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

Abstract

Biotic interactions are known to play an important role in shaping species geographic distributions and diversity patterns. However, the role of mutualistic interactions in shaping global diversity patterns remains poorly quantified, particularly with respect to interactions with invertebrates. Moreover, it is unclear how the nature of different mutualisms interacts with abiotic drivers and affects diversity patterns of mutualistic organisms. Here, we present a global-scale biogeographic analysis of three different ant-plant mutualisms, differentiating between plants bearing domatia, extrafloral nectaries (EFNs), and elaiosomes, based on comprehensive geographic distributions of ∼15,000 flowering plants and ∼13,000 ant species. Domatia and extrafloral nectaries involve indirect plant defenses provided by ants, while elaiosomes attract ants to disperse seeds. Our results show distinct biogeographic patterns of different ant-plant mutualisms, with domatium- and EFN-bearing plant richness decreasing sharply from the equator towards the poles, while elaiosome-bearing plants prevail at mid-latitudes. Contemporary climate, especially mean annual temperature and precipitation, emerge as the most important predictor of ant-associated plant diversity. In hot and moist regions, typically the tropics, domatium- and EFN-bearing plant richness increases with related ant guild richness, while in warm regions plants with elaiosomes are strongly linked to interacting ants. Our results suggest that ant richness in combination with climate drives the spatial variation of plants bearing domatia, extrafloral nectaries, and elaiosomes, highlighting the importance of mutualistic interactions for understanding plant biogeography and its response to global change.

Global biogeographic regions for ants have complex relationships with those for plants and tetrapods

“…The strong similarity between ant and plant regionalizations reveals the shared ecological and evolutionary processes, particularly highlighting the potential role of biotic interactions. A remarkable diversity of plants with elaiosomes and extra oral nectaries, structures particularly important in ant-plant mutualisms, are observed in spatial clusters that are shared by both ants and plants but absent in tetrapods, such as Holarctic and Indo-Paci c realms and the Cape region 48,52,54 . In fact, birds and mammals also play important roles in seed dispersal which can expand plant distribution ranges 55 , especially through long-distance dispersals 56 , and thereby, promote plant speciation 25,57,58 .…”

“…Ants are comparable to or even exceed most tetrapod groups in distribution range (near-globally spread) 36 , known species richness (~ 15,900 described species and subspecies) 43 and ecologically dominance in the many ecosystems they inhabit 44,45,46 . They have diverse interactions with plants, both directly through seed dispersal (with > 11,000 angiosperms species) to facultative and obligate protection mutualisms 47,48 to indirect interactions through sap-sucking insects 48 , which have resulted in associations regarding patterns of species distribution 49,50 , diversi cation 32,51,52,53 and richness 54 . These interactions may also lead to a stronger biogeographic congruence between ants and plants on a global scale compared to that between tetrapods and plants.…”

Generalized mutualisms promote range expansion in both plant and ant partners

“…Humans have also contributed to the non-native spread of ant species around the globe [35,[94][95][96]. EFN-visiting ant species were more likely to establish indoors, possibly because of the abundance of sugary, nectar-like foods present in human settlements, because they were co-introduced with ornamental plants in indoor locations like greenhouses, or because they are more often tropical in origin [97] and thus thrive in warmer indoor environments. By contrast, seed-dispersing ants often originate from and invade mid-latitude regions, and they royalsocietypublishing.org/journal/rspb Proc.…”

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

“…Data are available from the Dryad Digital Repository: https:// doi.org/10.5061/dryad.crjdfn39j (Luo et al 2023).…”