PhD student University of Toronto Toronto, Ontario, Canada
Many ant species visit extrafloral nectaries (EFNs) on plants—the nectar is a food resource to ants, which act as bodyguards. We asked if ant species that visit EFNs have larger range sizes than species that do not. We predicted that EFN-visiting ants would be more successful at colonizing new ranges by exploiting an additional food resource. We also predicted that plants bearing EFNs would have larger ranges due to protection from herbivory by visiting ants in new ranges.
We combined published data from: 1) a text-mined list of ant species likely to visit EFNs, 2) a recent ant phylogeny, to account for phylogenetic signal in range sizes of related ants, and 3) native and invaded range size data from the antmaps.org database. We found that ant species that visit EFNs had both larger native and larger invaded range sizes, even after accounting for phylogeny. Since the majority of EFN-producing plants are legumes, we analysed if EFN-bearing legumes had larger native and invaded range sizes than legumes without EFNs. We used range size data and a legume phylogeny from published literature and found that although there was no difference between legumes with and without EFNs in native range sizes, EFN-bearing legumes had larger invaded range sizes than legumes without EFNs.
This is one of few studies to examine the effects of mutualism on the geographic ranges of both interacting guilds at a global scale. Our results suggest that participating in mutualism promotes range expansions for both ants and legumes.
