Organic dairy farming: impacts on insect flower interaction networks and pollination
Stout, Jane Catherine Stout, Jane Catherine Power, Eileen Power, Eileen
Stout, Jane Catherine
Stout, Jane Catherine
Power, Eileen
Power, Eileen
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2012-07-02
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Abstract
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 improve
farmland biodiversity, it is not clear whether or not these approaches enhance wild plant pollination
and 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 contained
fewer taxa and niche overlap and plant ⁄ animal ratios were relatively low compared with previously
documented insect–flower interaction networks. Organic farms did attract higher numbers of bees
partly because of higher floral abundances (mainly Trifolium sp.). Hoverfly evenness was greater in
organic 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 of
insect–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 low
plant ⁄ animal ratios. Nonetheless, organic farming provided more flowers that attracted more
flower visitors and improved pollination of C. monogyna. We suggest that strategic management of
important 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, but
more research into hoverfly ecology is necessary before realistic conservation recommendations can
be made for this group. We conclude that organic farming, although not the solution in its present
form, can benefit insect biodiversity, insect–flower interaction networks and insect-mediated pollination.