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Seed Dispersal by Ants in a Deciduous Forest Ecosystem Seed Dispersal by Ants in a Deciduous Forest Ecosystem

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Seed Dispersal by Ants in a Deciduous Forest Ecosystem Seed Dispersal by Ants in a Deciduous Forest Ecosystem Seed Dispersal by Ants in a Deciduous Forest Ecosystem Seed Dispersal by Ants in a Deciduous Forest Ecosystem Mechanisms, Strategies, Adaptations by Elena Gorb National Taras Shevchenko University of Kyiv, Ukraine and Stanislav Gorb Schmalhausen Institute of Zoology, Kyiv, Ukraine Springer-Science+Business Media, B.Y. A C.I.P. Catalogue record for this book is available from the Library of Congress. ISBN 978-90-481-6317-5 ISBN 978-94-017-0173-0 (eBook) DOI 10.1007/978-94-017-0173-0 Printed on acid-free paper All Rights Reserved © 2003 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 2003. Softcover reprint of the hardcover 1st edition 2003 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. v Contents Foreword xi Preface xiii Introduction: an historical background 1 Chapter 1. The myrmecochorous syndrome 5 1. What is myrmecochory? 5 2. The concept of the myrmecochorous syndrome 6 3. Mechanisms of ant attraction 6 3.1 Diversity of elaiosomes 7 3.2. Elaiosomes originating from seed tissues 9 3.3. Elaiosomes originating from fruit tissues 11 3.4. Chemical composition of elaiosomes 13 3.5. Elaiosome compounds attracting ants 13 3.6. Effect of diaspore and elaiosome dimensions on diaspore 15 attractiveness for ants 4. Diaspore deposition into micro sites frequently visited by ants 16 5. Synchronisation of the plant fruiting periods with periods of 19 ant activity 6. Supplementary assimilating organs 21 7. The myrmecochorous syndrome in facultative myrmecochores 22 8. Other examples of ant-plant relationships 22 9. The myrmecochorous syndrome and criteria of 23 myrmecochory 10. Summary 24 Chapter 2. Diaspore removal by ants 25 VI 1. «Cafeteria» experiments 25 2. Morphology of diaspores of myrmecochorous plants 26 3. Removal rates of elaiosome-bearing seeds by Formica 28 polyctena workers 4. Removal rates of seeds by the ant species complex of the 28 forest 5. Do ants prefer seeds of particular plant species? 31 6. Do ants select seeds with the largest elaiosomes? 32 7. Are there differences in the body size of ant workers which 34 remove seeds of different plant species? 8. Summary 36 Chapter 3. Factors influencing diaspore removal 37 1. Effect of the diaspore size in Corydalis bulbosa and Corydalis 37 cava 1.1. Morphology and anatomy of diaspores 38 1.2. Removal rates of seeds 38 2. Effect of elaiosome, diaspore body, and their contents 39 2.1. Seed anatomy 40 2.1.1. Corydalis cava seeds 40 2.1.2. Pulmonaria obscura erems 41 2.2. Experiments with diaspores and juices from elaiosomes 43 and diaspore bodies 2.2.1. Corydalis cava seeds 44 2.2.2. Pulmonaria obscura erems 44 2.2.3. Diaspore structures that attract ants 45 3. Effect of diaspore aggregation 46 3.1. Cafeteria experiments with different degrees of seed 47 aggregation in the depot 3.2. Diaspore aggregation in obligate and facultative 49 myrmecochores 4. Summary 50 Chapter 4. Effect of the ant species complex on diaspore removal 53 1. Visits to seed depots by ant foragers and seed removal 54 1.1 Total seed removal at different microsites 54 1.2. Contribution of different ant species to seed removal 58 1.2.1. Formica polyctena territory 58 1.2.2. Myrmica rubra territory 58 1.2.3. Lasius fuliginosus territory 58 2. Microsite quality for the myrmecochore 59 3. Elaiosome consumption and seed removal 60 3.1. Duration of seed manipulation by ants 60 3.2. Number of seeds probed by ants prior to removal 61 VB 3.3. Elaiosome consumption 62 3.4. Interactions between workers of different ant species at 63 seed depots 4. Effect of ant recruitment behaviour and learning on seed 64 removal 4.1. Mark-recapture experiments 64 4.2. Recruitment and learning in ants and seed removal rates 67 5. Summary 68 Chapter 5. Diaspore transporting by ants 71 1. Methods of diaspore transporting 72. 2. Diaspore dropping during transport 74 3. Dependence of diaspore dropping on the ant worker size 75 4. Effect of diaspore dropping on dispersal distance 77 4.1 Complex of factors used in the computer model 77 4.2 Computer model 77 5. Summary 81 Chapter 6. Seed flow in ant territories 83 1. Direct observations of the seed flow 84 2. Soil seed material 85 2.1. Herbaceous species 85 2.2. Myrmecochores 87 2.3. Non-myrmecochores 89 3. Effect of ant workers on the vegetation 90 4. Seed flow in the territory of the Formica polyctena colony 91 4.1. Diaspore concentration in ant nests 91 4.2. Flow of diaspores of myrmecochores 91 4.3. Flow of diaspores of non-myrmecochores 93 5. Summary 94 Chapter 7. Secondary relocation of diaspores from ant nests 97 1. Composition of mature plants and seedlings in various 98 microsites 1.1. Mature plants 98 1.2. Seedlings 98 1.3. Effect of ants on the distribution of plants in the forest 101 2. Plant species composition of the soil seed pools at various 103 microsites 3. Distribution of diaspores within territories of ant colonies 106 3.1. Diaspore flow within territories of colonies of Formica 106 polyctena and Lasius fuliginosus ants 3.2. Effect of ant behaviour on the distribution of diaspores 107 3.3. Advantages for plants from the secondary relocation of 108 viii diaspores 4. Summary 108 Chapter 8. Comparative analysis of plant dispersal systems by 111 ants: diaspore concentration and redistribution 1. Variables used for simulation 111 2. What proportion of diaspores reaches ant nests? 113 3. Comparison of systems of diaspore dispersal by ants 114 3.1. Dispersal without secondary relocation of diaspores 114 3.2. Dispersal with secondary relocation of diaspores 117 4. Analysis of diaspore dispersal systems 118 5. Summary 122 Chapter 9. Ecological implications of myrmecochory 123 1. Selective advantages of myrmecochory 123 1.1. Hypotheses of selective advantages of myrmecochory 123 1.1.1. Hypothesis ofthe nest environment 123 1.1.2. Hypothesis of diaspore escape from predators 124 1.1.3. Competition avoidance hypothesis 124 1.1.4. Fire escape hypothesis 125 1.1.5. Hypothesis of the dispersal for distance 125 1.2. Recent studies of selective advantages of myrmecochory 126 2. Ant nests as microhabitats for myrmecochores 126 2.1. Viola odorata plants on nests of Formica polyctena ants 127 2.2. Advantages for plants growing on ant nests 129 3. Decrease of seedling density as a selective advantage of 130 myrmecochory 3.1. Spatial distribution of seedlings in Corydalis bulbosa 131 3.1.1. First year of the experiment 131 3.1.2. Second year ofthe experiment 133 3.2. Effect of ants on seed dispersal of Corydalis bulbosa 134 4. Effect of myrmecochory on the spatial distribution and 136 mortality rate of seedlings in Asarum europaeum 4.1. Spatial distribution and seedling mortality 138 4.2. Effect of ants on seed dispersal in A. europaeum 139 5. Summary 140 Chapter 10. Interactions between ants and non-myrmecochorous 143 plants 1. Interactions between the non-myrmecochore Galium aparine 144 and Formica polyctena ants 1.1. Removal and transport of diaspores 144 1.2. Dynamics of seedling density and plant growth 145 2. Asymmetry of interactions between non-myrmecochores and 149 IX ants 2.1. Plant concentration on the nest mounds 149 2.2. Why do ants remove and transport diaspores without 149 elaiosomes? 2.3. Character of interactions between non-myrmecochores 150 and ants 3. Summary 151 Chapter 11. Methods for studying myrmecochory 153 1. Study site 153 2. Plant species covered by the experiments 154 2.1. Obligate myrmecochores 155 2.2. Facultative myrmecochores 156 2.3. Non-myrmecochores 156 3. Ant species used in the experiments 157 4. Methods 157 4.1. Morphology and anatomy 157 4.2. Field observations and experiments 158 4.2.1. Studies on the myrmecochorous syndrome 158 4.2.2. «Cafeteria» experiments 159 4.2.3. Factors influencing diaspore removal rate 160 4.2.4. Effect of the ant species composition on diaspore 162 removal 4.2.5. Diaspore transport by ants 164 4.2.6. Plant diaspore flows on ant territories 165 4.2.7. Secondary relocation of diaspores by ants 165 4.2.8. Ecological aspects of the myrmecochory 165 4.2.9. Interactions between ants and non-myrmecochorous 168 plants 4.3 Soil seed bank 169 5. Summary 170 Conclusions and outlook 173 Glossary 177 References 185 Appendix 201 Index 217 xi Foreword In many nations, there is a fairy-tale about assiduous ants, which help a poor hard-working stepdaughter to sort out seeds. This idea about the relationship between ants and seeds is based on the knowledge about the immense invisible work performed by ants around the clock in fields and forests. Countless ants transport and deposit seeds and thereby influence the survival, death, and evolution of many plant species. In the evolution of plants, seed dispersal by ants (myrmecochory) has independently appeared many times in different lineages. More than 3000 plant species use the help of ants to be planted, and this is not the final number. Myrmecochory is a very interesting and rather enigmatic form of mutualistic ant-plant interrelations. This phenomenon is extremely complex, because of hundreds of ant species connected with hundreds of plant species.
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