Behaviorally mediated coexistence of dominant and subordinate symbiotic plant-ant species (Azteca pittieri and Cephalotes setulifer)

The myrmecophytic tree Cordia alliodora can be inhabited by several symbiotic ant species simultaneously. In particular, in parts of the C. alliodora range, trees are commonly inhabited by both Azteca pittieri and Cephalotes setulifer, although some trees are occupied by only one species. These two ant species differ dramatically in defensive behavior: A. pittieri ants recruit from plant domatia to attack intruding animals, and can defend the tree against herbivores, whereas C. setulifer ants avoid other animals and protect their colonies by phragmosis. When the ants of the two species come into contact, A. pittieri attacks and bites C. setulifer. How do these two species of ants coexist in single trees, given that one species is clearly dominant over the other? Maps of domatia showed that: (1) C. setulifer consistently occupy the peripheral domatia when trees are occupied by both species; and (2) C. setulifer colonies move between years towards the growing ends of plant shoots into new peripheral domatia. C. setulifer ants were more likely than A. pittieri to occupy new domatia on trees that were co-habited, which suggests that they are better at entering new domatia than A. pittieri. Once C. setulifer had entered a domatium, A. pittieri had trouble gaining access across the barrier formed by the head of C. setulifer. These behavioral differences together appear to allow these two species to partition niche space, in this case available C. alliodora domatia, within forests and within individual trees.