Wildflowers-pollinator-crab spider predator food-web as indicator of the agroecosystem biodiversity

Abstract

• The wildflower diversity promotes the diversity of pollinators. • The dominance of a few wildflowers increases pollinators characterized by constancy. • There is no close relationship between wildflower biodiversity and rates of pollinator visits. • Crab spiders are more abundant in less biodiverse wildflower communities. • Crab spiders appear to provide an ecosystem service that reduces the seed-set of dominant species, thus maintaining biodiversity. Wildflowers play a crucial role in the functionality of the agroecosystem food chain. In order to investigate the role of biodiversity in the relationships between wildflowers, relative pollinators and their crab spider predators, six wildflower communities, characterized by a different botanical complexity, were sown in a two-year experiment. The selected Mediterranean species flowered between March and September, with a peak during May. The indices of dominance (D) and biodiversity (H ') of the wildflower communities confirmed two expected levels of floristic complexity of the oligo-specific plant communities (only three species) in comparison to the poly-specific wildflower communities (a further 20 species for each oligo-specific plant community). The greater floristic biodiversity facilitated a greater pollinator biodiversity (bees, solitary bees, bumblebees, lepidoptera, diptera syrphidae and bombyliidae) but the respective total visitation rate was unchanged. In the case of the lower floristic complexity (oligo-specific plant communities), the dominance of bees increased, confirming their tendency to always choose the same wildflower species to visit. The evaluation of the crab spiders detected on flowers, waiting for pollinators, showed a significant reduction in the case of additional botanical complexity. Indeed, significant linear regressions (p < 0.05) showed a direct relationship between the number of crab spiders observed and the dominance indices of the various wildflower communities. The paper also discusses the possible ecological role of crab spiders in the biodiversity sustainability of the various wildflower communities.