Life on Earth is a wondrous thing. It will do everything it possibly can, to make sure it survives. Every organism in this world has a wonderful ability to adapt to changes in it’s surroundings. This adaptation is what allows it to tolerate small changes in it’s environment; be in temperature, humidity or salinity changes. But what happens when an organism is taken and transported to a completely new environment? What if the conditions there are vastly different from it’s native habitat?
Every species has a specific range within which it can tolerate ecological changes. This range is called ecological amplitude. Within this amplitude, an organism has three broad responses.
These are otherwise called ecads or morphologically-changed forms. When a species is transported to a new environment, it’s first response will be to develop abilities to survive there. For example, when a European comes to the tropics, the immediate response is increased production of melanin-his skin becomes darker. Such changes are quite common in plants. For example, a species of grass called Euphorbia hirta has two different ecophenes; one that has adapted to grow in dry, hard soils and the other that grows in places that have been heavily trampled.
You can see examples of this in humans as well; an American living in Africa, and one living in northern Europe will have differences in the features.
These differences among ecophenes and not permanent. They are just temporary variations to survive the new conditions. The body of the organism assumes that it is going to be in these new conditions for a short while only. Therefore, ecophenes from different habitats, when brought together, become similar. If that American from Africa was to move to northern Europe, he would start to grow fairer.
This reversibility is because there has been no change in the genetics of the two separate ecophenes.
However, if two of these ecophenes were to remain in their new habitat for too long, these morphological (physical) changes will start becoming permanent. The body figures that if I’m going to be here permanently, might as well make these adaptations permanent!
That’s why, if that American spends too long in Africa, he is going to develop a permanent tan. It will not go if he returns to America or goes to Northern Europe (Ok, I tried to Google “American with tan” for a picture here, and I got results with pictures of Donald Trump. Not kidding!)
Likewise, the grass Euphorbia hirta has two ecotypes as well. One that has permanently adapted to surviving in moist conditions, and the other adapted to surviving in dry conditions (within this dry, you have the two ecophenes explained above).
This permanence in the adaptations arise due to changes in genes. Two ecotones of an organism will show minor variations in their genetic stock.
Now, if two ecotones have been separated from each other for a very long time. The adaptations become a permanent part of the genes. They are still the same species, but their difference physically and genetically are very distinct. In fact, two ecospecies cannot produce viable off-springs (which the ecophenes and ecotones can).
These ecospecies, left alone for many, many generations, then develop sufficient changes in them to become a separate species.
That’s the long version of how new species are born. What happens if the environmental conditions exceed the ecological amplitude? Extinction.
The current extinction crisis is because of this very reason. The organisms are unable to adapt quickly because their amplitude is limited, with respect to the changing environment.