Food discovery ability in ground dwelling ants of a peruvian rainforest: Role of habitat and morphology

Background/Question/Methods

Ground-dwelling ant colonies are mostly generalist scavengers that compete for similar ephemeral resources and may optimize food collection by improving their ability to find resources fast (discovery ability). This study investigated the variation of discovery ability among ants in southwestern Amazonian communities, and explored the role of ant morphology and habitat on discovery ability within the framework of the size-grain hypothesis (SGH). The SGH’s basic assumption states an increase of the perceived environmental rugosity with decreasing body size, and predicts that the ratio leg to body size determines an ant’s ability to move within an environment of particular rugosity. In this study, bamboo and mixed canopy forests represented habitats of different degrees of environmental rugosity, from the more rugose (bamboo forest litter) to the less rugose (mixed canopy forest litter). By monitoring baits in the field, discovery ability was measured in two ways, (1) proportion of times a species found the bait first, and (2) time to discovery, i.e., period of time an ant took to discover a bait relative to the time the bait became available. The first measure was used to compare discoverer species composition between habitats; the second was used as the dependent variable in a hazard Cox’s regression analysis to test the role of body size and leg length (independent from body size) and habitat on discovery ability. 

Results/Conclusions

This study revealed that ground dwelling ants in this Amazonian rainforest community (31 species) vary in their ability to locate food resources and that ant morphology and habitat interact to influence discovery ability but not in the way predicted by the SGH. There was no role of body size in either bamboo or mixed canopy forests, and the positive effect of relative leg length on the speed of discovery was restricted to bamboo forests (i.e., the more complex treatment). It may be the case that ants perceive the bamboo and mixed canopy forest litter as environments of similar degrees of complexity. However, the fact that in mixed canopy forests discovery ability was influenced by neither body size nor relative leg length in any direction, suggests that discovery ability may be underlined by other traits than just morphology, such as species specific behavioral traits.