Explanation
Correct answer: B.
Choice B is the best answer because it most accurately states the main purpose of the text. The text begins by introducing research on variation in frugivorous birds’ feeding patterns based on the specific part of their habitat range the birds occupy. The text then explains that birds at the geographic edges of their range feed selectively based on beak size, whereas birds at altitude-based boundaries feed based on local competition with other species. Therefore, the main purpose of the text is to present research findings concerning how location within a habitat affects the feeding patterns of frugivorous birds.
Why the other choices are wrong
Choice A
Choice A is incorrect. Although the text does discuss studying habitats of frugivorous birds, it doesn’t address specific research methods.
Choice C
Choice C is incorrect. Although the text mentions territorial competition as a factor affecting the feeding patterns of frugivorous birds at elevation boundaries, nothing in the text suggests that such competition affects the boundaries of those birds’ habitats.
Choice D
Choice D is incorrect. Although the text mentions beak size as a key factor shaping frugivorous birds’ feeding patterns at the geographic boundaries of the birds’ natural range, it doesn’t compare the relative importance of different factors or indicate that habitat boundaries matter more than beak size. Instead, the text presents findings showing that different types of boundaries—geographic and elevational—are associated with different influences on feeding patterns.