Cambridge Studies in Ecology presents balanced, comprehen­ sive, up-to-date, and critical reviews of selected topics within ecology, both botanical and zoological. The Series is aimed at advanced final-year undergraduates, graduate students, re­ searchers, and university teachers, as well as ecologists in industry and government research. It encompasses a wide range of approaches and spatial, temporal, and taxonomic scales in ecology, including quanti­ tative, theoretical, population, community, ecosystem, histor­ ical, experimental, behavioural and evolutionary studies. The emphasis throughout is on ecology related to the real world of plants and animals in the field rather than on purely theo­ retical abstractions and mathematical models. Some books in the Series attempt to challenge existing ecological paradigms and present new concepts, empirical or theoretical models, and testable hypotheses. Others attempt to explore new approaches and present syntheses on topics of considerable importance ecologically which cut across the conventional but artificial boundaries within the science of ecology. CAMBRIDGE STUDIES IN ECOLOGY Editors: R. S. K. Barnes Department of Zoology, University of Cambridge H. J. B. Birks Botanical Institute, University of Bergen E. F. Connor Department of Environmental Science, University of Virginia R. T. Paine Department of Zoology, University of Washington, Seattle Megaherbivores The influence of very large body size on ecology Also in the series H. G. Gauch, Jf Multivariate Analysis in Community Ecology R. H. Peters The Ecological Implications of Body Size C. S. Reynolds The Ecology of Freshwater Phytoplankton K. A. Kershaw Physiological Ecology of Lichens R. P. McIntosh The Background of Ecology: Concept and Theory A. J. Beattie The Evolutionary Ecology of Ant-Plant Mutualisms F. I. Woodward Climate and Plant Distribution J. J. Burdon Diseases and Plant Population Biology J. I. Sprent The Ecology of the Nitrogen Cycle N. G. Hairston, Sr Community Ecology and Salamander Guilds H. Stolp Microbial Ecology: Organisms, Habitats and Activities R. N. Owen-Smith Megaherbivores: the Influence of Large Body Size on Ecology J. A. Wiens The Ecology of Bird Communities: Volume 1 Foundations and Patterns Volume 2 Processes and Variations N. G. Hairston, Sr Ecological Experiments R. Hengeveld DynamiC Biogeography C. Little The Terrestrial Invasion: an Ecophysiological Approach to the Origins of Land Animals P. Adam Saltmarsh Ecology M. F. Allen The Ecology of Mycorrhizae D. J. von Willert et al. Life Strategies of Succulents in Deserts: With Special Reference to the Namib Desert J. A. Matthews The Ecology of Recently-deglaciated Terrain: a Geoecological Approach to Glacier Forelands Megaherbivores The influence of very large body size on ecology R.NORMAN OWEN-SMITH University of the Witwatersrand • CAMBRIDGE ::: UNIVERSITY PRESS CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, Sao Paulo, Delhi, Dubai, Toky o, Mexico City Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this tide: www.cambridge.org/978052I426374 © Cambridge University Press 1988 This publication is in copy right. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 1988 First paperback edition 1992 A catalogue recordfor thispublication is available from theBritish Library Library of Congress Cataloguing in Publication Data Owen-Smith, R. Norman. Megaherbivores: the influence of very large body size on ecology R. Norman Owen-Smith p. cm. - (Cambridge studies in ecology) Bibliography: p. Includes index. ISBN 0 521 36020 x (hardback); 0 521 42637 5 (paperback) 1. Herbivora-Size. 2. Herbivora-Ecology. 3. Ungulata-Size 4. Ungulata-Ecology. 5. Mammals-Size. 6. Mammals-Ecology. I. Tide. II. Series. QL 737.U4095 1988 599·7-dcl9 88-6941 ISBN 978-0-521-23385-9 Hardback ISBN 978-0-521-27858-4 Paperback Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. 'Hints fo r an agenda: How big is it and how fa st does it happen?' (G. Evelyn Hutchinson 1975) Contents Prefa ce xiii 1 Prologue 2 Morphology, evolutionary history and recent distribution 6 Introduction 6 Morphology 6 Evolutionary origins and relationships 16 Paleontological diversity 20 Distribution of extant species 21 3 Food and other habitat resources 30 Introduction 30 Food 30 Water and other habitat needs 45 Comparisons with smaller ungulates 50 4 Space-time patterns of habitat use 53 Introduction 53 Temporal patterning of activities 53 Utilization of space 61 Comparisons with smaller ungulates 67 5 Body size and nutritional physiology 69 Introduction 69 Metabolic requirements 70 Gut anatomy 71 Food intake and digestion 72 6 Body size and fe eding ecology 82 Introduction 82 Diet quality 82 Foraging time 87 Home range extent 95 Trophic ecology of megaherbivores: summary 98 x Contents 7 Social organization and behavior 101 Introduction 101 Group structure 101 Male dominance relations 109 Courtship and mating 116 Responses to predators 124 Comparisons with smaller ungulates 131 8 Life history 133 Introduction 133 Infancy and juvenilehood 133 Adolescence and puberty 138 Reproduction by females 144 Reproduction by males 151 Mortality and lifespan 152 Comparisons with smaller ungulates 159 9 Body size and sociobiology 160 Introduction 160 Grouping patterns 160 Male dominance systems 167 Female mate choice 177 Summary 179 lO Body size and reproductive patterns 181 Introduction 181 Seasonality of reproduction 183 Age at first conception 185 Birth intervals 186 Maternal investment in reproduction 190 Offspring sex ratio 195 Summary 198 11 Demography 200 Introduction 200 Population structure 200 Population growth 212 Population density and biomass 221 Comparisons with smaller ungulates 225 12 Community interactions 226 Introduction 226 Impact on vegetation 226 Effects on other large herbivores 239 Comparisons with smqller ungulates 245 Contents Xl 13 Body size and population regulation 246 Introduction 246 Demographic models 248 Interactions with vegetation 257 Dispersal 260 Summary 264 14 Body size and ecosystem processes 265 Introduction 265 Biomass levels 265 Energy flux 274 Nutrient cycling 277 Ecosystem stability and disturbance 278 15 Late Pleistocene extinctions 280 Introduction 280 Pattern of extinctions 281 Climatic change 284 Human predation 289 The role of megaherbivores 292 Summary 296 16 Conservation 297 Introduction 297 Conservation objectives 298 Problems of overabundance 299 Problems of overexploitation 307 Summary 308 17 Epilogue: the megaherbivore syndrome 309 Faunal patterns 309 Social and life history patterns 312 Demographic patterns 313 Community and ecosystem patterns 314 Appendixes 317 Appendix I 317 Appendix II 325 References 331 Index 364 Preface Like the animals it describes, this book has had a long gestation. It started as a Ph.D. thesis on the white rhinoceros, grew into a monograph on rhinocer­ oses, expanded to include other similarly large herbivores, and then settled on the focus adopted in the pages that follow: the consequences oflarge size for the ecology of animals such as elephants, rhinoceroses and hippo­ potami, and by implication extinct species of similar size. I hope that this work will be of interest to a variety ofreaders. Firstly, it is written fo r biologists interested in allometric scaling effects on ecological processes. The correlates of a body mass at the upper limit of the size range among mammalian herbivores are analyzed at various levels, including ecophysiology, behavioral ecology, demography, community interactions and ecosystem processes. Secondly, the book should be an aid to profes­ sional conservationists and wildlife managers concerned about the future survival of such large mammals. Scientificfa cts about these species must be given due cognizance if management actions are to achieve their desired objectives. Thirdly, it is directed towards paleobiologists interested in the ecological roles that similarly large mammals played in the faunas and ecosystems of the past. In particular potential causes of the extinctions of the so-called megafauna during the late Pleistocene are assessed. Finally, I hope that this book will be illuminating to all those who have marvelled at the ways of living of these largest among land animals, whether in the wild or on film. The fe atures of their ecology and behavior are compared and contrasted with those of lesser ungulates. I owe many debts of gratitude to people who have contributed help or ideas at various stages of the life history of this manuscript. It was a suggestion made by George A. Petrides, then Visiting Professor of Wildlife Management at the University of Pretoria, that firstdrew me into a study of the white rhinoceros. RudolfC. Bigalke, then Principal Research Officerof the Natal Parks Board, made the study possible