Dispersal and founder effects shape yellow hawkweed invasion in patagonian rangelands: Insights from a spatially explicit spread model

Biological invasions are a major driver of environmental change threatening biodiversity and ecosystem services. Hieracium pilosella L., a perennial herb native to Europe and Asia, has aggressively invaded the grasslands of Argentina's Fuegian steppe, reducing forage quality and livestock productivity. Using field-based estimates of plant cover, vegetation community maps, and disturbance layers, we developed and calibrated a spatially explicit, pattern-oriented simulation model to evaluate invasion dynamics. We compared alternative model versions that differed in terms of seed dispersal ranges and invasion origins. The version including long-distance dispersal from disturbed hotspots best reproduced observed patterns, with mean error rates below 4.5 %. Using Sequential Monte Carlo and Approximate Bayesian Computation, we calibrated key parameters related to growth, dispersal, and recruitment. Validation with independent data showed that 5.6 % of parameterizations successfully matched observed invasion patterns. Sensitivity analysis revealed that regional frequency is driven mainly by growth and dispersal across all community types, while regional cover is most sensitive to growth in shrublands. Without human intervention, simulations predict that after 75 years regional frequency could reach 86.8 % (±2.18 %, 99 % CI), with a cover of 4.86 % (±0.75 %, 99 % CI). Worst-case scenarios project up to 8.7 % cover and 91 % frequency by 2045. Despite high frequency, invasion patterns remain spatially heterogeneous: dense cover dominates the north, while spread is limited in the south by wetlands and floodable meadows. This calibrated model provides valuable insights into regional invasion dynamics and offers a framework for prevention and management strategies.