The Ants of Small Bahamian Cays

Ants are ubiquitous in the Bahamas, and are found even on the smallest cays, Surveys for ants on over 260 small cays in four archipelagos (Exuma Cays, Great Exuma, Andros, and Abaco) over a 14-year period have revealed a number of generalized patterns of ant species distributions: (1) Ants are almost always present on small cays with terrestrial vegetation, but are never present on cays without vegetation, (2) If a small cay has only one ant species, it will almost always be Brachymyrmex obscurior. (3) If a small cay has two ant species, the second (after B. obscurior) is usually Dorymyrmex pyramicus, (4) Ant species compositions on small cays change very little over time, (5) The distributional patterns of ants on small cays are similar throughout the Northern and Central Bahamas, Thus, the ants inhabiting small cays in the Bahamas are not a random assortment of the larger species pool in the region, but rather a very predictable subset of species. The underlying mechanisms of these patterns appear to be largely associated with the presence and type of vegetation present, which in turn is dependent upon various physical variables such as island size, elevation, and exposure to winds, waves, and tides. Introduction Ants are common and important components of many tropical and subtropical ecosystems (e.g., Hölldobler and Wilson 1990), and the Bahamas are no exception, Ants have been collected and species lists published for most of the larger and a number of the smaller islands in the archipelago (Wheeler 1905, 1934, Mann 1920, Smith 1954, Deyrup 1994, Deyrup et al. 1998, Morrison1998a), While such lists for the larger islands are likely to underestimate true species richness due to limited collecting effort, these collections do reveal the diversity and ubiquity of Bahamian ants. Ants are frequently found in marginal or ‘inhospitable’ habitats (Hölldobler and Wilson 1990), and the Bahamas contain thousands of small cays representing such potential ant habitat. Elsewhere I have described the metapopulation dynamics of ants inhabiting these small cays, focusing on rates of immigration and extinction (Morrison 1998b, 2002). In this contribution, I focus on generalized patterns of ant distribution on very small cays, and address the possible underlying mechanisms, I pose the question of whether the ants inhabiting small cays are simply a random assortment of the larger species pool in the region, or a deterministically derived subset of species. In other words, it is possible to predict which species of ant one may fi nd on a small Bahamian cay with a large degree of accuracy? Furthermore, will such a prediction, or its accuracy, differ among the various archipelagos of the Bahamas?