About the Book
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.
Table of Contents
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
