I don't know if this question has answer choices, but it can be said that this study is about environmental or behavioral adaptation in mice. More specifically, you might even say this is an example of dietary adaptation in a population representing one generation. Such adaptation is characteristic of evolution over large time-spans, but this study can show that even within a single generation, adaptation can occur under extreme conditions, like the abrupt absence of a major food source. Due to the drought, the mice must adapt to a minor food source for several years, but by the time the drought has ended, the mice are already accustomed to their diet and do not necessarily fall right back to eating mainly berries. The paper's title includes the word "selection" to show that the mice actively choose what to eat based on what is most available/efficient at the time.
