Practice question

The marginal value theorem states that a forager should leave a patch when its instantaneous capture or energy-gain rate has declined to the average rate attainable across the environment, including travel time between patches. Early in a patch visit, profitable items are readily found and marginal return is high. Continued exploitation depletes the patch, so each additional unit of time yields less. Once the marginal return equals the habitat-wide average, staying longer would lower long-term intake; departing for a new patch raises it. Maximum total energy within the current patch is not the objective because reaching complete depletion can waste substantial time. “Falls below minimum” lacks a defined comparison, and handling time need not become zero. Graphically, the optimal point is where a tangent drawn from the negative travel-time intercept touches the cumulative gain curve. This rule assumes knowledge or evolved estimation of patch quality and average environmental profitability. Predation risk, competition, and incomplete information may shift actual departure, but the equality of marginal and average gain is the theoretical benchmark.