Dolphins and porpoises are closely related species. name three pieces of evidence for evolution you could look at that would support this claim:  

similarities among organisms alive today, similarities in DNA, similarities of embryos

Explanation:

there are five types of evidence,

ancient organisms remains, fossil layers

are the other two, and they dont seem to apply to currently living creatures

Both the porpoise and dolphins are categorized in similar mammalian order Cetacea. Both exhibit streamlined body, their hindlimbs are vestigial, forelimbs got modified into flippers, and both primarily eat fish.  

The porpoises and dolphins are evolutionarily closely associated as both are toothed whales, in comparison to another group of Baleen whales. All the individuals of Cetacea are the progenies of terrestrial ungulates. The primitive ancestors first originated into the sea about fifty million years ago, and about 35 million years ago, there took a partition in the two distinct lines, of these the toothed whales established a strong sense of echolocation.  

Well

1. It's definitely not population because in the question itself it says in DIFFERENT populatons,

2.it's not Ecosphere because that has to do with the planet not a collection of organisims.

3.A community is where there are animals that have something in common meaning not different.

4.Therefore, the answer is Ecosystem