Impact of introduction pathways on the spread and geographical distribution of alien species: Implications for preventive management in mediterranean ecosystems

Aim: To test whether alien species with contrasting introduction pathways differ in range size, geographical distribution and their relationship with environmental variables. Location: Catalonia (NE Spain). Methods: We obtained records of 869 alien species from the Catalan alien species database at the 10-km UTM cell scale. For each species, we assigned its introduction pathways and minimum residence time (MRT). We then analysed species' range sizes in relation to their pathways and taxonomic group while accounting for MRT through linear models. We identified hotspots of alien species richness across pathways through local Gi* statistics, and we analysed their spatial congruence. We assessed the environmental drivers of alien species richness across pathways, by means of ordination methods. Results: Range size was mostly equivalent among pathways, with species that escape or spread unaided reaching smaller range size than species introduced with contaminated commodities. Among taxonomic groups, range was smaller for terrestrial invertebrates compared to plants. The spatial pattern of hotspots of alien species richness showed low congruence across pathways. Proxies that pool the effect of colonization and propagule pressure were the main drivers increasing alien species richness across pathways (except for the unaided pathway). Main conclusions: Differences among pathways can be related to a lack of human aid (unaided and contaminant pathways) and to trait selection (escape and contaminant pathways), while differences among taxonomic groups (terrestrial invertebrates and plants) may be related to dispersal capacity. The remaining pathways and taxonomic groups were similar in range size, suggesting shared underlying factors. Invasion risk from different human socio-economic activities is spread over our study area rather than concentrated in unique high-risk areas This can be the foundation for a prevention scheme that monitors areas susceptible to invasion for the different pathways