Group living and optimal foraging – costs and benefits of behaviour

What it shows

Many animals live in groups, but group living has costs as well as benefits. In this agent model a predator attacks a school of sardines, a flock of wood pigeons or a herd of zebras. More eyes spot the predator earlier, a tight group confuses it, and each animal's risk is diluted by the others, yet all of them share the same food. You measure survival, food per animal and fitness for different group sizes and find the best size. Two foraging screens apply optimal foraging theory: how long a great tit should stay in each bush, and which mussel size a shore crab should choose.

How to use

On Living in groups, choose the Animal, set Group size and Cohesion, then press Run season or Run 10 seasons; each run adds a row to the table and a point to the graph. On Patch time, set the Travel time between patches and the Time spent in each patch, then press Run foraging trip. On Prey choice, set the Mussel length and press Offer a mussel. Then answer the questions under Check yourself.

Parameters you can change

• Opening screen Living in groups, Patch time, Prey choice
• Animal Fish school (sardines), Bird flock (wood pigeons), Herd (zebras)
• Group size 1–50
• Cohesion 0–100 %
• Travel time between patches 5–60 s
• Time spent in each patch 2–90 s
• Mussel length 10–40 mm

Questions to explore

1. Why does each animal's chance of survival rise as the group gets bigger, although the predator attacks just as often?
2. Why is the group size with the highest fitness smaller than the group size with the highest survival?
3. Why should a forager stay longer in each patch when the patches are farther apart?