Trunk trails and the searching strategy of a leaf-cutter ant, Atta colombica

Summary

Atta colombica uses chemical mass recruitment that allows the rapid exploitation of resources. Most foragers thus search only within patches. Accumulation of ‘extra’ foragers at patches results in sampling of alternate food items and area-restricted search as patch resources are depleted.

Individual workers have a higher probability of removing a leaf fragment the earlier they arrive at a bait. Workers that arrive when much of the resource is gone travel further on the bait (within the patch) but do not spend significantly more time at the patch. They ‘give up’ after 50–80s.

Foraging effort is centered on the extensive trail system, not on the nest a predicted by time and energy foraging models. Search effort is also trail centered. The probability that an item will be discovered decreases with distance from the trail and increasing litter depth. Trail traffic and trail quality together mave no significant effect although this may be because they act antagonistically.

Economic considerations predict that trials should be built to high quality and very productive sites. If trails are built as a result of recruitment and recruitment reflects patch quality and productivity, characteristics of forage sites are physically embodied in the trail system.

Leaf cutter foraging is better understood as a long term optimization that effectively exploits resources over the lifetime of the colony than as ‘prudent’ predation that ‘husbands’ resources.