University of Michigan
Department of Ecology and Evolutionary Biology

The ants of Melanesia were famously studied by E.O. Wilson in the 1950s and inspired him to develop theories such as the taxon cycle and the “Equilibrium Theory of Island Biogeography.” The system has not been revisited until now.

Evan Economo, Michigan Fellow, and Professor Lacey Knowles have received a two-year grant from the National Science Foundation for nearly $380,000 for a project that builds upon Economo’s recent work on ant biodiversity in the Pacific Islands.

In the last few years, Economo and his collaborator Eli Sarnat, University of Illinois, have been collecting and reorganizing the ant biodiversity in the region. Their resulting book, “The Ants of Fiji,” will be published in 2012, providing a comprehensive treatment of the fauna of the archipelago.

There are 429 known ant genera, but over 10 percent of ant species belong to the single hyperdiverse genus Pheidole, according to Economo. Likewise, certain geographic areas (e.g. New Guinea) are diverse in species, phenotypes, and ecological strategies while others (e.g. Samoa) are much less diverse.

“The reasons for these patterns represent a puzzle for biologists,” he said. “This project investigates the macroevolutionary dynamics of Pheidole lineages in the island systems of the Indo-Pacific. The approach uses multilocus phylogenetics to reconstruct the evolutionary history of Pheidole, establishing when and where different species, phenotypes, and ecological strategies evolved. Using statistical and theoretical methods, this information will be used to test hypotheses for the forces shaping biodiversity.”

Economo and Sarnat previously analyzed the ecological structure of the entire ant fauna of the Fijian archipelago, and tested Wilson’s theory of the taxon cycle. So far, the theory performs remarkably well, he said, although other explanations are still possible for the same patterns. In particular, Pheidole, has had interesting phenotypic and ecological changes associated with an evolutionary radiation within Fiji.

“The goal of the current program is to look deeper into the evolutionary dynamics of Pheidole and test alternative theories for the processes generating these patterns,” said Economo.

“The project addresses a fundamental question of biology; whether the course of evolution and the biodiversity patterns we observe are inevitable or the outcomes of random chance. Addressing this question is a necessary step toward predicting the future dynamics of ecosystems in this time of unprecedented change. This is especially true for ants, one of the most ubiquitous and ecologically dominant animal groups on the planet. In the modern era, ‘invasive’ ants are now being transferred around the globe by humans and are causing damage to both economic interests and natural ecosystems. Understanding the historical dynamics of ant evolution will allow us to better predict the future evolutionary consequences of these modern colonizations.”

Image:  Fijian ant species, Pheidole pegasus, from Fiji with an unusual "spinescent" morphology.