Do roads and hedges influence patterns of pollinator foraging movement and consequent plant gene flow in a UK agricultural landscape?

This thesis investigates the influence of hedges and roads (linear landscape features) on the patch-to-patch foraging movements of insect pollinators and consequent pollen- mediated gene flow in white clover, Trifolium repens. Experimental arrays were located within the lowland UK agricultural landscape incorporating a range of patch separation distances from 25m to 250m (using both artificial and natural linear features). Mark-re-sight, “residence” (the number of visits per foraging bout) and pollen transport observations were used to observe pollinator movement characteristics between experimental patches and re-parameterise an existing model of patch-to-patch gene flow. Levels and directions of plant gene flow were observed with phenotypic and isozyme markers, allowing validation of model predictions. Harmonic radar technology was used for the first time to track butterfly flight paths; data support the hypothesis of a 150 to 200m perceptual range, and non-random flight direction but limited association to wind direction, hedges, tracks or fence lines. Mark-re-sight observations indicated similar levels of patch visitation regardless of patch location, and trap-lining by Bombus spp. only between patches 50m or less apart. A single track road significantly enhanced gene flow between connected patches and was not a barrier to gene flow across it. In contrast, a hedge did not facilitate enhanced gene flow between connected patches and was a partial barrier where it occurred between patches. Model predictions of gene flow (1.3%, range 0.8 to 2.5%) agreed well with observed levels (ranging from 0.2 to 31.4%). It is proposed that pollinator movement observations alone could not provide an accurate means of estimating low level gene flow unless the variables of residence and pollen carryover were also considered. The possible influence of spatial and temporal variables including the role of hetero-specific forage on pollinator foraging movements and consequent plant gene flow from the local to landscape scale is also discussed