Insect Diversity Conservation

Transcription

1 Insect Diversity Conservation This groundbreaking book is an up-to-date global synthesis of the rapidly developing and important field of insect conservation biology. Insects are by far the most speciose organisms on earth, yet barely known. They play important roles in terrestrial ecological processes and in maintaining the world as we know it. They therefore present particular conservation challenges, especially as a quarter may well become extinct in the next few decades. This book first addresses the ethical foundation of insect conservation, and asks why we should concern ourselves with conservation of a butterfly, beetle or bug. The success of insects and their diversity, which have survived the comings and goings of glaciers, is now facing a more formidable obstacle:the massive impact of humans. After addressing threats, from invasive alien plants to global climate change, the book then explores ways in which insects and their habitats are prioritized, mapped, monitored and conserved. Landscape and species approaches are considered. Restoration, and the role of conventions and social issues are also discussed. The book is for undergraduates, postgraduates, researchers and managers both in conservation biology or entomology and in the wider biological and environmental sciences. MICHAEL J. SAMWAYS is Professor of Entomology at the University of Stellenbosch, South Africa. He is internationally known as a conservation biologist and policy advisor.

2 Insect Diversity Conservation MICHAEL J. SAMWAYS University of Stellenbosch, South Africa

3 published by the press syndicate of the university of cambridge The Pitt Building, Trumpington Street, Cambridge, United Kingdom cambridge university press The Edinburgh Building, Cambridge, CB2 2RU, UK 40 West 20th Street, New York, NY , USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcón 13, Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa C 2005 This book is in copyright. 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 2005 Printed in the United Kingdom at the University Press, Cambridge Typeface Swift 9.5/14 pt. System LATEX2ε [tb] A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication data Samways, Michael J. Insect diversity conservation /. p. cm. Includes bibliographical references and index. ISBN (hardback:alk. paper) -- ISBN (pbk.:alk. paper) 1. Insects--Ecology. 2. Wildlife conservation. 3. Biological diversity conservation. I. Title. QL496.4S dc ISBN hardback ISBN paperback The publisher has used its best endeavours to ensure that the URLs for external websites referred to in this book are correct and active at the time of going to press. However, the publisher has no responsibility for the websites and can make no guarantee that a site will remain live or that the content is or will remain appropriate.

4 Contents Preface Cover picture page ix xi Part I The need for insect diversity conservation 1 1 Ethical foundation for insect conservation Introduction Environmental philosophy and insect conservation Insect utility Insect rights and species conservation Spiritual conceptions Summary 15 2 The special case of insects in conservation biology Introduction Insect radiation Bauplan, flight and insect conservation Polymorphisms Insect diversity and the landscape Global insect species richness Survival in prehistorical times Current extinctions The taxonomic challenge The perception challenge Pest insects and population crashes Summary 37 3 Insects and the conservation of ecosystem processes Introduction Insects as keystone organisms Insect ecosystem engineers and soil modifiers Insects as food for other animals Insect dispersal Insect pollinators Insect herbivores Insect parasitoids and predators Insects and disease 50 v

5 vi Contents 3.10 Ecosystem diversity and insect diversity Insects and the naturally changing landscape Significance of ecological connectance Summary 54 Part II Insects and the changing world 57 4 Degradation and fragmentation of ecosystems Introduction Environmental contamination Pesticides Agriculture and afforestation Urbanization and impact of structures Deforestation and logging Transformation of grasslands, savanna and Mediterranean-type ecosystems Deterioration and loss of aquatic systems Pressure on special systems Overcollecting Summary 87 5 Responses by insects to the changing land mosaic Introduction Behavioural responses Population response and local extinction Community response and long-term prognosis Genetic changes Summary Threats from invasive aliens, biological control and genetic engineering Introduction Invasive alien plants Invasive alien vertebrates Invasive alien insects Risks of introducing insect natural enemies Risks of introducing insect pathogens Risks of genetic engineering Summary Global climate change and synergistic impacts 136

6 Contents vii 7.1 Introduction Ecosystem response to global climate change Changes in species geographical ranges Synergisms and future perspectives Summary 149 Part III Conserving and managing insect diversity Methods, approaches and prioritization criteria Introduction Towards an Earth ethic Identifying geographical areas for conservation action Systematic reserve selection Use of surrogates in conservation planning Coarse and fine filters Plant surrogates Animal surrogates Phylogenetic considerations Are umbrella and flagship species of value in conservation planning? Summary Mapping, inventorying and monitoring Introduction Mapping Inventorying Monitoring Red Listing Application of IUCN Red List Criteria at regional or national levels Insects as bioindicators Reference sites Summary Managing for insect diversity Introduction Importance of parks, reserves and remnant patches Importance of landscape heterogeneity Countryside-wide management Importance of patch size relative to habitat quality Simulating natural conditions and traditional practices 222

7 viii Contents 10.7 Corridors Landscape management in urban areas Summary Restoration of insect diversity Introduction Principle of restoration triage Restoration of species or processes? Coarse-filter and fine-filter approaches to restoration Insect gardening Species-specific recovery plans Summary Conventions and social issues in insect diversity conservation Introduction The international arena National issues Overcoming the perception challenge Butterfly houses and increasing conservation awareness Deadstock trade Butterfly farming Summary 263 References 266 Index 316

8 Preface Some say that the cockroach will be the last species on Earth to survive. Then it has been calculated that one gravid aphid, left to reproduce with zero mortality, will, after one year, cover the globe with an aphid layer over 140 km thick. Not forgetting too, that flies and fleas vector disease. So, why should we even consider conserving insects? Quite simply, without insects, the likelihood is that the world as we know it would be radically changed in a matter of days. Besides, it is only a tiny minority of insects that harm our lives. These two faces of insects, friend and foe, are just one of the several paradoxes that characterize insect conservation from other facets of taxon-based conservation biology. Our impacting on landscapes can turn a benign insect species into a pest, while, on the other hand, it may cause an extinction of another species. Focusing on the land mosaic, its composition, structure and function, is thus central to insect conservation. We have no idea of the outcomes from our modification of the biosphere. Blindfolded, we are turning the many faces of the Rubik Cube of biological diversity conservation in the hope that all the faces will match. It is not that we are incapable, it is just that the world is so complex. A thousand species, for example, in the same community (not an unreasonable figure) potentially produces 0.5 million interactions. In addition, strengths of those interactions, and hence outcomes, also vary. Bleak as this may seem, we are beginning to lift the blindfold and make rational decisions for conserving biological diversity. Insects and their interactions are a major component of that diversity. Indeed, insects are virtual ambassadors for biological diversity. These little animals, by their great variety and abundance, play an unheralded yet pivotal role in our, and many other organisms, lives. We now have a major challenge before us:how do we go about conserving this largely unseen, unknown majority? The ambassadorial status of insects for terrestrial and aquatic ecosystems is the reasoning behind the title Insect Diversity Conservation. Biological is simply replaced by Insect. This is not in pursuit of entomological chauvinism but rather to emphasize that insects are central, yet with many special features, to biodiversity conservation. The aim here is to overview and critically appraise the conservation of insect diversity. It focuses strongly on the variety and differences among insects, and links these to landscape and other large-scale conservation initiatives. After all, insects do not rule the world alone. This is not, though, to ignore special cases where a particular insect species requires particular conservation attention. ix

9 x Preface Conservation cannot be done without clearly defining our feelings and motives for why we are doing it. This goes beyond simply the utilitarian value of insects for us. This field of environmental ethics in relation to insects is therefore addressed in the first chapter, and is a foundation for all that follows. In Chapter 2, the special case for insects, in comparison with and in contrast to other organisms, is argued. This is not to say that insect conservation is tangential to mainstream conservation. Rather, it is central, especially as insects play so many keystone roles in non-marine ecosystems. These roles and others are discussed in Chapter 3. These first three chapters together are the launching point for the rest of the book, and address why there is the need for insect diversity conservation. Part II (Chapters 4--7) addresses threats to insect variety, and emphasizes that many of these threats are multiplicative, with one threat compounding another. Part III (Chapters 8--12) then reviews the options that we have to ameliorate these threats. As insects are now featuring much more strongly in biodiversity conservation, the field of insect conservation biology has grown enormously in recent years. It is clear too that there are many varying, even conflicting conclusions when various studies are compared. These differences seem to arise mainly from three different perspectives:differences in spatial scale of the study, differences in biogeographical regions, and differences in the focal taxa used. This is healthy and indicative of a rapidly growing field of study. Nevertheless, some general principles are beginning to emerge, and in terms of management, these are synthesized in Part III. Insect conservation has been a rapid growth area in recent years, often with intense debate. In response, I really do appreciate the stimulating feedback from Jonathan Ball, Andy Beattie, Steve Compton, Eduardo Galante, Henk Geertsema, Justin Gerlach, Jeff Lockwood, Melodie McGeoch, Tim New, Paul Pearce-Kelly, Andrew Pullin, Nigel Stork and Stuart Taylor, as well as the lively minds of my research students over the years. Many authors kindly made available text figures, and these are acknowledged with each figure. This work would not have been possible without the amazing support of Colleen Louw (processing text), Stuart Taylor (processing figures) and James Pryke (processing references). Anni Coetzer produced the beautiful cover and text illustrations, so rich in symbolism. Ward Cooper and Jo Bottrill saw production of the book to its completion. My warm thanks to these friends for making this such an enjoyable enterprise.

10 Cover picture In an ever-changing, human-transformed world, we often overlook the importance of each little creature in our earthly ecosystem. Conscious and moral Man holds the future well-being of the world in his hand. Yet the race is against time, that these noble efforts are not in vain. Insects are an ancient, ecologically significant and beautiful component of the world, symbolized here by the dragonfly. The variety of insect life around us, be it in our garden or city park, are a constant reminder that these small but numerous animals are part of the fabric and health of our planet. By destroying these living creatures and their habitat, the delicate glass of our ecosystem will shatter, leaving us with a transformed, bare world, devoid of colour and life as we once knew it. Time is now short for ensuring the future of this amazing insect diversity. Anni Coetzer xi