Power EF, Stout JC, Organic dairy farming: impacts on insect flower interaction networks and pollination, Journal of Applied Ecology, 48, 3, 2011, 561 569
Journal of Applied Ecology 48 3
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.
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