Invasive Ant Alters East African Savannah Landscape via the Disruption of Native Ant-Plant Mutualisms

Abstract

Mutualisms can be important for maintaining biodiversity and function within ecosystems. An invasive species can disrupt these key ecological relationships. Recently, populations of the big-headed ant (Pheidole megacephala) have appeared in the savannahs of East Africa. This region’s overstory is characterized by Acacia drepanolobium, an ant-plant mutualist. We examined the interactions of the big-headed ant with this mutualism and found that the invader extirpates native plant-ants, save for a poorly mutualistic species. This reduction in native ant diversity leads to lower survivorship of the host tree due to increases in herbivore damage. Our results show how the big-headed ant’s interruption of the native ant-acacia mutualism has the potential to eliminate tree cover in the savannah, an event that could result in sweeping alterations to ecosystem structure.