57 Cooperative Foraging

Key Idea: Cooperative behaviour in gathering food increases the chances of foraging success and improves efficiencies. Cooperating to gather food can be much more efficient than finding it alone. It increases the chances of finding food or capturing prey. Cooperative hunting will evolve in a species if there is a sustained benefit to the participants, the benefit for a single hunter is less than that of the benefit of hunting in a group, and cooperation within the group is guaranteed.

Alex Wild Public Domain Worker castes in army ants

Cooperative foraging in ants often involves division of labour. Leaf-cutter ants harvest parts of leaves and use them to cultivate a fungus, which they eat. Workers that tend the fungus gardens have smaller heads than the foragers, which cut and transport the leaves. Similarly, army ants have several distinct worker castes. The smaller castes collect small prey, and larger porter ants collect larger prey. The largest workers defend the nest. Honeybees forage for nectar, gathering it from flowers and taking it back to the nest. If a particularly good nectar source is found, the bee will perform one of two dances when it returns to the nest. If the source is distant the bee performs the waggle dance. If the food source is very close (less than 50 m) the honeybee will perform a round dance. The honeybee's round dance stimulates other workers to leave the hive and search within 50 m for a food source. The mountain caracara in Peru (above) forages in groups of three or four, looking for prey hidden around rocks. Working together, the birds are able to overturn rocks far bigger than any individual could move. If a bird finds a rock that is worth turning over, it produces a high pitched call to attract the others. In most cases, only one bird (usually the initial caller) benefits from overturning the rock. However, the other birds may benefit when other rocks are overturned later (reciprocal altruism).

Army ants foraging

There are two species of army ant that have quite different raiding patterns (right): Eciton hamatum whose columns go in many directions and Eciton burchelli, which is a swarm-raider, forming a broad front. Both species cache food at various points along the way. Through group cooperation, the tiny ants are able to subdue prey much larger than themselves, even managing to kill and devour animals such as lizards and small mammals. This would not be possible if they hunted as individuals. Food caches Multiple advancing fronts Single, broad advancing front

Swarm raider

Food caches

Column raider

Temporary nest Temporary nest

1. What are the advantages of cooperative food gathering?

2. What conditions favour group cooperation in food gathering?

3. Describe how the division of roles within ants increase the colony's success in obtaining food:

4. (a) Describe the advantages of reciprocal altruism in mountain caracara:

(b) Suggest why this a successful strategy even when birds do benefit all the time: