Landscape homogenization strengthens the fitness benefits of plant species' centrality in pollination networks

Abstract

Understanding how plant–pollinator interactions vary along disturbance gradients and influence community function is essential to comprehend how pollination services can be maintained in increasingly anthropized landscapes. Recent studies found positive relationships between plant fitness and centrality in interaction networks (i.e., high proximity to other plants via shared pollinators). However, this relationship might vary depending on communities' landscape context and species' functional traits. We hypothesized that the fitness benefits of centrality might be higher in homogeneous landscapes than in heterogeneous landscapes, as the former might favor generalist species and behaviors. We also expected stronger positive relationships between centrality and fitness in pollinator-dependent actinomorphic species compared to autogamous species that do not depend on pollinators or zygomorphic species that are pollinated by a small set of specialized species. Here, we combined field samplings and experiments to study how centrality related to fitness (seeds produced) in 11 plant species from 20 communities along a gradient of landscape heterogeneity. For that, we assessed changes in the centrality–fitness relationship associated with landscape variations and species' functional groups: autogamous species, entomophilous-actinomorphic species, and entomophilous-zygomorphic species. We found that centrality positively influenced plant fitness in more homogeneous landscapes, whereas it had a null effect on fitness in more heterogeneous landscapes. Furthermore, centrality was irrelevant for the fitness of mostly autogamous plant species but influenced the fitness of mostly entomophilous species, increasing the reproductive output in actinomorphic species while decreasing it in zygomorphic ones. For the first time, we show that the relationship between interaction structure and function varies with the landscape context and the group of species evaluated. Our study also highlights the importance of conserving heterogeneous landscapes to maintain effective specialized interactions, as the higher fitness benefits of centrality in homogeneous landscapes might drive feedback cycles of increased generalization over time in communities within these landscapes.