Explanation
Correct answer: B.
Choice B is the best answer because it presents a finding that, if true, would most directly support the researchers’ hypothesis that the smaller maximum size of PCFG whales is an adaptation to resource opportunities particular to their foraging range. The text explains that PCFG whales, a subgroup of ENP gray whales, forage along the coasts of Northern California and British Columbia rather than in the Arctic, where the main ENP group forages. The text goes on to state that PCFG whales reach smaller maximum sizes than other ENP gray whales despite having similar pre-maximum growth rates. If PCFG whales tend to forage in shallow, rocky kelp beds that whales as large as those in the main group cannot access, that would indicate that smaller body size confers a direct advantage in this foraging range—namely, access to a food source that larger whales cannot reach.
Why the other choices are wrong
Choice A
Choice A is incorrect because a finding describing recent trends in average body size for both groups of whales wouldn’t address whether the smaller maximum size of PCFG whales reflects an adaptation to their foraging environment. Recent stability or change in average size doesn’t speak to why the size difference between PCFG whales and the main ENP group exists.
Choice C
Choice C is incorrect because a finding about PCFG whales’ proximity to ports and urban populations wouldn’t address the resources available to PCFG whales or the relationship between body size and foraging. Proximity to human activity is irrelevant to a hypothesis about body size being an adaptation to resource opportunities.
Choice D
Choice D is incorrect. Although a finding about a certain prey species being available in the PCFG whales’ foraging waters but not in the main group of ENP whales’ foraging waters would establish that the PCFG foraging range offers distinct prey species, it wouldn’t connect the availability of those prey species to body size in a way that would explain the PCFG whales’ smaller size. Without indicating that the available prey in the PCFG range favors smaller whales, the finding falls short of supporting the hypothesis that smaller size is an adaptation to resource opportunities.