Opportunistic or selective? Plasticity in the diet of the leaf-cutting ant Acromyrmex lobicornis in NW Patagonia

Abstract

We assessed the environmental abundance of plant species on the diet composition of nine nests of the leaf-cutting ant, Acromyrmex lobicornis, in northwestern Patagonia, during spring and summer. We used Ivlevs electivity index to determine which spe- cies were selected (if the species proportion in the diet was larger than in the foraging area), rejected (if the species proportion in the diet was smaller than in the foraging area), or harvested opportunistically (if the species were harvested in the same proportion to their environmental abundance). A. lobicornis harvested on a large percentage of the available species, but most of its diet was composed by only few preferred plant species. While in summer the majority of its diet was selectively harvested, in spring an important part of the diet was harvested proportional to the environmental abundance of plant species. Our results suggest that temporal and spatial changes from opportunistic to selective foraging seem to depend on the balance between the abundance and the palatability of the resources, which may vary among nests and seasons.