Harvest Dynamics

Abstract

To assess the impact of a herbivore on the vegetation it is essential to quantify the proportion of plant material which is removed from the standing crop by this particular species. The amount of harvested biomass carried into nests of leaf-cutting ants has been estimated by several authors (Hodgson 1955; Cher-rett 1968; Blanton and Ewel 1985; Haines 1978). Only one publication (Lugo et al. 1973) quantifies the biomass flow caused by the activity of the ants and its influence on the energy flow in a forest. However, most of these studies cover only a short time and, thus, offer little opportunity for extrapolation to seasonally influenced habitats. In order to get this necessary long-term information on the quantitative and qualitative aspects of the harvesting activities of leaf-cutting ants and their impact on the vegetation, the foraging activities of 25 colonies of Atta colombica in the study area were monitored during 1993-1994 and 1997-1998. Two of these colonies were monitored in particular detail, making it possible to quantify the amount of foliage harvest per day, per season, and per year and to determine all plant species harvested throughout this time. Further, with respect to the unexplained variability of the circa-dian activity between leaf-cutting ant colonies (e.g., Lewis et al. 1974b; Pilati and Quiran 1996), information about the daily foraging cycle and its causes was collected (see also Wirth et al. 1997).