Spread dynamics of invasive species in the Iberian Peninsula

The continued spread of invasive species represents a major threat to biodiversity and ecosystem functioning, yet the extent to which invasive species are approaching spatial saturation remains poorly understood. Quantifying invasion dynamics across taxa and regions is therefore critical for understanding ongoing range expansion and identifying species at different stages of invasion so that management actions are applied efficiently. We quantified the spatial and temporal dynamics of the spread of 39 invasive species of European Union concern established in the Iberian Peninsula. Using occurrence records from the Global Biodiversity Information Facility , we estimated multiple complementary metrics of invasion dynamics, including occupied area derived from concave hulls, the greatest pairwise Euclidean distance, maximum distance shift, number of occupied 10 × 10 km grid cells, and the magnitude and direction of centroid shifts over time. Spread dynamics varied substantially among species. Ailanthus altissima occupied the largest area and the greatest number of cells across the peninsula, whereas the marine macroalga Rugulopteryx okamurae exhibited the greatest pairwise Euclidean distance, and the highest maximum distance shift. Centroid shifts were heterogeneous in both magnitude and direction, with a prevalence of eastward movements. Lag phases varied widely, ranging from 1 to 22.6 years, with nine of the modelled species exhibiting prolonged lag phases (>10 years). Inflection points were reached by 24 species, of which 11 species had already attained saturation by 2024. Despite increased awareness and regulatory frameworks to curb their spread, most invasive species in the Iberian Peninsula continue to expand. Our results highlight pronounced interspecific differences in invasion dynamics and emphasise the value of integrating spatial and temporal metrics to assess invasion stage and trajectory across large regions. We propose a prioritisation framework in which the invasion stage of invasive species is considered: species in the lag phase should be targeted for immediate eradication, while high-velocity spreaders require containment strategies to mitigate further socio-economic and ecological impacts.