Prey size reverses the outcome of interference interactions of scavenger ants

Abstract

In the guild of scavenger ants in the Mediterranean habitats studied, there was a separation of prey on the basis of size: small species took small food items, and large ants collected large items. Nevertheless, some species enlarged their range of prey sizes through social mechanisms: Aphaenogaster senilis through recruitment in relatively small retrieval groups and subsequent cooperative carrying, and the small dominant species (Pheidole pallidula, Tapinoma nigerrimum, Tetramorium semilaeve) through mass recruitment and subsequent prey dissection. Individually foraging and group-recruiting species were more likely to suffer prey interference and loss when prey were larger, whereas mass-recruiting species showed the opposite pattern, losing fewer prey to opportunistic species as prey size increased. These small ants recruited large numbers of workers on very large prey and dominated them before the other species could dissect and carry them to their nests. Each species displayed only one of these strategies, and, thus, prey size was the main factor determining the success of each strategy. Large subordinate species increased exploitation of very large prey by foraging when the three mass-recruiting species were not active, whereas the three small dominant species increased the exploitation of medium-sized and large items by foraging at night, when the diurnal large species were absent. These dominant mass-recruiting species, however, did not differ from each other in respect to prey size and activity period.