Morphological changes in Camponotus punctulatus (Mayr) anthills of different ages

In north-eastern Argentina, Camponotus punctulatus builds large numbers of big and coherent anthills after abandonment of rice cultivation. These anthills easily reach 1 m in height and 2 m in diameter, and a density of 1800 nests ha−1. We studied the internal morphology of C. punctulatus aged anthills of 4, 6 and 15 years, respectively, by describing and quantifying, meso- and macroporosity of undisturbed soil samples using image analysis. Four different parts were distinguished on these cone-shaped anthills: the loose granular cortex, the summit, the core of the anthill and the base of the anthill at ground level. The percentage of macroporosity in anthills significantly differed between the parts of the anthill, but changed little with age except for the 15 year old anthill that had increased percentages of mesopores and macropores with rounded and irregular shapes. Walls of the chambers and galleries were highly compacted, highlighting intense ant activity in the anthills, although it was localised mainly in the upper central part. After 6 years the anthills became surrounded by a discontinuous peripheral depression, which likely affects water drainage and infiltration. In 15 year old anthills the lateral depressions became a continuous ditch where water accumulates giving place to a constant wetted zone inside the anthill. Our results support the previous consideration of C. punctulatus as an ecosystem engineer, although in this case related to the changes produced on the soil surrounding the anthills which may affect the survival and distribution of other soil organisms.