Evolution's Wedge: Competition and the Origins of Diversity (Volume 12) (Organisms and Environments)

Evolutionary biology has long sought to explain how new traits and new species arise. Darwin maintained that competition is key to understanding this biodiversity and held that selection acting to minimize competition causes competitors to become increasingly different, thereby promoting new traits and new species. Despite Darwin’s emphasis, competition’s role in diversification remains controversial and largely underappreciated. In their synthetic and provocative book, evolutionary ecologists David and Karin Pfennig explore competition's role in generating and maintaining biodiversity. The authors discuss how selection can lessen resource competition or costly reproductive interactions by promoting trait evolution through a process known as character displacement. They further describe character displacement’s underlying genetic and developmental mechanisms. The authors then consider character displacement’s myriad downstream effects, ranging from shaping ecological communities to promoting new traits and new species and even fueling large-scale evolutionary trends. Drawing on numerous studies from natural populations, and written for a broad audience, Evolution’s Wedge seeks to inspire future research into character displacement’s many implications for ecology and evolution. Content: Preface 1. Discovery of a Unifying Principle Introduction A Brief History Detecting Character Displacement Phenomena Mistaken for Character Displacement What Constitutes Character Displacement? Conflation of Process and Pattern Reproductive Character Displacement versus Reinforcement Terminology A Unifying Principle Summary Further Reading Box 1.1: Alternative Manifestations of Character Displacement Box 1.2: Suggestions for Future Research 2. Why Character Displacement Occurs Introduction Why Ecological Character Displacement Occurs RESOURCE COMPETITION COMPETITIVE EXCLUSION SPECIES COEXISTENCE RESOURCE PARTITIONING VIA CHARACTER DISPLACEMENT VS. SPECIES SORTING Why Reproductive Character Displacement Occurs REPRODUCTIVE COMPETITION REPRODUCTIVE EXCLUSION REPRODUCTIVE PARTITIONING VIA CHARACTER DISPLACEMENT VS. SPECIES SORTING Summary Further Reading Box 2.1: Alternative Models of Species Coexistence Box 2.2: Is Competitively Induced Plasticity Character Displacement? Box 2.3: Suggestions for Future Research 3. When Character Displacement Occurs Introduction Facilitators of Character Displacement STANDING VARIATION STRONG SELECTION ECOLOGICAL OPPORTUNITY LACK OF ANTAGONISTIC GENETIC CORRELATIONS GENE FLOW INITIAL DIFFERENCES Variation in the Expression of Character Displacement How Ecological and Reproductive Character Displacement Facilitate Each Other ECOLOGICAL DIVERGENCE AS A FACILITATOR OF REPRODUCTIVE DIVERGENCE REPRODUCTIVE DIVERGENCE AS A FACILITATOR OF ECOLOGICAL DIVERGENCE WHY ONE FORM IS NECESSARY TO FACILITATE THE OTHER How Ecological and Reproductive Character Displacement Can Impede Each Other Summary Further Reading Box 3.1: Suggestions for Future Research 4. How Character Displacement Unfolds Introduction Mechanisms of Divergence GENETICALLY CANALIZED DIVERGENCE ENVIRONMENTALLY INDUCED DIVERGENCE Tempo and Mode of Character Displacement HOW MECHANISMS DIFFER IN SPEED OF DIVERGENCE THE PLASTICITY-FIRST HYPOTHESIS EMPIRICAL TESTS OF THE PLASTICITY-FIRST HYPOTHESIS Summary Further Reading Box 4.1: Suggestions for Future Research 5. Diversity and Novelty Within Species Introduction How Intraspecific Character Displacement Works Intraspecific Character Displacement: Observational Evidence Intraspecific Character Displacement: Experimental Evidence Evolution of Alternative Phenotypes FREQUENCY-DEPENDENT DISRUPTIVE SELECTION AND THE EVOLUTION OF ALTERNATIVE PHENOTYPES EVOLUTION OF RESOURCE POLYMORPHISM EVOLUTION OF MATING POLYMORPHISM Intraspecific Character Displacement and Species Diversity Character Displacement Within Versus Between Species Summary Further Reading Box 5.1: Suggestions for Future Research 6. Ecological Consequences Introduction Evolution of the Niche Partitioning of Resources and Reproduction: A Reprise Community Organization Character Displacement and Darwinian Extinction Species Distributions and Geographic Mosaics Character Displacement and Species Ranges Summary Further Reading Box 6.1: Individual Variation and the Coexistence of Species Box 6.2: Suggestions for Future Research 7. Sexual Selection Introduction How Sexual Selection Works How Character Displacement Affects Sexual Selection EFFECTS OF PHENOTYPIC SHIFTS EFFECTS OF HABITAT SHIFTS Implications of Character Displacement's Effects on Sexual Selection How Sexual Selection Affects Character Displacement A Cautionary Note: Process Versus Pattern Summary Further Reading Box 7.1: Suggestions for Future Research 8. Speciation Introduction What are Species? How are Species Boundaries Maintained? Evolution of Isolating Mechanisms Character Displacement's Role in Speciation HOW CHARACTER DISPLACEMENT FINALIZES SPECIATION HOW CHARACTER DISPLACEMENT INITIATES SPECIATION HOW INTRASPECIFIC CHARACTER DISPLACEMENT INITIATES SPECIATION Summary Further Reading Box 8.1: Selection and the Evolution of Reproductive Isolation Box 8.2: Suggestions for Future Research 9. Macroevolution Introduction Competition in the Fossil Record Methods for Studying Macroevolution: Rewinding the Tape of Life Adaptive Radiation SPECIES PROLIFERATION DIVERGENT EVOLUTION Evolutionary Escalation Macroevolution: Red Queen or Court Jester? Summary Further Reading Box 9.1: Suggestions for Future Research 10. Major Themes and Unsolved Problems Introduction Major Themes of the Book CHARACTER DISPLACEMENT IS A PROCESS, NOT A PATTERN CHARACTER DISPLACEMENT CAN PRODUCE DIFFERENT FORMS OF TRAIT EVOLUTION ECOLOGICAL AND REPRODUCTIVE CHARACTER DISPLACEMENT INTERACT PHENOTYPIC PLASTICITY CAN MEDIATE CHARACTER DISPLACEMENT CHARACTER DISPLACEMENT PROMOTES DIVERSIFICATION AT MULTIPLE LEVELS CHARACTER DISPLACEMENT AND SEXUAL SELECTION INTERACT CHARACTER DISPLACEMENT HAS MACROEVOLUTIONARY IMPLICATIONS Some Unsolved Problems Summary Cover 2 Title Page 5 Copyright Page 6 Table of Contents 7 Preface 11 Chapter 1. Discovery of a Unifying Principle 17 A Brief History 20 Detecting Character Displacement 26 Phenomena Mistaken for Character Displacement 30 What Constitutes Character Displacement? Conflation of Process and Pattern 35 Reproductive Character Displacement Versus Reinforcement 36 Terminology 37 Box 1.1: Alternative Manifestations of Character Displacement 38 A Unifying Principle 41 Box 1.2: Suggestions for Future Research 42 Summary 43 Further Reading 43 Chapter 2. Why Character Displacement Occurs 45 Why Ecological Character Displacement Occurs 46 Box 2.1: Alternative Models of Species Coexistence 52 Box 2.2: Is Competitively Induced Plasticity Character Displacement? 60 Why Reproductive Character Displacement Occurs 64 Box 2.3: Suggestions for Future Research 69 Summary 70 Further Reading 70 Chapter 3. When Character Displacement Occurs 73 Facilitators of Character Displacement 74 Variation in the Expression of Character Displacement 81 How Ecological and Reproductive Character Displacement Facilitate Each Other 85 How Ecological and Reproductive Character Displacement Can Impede Each Other 93 Box 3.1: Suggestions for Future Research 94 Summary 94 Further Reading 95 Chapter 4. How Character Displacement Unfolds 97 Mechanisms of Divergence 98 Tempo and Mode of Character Displacement 109 Summary 118 Box 4.1: Suggestions for Future Research 119 Further Reading 120 Chapter 5. Diversity and Novelty Within Species 121 How Intraspecific Character Displacement Works 122 Intraspecific Character Displacement: Observational Evidence 124 Intraspecific Character Displacement: Experimental Evidence 126 Evolution of Alternative Phenotypes 127 Intraspecific Character Displacement and Species Diversity 142 Character Displacement Within Versus Between Species 145 Summary 146 Box 5.1: Suggestions for Future Research 147 Further Reading 147 Chapter 6. Ecological Consequences 149 Evolution of the Niche 150 Partitioning of Resources and Reproduction: A Reprise 152 Box 6.1: Individual Variation and the Coexistence of Species 155 Community Organization 159 Character Displacement and Darwinian Extinction 162 Species Distributions and Geographic Mosaics 166 Character Displacement and Species Ranges 167 Summary 169 Box 6.2: Suggestions for Future Research 170 Further Reading 171 Chapter 7. Sexual Selection 173 How Sexual Selection Works 175 How Character Displacement Affects Sexual Selection 176 Implications of the Effects of Character Displacement on Sexual Selection 184 How Sexual Selection Affects Character Displacement 190 A Cautionary Note: Process Versus Pattern 191 Box 7.1: Suggestions for Future Research 192 Summary 192 Further Reading 193 Chapter 8. Speciation 195 What are Species? 195 How are Species’ Boundaries Maintained? 198 The Evolution of Isolating Mechanisms 199 Box 8.1: Selection and the Evolution of Reproductive Isolation 202 Character Displacement’s Role in Speciation 205 Summary 218 Box 8.2: Suggestions for Future Research 219 Further Reading 219 Chapter 9. Macroevolution 221 Competition in the Fossil Record 223 Methods for Studying Macroevolution: Replaying the Tape of Life 227 Adaptive Radiation 229 Evolutionary Escalation 240 Macroevolution: Red Queen or Court Jester? 244 Summary 245 Box 9.1: Suggestions for Future Research 246 Further Reading 246 Chapter 10. Major Themes and Unsolved Problems 249 Major Themes of the Book 250 Some Unsolved Problems 254 Summary 258 References 259 Index 307

Evolutionary biology has long sought to explain how new traits and new species arise. Darwin maintained that competition is key to understanding this biodiversity and held that selection acting to minimize competition causes competitors to become increasingly different, thereby promoting new traits and new species. Despite Darwin's emphasis, competition's role in diversification remains controversial and largely underappreciated.

In their synthetic and provocative book, evolutionary ecologists David and Karin Pfennig explore competition's role in generating and maintaining biodiversity. The authors discuss how selection can lessen resource competition or costly reproductive interactions by promoting trait evolution through a process known as character displacement. They further describe character displacement's underlying genetic and developmental mechanisms. The authors then consider character displacement's myriad downstream effects, ranging from shaping ecological communities to promoting new traits and new species and even fueling large-scale evolutionary trends. Drawing on numerous studies from natural populations, and written for a broad audience, Evolution's Wedge seeks to inspire future research into character displacement's many implications for ecology and evolution.