Gene flow at the landscape level

The distribution of fields and fragmentation of habitat in agricultural lan dscapes has a dominant effect on the rate of gene flow among crops and fera l or wild relatives. An approach to quantifying the salient factors is illu strated with reference to experimental and theoretical studies of oilseed r ape crops and feral brassicas. Existing models of long distance pollen move ment underestimated gene flow when compared with measurements of pollen con centration and pollination in an agricultural context. The evidence indicat es that large pollen sources, such as crop fields, interacted on a regional scale to increase gene flow. The value of modelling landscape-scale gene f low for synthesis and forming hypotheses is illustrated. Existing approache s, based on pollen-trap measurements from what were presumed to be single s ource fields-need to be modified to account for multi-source interference.