Stochastic modelling of feral plant populations with seed immigration and road verge management

The escape of cultivated species from fields could induce changes in the natural balance of semi-natural habitats. We therefore developed a modelling approach to highlight the determinants of feral population dynamics in the case of winter oilseed rape. This stochastic stage-structured model encompasses roadside verge management, seed immigration, seed bank and density-dependence. Within the framework of comparative demography, the elasticity decomposition of the extinction probability was performed according to the three main processes of population dynamics highlighted by the one-at-a-time elasticity analysis: management, seed bank and rosette survival. Despite large extinction probabilities, populations persisted at least 5 years. Results showed that anthropogenic processes (management, seed transport, cropping) and intrinsic processes (local recruitment, seed bank) both govern population persistence. Models of oilseed rape escaped from fields should thus include these two types of processes. Results also highlighted the interaction between seed bank and seed immigration: increasing immigration frequency increased the positive impact of seed bank on population persistence. Intraspecific comparisons via elasticity decomposition could be adapted to other cultivated species to quantify general processes in escape from fields. Such approaches are crucial for understanding how feral populations could facilitate (trans-)gene transfer to crops and wild relatives and to choose optimal control strategies to limit their spread.