AOBPreview published online on September 21, 2009
Annals of Botany, doi:10.1093/aob/mcp236
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Pollination biology of fruit-bearing hedgerow plants and the role of flower-visiting insects in fruit-set
1 Plant and Invertebrate Ecology Department
2 Biomathematics and Bioinformatics Department, Rothamsted Research, Harpenden, Herts. AL5 2JQ, UK
3 School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK
4 The Allerton Research and Educational Trust, Loddington House, Loddington, Leicestershire LE7 9XE, UK
* For correspondence. E-mail jenny.jacobs{at}bbsrc.ac.uk
Received: 18 March 2009 Returned for revision: 16 June 2009 Accepted: 5 August 2009
Background and Aims: In the UK, the flowers of fruit-bearing hedgerow plants provide a succession of pollen and nectar for flower-visiting insects for much of the year. The fruits of hedgerow plants are a source of winter food for frugivorous birds on farmland. It is unclear whether recent declines in pollinator populations are likely to threaten fruit-set and hence food supply for birds. The present study investigates the pollination biology of five common hedgerow plants: blackthorn (Prunus spinosa), hawthorn (Crataegus monogyna), dog rose (Rosa canina), bramble (Rubus fruticosus) and ivy (Hedera helix).
Methods: The requirement for insect pollination was investigated initially by excluding insects from flowers by using mesh bags and comparing immature and mature fruit-set with those of open-pollinated flowers. Those plants that showed a requirement for insect pollination were then tested to compare fruit-set under two additional pollination service scenarios: (1) reduced pollination, with insects excluded from flowers bagged for part of the flowering period, and (2) supplemental pollination, with flowers hand cross-pollinated to test for pollen limitation.
Key Results: The proportions of flowers setting fruit in blackthorn, hawthorn and ivy were significantly reduced when insects were excluded from flowers by using mesh bags, whereas fruit-set in bramble and dog rose were unaffected. Restricting the exposure of flowers to pollinators had no significant effect on fruit-set. However, blackthorn and hawthorn were found to be pollen-limited, suggesting that the pollination service was inadequate in the study area.
Conclusions: Ensuring strong populations of insect pollinators may be essential to guarantee a winter fruit supply for birds in UK hedgerows.
Key words: Blackthorn, bramble, Crataegus monogyna, frugivorous birds, hawthorn, Hedera helix, hedgerows, ivy, insect pollination, Prunus spinosa, Rubus fruticosus, Rosa canina