Answer:
The right answer to this question is: Selective pressure.
Step-by-step explanation:
When learning about Darwin's theory, the evolution, we learned that organisms can adapt themselves with time due to the pressure of the environment and mutations. On these four islands, what could have happened is that the same selective pressure happened on four of them, one pressure that can be mentioned and it's a very big problem nowadays is global warming. If this species is sensitive to the global warming problem, it'll probably die or adapt itself on the next generations, having the possibility of developing the same ecomorphs on all four islands.