Behavioral Isolation — Definition & Examples

An Example of Isolating Behaviors

Behavioral isolation prevents members of a species from mating. It's one of many processes that lead to speciation. Through this process, members of a population diverge over time in their behaviors. This continues until they can no longer mate. They then become separate species.

Behavioral isolation also prevents species that just diverged from interbreeding. This keeps the two species from merging to become the same species again.

Let's look at an example. There are two frog species living in the same environment. Two members from these related species could technically mate. However, they do not mate due to behavioral barriers.

How does behavioral isolation cause this? Well, if courtship behaviors are too different, then the individuals don't recognize each other as potential mates. This means they won't breed. In these cases, the two species will never get to the point of reproducing with each other, even if in theory the two species could physically produce healthy offspring.

Here's an example of how isolation could develop and lead to speciation:

Say the males of a particular bird species attract mates by dancing. In a population of these birds, there is variation between how each bird dances. This variation in dancing behavior is also heritable, meaning the behavior can be passed from parent to offspring.

Female birds now come looking for suitable and healthy mates to carry on their genetic lines. They watch all the males dance, and wouldn't you know it, their preferences for mates vary just like the dances vary. Some of the lady birds like one male's dance, while others might like another bird's dance better.

The lady birds have chosen their mates, and now they pair off with their chosen mating partners.

Now that the females have chosen their partners based on which mating behaviors they find most attractive, they mate with them.

The birds mate and have offspring. Since offspring inherit traits from their parents, they also have distinct mating behaviors. The sons from a set of parents will have similar mating dances to their dads, and the daughters will prefer certain dances, just like their moms.

If this continues for many generations, at some point the bird species will likely diverge over time to form new species.

What Is Behavioral Isolation?

It's a type of reproductive isolation, meaning it prevents some members of a population from mating with others. It is also a type of pre-zygotic barrier because it happens before two organisms try to reproduce.

This type of isolation is based on how members of a species find and choose mates. Many species have very specific behaviors and rituals that they carry out before reproducing. In these species, most often the female will prefer to mate with a male who can display that behavior.

Behavioral isolation can include auditory, visual, and chemical stimuli which alert a potential mate.

An auditory stimulus would be a type of call or song.

A visual stimulus would be a dance or some type of ritual display.

A chemical stimulus would be produced by pheromones. These are chemicals secreted by one organism which can evoke a response from another organism.

How Does It Lead to Speciation?

Suppose we have one population of very similar organisms which can reproduce with one another. All of these organisms would be considered one species. However, if some of the females only mate with males in the population who can make a specific sound, this is called behavioral isolation.

This can lead to speciation over time. As more time goes by, the subgroups continue to become different until they are no longer able to interbreed. They become two different species.

Once speciation occurs, the isolating behaviors ensure mating only happens between members of the same species by making it easy to recognize potential mates. This also prevents the waste of energy and time on looking for and mating with individuals that won't produce fertile or viable offspring.

Why Is It Beneficial?

Limiting the number of potential mates and narrowing the gene pool is not always beneficial to an organism. However, while behavioral isolation can have a negative impact on an individual, it will benefit the entire species as a whole. Environmental pressures that an entire population faces lead to small changes that can cause isolating behaviors and then (possibly) speciation.

Isolating Mechanisms

Behavioral isolation is a mechanism of evolution that can lead to speciation. It is sometimes called ethological isolation. This happens when two populations of the same species develop some difference in behavior. A common example is mating rituals. Due to differences in their behaviors, the populations may be unable to recognize each other as potential mates. Over a long time with no interbreeding, behavioral isolation can lead to speciation.

Different mating rituals can lead to isolation. One example is birds singing different songs to attract mates. Other examples include different preferences in breeding calls, mating dances, and pheromones.

Fireflies find mates using distinct patterns of flashing. Only members of the same species can recognize the specific flashing pattern as a potential mate. Each species has its own unique pattern of flashing, which prevents interbreeding.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Speciation}}$ : One species splitting into two distinct species

$\color{#8925AE}{\text{Isolating Mechanisms}}$ : Types of isolation that lead to the formation of a new species

$\color{#8925AE}{\text{Behavioral Isolation}}$ : A portion of a species undergoes a behavior change and no longer mates with the other part of the species

$\color{#8925AE}{\text{Geographic Isolation}}$ : A portion of a species becomes separated by geography and can no longer mate with the other part of the species

$\color{#8925AE}{\text{Temporal Isolation}}$ : A portion of a species changes the time they are awake or time they breed, and they can no longer mate with the other part of the species

Differences in Mating Behaviors

Behavioral isolation leads to speciation. This is defined as the divergence of one species into multiple distinct species over time. For this reason, it is sometimes referred to as a "mechanism" of speciation.

Behavioral isolation occurs when populations of the same species begin to develop different behaviors that are not recognized or preferred by members in another population.

The most common example of behavioral differences is mating calls. Two populations of the same species can have slightly different mating calls. Over time, members begin to prefer their own population's mating call. Eventually, members will begin to not respond to populations other than their own. Eventually, these two populations will develop into two separate species, as they only breed within their population.

What's a Specific Example?

Meadowlarks display behavioral isolation. Western meadowlarks and eastern meadowlarks may look very similar. However, they are actually two distinct species that arose from the same species. The western meadowlark uses a different mating call than that of the eastern meadowlark. Western meadowlarks do not respond to the mating calls of the eastern meadowlark, and vice versa. Because the two populations do not mate, they are no longer considered members of the same species.

This type of isolation is an example of a pre-zygotic barrier because it prevents mating before the formation of a zygote. Other forms of pre-zygotic barriers are temporal isolation, ecological isolation, and mechanical isolation.

(Video) The Bowerbird's Grand Performance

by BBC Earth

Birds have some pretty interesting mating rituals. In this video, you will see the flashy mating behavior of a male bowerbird. This unique mating behavior allows females to recognize members of their own species.

(Video) Behavioral Isolation

by Buzzle

This video talks about how differences in behavior can lead to isolation. This is a type of prezygotic barrier. It prevents different species from mating and creating fertile offspring. You will also see some examples of it in nature.