The Taxon Cycle in Melanesian Ants

My work with taxon cycles began when I realized the evolutionary history of the Pheidole roosevelti group matched E.O. Wilson’s hypothesis for explaining the distribution of island endemic ants in Melanesia. The hypothesis predicts that the insular, geographically isolated, high-elevation endemic ant species of Melanesia descended from geographically widespread, low-elevation, disturbance-tolerant ancestors. The phylogeny reconstructed by Corrie Moreau suggested that the highly localized, high-elevation, highly specialized roosevelti group descended from a regular looking generalist ancestor that was likely widespread across low-elevation habitats. Evan Economo and I added further evidence to this prediction by reconstructing the character states of the hypothesized roosevelti group ancestor.


Economo & Sarnat, 2012

Economo and I also tested the hypothesis by analyzing the distributions of 183 Fijian ant species belonging to four endemism classes across disturbance and elevation gradients. Our analyses indicate lineages shift toward primary habitats, higher elevation, rarity, and ecological specialization with increasing level of endemism, consistent with taxon cycle predictions.

Evan Economo, Lacey Knowles and I recently received an NSF grant to continue our research testing various components of the taxon cycle [NSF DEB 1141989.  $378,522.  “Evolving hyperdiversity in phenotypic, ecological, and geographic networks: testing the taxon cycle and alternatives in Indo-Pacific Pheidole.”]. We will develop a regional Indo-Pacific phylogeny for Pheidole and test macroevolutionary and biogeographic theory.


Economo, EP & Sarnat, EM (2012) Revisiting the ants of Melanesia and the taxon cycle: historical and human-mediated invasions of a tropical archipelago. American Naturalist, 180, E1-E16. [pdf].

Sarnat, EM & CS Moreau (2011) Biogeography and morphological evolution of a Pacific island ant radiation. Molecular Ecology 20:114-130. [pdf]

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