Character Displacement: The Best Example and Why It Matters in Evolution

Understanding how species interact and evolve is fundamental to ecology and evolutionary biology. Among the most important concepts in this field is character displacement—an evolutionary process that explains how similar species living together evolve differences to reduce competition. This article explores what character displacement is, identifies the most appropriate example from a set of statements, and explains why this concept is crucial for understanding the diversity and coexistence of life.

What Is Character Displacement?

Character displacement is the phenomenon where differences among similar species are accentuated in regions where their distributions overlap (sympatry), but are minimized or lost where the species do not overlap (allopatry)157. This pattern results from evolutionary changes driven by competition for limited resources, such as food or habitat. The classic explanation of character displacement was provided by William L. Brown Jr. and E. O. Wilson in 1956, who observed that closely related species become more distinct when they live together compared to when they live apart.

The Core of Character Displacement

The essence of character displacement lies in the following pattern:

• Allopatric populations: When similar species live in different areas, they are often morphologically, ecologically, or behaviorally similar.

• Sympatric populations: When these species live together, they evolve differences that reduce competition, making them more distinct from each other.

These differences can be in morphology (such as body size or beak shape), behavior, or physiology. The process is driven by natural selection favoring individuals that compete less with the other species.

The Most Appropriate Example of Character Displacement

Given the following statements, let’s analyze which best exemplifies character displacement:

1. Two related species depending on the same prey species avoid competition by feeding at different times of the day.

   • This describes niche partitioning or temporal partitioning, not character displacement. The differences are behavioral and not necessarily evolutionary or morphological.

2. The body sizes of two related species are very similar when they are allopatric, but in geographical areas of sympatry, one species is significantly smaller than the other.

   • This is the classic example of character displacement. The species are similar when apart but evolve differences in body size when together, reducing competition.

3. The food niche of a species is generally wider in the absence of competing species than in their presence.

   • This describes niche contraction or competitive release, not character displacement.

4. Closely related species can coexist if their densities are regulated by a predator.

   • This refers to a coexistence mechanism via predation, not character displacement.

Conclusion:
The most appropriate example of character displacement is statement (2):
The body sizes of two related species are very similar when they are allopatric, but in geographical areas of sympatry, one species is significantly smaller than the other.

Why This Example Best Illustrates Character Displacement

This example perfectly captures the essence of character displacement:

• Allopatric similarity: When the species live apart, their body sizes are similar.

• Sympatric divergence: When they live together, one species becomes significantly smaller, reducing competition for resources.

This pattern is the result of evolutionary change driven by competition, not just behavioral adjustment. It is a heritable, morphological difference that allows the species to coexist by partitioning resources.

Real-World Examples of Character Displacement

Character displacement is observed in a variety of organisms:

• Darwin’s Finches: On the Galápagos Islands, finch species have similar beak sizes when living apart but evolve distinct beak sizes when living together, allowing them to specialize on different seeds.

• Anolis Lizards: In the Caribbean, lizard species show differences in body size and limb length when coexisting, enabling them to use different parts of the habitat.

• Salamanders: In the Appalachian Mountains, salamander species exhibit differences in body size only when they share the same environment.

These examples demonstrate how character displacement promotes biodiversity by allowing similar species to coexist through evolutionary divergence78.

The Mechanism Behind Character Displacement

Character displacement is driven by the following steps:

1. Competition: Two similar species compete for the same limited resource.

2. Natural Selection: Individuals that are least like the competing species in resource use have a survival advantage.

3. Evolutionary Change: Over time, the species evolve differences in traits that reduce competition, such as body size, beak shape, or feeding behavior.

This process is rooted in the principle of competitive exclusion (Gause’s Law), which states that two species cannot indefinitely occupy the same niche in a stable environment unless they differentiate156.

Types of Character Displacement

Character displacement can take two main forms:

• Ecological Character Displacement: Involves changes in traits related to resource use, such as feeding habits or habitat preference.

• Reproductive Character Displacement: Involves changes in traits related to mating or reproduction, such as mating calls or courtship behaviors, to reduce hybridization between species.

Both types help species reduce competition and coexist more harmoniously7.

The Importance of Character Displacement in Ecology

Character displacement is a key concept in ecology and evolutionary biology because it:

• Promotes Biodiversity: By allowing more species to coexist in the same habitat, character displacement increases overall biodiversity.

• Drives Speciation: The evolutionary changes that result from character displacement can lead to the formation of new species.

• Structures Communities: Character displacement helps shape the structure of ecological communities by promoting niche differentiation and reducing competition.

Character Displacement vs. Other Ecological Concepts

It is important to distinguish character displacement from other related concepts:

• Niche Partitioning: A broader concept where species divide resources to avoid competition. Character displacement is a specific type of niche partitioning that involves evolutionary change.

• Competitive Release: When a species expands its niche in the absence of competitors. This is not character displacement.

• Predator-Mediated Coexistence: When predators regulate the densities of competing species, allowing them to coexist. This is not character displacement.

The Role of Competition in Character Displacement

Competition is the driving force behind character displacement. When two species compete for the same resource, natural selection favors those that can exploit a slightly different niche. Over time, this leads to the evolution of distinct traits that reduce competition and allow both species to survive and reproduce.

Evidence for Character Displacement

Numerous studies provide evidence for character displacement:

• Morphological Differences: Species in sympatry are more distinct in traits related to resource use than those in allopatry.

• Behavioral Differences: Species may evolve different behaviors to reduce competition.

• Physiological Differences: Species may evolve different physiological adaptations to exploit different resources.

These differences are often genetically based and can be passed on to future generations157.

The Impact of Character Displacement on Conservation

Understanding character displacement is important for conservation because it:

• Highlights the Importance of Species Interactions: Maintaining the natural interactions between species is crucial for preserving biodiversity.

• Guides Habitat Management: Protecting habitats that allow for natural competition and niche differentiation can help preserve the evolutionary potential of species.

• Informs Restoration Efforts: Restoring ecosystems should consider the role of competition and character displacement in shaping community structure.

Summary Table: Character Displacement at a Glance

Conclusion

Character displacement is a fundamental evolutionary process that explains why similar species evolve differences when they live together but remain similar when apart. The most appropriate example is when the body sizes of two related species are similar when allopatric but diverge when sympatric. This process is driven by competition and natural selection, leading to evolutionary changes that promote biodiversity and species coexistence. Understanding character displacement is essential for appreciating the complexity of species interactions and for guiding conservation and management efforts in a changing world.