Karin Pfennig & David Pfennig 
Evolution’s Wedge 
Competition and the Origins of Diversity

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.

Inhaltsverzeichnis

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

Über den Autor

David W. Pfennig is Professor of Biology at the University of North Carolina. Karin S. Pfennig is Associate Professor of Biology at the University of North Carolina.