Assessing the effects of habitat fragmentation on plant pollinator networks in dune slacks using metabarcoding and linking the network structures with plant fitness

A classic prediction of co-evolutionary theory is that mutualists should restrict their associations to a limited number of high-quality partners in order for the interaction to remain stable. However, in practice most mutualists either simultaneously or sequentially associate with multiple partners that confer the same reward. One of the best-known mutualisms is between plants and animal pollinators. In this mutualism, generalist plants that have multiple pollinators are expected to have a fitness advantage compared to specialist plants that have few pollinators due to different processes (e.g. sampling effects, portfolio effects, complementarity). Yet, fitness costs in generalists may arise by associating with multiple pollinators, for example as a result of pollen (and ovule) discounting or stigma clogging (or improper pollen transfer). Moreover, these effects can be expected to depend on the availability and abundance of the various partners, which are likely to vary across populations within the landscape and therefore to affect interactions between partners (network structure) and plant fitness. How partner availability shapes network structure and plant fitness remains poorly understood. The major aim of this study is to investigate the relationship between partner diversity, network structure and individual plant fitness in coastal dune slacks. We will take advantage of the highly fragmented dune area along the Belgian coast, where both plant and insect diversity and abundance depend on the size and isolation of dune slack patches. We predict that, due to a limited number of pollinators, plant-pollinator networks will develop into more generalist systems in the more fragmented dune slacks, yet that this results in decreased plant fitness. We further predict that plants with specialized pollination systems will suffer larger fitness costs than generalist plants and therefore are more susceptible to fragmentation than generalist plants. To test these predictions, we will construct and analyze plant-pollinator networks using a novel meta-barcoding approach across a range of fragmented dune slacks varying in size and spatial isolation and will assess the effects of network structure and niche breadth on pollen deposition (contribution of conspecific and heterospecific pollen) and fitness (seed set and quality) in both specialist and generalist plant species. Ultimately, the results of this project will contribute to a better understanding of the unique biodiversity of coastal dune slacks which, due to human modification of the environment, are in decline in Europe.