The Biology of African Savannahs Second Edition
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The Biology of African Savannahs THE BIOLOGY OF HABITATS SERIES This attractive series of concise, affordable texts provides an integrated overview of the design, physiology, and ecology of the biota in a given habitat, set in the context of the physical environ- ment. Each book describes practical aspects of working within the habitat, detailing the sorts of studies which are possible. Management and conservation issues are also included. The series is intended for naturalists, students studying biological or environmental science, those begin- ning independent research, and professional biologists embarking on research in a new habitat. The Biology of Streams and Rivers Paul S. Giller and Björn Malmqvist The Biology of Soft Shores and Estuaries Colin Little The Biology of the Deep Ocean Peter Herring The Biology of Lakes and Ponds, 2nd Edition Christer Brönmark and Lars-Anders Hansson The Biology of Soil Richard D. Bardgett The Biology of Mangroves and Seagrasses, 2nd Edition Peter J. Hogarth The Biology of Polar Regions, 2nd Edition David N. Thomas et al. The Biology of Deserts David Ward The Biology of Caves and Other Subterranean Habitats David C. Culver and Tanja Pipan The Biology of Alpine Habitats Laszlo Nagy and Georg Grabherr The Biology of Rocky Shores, 2nd Edition Colin Little, Gray A. Williams and Cynthia D. Trowbridge The Biology of Coral Reefs Charles R.C. Sheppard, Simon K. Davy, and Graham M. Pilling The Biology of Disturbed Habitats Lawrence R. Walker The Biology of Freshwater Wetlands, 2nd Edition Arnold G. van der Valk The Biology of Peatlands, 2nd Edition Håkan Rydin and John K. Jeglum The Biology of African Savannahs, 2nd Edition Bryan Shorrocks and William Bates The Biology of African Savannahs SECOND EDITION Bryan Shorrocks Ph.D. Emeritus Professor University of Leeds and Honorary Professor University of York Environment Department University of York Heslington, York United Kingdom and William (Bill) Bates, Ph.D. Wildlife Bioacoustics Research Professor Emeritus of Zoology University of British Columbia Kelowna, British Columbia Canada 1 The Biology of African Savannahs. Second Edition. Bryan Shorrocks & William Bates. © Bryan Shorrocks & William Bates 2015. Published 2015 by Oxford University Press. 1 Great Clarendon Street, Oxford, OX2 6DP, United Kingdom Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries © Bryan Shorrocks & William Bates 2015 The moral rights of the authors have been asserted First Edition published in 2007 Impression: 1 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by licence or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this work in any other form and you must impose this same condition on any acquirer Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016, United States of America British Library Cataloguing in Publication Data Data available Library of Congress Control Number: 2014946890 ISBN 978–0–19–870270–2 (hbk.) ISBN 978–0–19–870271–9 (pbk.) Printed and bound by CPI Group (UK) Ltd, Croydon, CR0 4YY Links to third party websites are provided by Oxford in good faith and for information only. Oxford disclaims any responsibility for the materials contained in any third party website referenced in this work. Bryan and William would like to dedicate this book to Jo and Jeannie who also love Africa and have supported them in all their adventures. Preface to the First Edition This book is an introduction to African savannahs and their biology, concen- trating on large mammal ecology, behaviour, and conservation. Although it is a book on savannahs I hope that it sets out its ideas within a general frame- work of ecological and behavioural ideas. In my 40 years as an ecologist I have worked on both temperate and tropic- al terrestrial ecosystems. I have carried out field surveys, field experiments and built mathematical and computer models. I believe all these elements are essential for understanding Nature, and they all appear in this book. You cannot simply watch wildlife populations and communities in order to understand how they function. You have to employ field manipulations, either natural or artificial, to tease out the possibilities. You have to describe what you see not just in words but in mathematical models, to allow your less precise verbal suspicions to be tested. And savannah ecology must fit comfortably within the framework of general ecological ideas. There can be no special pleading or special mechanisms that other ecologists just don’t understand. I have tried to present such an encompassing view of savannah ecology and behaviour. African savannahs are magical places. The brightness of the light, the inten- sity of the colours, and the beauty and excitement of the wildlife, and of course the people. These savannahs are worth preserving for future gener- ations and I hope, in a small way, this book will generate an interest that helps them survive. I would like to thank all the people that have helped in my savannah work in East Africa, in particular the people at the Mpala Research Centre, in Laiki- pia, Kenya. Their help and insights have been invaluable during my frequent stays there. Finally my thanks to Paul Ward who, over several beers, over several nights, while running an undergraduate field course in Derbyshire reawakened my latent interest in Africa and its wildlife. Bryan Shorrocks June 2007 Preface to the Second Edition Once again this book is an introduction to African savannahs and their biol- ogy, concentrating on large mammal ecology, behaviour, and conservation. However, this second edition contains new material and many updates. These include hundreds of new references, new technique boxes, updated distribu- tion maps for the mammals and some birds, and an expanded focus on the conservation of African savannahs. Also new to the second edition is a com- panion website, <http://africansavannahs. shawwebspace.ca/>. This website contains additional information pertaining to African savannahs, including Soundscape ecology audio files and analysis, videos, the latest news on con- servation efforts, new journal article citations, and an interactive blog. As BS said in the preface to the first edition, these savannahs are worth preserving for future generations and we hope, in a small way, this book will again gen- erate an interest that helps them survive. Hopefully many of our readers will be young Africans, as the survival of African national parks and reserves will ultimately be determined by future generations of Africans. We would like to thank all the people that have helped us in our savannah work in southern Africa and East Africa. BS is grateful to the people at the Mpala Research Centre, in Laikipia, Kenya, and the staff at Etosha National Park, Namibia. Their help and insights have been invaluable during frequent stays there. WB is especially grateful to Chris McBride, who runs a camp in Zambia, for transmitting insights related to lion behaviour. The authors also want to thank the staff at OUP, especially Lucy Nash and Ian Sherman, for their continual encouragement and help. Bryan Shorrocks and William Bates November 2014 Contents 1 Savannahs 1 Distribution world-wide 2 African savannahs 9 2 The Vegetation 27 Rainfall, plant biomass and grass–tree mixture 27 Morphology and life history 30 Grasses 38 Trees 41 Local vegetation patterns: the Serengeti–Mara ecosystem 57 3 The Animals 65 The insects 65 The birds 69 The mammals 74 4 Single-species Populations 137 Estimating numbers 138 What changes numbers? 153 Population models 163 Other species in other areas 168 5 Species Interactions 182 Predator–prey type interactions (+ −) 183 Competitive interactions (− −) 210 Mutualistic interactions (+ +) 227 6 The Savannah Community and Its Conservation 237 Energy flow and food webs 238 Assembly rules 252 X CONTENTS Island biogeography 257 Conserving savannah ecosystems 264 References 279 Index 309 1 Savannahs Savannahs constitute one of the largest biomes of the world, comprising about 20% of the land surface. Stated simply, they are tropical and subtropical grasslands, with scattered bushes and trees. Most savannah occurs in Africa, with a smaller amount in South America, India and Australia. In Africa the trees tend to be deciduous, while in South America and Australia they tend to be evergreen. Savannahs occur around the equator, (between the Tropic of Capricorn and the Tropic of Cancer), where it is warm, but relatively dry. Most experience seasonal drought and the vegetation is influenced by rain- fall, soil type, grazing, browsing and fire. The word savannah, or savanna, is probably derived from a 16th century Spanish word zavanna, meaning ‘treeless plain’. It was recorded in 1535, by the Spanish historian Gonzalo Fernandez de Oviedo, as coming originally from Carib, a language spoken in northern South America and the Caribbean. Savannah therefore shares its origin with other well known words such as barbecue, cannibal and papaya. Like many plants that are found in warmer and drier regions, the dominant grasses in savannahs tend to be C4 plants. Only in some very wet environ- ments do C3 grass species become abundant. The terms 3C and C4 refer to the type of CO2 trapping mechanism (photosynthesis) used by the plant. C4 plants have evolved a secondary carbon fixation pathway. CO2 is first com- bined into a 4-carbon compound, in the mesophyll cells of the leaf, and then passed to the cells around the leaf veins where the CO2 is released at high concentrations.