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Disruption of native ant/seed interactions by invasive ants is predicted by body size.
Ness, Joshua*,1, Bronstein, Judith1, Andersen, Alan2, Holland, J.1, 1 University of Arizona, Tucson, Arizona2 CSIRO Tropical Ecosystem Research Centre, Winnellie, NT, Australia
ABSTRACT- Ecologists have long sought to link the traits of individual species to their influences on communities and ecosystems. This challenge becomes more urgent as an increasing array of exotic species disrupts processes within invaded communities. We demonstrate that the mean and maximum distances that ants transport seeds adapted for ant dispersal increase exponentially with ant body size. These patterns occur in three of the four largest ant subfamilies (Dolichoderinae, Formicinae, and Myrmicinae, but not Ponerinae). Ant body size is a useful predictor because it incorporates many of the variables known to influence seed dispersal distance, including worker-to-seed mass ratio, group vs. solitary foraging, foraging range, ant nest distribution, as well as the likelihoods that ants will collect seeds or drop them in mid-transport. We suggest that many of the benefits plants receive from this mutualism increase with dispersal distance. Such benefits include reduced competition between related plants, patch colonization, access to different microhabitats, and escape from high density patches where seeds are vulnerable to density-dependent natural enemies (e.g. small mammals and pathogens). Invasive ants are smaller than most seed dispersing ants, and seed dispersal distances are reduced in sites occupied by invasive ants, relative to sites with other ants. The link between ant body size and seed dispersal distance, combined with the dominance of invaded communities by these typically small ants, provides a simple, mechanistic explanation for the disruption of native ant-seed dispersal mutualisms in habitats invaded by exotic ants.
Key words: myrmecochory, solenopsis , exotic species, mutualism