Explanation
Correct answer: B.
Choice B is the best answer because it most logically completes the text’s discussion of Hertel et al.’s study of dietary mix variation among female brown bears. According to the text, the researchers evaluated genetics, local resource availability, and social learning as factors in female brown bears’ trophic position, or position in the food web. According to the text, daughters tended to settle near their mothers after separating and held the same trophic positions as the mothers for two years, but no longer did by the fifth year—a temporary similarity that may reflect a socially learned behavior that faded over time after separation. Additionally, the text states that the degree of similarity in trophic position between nonmaternal relatives (e.g., cousins) was the same as that between unrelated individuals, suggesting that genetics don’t significantly influence dietary mix, and the text also states that there was modest similarity in the trophic positions of unrelated individuals in similar habitats, suggesting that environmental conditions (which would include resource availability) may have some influence on dietary mix. Taken together, the findings suggest that while environmental constraints can’t be ruled out as a contributing factor, dietary mix among female brown bears may reflect a social learning effect that eventually diminishes.
Why the other choices are wrong
Choice A
Choice A is incorrect because the text notes that daughters tended to settle near their mothers after separating—that is, that they often didn’t leave the maternal habitat. Therefore, changes in resource availability in the mothers’ habitats would likely have affected the daughters similarly instead of causing their dietary mix to differ from that of their mothers. Further, the form of social learning addressed by the text is that between mothers and daughters; although the daughters no longer held the same trophic position as their mothers five years after separating from them, the text doesn’t address the possibility that the daughters’ divergence from the dietary behaviors of their mothers is the result of learning from other bears or suggest that the daughters even interacted with other adult bears in a substantive way.
Choice C
Choice C is incorrect. Instead of suggesting that environmental conditions are the most important factor in dietary mix variation and that social learning isn’t a factor, the findings discussed in the text suggest that environmental conditions may have some effect (since there was modest similarity in dietary mix between unrelated bears in similar habitats, or similar environmental conditions) and that social learning may be a factor (since daughters held the same trophic positions as their mothers for two years after separating but not for five years, which may reflect daughters maintaining dietary behaviors they learned from their mothers but changing their behaviors over time).
Choice D
Choice D is incorrect because the findings presented in the text argue against, not for, genetics as a significant factor in variation in dietary mix. The text indicates that independent of their habitats, the degree of similarity in dietary mix between nonmaternal relatives, like cousins, was the same as that between unrelated individuals. This means that genetic relatedness didn’t have a detectable effect on dietary mix independent of shared habitat.