Effect of gnawing by Microcavia australis (Rodentia, Caviidae) on Geoffroea decorticans (Leguminosae) plants

The impact of gnawing by Microcavia australis on the survival of Geoffroea decorticans plants was studied in the Monte Desert of Argentina. Sampled pl ants (N = 105) were selected randomly from two different colonies of M. aus tralis. For each plant sampled the following properties were measured: the diameter of the trunk at ground level; the distance to the nearest burrow o f M. australis; the proportion of the trunk perimeter that had been gnawed; and the condition of the plants. It was found that gnawing by M. australis has a negative impact on the survival of G. decorticans plants. Damage of the plants is inversely related to the distance from the burrow systems (r( s) = -0.283, p < 0.003) and to the proportion of the trunk perimeter gnawed (r(s) = -0.554, p < 0.0001). The differential survival of plants with a la rger diameter trunk and of plants farther away from M. australis colonies m ay have long-term effects on the abundance and distribution of G. decortica ns. (C) 1999 Academic Press.