Conclusions: Ecosystem Perspectives

Abstract

Because of their multifarious effects on the vegetation, leaf-cutting ants have been denoted as key species of Central American rainforest ecosystems (Fowler et al. 1989; Perfecto and Vandermeer 1993). First, they have long been identified as important herbivores in tropical rainforests. As discussed previously (Chap. 12), foliage removal by ants undoubtedly has direct effects on individual plants with some losing up to 40% of their leaves. However, when scaling this patchily distributed herbivory up to the whole ecosystem (Fig. 52), and comparing it with the estimated 15% consumption of annual leaf production by all herbivores on BCI (Leigh and Windsor 1982), one is tempted to conclude that the effect of leaf-cutting ants at the ecosystem level is practically negligible. On the other hand, much of the information on the activities of leaf-cutting ants in tropical rainforests, including the material in this book, points in the direction that the overall effects of leaf-cutting ant activity in tropical rainforests may go well beyond the simple removal of foliage. These effects include enhancement of nutrient availability through the enrichment of soil from nest refuse dumps (Haines 1975; Farji Brener and Silva 1995) and the transfer of nutrients to upper soil layers during nest construction (Weber 1972a,b; Perfecto and Vandermeer 1993). Their nests can contain several thousand chambers comprising a total volume of up to 20 m³ (Weber 1966). However, there are also more direct effects of these ants on the vegetation: understory vegetation growing on or overhanging the immediate nest surface is constantly cleared, frequently resulting in understory gaps near nest sites. Moreover, the ants can directly affect vegetation succession through the destruction of numerous flowers of forest tree species (Haines 1975), and can also significantly contribute to seed dispersal of certain forest plants (Roberts and Heithaus 1986; Kaspari 1993, 1996; Dalling and Wirth 1997).