The multidimensional nutritional niche of fungus‐cultivar provisioning in free‐ranging colonies of a neotropical leafcutter ant

Abstract

Foraging trails of leafcutter colonies are iconic scenes in the Neotropics, with ants collecting freshly cut plant fragments to provision a fungal food crop. We hypothesised that the fungus‐cultivar's requirements for macronutrients and minerals govern the foraging niche breadth of Atta colombica leafcutter ants. Analyses of plant fragments carried by foragers showed how nutrients from fruits, flowers and leaves combine to maximise cultivar performance. While the most commonly foraged leaves delivered excess protein relative to the cultivar's needs, in vitro experiments showed that the minerals P, Al and Fe may expand the leafcutter foraging niche by enhancing the cultivar's tolerance to protein‐biased substrates. A suite of other minerals reduces cultivar performance in ways that may render plant fragments with optimal macronutrient blends unsuitable for provisioning. Our approach highlights how the nutritional challenges of provisioning a mutualist can govern the multidimensional realised niche available to a generalist insect herbivore.

Abstract

Free‐ranging leafcutter ants forage nutritionally and chemically diverse plant fragments to fit the requirements of their fungal food crop. However, these foraged plant fragments can also contain nutrients in excess of the cultivar's tolerance, which can limit fungal production. Results obtained from in vitro cultures suggest that the mineral composition of plant fragments might influence the suitability of the nutrient blends provided to the fungal culture, thus allowing the cultivar to exploit apparently toxic blends of nutrients.