Isolating Mechanisms — Definition & Examples

What Are Isolating Mechanisms in Evolution?

Isolating mechanisms are types of isolation, like behavioral and geographic, that can lead to the formation of new species. Don't forget that biologists define species as populations that can breed and produce fertile offspring. One species becoming two is called speciation. So basically, mechanisms of isolation can lead to speciation.

Like the name suggests, isolation happens when part of a population becomes separated and stops breeding with the other part. After a long enough time being separated, the two populations might not be able to produce offspring with each other, called reproductive isolation. At this point, both parts of the populations evolve towards being two completely separate species.

What Are the Types of Isolating Mechanisms?

The three types of isolation are called behavioral isolation, geographic isolation, and temporal (time) isolation.

Behavioral isolation happens when some kind of behavior changes within a population, like how males court females with songs. If half the population uses one song to attract females and the other half is using a different song, the two parts will not mix, and they become isolated.

Geographic isolation is easier to visualize. It happens when a population is somehow divided by geography, like back when the continents separated. On a smaller scale, populations can become separated by rivers, mountains, or bodies of water. A type of squirrel actually became two separate species because the grand canyon divided the population.

Temporal isolation means that the population was divided by time. Temporal is a fancy way of saying time. If half of a population mates in January and the other half mates in June, they will eventually become different species. Because they mate in different months, the two parts of the population can't breed with each other.

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

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

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

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

What Causes Isolation?

There is a wide range of factors that can isolate species from one another. Isolating mechanisms, in the end, cause speciation by preventing two species from mating with one another. Speciation occurs when two species can no longer mate and produce a viable offspring.

Isolating mechanisms come in two main types: separation due to geographic isolation and separation which occurs in the same location.

Geographically separated species are more common. For example, a single shrimp population used to live where Panama now resides. After the formation of the land bridge that separates the Caribbean Sea and the North Pacific Ocean, different species of shrimp descended from the original shrimp species as each adapted to its unique environment.

Although less common, it is possible for the divergence between populations to occur when they still reside in the same location.

An example of this is between the Hawthorne and Apple Maggot Flies. Although they live in the same location, certain individuals of the original species preferred feeding on the Hawthorne tree while others preferred the apple tree. Therefore, there was a divergence of species as the life cycles of some flies began to line up more with the Hawthorne tree while others began to line up more with the life cycle of the apple tree.

Eventually, these two species were separated both by time and behavior, since one's life cycle depended on when the Hawthorne tree's fruit matured, while the other's life cycle depended on when the apples matured. After a while, gene flow between the two groups stopped, and they became separate species.

Types of Isolating Mechanisms

Isolation is what keeps species separated. This can include things like their geographic location, their mating seasons, their behaviors, and the biochemical properties of their reproductive process. These factors are called prezygotic isolation mechanisms because they happen before an organism is born.

Basically, if a sperm cell and an egg cell are able to fuse, fertilize, and result in a living offspring, the parents are of the same species.

As you may have guessed, we can also have postzygotic isolation. An example is when horses and donkeys mate and create a mule. This hybrid species is sterile, meaning that it can't reproduce. This isolates the mule from interacting (reproducing) with other species.

Isolation is a driving force behind evolution because the changes that build up in different populations over time is what causes the evolution of new species. When two populations are isolated by enough mechanisms, they can be considered different species. This process is called speciation.

How Do We Get New Biological Species?

Isolating mechanisms are the ways in which groups of organisms become separated for long enough to develop into different species. They help cause speciation. Some examples include geographic, temporal, reproductive, and behavioral isolation.

For two groups of organisms to be considered separate species, they must not be able to produce viable offspring. This means that they can't have children that can also have children.

Hybrid Offspring

For example, horses and donkeys produce mules, but mules are unable to reproduce. This is called hybrid sterility. Therefore, horses and donkeys are different species. For horses and donkeys to have evolved into separate species, they must have become separated by an isolating mechanism at some point in their evolutionary past.