ECOLOGICAL INSULATION: MECHANISM AND EXAMPLES - BIOLOGY - 2025

The organic insulation is a mechanism with which the occurrence of interbreeding between two species is avoided that could produce hybrid offspring. A hybrid offspring is the result of the mixture of two individuals of different species.

For example, the mule or mule is a hybrid animal that originates as a result of the crossing of a donkey (Equus africanus asinus) with a mare (Equus ferus caballus). This animal shares some traits with both parent species.

Figure 1. Mule. Source: Pixabay.com

Also, the hinny is a hybrid species that results from the crossing of a donkey with a horse. Mules and hinnies have different genes. The mule is a stronger and larger animal than the hinny, and both are almost always sterile. In the rare cases of fertility in mules and hinnies, the young are weak and very underweight, with little chance of survival.

There are 5 ecological isolation processes that serve the function of preventing two different species from having hybrid or mixed offspring: ecological isolation, temporary isolation, behavioral isolation, spatial isolation, and mechanical / chemical isolation.

Ecological isolation mechanism

Ecological or habitat isolation is one of the 5 isolation mechanisms that prevent interbreeding between different species, prior to the formation of the zygote or egg (precigotic isolation mechanism).

This mechanism occurs when two species that could genetically interbreed have reproductive barriers because they live in different areas. This is how different populations can occupy the same territory but live in different habitats, and therefore do not physically meet each other.

In addition to the other isolation mechanisms, ecological isolation avoids the production of hybrid species that do not favor the growth and development of biological populations, since most hybrid individuals are sterile, that is, they are incapable of reproducing.

The species involved in hybrid crossing are considered to have an energy expenditure that is not successful. Additionally, these reproductive isolation mechanisms play a crucial selective role in speciation.

Speciation is the process by which new species are formed. The speciation process is the one that has originated the diversity of organisms or biological diversity.

Examples of ecological insulation

Below are several examples of ecological insulation.

Ecological isolation in mammals

In India there are the tiger (Panthera tigris) and the lion (Panthera leo), two species of the same family (Felidae), which have the ability to interbreed.

However, the tiger lives in the jungle and the lion lives in the grasslands; as the two species live in different habitats, their physical encounter does not occur. Each species, both the lion and the tiger, are isolated in their habitats.

Ecological isolation in insects

The Anopheles maculipennis group consists of 6 species of mosquitoes, some of which are associated with the transmission of malaria. Although these 6 species are very similar and morphologically indistinguishable, they can rarely produce hybrids, because they are isolated for their reproduction and interbreeding, in part by reproducing in different habitats.

While some species of Anopheles maculipennis breed in brackish water, others do so in fresh water. Among the species that mate in fresh waters, there are some that do so in running waters and others that prefer stagnant waters.

Ecological isolation in birds

One of the most cited examples of ecological isolation is the case of two closely related birds of the genus Turdus, such as the common blackbird (Turdus merula), and the white-capped blackbird (Turdus torquatus).

Figure 2. Male common blackbird. (Turdus merula). Source: AnemoneProjectors

The population of T. merula, a species that inhabits timber tree areas in forests and urban gardens, is ecologically isolated from T. torquatus, a species that breeds in high mountain areas. Therefore, the chances of these species producing a hybrid is practically nil.

Figure 3. White-capped blackbird (Turdus torquatus). Source: Andrej Chudý from Slovakia

Ecological isolation in amphibians

Reproductive ecological isolation is also observed in different species of frogs. One of the many examples of this case is found in North America.

In North America the population of the northern red-legged frog (Rana aurora) is isolated from the population of the American bullfrog (Rana catesbeiana), since the former mates in ephemeral, fast-moving streams of water, and the latter does so. does in permanent wells or ponds.

In Australia, the crucifix frog (Notaden bennettii) and the desert tree frog (Litoria rubella) are found in desert environments. However, they are highly unlikely to mate, since the crucifix frog lives below ground and only moves to the surface when it rains, while the desert tree frog is a tree species.

Ecological isolation in fish

Another interesting example of this type of ecological reproductive isolation is observed in the spiny fish of the Gasterosteidae family. These fish have an elongated and fine body (fusiform), with 2 to 16 spines in their dorsal area and lack scales, although some species have a kind of bony plate armor.

While freshwater Gasterosteidae fish species live in flowing waters throughout the year, marine species found in the sea in winter migrate to river estuaries in spring and summer to mate.

In this case, the factor that acts as a reproductive barrier that prevents the two groups from interbreeding is adaptation to different salt concentrations.

Ecological insulation in plants

Another example of ecological isolation occurs in the case of the two species of spider plants of the genus Tradescantia, the Ohio spider plant (Tradescantia ohiensis) and the zigzag spider plant (Tradescantia subaspera).

Both plants live in common geographic areas, but are unable to interbreed due to the difference in habitats. T. ohiensis grows in sunny areas, while T. subaspera prefers shady areas with little sun.

Additionally, these plants bloom at different times of the year, that is, they also present temporary isolation.

We can conclude that in ecological isolation the separation of groups of organisms occurs as a result of changes in their ecology or changes in the environment in which they live.

References

1. Bradburd, GS, Ralph, PL and Coop, GM (2018). Disentangling the effects of geographic and ecological isolation on genetic differentiation. 67 (11): 3258-3273. doi: 10.1111 / evo.12193
2. Fraser, IC, Morrison, AK, McC Hogg, A., Macaya. EC, van Sebille, E. et all. (2018). Antarctica's ecological isolation will be broken by storm-driven dispersal and warming. Nature Climate Change. 8: 704–708.
3. Gray, LN, Barley, AJ, Poe, S., Thomson, RC, Nieto ‐ Montes de Oca, A. and Wang, IJ (2018). Phylogeography of a widespread lizard complex reflects patterns of both geographic and ecological isolation. Molecular Ecology banner. doi: 10.1111 / mec.14970
4. Hodges, SA and Arnold, ML (2018). Floral and ecological isolation between Aquilegia formosa and Aquilegia pubescens. Proceedings of the National Academy of Sciences of the United States of America. 91 (7): 2493-2496. Doi: 10.1073 / pnas.91.7.2493
5. Schaefer, M. (1972). Ecological isolation and the importance of competition, exemplified by the distributional pattern of the lycosids of a coastal landscape. Oecology. 9 (2): 171-202. doi: 10.1007 / BF00345881