The marginal value theorem predicts when to leave a depleted patch.

The marginal value theorem predicts when to leave a depleted patch.

• A. The patch is completely exhausted.
• B. The current patch's instantaneous intake rate falls below the average rate achievable by leaving to search for a new patch, accounting for travel time.
• C. Predator risk is high.
• D. Energy reserves have reached a fixed threshold.

Answer: (B)

The main idea being tested is how a forager should time leaving a depleting resource patch to maximize long-term energy gain. The marginal value theorem says you should leave when the current patch’s instantaneous rate of gain drops below the average rate you could achieve by moving to a new patch, taking into account the travel time. In other words, as you harvest, the patch becomes less productive, but you still pay the cost (time and energy) to get to another patch. The optimal moment to leave is when the immediate payoff from staying equals the expected payoff from searching elsewhere, which sets the best possible long-term intake rate. This leaves room for leaving before the patch is completely exhausted, because continuing to stay would yield diminishing returns and reduce the overall rate of energy gain. Factors like predator risk or a fixed energy threshold can influence foraging decisions in other models, but they do not define the leave-and-motivate rule of the marginal value theorem itself.

The main idea being tested is how a forager should time leaving a depleting resource patch to maximize long-term energy gain. The marginal value theorem says you should leave when the current patch’s instantaneous rate of gain drops below the average rate you could achieve by moving to a new patch, taking into account the travel time. In other words, as you harvest, the patch becomes less productive, but you still pay the cost (time and energy) to get to another patch. The optimal moment to leave is when the immediate payoff from staying equals the expected payoff from searching elsewhere, which sets the best possible long-term intake rate.

This leaves room for leaving before the patch is completely exhausted, because continuing to stay would yield diminishing returns and reduce the overall rate of energy gain. Factors like predator risk or a fixed energy threshold can influence foraging decisions in other models, but they do not define the leave-and-motivate rule of the marginal value theorem itself.