The Economics of Eating
Foraging is the behavior of searching for, capturing, and consuming food. Optimal Foraging Theory (OFT) predicts natural selection favors foragers maximizing net energy intake per unit of time, balancing energetic payoff against time spent working.
A prey item's profitability is its energy content divided by its handling time (the time needed to capture and process it). Profitability is calculated as , where is energy and is handling time. Search time is the time spent actively looking for the next item or patch.
| Concept | Definition | Formula / Detail |
|---|---|---|
| Profitability | Energy yielded per unit of effort | ( = energy, = handling time) |
| Search time | Effort spent finding alternatives | Increases as high-yield items deplete |
Foragers are predicted to always prefer prey with the highest profitability available in their immediate environment.
Patch Choice and MVT
The Marginal Value Theorem (MVT) extends OFT to patchy environments. As a forager consumes food in a patch, the local rate of energy gain declines because the easiest items are gone and remaining ones take longer to find.
MVT predicts the forager must leave the patch exactly when its marginal capture rate (the rate right now) drops to equal the environmental average (the overall achievable rate across the habitat, factoring in travel time to fresh patches).
| Rate Type | Meaning | Action Trigger |
|---|---|---|
| Marginal capture rate | Current declining gain within a patch | Drops as resources are depleted |
| Environmental average | Overall achievable rate with travel | Dictates the exact moment of departure |
Common pitfall: Assuming a forager should stay in a patch until it is empty. MVT proves leaving too late wastes time that could be spent gaining food faster elsewhere.