Question

in many agricultural environments, the banks of streams are kept forested to protect water quality, but it’s been unclear what effects these forests may have on stream biodiversity. to investigate the issue, biologist xingli giam and colleagues studied an indonesian oil palm plantation, comparing the species richness of forested streams with that of nonforested streams. giam and colleagues found that species richness was significantly higher in forested streams, a finding the researchers attribute to the role leaf litter plays in sheltering fish from predators and providing food resources. which choice best states the main purpose of the text? choose 1 answer: a it explains the differences between stream - protection strategies used in oil palm plantations and stream - protection strategies used in other kinds of agricultural environments. b it presents a study that addresses an unresolved question about the presence of forests along streams in agricultural environments. c it discusses research intended to settle a debate about how agricultural yields can be increased without negative effects on water quality. d it describes findings that challenge a previously held view about how fish that inhabit streams in agricultural environments attempt to avoid predators.

Explanation:

• Option A: The text doesn't compare stream - protection strategies between oil palm plantations and other agricultural environments. It focuses on the effect of forested stream banks on biodiversity, so A is incorrect.
• Option B: The text starts by saying it's unclear what effects these forests (stream - side forests) have on stream biodiversity. Then it presents a study by Giam and colleagues that addresses this unresolved question. This option matches the main purpose of the text.
• Option C: The text is not about increasing agricultural yields without negative effects on water quality. It's about the effect of forested stream banks on stream biodiversity, so C is incorrect.
• Option D: The text doesn't challenge a previously held view about how fish avoid predators. It presents a study on the effect of forested streams on biodiversity and attributes the higher species richness to leaf litter's role in protecting fish and providing food, so D is incorrect.

Answer:

B. It presents a study that addresses an unresolved question about the presence of forests along streams in agricultural environments.