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Difficulty: MediumCommand of Evidence: Textual

Biologist Dr. Elena Rostova and colleagues investigated the foraging behavior of the red harvester ant (*Pogonomyrmex barbatus*). The team hypothesized that the rate at which outbound foragers leave the nest is regulated not by the absolute abundance of food in the surrounding environment, but by a feedback loop based on the arrival rate of returning foragers carrying food. According to the researchers, this mechanism prevents the colony from wasting energy sending foragers out when food is scarce or when environmental conditions make foraging inefficient.

Which finding, if true, would most directly support the researchers' hypothesis?

  1. Outbound foraging rates did not increase when food abundance in the foraging area was doubled if the rate of returning foragers was kept constant, but increased significantly when the rate of returning foragers was artificially accelerated even with no extra food available.Answer
  2. B
    Individual foragers that returned to the nest without food were observed to re-emerge more quickly than those that returned with food, suggesting a compensatory search strategy.
  3. C
    Ant colonies that adjusted their outbound foraging rates based on absolute food abundance in the area conserved more total energy than did colonies that relied on feedback from returning foragers.
  4. D
    Outbound foragers were observed to travel longer distances and explore new territories when the rate of returning foragers decreased, eventually leading to the discovery of new food sources.

Answer

Outbound foraging rates did not increase when food abundance in the foraging area was doubled if the rate of returning foragers was kept constant, but increased significantly when the rate of returning foragers was artificially accelerated even with no extra food available.
The correct option directly supports the hypothesis by showing that outbound foraging activity is dictated by the rate of returning foragers and is independent of the absolute abundance of food. In the described scenario, when food abundance is changed but the return rate is held constant, there is no change in outbound rate. Conversely, when the return rate is increased artificially, the outbound rate increases even if food is not abundant. This isolates the two factors and confirms the causal relationship hypothesized by the researchers.

Step-by-Step Solution

1
Identify the researchers' primary hypothesis.
The rate of outbound foragers leaving the nest is regulated by the arrival rate of returning foragers carrying food, rather than the absolute abundance of food in the environment.
This establishes the specific causal link that the correct evidence must support.
2
Evaluate the options to find one that isolates and tests these two variables (food abundance vs. returning foragers rate).
The option showing that outbound rates only change in response to returning foragers' rate—and not to food abundance—directly supports the hypothesis.
By showing that manipulating the rate of returning foragers controls outbound activity while manipulating food abundance does not, it confirms the proposed mechanism.

Key Concept

Command of Evidence: Textual
Estimated Time:1m 30s
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Command of Evidence: Textual

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