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Dara Stanley (PhD student)

Dara Stanley

Research Profile

PhD: Pollinators and pollination in changing agricultural landscapes; investigating the impacts of bioenergy crops (2008-2012, EPA funding, www.tcd.ie/research/simbiosys)

Pollinators, and the pollination services they provide, are essential for the reproduction of the majority of angiosperms, but also for a wide variety of crops. However pollinators are increasingly threatened by many human activities including land use change and agricultural intensification. A major shift in agricultural land use is beginning with the widespread promotion and cultivation of bioenergy crops as an alternative fuel source to combat climate change, with potentially major implications for biodiversity. The aim of this thesis was to examine the impacts of changes in agricultural regions, specifically the growth of bioenergy crops, on pollinators and pollination services in Ireland.

Using a large network of commercial fields, I investigated the impacts of growing two model bioenergy crops (oilseed rape Brassica napus L. and Miscanthus X giganteus) on pollinator diversity, abundance and community composition in comparison to the crops they replace in the landscape. I found varying effects of bioenergy production on different pollinator taxa, with the solitary bees the group most affected. Higher abundances and species richness of solitary bees were found in bioenergy crops than in conventional ones, and community composition of this group differed between bioenergy crops also. This may be due to increased floral resources in the bioenergy crops, although perennial Miscanthus did not provide more nesting resources for bumblebees than annual crops. Overall, field margins and hedgerows were the most important habitats for pollinators. This indicates that bioenergy production at the field scale in agricultural areas does not have negative implications for pollinators and may even have positive benefits for some taxa, and that a variety of crop types within the landscape can be beneficial for solitary bees.

In the same fields, I used plant-pollinator networks to examine effects of mass flowering oilseed rape during and after flowering, different bioenergy crops, and the composition of the landscape surrounding the fields on the interactions between flower visiting insects and plants. Networks were robust to changes in a mass flowering resource, but replacing arable land with bioenergy crops caused changes in network structure. However, landscape context also affected network properties, suggesting that both local and landscape effects should be considered when studying species interactions and resulting pollination services.

The most common visitors to mass flowering oilseed rape in Ireland are a cryptic bumblebee complex, but little is known about the proportions or requirements of the different cryptic species. I investigated, using molecular methods, what the proportions and colony densities of the different species were in spring oilseed rape fields, in comparison to the second most common bumblebee visitor. I found different proportions and colony densities of the different cryptic species, and that the different species responded differently to the composition of landscape surrounding the fields suggesting different ecological requirements. Interestingly, large numbers of bumblebee colonies (up to 880) were found to use individual spring oilseed rape fields as a resource.

Although oilseed rape provides forage resources for pollinators when the crop is in flower, pollinators are often associated with semi-natural habitats and field margins. I investigated whether pollinators use wild plants as a forage resource in addition to oilseed rape when the crop is in flower, and whether this has implications for pollination services to these wild species. I found that oilseed rape shares pollinator taxa and individuals with a variety of wild plants in the margins and hedgerows, and that the majority of insects foraging on oilseed rape also carried wild plant pollen. However, little crop pollen becomes deposited on wild plant stigmas suggesting this is not a mechanism for interference with pollination services to wild plants.

Lastly, in a final study I examined the pollinators and pollination of oilseed rape in Ireland. Oilseed rape is visited by a wide range of insect species, with bumblebees the most abundant pollinators followed by honeybees. Winter oilseed rape produces more seed with insect pollination, showing that insects can improve crop yields, and therefore market value, of the crop in Ireland.

Finally, I conclude with a synthesis of results and some methodological considerations. I propose some suggestions for both pollinator conservation in farmland, and bioenergy policy to mitigate impacts on biodiversity. I also highlight some potential areas for further research.

 

Contact details

Botany Building, School of Natural Sciences, Trinity College Dublin, Dublin 2. Tel: +353-1-8962208 Email stanleyd@tcd.ie

 

 

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Last updated 11 September 2013 botany@tcd.ie.