Interactions outside local patches contribute to the compound topology of plant–pollinator networks in fragmented dune slacks

Plants and pollinators engage in ephemeral interactions that are essential for both plant reproduction and pollinator fitness. Most plant species interact with multiple pollinator species and, similarly, most pollinators visit multiple plant species, leading to complex networks of interactions. A better understanding of the factors that affect the structure of these networks is crucial for effective biodiversity conservation. While previous research has shown significant negative impacts of habitat fragmentation on plant and pollinator diversity, far less is known about how habitat fragmentation contribute to the overall network structure. In this study, we used DNA metabarcoding to construct pollen transport networks across nineteen dune slacks along a fragmentation gradient at the Belgian coast. For each network, we investigated the impact of patch area, connectivity, and floral diversity on network size, connectance, nestedness and modularity. We found a total of 3222 unique pairwise interactions involving 139 insect species and 261 plant species, with a substantial proportion of pollen coming from plants growing outside dune slacks, indicating frequent foraging beyond local patches. Networks were not significantly nested, while most were significantly modular and showed a hierarchical compound structure. Importantly, no significant relationships were found between network measures and patch area or connectivity, indicating that local patch characteristics had little impact on network structure. We conclude that plant-pollinator networks in fragmented landscapes with a permeable landscape matrix are able to maintain network characteristics, in part through interactions with plants outside the local patch, and that pollen metabarcoding is a valuable tool to reveal the impact of pollinator foraging behavior on plant?pollinator interaction networks in fragmented landscapes.