Habitat loss, not fragmentation per se, drives structural changes and species turnover in plant–vertebrate pollinator networks

When natural areas are converted for human use, resulting changes in the landscape often lead to habitat loss and fragmentation, which can disrupt key ecological interactions such as pollination by animals. In this study, we investigated the independent effects of habitat loss and fragmentation on the structure and composition of plant-vertebrate pollinator interaction networks, focusing on interactions mediated by birds and bats in the Neotropical region. We assessed how landscape structure influences network properties, including plant and pollinator richness, number of interactions, connectance, nestedness and modularity. We also evaluated the potential of indirect effects to propagate through the network (i.e. species changes driven by cascading interactions across the network), the occurrence of extinction cascades (sequential species losses triggered by the disappearance of key mutualistic partners), and interaction dissimilarity across landscapes. Our results show that habitat loss (i.e. reduced forest cover) is associated with lower plant and pollinator richness, fewer interactions, reduced nestedness, increased connectance and vulnerability to cascading effects. Species turnover emerged as the main driver of interaction dissimilarity between contrasting landscapes (e.g., sites with high vs. low forest cover), whereas in more similar landscapes, where species pools overlap, rewiring of interactions played a larger role. In contrast, fragmentation per se (i.e. independent of habitat amount) had no significant effect on any of the network metrics analyzed. These findings suggest that habitat loss and changes in species composition, rather than fragmentation per se, shapes the structure and dynamics of plant-vertebrate pollinator networks in distinct landscapes.