Organic dairy farming: impacts on insect flower interaction networks and pollination

摘要

1. Pollination interactions comprise a network of connections between flowers and insect visitors.They are crucial for reproductive success in many angiosperms but are threatened by intensive agricultural practices. Although less intensive approaches, including organic farming, could improvefarmland biodiversity, it is not clear whether or not these approaches enhance wild plant pollinationand the stability of insect–flower interaction networks.2. We investigated the effects of organic vs. conventional farming on insect–flower interaction network size and structure, bee and hoverfly diversity, and pollination in 10 pairs of organic and conventional dairy farms in the Republic of Ireland.3. We found that insect–flower interaction networks on organic farms were larger and more asymmetrically structured than networks on conventional farms. Overall, however, networks containedfewer taxa and niche overlap and plant ⁄ animal ratios were relatively low compared with previouslydocumented insect–flower interaction networks. Organic farms did attract higher numbers of beespartly because of higher floral abundances (mainly Trifolium sp.). Hoverfly evenness was greater inorganic farms but neither abundance, richness nor evenness was related to floral abundance, suggesting organic farms provide additional resources for hoverflies. Pollination of Crataegus monogyna hawthorn was higher on organic farms, although pollen deposition was limited.4. Synthesis and applications. Organic dairy farming can increase the size and alter the structure ofinsect–flower interaction networks. However, network stability was not improved and all networks(organic and conventional) were vulnerable because of their small size, low niche overlap and lowplant ⁄ animal ratios. Nonetheless, organic farming provided more flowers that attracted moreflower visitors and improved pollination of C. monogyna. We suggest that strategic management ofimportant flowers for pollinators in hedgerows and pastures should be endorsed in agri-environmental schemes. Sowing Trifolium spp., and allowing these plants to flower, could benefit bees, butmore research into hoverfly ecology is necessary before realistic conservation recommendations canbe made for this group. We conclude that organic farming, although not the solution in its presentform, can benefit insect biodiversity, insect–flower interaction networks and insect-mediated pollination.