Ant-plant specialisation depends on network type, but not disturbance, elevation, or latitude.

The ecological factors driving specialisation in species interaction networks along environmental gradients at large spatial scales are poorly understood. Although such drivers can have synergistic impacts, previous work has mainly assessed effects of network type and the abiotic environment separately. We conducted a meta-analysis of existing network data to assess the interactive effects and relative importance of these drivers of specialisation in ant-plant networks at global scales. We collated 74 ant plant networks from 1979–2023, categorised into four network types: plants that provide ants nesting sites (myrmecophytes); plants that provide only food sources (myrmecophiles); plants for which ants disperse seeds (myrmecochories); plants on which ants forage only (foraging). We explored how network specialisation varies between interaction types with elevation, latitude, and anthropogenic disturbance. We used a standard measure of network specialisation (H2’), tested whether standardising this against network null models influenced results (H2’ z-score), and measured phylogenetic network specialisation (dsi*). We found that H2’ was strongly affected by habitat disturbance, elevation and interaction type in a manner congruent with previous work, However, these effects disappeared once H2’ was standardised (H2’ z-score). The disappearance of these effects indicates that previous results may relate to variation in network structure rather than specialisation. This is supported by the existence of correlations between network species richness/weighted connectance and H2’. Phylogenetic network specialisation (dsi*) was greater for myrmecophytes than for other three network types. This probably relates to closer co-evolution between partners in myrmecophytic network. Phylogenetic network specialisation did not vary significantly with elevation, latitude or anthropogenic disturbance. Our results demonstrate that ant-plant network types, in this case relating to strength of mutualistic interaction, is the main driver of network specialisation, and that previously reported impacts of latitude, elevation and anthropogenic habitat disturbance are likely to have been mediated mediated via correlations with network size.