Question

question 19
researchers hypothesized that a decline in the population of dusky sharks near the mid-atlantic coast of north america led to a decline in the population of eastern oysters in the region. dusky sharks do not typically consume eastern oysters but do consume cownose rays, which are the main predators of the oysters.
which finding, if true, would most directly support the researchers’ hypothesis?
a) declines in the regional abundance of dusky sharks’ prey other than cownose rays are associated with regional declines in dusky shark abundance.
b) eastern oyster abundance tends to be greater in areas with both dusky sharks and cownose rays than in areas with only dusky sharks.
c) consumption of eastern oysters by cownose rays in the region substantially increased before the regional decline in dusky shark abundance began.
d) cownose rays have increased in regional abundance as dusky sharks have decreased in regional abundance.

Explanation:

The researchers' hypothesis is that a decline in dusky sharks (which eat cow-nose rays) leads to a decline in western oysters (since cow - nose rays eat oysters). We need to find the option that supports this causal chain.

• Option A: Talks about other prey of dusky sharks and their relation to shark abundance, not related to oysters. Eliminate.
• Option B: Compares areas with both sharks and rays to areas with only sharks. It doesn't show the causal link between shark decline, ray increase, and oyster decline. Eliminate.
• Option C: Shows that before sharks declined, rays were already eating more oysters. This doesn't support the idea that shark decline causes oyster decline. Eliminate.
• Option D: Shows that as dusky sharks declined, cow - nose rays increased. This is consistent with the hypothesis that shark decline leads to ray increase (since sharks eat rays), and by extension, ray increase would lead to oyster decline (since rays eat oysters). This supports the hypothesis.

Answer:

D. Cow - nose rays have increased in regional abundance as dusky sharks have decreased in regional abundance.