CHAPTER 1
 INTRODUCTION

 Ant-plant protection mutualisms are common throughout the tropics and have

fascinated naturalists and ecologists for over a century (reviewed in Beattie 1985 and

Heil and McKey 2003). Amongst ant-plant protection mutualisms, the symbioses

between myrmecophytes, plants that produce cavities in their stems or leaves in which

ants nest, and their resident ants are considered to be the most specialized (Beattie 1985).

Although there is substantial variation in myrmecophyte-ant relationships, these

mutualisms are maintained by the reciprocal benefits afforded to both parties from

participating in the symbiosis. The ants receive housing and often food from the plant,

whereas the benefits to the plants include protection from herbivores, removal of

encroaching vegetation and, in some cases, fertilization from ant waste. At least 400

plant species in over 100 genera produce structures for housing ants, and at least that

many ant species are myrmecophyte-nesting specialists (Beattie 1985, Davidson and

McKey 1993). Myrmecophytes have served as model systems for studying diverse topics

in ecology and evolution, including plant defense strategies, conditional outcomes of

interspecific interactions, the evolution and maintenance of mutualisms, trophic cascades,

and mechanisms of species coexistence (reviewed in Bronstein 1998 and Heil and

McKey 2003).

 Most myrmecophyte species are occupied by more than one ant species (Fonseca

and Ganade 1996). Ant communities of myrmecophytes often vary temporally according

to plant age or random variation (e.g., Alonso 1998, Palmer et al. 2000) and spatially due