Tree killing by herbicide producing ants for the establishment of pure Tococa occidentalis populations in the Peruvian Amazon

Abstract

Populations of Tococa occidentalis (Melastomataceae) and the inhabiting ants (Myrmelachista sp.) were observed for more than eight months in the Peruvian Amazon (Sira mountains). They represent a complex coevolutionary system: the plants offer shelter (leaf domatia, hollow stems) and food (leaf glands), whereas the ants kill all surrounding plants, including large trees up to 10 m, by chemical weapons. Experiments with exposed plants revealed a highly specialized way to attack meristematic tissue and leaf nervature, which leads to a quick decay of the plant individuals. The clearing of the vegetation by the ants allows the Tococa population to expand mostly by vegetative shoots to large monocultures (up to 30 m in diameter) free from any other plant species. Artificially introduced plant individuals, from different T. occidentalis populations, are regarded as a foreign species by the ants. The succession of such a Tococa-Myrmelachista system begins with one or a few founder plants on a light place in the midst of the vegetation. Myrmelachista soon inhabits their host plants which otherwise would not survive and begin to clear the place from all foreign plant species. Tococa expands quickly, forming circle shaped populations. Distantly situated canopy trees shade the Tococa population after a number of years and cause their decay. The whole place appears contaminated for years and no other plant can establish itself. Some of the consequences of these open places are erosion and a severe influence on the regeneration of the forest. © 1992 Chapman & Hall.