What characteristic allowed the same ecomorphs to be produced on all four islands even though the original species were different on each island?

The characteristic that allowed the same ecomorphs to be produced on all four islands even though the original species were different on each island is called identical selective pressures.

To add, selective pressure is any phenomena which alters the behavior and fitness of living organisms within a given environment.

       The right answer to this question is: Selective pressure.

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.