The nature of gorillas' main food, foliage, is such (widespread and abundant) that competition is minimal. Consequently, any benefits from cooperation in competition are also minimal. This chapter, which examines gorilla female strategies and society, focusing on their food and grouping, provides an overview of gorillas' food, competition and cooperation, and emigration. (pages 147 - 174)
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Female Strategies: Male Influences on Females' Competition, Cooperation, and Grouping - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0006
[gorilla females, Pan, Pongo, cooperation, competition, grouping, gorilla society, group size, males]
A major facet of gorilla society is the absolute dominance of the male over females, which correlates with his being twice their size. For instance, he supplants the average female nearly ten times more often than does the average other female in the group. Not only does his dominant presence make competition and cooperation among females themselves almost irrelevant, but the male also actively diminishes the effects of the females' competition and cooperation by preventing dominant females from exerting their competitive advantage through his usual help of subordinates against dominants. The effect of males is so strong that group size of gorillas is unlikely to be limited by competition among females, because an extra female is going to make so little difference by comparison to the competition already imposed by the one male. This chapter explores gorilla female strategies in comparison with Pan and Pongo, focusing on male influences on females' competition, cooperation, and grouping. (pages 175 - 186)
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Female Strategies: Male Influences; Joining a Protective Male - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0007
[gorilla females, Pan, Pongo, gorilla males, infanticide, predators, anti-predation, defense, grouping]
Gorillas are preyed upon, and in some populations, infanticide has at times been common. This chapter argues that, in the face of the obvious feeding costs imposed by a male upon females, the only reason for females to group with males is to obtain protection against predators or infanticidal non-father males, or both. Several lines of evidence indicate that females join males, rather than groups, and that groups result from independent choice by several females of the same male. Observational evidence supports the anti-predation argument for grouping: the male is almost the only protector of a group, and the females act as if he protects them. Observational and modeling evidence also support the anti-infanticide hypothesis. Females that lose their main protective male lose their infants to other males. Also, modeled females that range alone suffer a far higher risk of infanticide than do those that range with a male. The chapter shows that female gorillas associate with a male for defense against predators, and compares gorilla female strategies with those of Pan and Pongo. (pages 187 - 224)
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Female Strategies: Male Influences; Emigration and Choice of Males - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0008
[gorilla females, Pan, Pongo, mate choice, inbreeding, gorilla males, emigration, mating strategies]
Emigration by female gorillas, and especially their immediate transfer to another male, makes gorilla society unusual among group-living mammals. The nature and distribution of food explains only why females can emigrate and travel with a new male, but not why they do so. Mating and rearing strategies, not feeding strategies, explain females' emigration. Breeding females that leave one male for another do so, the circumstances suggest, to find a more powerful protector. Females born into a group are forced to emigrate to avoid inbreeding if their father is successful enough to be still alive and still the main breeding male when they mature. In other words, the male's mating strategy of long-term monopoly of a group of females constrains the females' mating strategies. However, the costs of inbreeding are only relative. If either the costs of emigration or benefits of staying outweigh the costs of inbreeding, daughters should stay. This chapter examines gorilla female strategies in comparison with Pan and Pongo, focusing on male influences, emigration, and mate choice. (pages 225 - 240)
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Female Strategies: Conflict, Compromise, and Cooperation Between the Sexes - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0009
[gorilla females, gorilla society, food, conflict, compromise, cooperation, emigration, gorilla males, grouping]
Gorilla female society can be described as one of groups of mostly unrelated females that transfer between males, especially at maturity. The grouping is allowed by the distribution of the gorilla's main food (widespread, dense vegetation), which results in a lack of contest competition and therefore of cooperation in competition. Lack of competition allows grouping, whereas lack of benefits from cooperation allows emigration. The grouping, which is a result of several females choosing one male with which to associate, is explained by the benefits to the females of proximity to a protective male twice the females' size. Protection is afforded against predators and infanticidal males. Breeding females emigrate to find more powerful males, while nubile females emigrate to avoid breeding with relatives. This chapter, which discusses gorilla female strategies, focusing on conflict, compromise, and cooperation between the sexes, also examines gorilla society and their food, as well as the male's influence on emigration by females. (pages 241 - 250)
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PART 4. MALE STRATEGIES AND GORILLA SOCIETY
Male Strategies and Society: Influences of the Environment and of Females - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0010
[gorilla males, gorilla females, Pan, Pongo, predation, infanticide, territoriality, association, environment]
Male animals have a variety of options for finding a fertilizable female. The male can roam in search of the females, defend areas that females frequent, attract females to himself, or stay with females once they are found. The strategy that the male adopts strongly determines the nature of the species' society. The gorilla's folivorous diet allows a short daily distance traveled; even necessitates it. At the usual low population densities of this large-bodied species, the short daily distance means that gorilla males are unable to use territorial defense as a means of access to females, and are committed to permanent association with females if they are to reliably find females when they are in estrus. Once a male is committed to remaining with the females, he is then committed to protect them and their offspring from harm. This chapter, which explores gorilla male strategies and society in comparison with Pan and Pongo, focusing on the influences of females and the environment, also looks at association and territoriality as a means for male gorillas to access females, along with predation and infanticide. (pages 253 - 266)
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Male Mating Strategies and Gorilla Society - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0011
[gorilla males, gorilla females, Pan, Pongo, mating strategies, gorilla society, breeding, group size, mating competition]
Male mating strategies have a large impact on gorilla society. They help to explain the stability of gorilla groups (long male breeding tenure and female group tenure), as well as group composition, in particular the number of males. Male mating competition influences both male and female dispersal and female residence decisions. As indicated by the extreme sexual dimorphism of gorillas and the single-male, multi-female composition of groups, male gorillas compete intensively for exclusive, long-term access to females. At its most serious, this rivalry includes damaging, sometimes fatal, aggression between males, and infanticide. This chapter examines gorilla male mating strategies and gorilla society in comparison with Pan and Pongo. It discusses mate acquisition versus mate retention and offspring protection, the influence of females on the stability of male–female associations, breeding success and mating competition, coercion and mate-guarding, the wooing of females by subordinate males, the interaction of male and female strategies, and the perpetuation of group structure. The chapter also looks at ecological constraints on group size, male mating competition, and male emigration. (pages 267 - 304)
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Male Strategies and the Nature of Society: Conflict, Compromise, and Cooperation Between the Sexes - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0012
[gorillas, gorilla society, gorilla males, gorilla females, conflict, compromise, cooperation, mating competition]
Although gorilla society might seem permeated by the influence of males on females, the relatively thin distribution of females in the environment in fact affects the distribution of males. It forces the males to stay with females instead of roaming in search of them. Concomitantly, mating competition among males, particularly the use of infanticide, forces females to associate with a protective male (who also protects them against predators), instead of roaming alone. Hence, gorilla society is one of stable, cohesive groups. While gorillas are a classic single-breeding-male society, with all the associated behavioral and anatomical correlates, some questions remain. This chapter explores gorilla male strategies and the nature of gorilla society, focusing on conflict, compromise, and cooperation between the sexes. (pages 305 - 310)
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PART 5. GORILLA SOCIETY: THE FUTURE
Gorilla and Primate Socioecology: The Future - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0013
[gorillas, gorilla society, socioecology, diets, community structure, predation, infanticide, sexual selection, compromise, mating]
The gorilla is a folivore that lives in one-male, multi-female social groups, between which females transfer, and from which no breeding male is ousted by an immigrant outsider. This society, with its many additional complexities, is the outcome of compromise between male and female tactics and strategies of survival, mating, and rearing. The environment affects the optimum tactics and strategies of both male and female gorillas. These tactics and strategies interact with one another in ways dependent on the payoffs to each sex, the outcome of which interactions is the society that we see. What do we need to add to our current knowledge and understanding of gorilla society in particular, primate socioecology in general? This chapter suggests nine areas of future work relating to diets, the fate of dispersers, the nature of community structure in primate populations, protection against predation and protection against infanticide, the relative roles of environmental influences and sexual selection in determining the nature of gorilla society, and human behavioral and social ecology. (pages 313 - 336)
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Socioecology and Gorilla Conservation - Alexander H. Harcourt
DOI: 10.7208/chicago/9780226316048.003.0014
[gorillas, socioecology, Africa, conservation, ecosystems]
Africa's gorilla numbers are going to crash in this century. However, the dedication of some of Africa's conservationists and the remarkable story of the success of mountain gorilla conservation in eastern Africa are grounds for hope. This chapter discusses the conservation of gorillas and the relevance of socioecology to conservation. It addresses a host of important questions: What are the threats that cause conservation to be necessary? What should we conserve? What ecosystems, communities, species, and populations are most in need of conservation? Does the gorilla need a special conservation effort? How much do we need to conserve? Where should we implement the conservation effort? How should we conserve? Stories of the gorilla's demise in the wild in the next twenty-five years are grossly exaggerated. Gorillas are going to be around for a lot longer than is the Sumatran orangutan. Over the next one hundred years, however, we cannot see any alternative scenario to a huge crash in gorilla numbers as forest outside of reserves is destroyed. (pages 337 - 376)
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References
Author Index
Subject Index
