Leaf-cutting ant nests in temperate environments: mounds, mound damages and mortality rates in Acromyrmex lobicornis

FARJI-BRENER, ALEJANDRO GUSTAVO

Stud. Neotrop. Faun. Environm

Año: 2000 p. 131 - 138

The mounds of ant nests have been characterized as structures that facilitate the colonization of habitats subject to extremes of temperature. My objective was to investigate the importance of the mound of Acromyrmex in this process. In the most climatically rigorous environment that this ant genus lives (northwestern Patagonia), I determined (1) the thermoregulatory capacity of the Acromyrmex lobicornis nest-mound, (2) the influence of mound damages on the mortality or abandonment rate of Acromyrmex lobicornis nests, and (3)  I compared, from the existing literature, the distribution limits between the species of Acromyrmex that do and do not construct mounds. The results show that the mounds of Acromyrmex lobicornis function as “thermal buffers” by diminishing the effects of external thermal variations, and previous mound damage increased mortality or abandonment only in nests that have mounds constructed on bare ground. The mounds constructed surrounding the base of a plant increased their diameter faster and recovered better from perturbations, which may be due to the structurally supportive nature of plant stems that facilitate construction of the mound or its repair after disturbance. Because these ants produce a nutrient-rich dump that is colonized principally by exotic plants, the high mortality or abandonment rate of ant nests influences the surrounding plant community as well as its own population dynamic. At a larger scale, the species of Acromyrmex that construct mounds have more southerly range limits than species that do not construct mounds, suggesting that mounds are important structures for leaf-cutting ants that colonize temperate environments.