The Economics of Eating
Foraging is the behavior of searching for, capturing, and consuming food. Optimal Foraging Theory (OFT) predicts that natural selection favors foragers that maximize net energy intake per unit of time spent foraging — not simply the most food, but the most energetic payoff per unit of effort. This means weighing the energy content of a food item against its handling time (the time needed to capture and process it) and the search time needed to find alternatives. A prey item's profitability is its energy content divided by its handling time; foragers are predicted to prefer prey with the highest profitability available.
The Marginal Value Theorem (MVT) extends this logic to patchy environments. As a forager consumes food within one patch, the local rate of energy gain declines — the easiest items are taken first, and what remains gets harder to find or process. MVT predicts the forager should leave the patch exactly when its marginal capture rate (the rate right now) drops to the average capture rate available across the whole environment, including travel time to a fresh patch.
| Concept | Definition |
|---|---|
| Profitability | Energy content / handling time |
| Search time | Time spent finding the next item or patch |
| Marginal capture rate | The current, declining rate of gain within a patch |
| Environmental average | The overall achievable rate, including travel between patches |
Common pitfall: assuming a forager should stay in a patch until it is completely emptied. MVT says otherwise — leaving too late wastes time that could be spent gaining food faster elsewhere, so the optimal departure point is set by the environment's average, not by how much food is technically still left.