Behavioural complementarity among frugivorous birds and lizards can promote plant diversity in island ecosystems

The behavioural complementarity of fruit‐eating animals is thought to exert a key role in plant community assembly. However, a mechanistic understanding of the causal links between the two processes is still lacking. This study assesses whether complementarity between dispersers in feeding and microhabitat‐use behaviour enhances community‐scale dispersal services, resulting in a more diverse community of seedlings. We used a Bayesian approach to connect a comprehensive database of seed dispersal effectiveness at a community scale with a transition probability model that accounts for behavioural complementarity. Our model system was the thermosclerophyllous shrubland of the Canary Islands. There, fleshy‐fruited plants rely on two types of frugivores: lizards and birds. Lizards consumed all plant species and preferentially used open areas, whereas birds foraged for small single‐seeded fruits and dispersed their seeds beneath plants. Through feeding on different sets of plants, they generated a rich seed‐rain community. By diversifying the microhabitat of deposition, more species could find suitable recruitment sites. Distinct foraging and microhabitat‐use choices led to complementary dispersal services. Lizards ensured that all plant species were present in the seedling community, while birds promoted a more even distribution of them. As a result, diversity in the community of seedlings was enhanced. Overall, our work underscores that behavioural complementarity promotes diversity in the early‐regenerating plant communities. These enhanced dispersal services rely on the presence of all functional groups. Thus, in communities where frugivores display unique behaviours, preserving a diverse community of dispersers should be a conservation target. A free Plain Language Summary can be found within the Supporting Information of this article.