Contents PART 1. 1 Speciation, Adaptive Radiation, and Evolution 3. 2 Daphne Finches: A Question of Size Heritable Variation 41

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1 Contents List of Illustrations List of Tables List of Boxes Preface xvii xxiii xxv xxvii PART 1 ear ly problems, ea r ly solutions 1 1 Speciation, Adaptive Radiation, and Evolution 3 Introduction 3 Adaptive Radiation of Darwin s Finches 4 Species and Speciation 9 Daphne 10 Evolution Observed 12 Chapters of the Book 15 Summary 16 2 Daphne Finches: A Question of Size 17 Introduction 17 Testing the Hypothesis 21 availability of food 22 diets of G. fortis and G. fuliginosa 22 differences in seed supply 27 G. fuliginosa on los hermanos 28 Association between Beak Size and Diet 30 Adaptive Landscapes 30 Can G. scandens Be Ignored? 35 Why Is G. fuliginosa Absent? 37 Discussion 39 Summary 39 3 Heritable Variation 41 Introduction 41

2 x Contents Estimating Heritable Variation 43 Heritable Variation 44 Potential Biases 46 Extra- Pair Paternity 46 Misidentified Paternity 47 Maternal Effects 47 Genotype Environment Correlation 48 Conclusions on Bias 49 Heritabilities: A Comparison of Species 49 Summary 53 4 Natural Selection and Evolution 55 Introduction 55 Expectations 56 Natural Selection 57 Causes of Selective Mortality 59 The Targets of Selection 61 Evolution in Response to Selection 62 Selection Occurs Repeatedly 63 Selection Oscillates in Direction 67 Evolutionary Response 73 Selection in Opposite Directions 74 Conclusions 75 Summary 75 5 Breeding Ecology and Fitness 77 Introduction 77 Basic Breeding Biology 78 Annual Variation in Reproduction in 81 Relation to Rain 81 Predicting Reproductive Success 87 The Cohorts of Four Later Cohorts 89 The Contribution of Morphology to Fitness 90 The Contribution of Offspring to Parental Fitness 93 Longevity 93 Inbreeding 96 Variation in Fitness 97 Discussion 99 Summary 100

3 PART 2 Contents xi Dev eloping a Long- Ter m Perspectiv e A Potential Competitor Arrives on Daphne 103 Introduction 103 Founder Event 105 Causes 105 First Few Generations 106 Inbreeding 107 Fitness Costs of Inbreeding 107 Immigration 108 Selection 109 Genetic Diversity 111 Losses and Gains of Alleles 112 The Source of Immigrants 112 Nonrandom Colonization 115 Song 115 Colonization Success 117 Summary Competition and Character Displacement 122 Introduction 122 Competition and Diet Overlap 123 Effects of Competition on Survival 123 Character Displacement 125 Strength of Selection 128 The Causal Role of G. magnirostris 129 High impact on food supply 130 Superior feeding efficiency on shared component of the diet 130 Parallel decline due to starvation 130 Key difference between 1977 and Evolution of a Displaced Character 132 G. fortis and scandens Compared 133 Some Implications 134 Summary Hybridization 138 Introduction 138 Background 139

4 xii Contents Frequency of Hybridization 141 Causes of Hybridization 141 A Scarcity of Conspecific Mates 141 Imprinting 143 Song Inheritance 143 Perturbation of Imprinting 149 G. magnirostris 153 Fitness Consequences of Hybridization 156 Viability 156 Fertility 160 Overall Fitness 160 The Mating Pattern of Hybrids 163 Conclusions 164 Summary Variation and Introgression 166 Introduction 166 Morphology of Hybrids 169 Effects of Hybridization on Variation 169 Comparison of G. fortis and G. scandens 171 Conspecific Gene Flow 174 Hybridization versus Mutation 174 Correlations 176 Evolutionary Potential 177 Discussion 178 Summary 179 PART 3 Hy br idization a nd Speciation Long- Term Trends in Hybridization 183 Introduction 183 A Question of Identity 184 Blurring of Genetic Distinctions 185 Blurring of Morphological Distinctions 188 Morphological Convergence 190 Frequencies of Hybrids 191 Morphological Variation 192 Allometry 194 Genetic Convergence 196

5 Contents xiii Two Species or One? 199 Plumage and Behavior 201 Discussion 201 Summary Long- Term Trends in Natural Selection 205 Introduction 205 Selection 207 G. fortis 207 G. scandens 207 Ecological Causes 207 Stabilizing Selection 211 Morphological Trends 211 G. fortis 211 G. scandens 213 G. magnirostris 216 The Possible Role of Selection on G. magnirostris 219 Immigration 223 The Cause of the Beak- size Trend 224 Allometry of Means 224 Natural and Artificial Selection 226 Conclusion 226 Summary Speciation 229 Introduction 229 Morphological Transformation in Speciation 230 Species That Differ in Size 231 Species That Differ in Shape 232 Genetic Transformation in Speciation 234 Growth after Hatching 236 Rapid Tempo of Speciation 238 Interactions in Sympatry 239 A Mechanism Producing Song Divergence 241 Summary Speciation by Introgressive Hybridization 245 Introduction 245 A Hybrid Arrives on Daphne 247 Descendants 248 Phase 1: The Start of a New Lineage 248 The phenotypic uniqueness of

6 xiv Contents Phase II: Generations Phase III: Endogamy and Reproductive Isolation 253 Origin of Reproductive Isolation 260 Fate of the A Line of Descent 260 Success of the Lineage So Far 263 Intrinsic Factors 263 Extrinsic Factors 265 Future Prospects 265 Summary 267 PART 4 Sy ntheses The Future of Finches on Daphne 271 Introduction 271 The Past as Context of the Present 272 Merge- and- diverge Dynamics 275 The Present as a Guide to the Future 275 Global Warming and Galápagos 276 Finch Futures 279 Means and Extremes 279 G. fortis, scandens, and fuliginosa 280 G. magnirostris 280 Hybrid Lineage 281 Invasive Plant Species and Disease 283 Genomes for the Future 284 Summary Themes and Issues 287 Introduction 287 Speciation, Selection, and Hybridization 289 Evolution 289 Ecological Importance of Food: The Daphne Perspective 290 Behavioral Barrier to Interbreeding 291 Size and Hybridization 293 Phylogenetic Implications of Hybridization 294 Ephemerality of Species 294 Predictability and Evolvability 296 Overview 298 Summary 299

7 Contents xv 16 Generalization 300 Generalizing When N = The Small Population Syndrome 301 The Medium Population Syndrome 302 Large Islands 303 Beyond Galápagos 304 The Specter of Extinction, the Big Unknown 306 Summary Epilogue 310 Reflections on the Value of Long- Term Studies 310 Long- term Dynamics of a Color Polymorphism 311 Rare Events and Their Consequences 315 Changes in Perspective 316 Coda 319 Appendixes 321 Appendix 1.1 Daphne Plants 321 Appendix 1.2 Measurements of Finches 323 Appendix 1.3 Other Species of Darwin s Finches 324 Appendix 3.1 Mapping Breeding Locations 324 Appendix 3.2 Annual Changes in Measurements 324 Appendix 5.1 Extra- pair Mating 326 Appendix 5.2 Visitors and Predation 327 Appendix 9.1 Variation and Mortality 328 Appendix 10.1 On the Dangers of Extrapolation 331 Appendix 10.2 Plumage 331 Appendix 11.1 Samples of Measurements for Selection Analyses 332 Appendix 13.1 Identification of Breeders 335 Appendix 17.1 Nestling Beak Color Polymorphism 335 Abbreviations 341 Glossary 343 References 353 Subject Index 389