Character Displacement: Definition & Example

Character Displacement: Definition & Example
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  • 0:01 Competitive Exclusion
  • 1:25 Niche Usage
  • 2:39 Character Displacement
  • 3:57 Darwin's Finches
  • 5:08 Anolis Lizards
  • 6:10 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
In this lesson, we'll explore the evolutionary phenomenon of character displacement. We'll learn how natural selection, as well as sexual selection, acts to reduce competition between similar species.

Competitive Exclusion

Have you ever noticed how organisms seem to appear perfectly designed to utilize and exploit specific resources within their environment? Just look at the wide and diverse variety of bird beaks.

Bird Beak Diversity

Each one seems suited to feed on a particular type of food. Pointy beaks are great for digging insect out of crevices, while thick stumpy beaks are perfect for cracking thick nuts and seeds. This wide diversity of specialization also reduces competition among bird species, meaning birds living in the same habitat feed on different food items with very little overlap.

This absence of identically overlapping resource utilization (resources being food, territory, or some other environmental factor) was first explained by a Russian ecologist named Georgy Gause. Gause recognized that two species could not compete for the exact same resources and coexist at the same population levels - one species was always more successful and would outcompete the other, excluding them from the resource. As a result, one species would thrive while the other would eventually be exterminated. This is why no two coexisting species of bird feed on the exact same food items. Instead, there is always some variation among their diets, and these variations led to the amazing evolutionary radiation of beak designs.

Niche Usage

So, what does this really mean, and why is it such a big deal? Well, if you, as a scientist, were able to establish the premise of Gause's Law, you could study two very similar, coexisting species (such as two species of finches, for example) and explore the little structural differences in the shape and size of their beaks. You could then compare those with the species' fundamental niches, the resources that they could theoretically use based on their physical traits, versus their realized niches, the resources that they actually use.

By relying on Gause's Law, you could then assume that the difference between two species' theoretical and actual usages (as well as the associated slight beak shape and size differences) is the product of some evolutionary adaptation or shift where natural selection favored those finches that fed on items that other similar species did not. This diet 'diversification' would, as a result, reduce competition for food between the two similar species and result in slight physical variations, making them better adapted to thriving in their particular 'realized niches'. One explanation for such an evolutionary shift is a phenomenon called character displacement.

Character Displacement

Character displacement is an evolutionary divergence that occurs when two similar species inhabit the same environment. In this instance, natural selection favors those organisms that develop modifications (either behavioral, morphological, or physiological) that reduce their competitive pressures for resources, thus increasing their chance for survival.

This 'character divergence' (or 'displacement'), being an overt feature, makes the two coexisting species easily distinguishable from one another. However, when they occur alone, this divergent character is absent, making the two independently occurring species nearly indistinguishable. This independent and indistinguishable state is known as competitive release, where, in the absence of a similar species, one species is essentially released from the constraints of the competitive pressure imposed by the other similar organism and, in turn, is able to expand its niche to absorb resources that the other similar species would have utilized, had it been present.

Wow! I know that sounded like a lot of complicated talk, so let's take a moment to look at a few classic examples to make sense of character displacement. Two of the most notable examples are two species of Darwin's finches and the island dwelling Anolis lizards.

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