Climate and ant diversity explain the global distribution of ant-plant mutualisms

Biotic interactions play an important role in shaping species geographic
distributions and diversity patterns. However, the role of mutualistic
interactions in shaping global plant diversity patterns remains poorly
understood, particularly with respect to interactions with invertebrates.
It is unclear how the nature of different mutualisms interacts with
abiotic drivers and affects the distribution of mutualistic organisms.
Here, we present a global-scale biogeographic analysis of three distinct
ant-plant mutualisms, differentiating between plants bearing domatia,
extrafloral nectaries (EFNs), and elaiosomes, based on comprehensive
geographic distributions of ~19,000 flowering plants and ~13,000 ant
species. Domatia and extrafloral nectaries involve indirect plant defences
provided by ants, while elaiosomes attract ants to disperse seeds. Our
results reveal distinct biogeographic patterns of different ant-plant
mutualisms, with domatium- and EFN-bearing plant diversity decreasing
sharply from the equator towards the poles, while elaiosome-bearing plants
prevail at mid-latitudes. Present climate, especially mean annual
temperature and precipitation, emerge as the strongest predictors of
ant-associated plant diversity. In hot and moist regions, typically the
tropics, the representation of EFN-bearing plants increases with the
proportion of potential ant partners while domatium-bearing plants show no
correlation with ants. In dry regions, plants with elaiosomes are strongly
linked to interacting ant seed dispersers. Our results suggest that ants
in combination with climate drive the spatial variation of plants bearing
domatia, extrafloral nectaries, and elaiosomes, highlighting the
importance of mutualistic interactions for understanding plant
biogeography.