An evolutionary biologist makes decisions about whether to consider three different populations of damselflies as separate species, based on observations of the individuals with which these damselflies will mate. All combinations of these populations are able to mate with one another and all combinations produced offspring. This biologist is most likely employing species concept.

Biological

Explanation:

The biological species concept differentiates one species from the others on the basis of reproductive isolation. It assumes that the two organisms that belong to different species can not interbreed to produce a viable and fertile progeny. On the other hand, the members of the same species can reproduce with each other to produce progeny. In the given example, the populations of damselflies are observed for their reproductive behavior. Since the flies of all the populations are able to breed with each other, they belong to the same biological species.