Ontogenetic succession in Amazonian ant trees

Abstract

In the tropical rain forest of the Central Amazon, a small guild of specialized plant-ants nest exclusively inside the leaf domatia of Tachigali (Caesalpinaceae). Since normally each plant houses a single ant colony, the number of unoccupied plants in the environment is quite low and the number of potential colonizer queens is high, the conditions for intense intra and interspecific competion for nesting site are set. This study describes an intriguing ecological pattern that explains how this ant guild can coexist using exclusively Tachigali plants as nesting site. We found that each of the eight different ant species occurs in plants of different heights (Kruskal-Wallis test statistics = 148.6, d.f. = 7, P < 0.001). This spatial pattern emerges due to interspecific ant colony replacements along the ontogeny of the tree. We discuss that this pattern can be seen as an ontogenetic succession since an organism's ontogeny is defining a non-seasonal, directional and continuous pattern of colonization and extinction of interacting populations. Ontogenetic succession can be classified at the same level of another class of succession that has been termed degradative succession. The ontogenetic succession view highlights chains of indirect interactions that are mediated by the focal organism and has the potential to produce unexpected outcomes in population interactions and community structure. We suggest that ontogenetic succession should be widespread in nature and that the concept can contribute to our understanding of the temporal and spatial organization of the world biodiversity.