A tale of two islands: The taxon cycle and anthropogenic impacts on de novo island ant faunas in the western tropical Pacific

Ants (Hymenoptera: Formicidae) have been instrumental in our understanding of both island biogeography and the ecology of invasive species, especially in the tropical Pacific islands. In this study, I describe the taxonomic composition of two small Pacific islands in the Republic of Palau. They are roughly the same size and less than 2km apart, but one island, Fanna, has no history of human habitation, and the other, Sonsorol, has been continuously inhabited for at least the past 400 years. Sonsorol and Fanna are among the closest oceanic islands to Papua New Guinea, Wallacea, and the Phillipines, and thus constitute a critical part of our understanding of the biogeography of this region. Noteworthy findings regarding the fauna include the absence of Odontomachus simillimus, the presence of Anoplolepis gracilipes, and several putative endemic species on both islands. Using these ant faunae as study cases, I show how assemblage-level properties such as ecomorphometrics and phylogenetic beta-diversity can inform our understanding of the anthropogenic impacts on ecological and evolutionary forces shaping ant assemblages. I place these findings in the context of Wilson's taxon cycle, and explore ways by which we might move closer to the generalized use of ants as biomonitoring tools.