Does the afrotropical army ant Dorylus (Anomma) molestus go extinct in fragmented forests?

Abstract

Swarm-raiding army ants are extremely polyphagous nomadic predators inhabiting tropical forests. They are considered keystone species because their raids can regulate the population dynamics of their prey and because a plethora of both invertebrate and vertebrate species are obligatorily or facultatively associated with them. Field observations and mathematical modelling suggest that deforestation and accompanying forest fragmentation cause local extinctions of the neotropical swarm-raiding army ant Eciton burchellii which in turn have negative effects on its associated fauna. The aim of this study was to examine whether afrotropical army ants are affected by forest fragmentation in the same way. Surveys of Dorylus (Anomma) molestus colonies were carried out in forest fragments of different sizes and in the matrix habitat at two sites in Eastern Kenya, along the Lower Tana River and in the Taita Hills. There was no significant relationship between the presence of D. molestus, forest patch size and distance to the nearest neighbouring patch at either of the sites. Colonies were often found outside the forest and can survive long enough in dry scrubland areas to reach new forest patches as far as 2 km away. We conclude that populations of this army ant species are less vulnerable to fragmentation than those of the neotropical E. burchellii, and that D. molestus can survive better in matrix habitat between forests because of several key differences in the foraging and nesting behaviour of the two species. Finally, we present a simple scenario describing the complex D. molestus population dynamics along the Lower Tana River and discuss the implications of our findings for conservation-oriented management of the two forest systems

Keywords: Dorylinae; forest fragmentation; riverine forest; Tana River; Taita HillsJournal of East African Natural History Vol. 95 (2) 2006: pp. 163-179