The Human Element

5 Effort: Why We Follow the Path of Least Resistance

The common shore crab, which lives among the rocks and tide pools of the Pacific Coast, has a puzzling habit. It is a surprisingly picky eater. Shore crabs feed on mussels. And much like the story of Goldilocks, shore crabs cast aside mussels with small shells and ignore the large ones. But there's a medium‐sized mussel that's just right. On the surface, this seems like a dysfunctional strategy. Why would these crabs skip over so many potential meals? The answer can be found in a model of animal behavior called optimal foraging theory.

All living things require nutrients to survive. Unlike plants, animals have the capacity to travel to find the resources they need. Whether they spend their entire life foraging in a small pond or traveling thousands of miles in pursuit of prey, the principle is the same. Animals search their environment to find food.

Mobility has huge advantages. If the immediate area is resource scarce, animals can move on to something better. But mobility has its drawbacks. Movement consumes energy. Optimal foraging theory states that all animals are programmed to find the most efficient way to gather resources. Animals are designed to weigh the costs (energy spent) against the benefits (energy gained) when gathering food to maximize energy intake.

It is this cost‐benefit analysis that explains why the shore ...