Effect of introduction pathways on the invasion success of non-native plants along environmental gradients

Abstract

Our understanding on the role of introduction pathways on plant invasions is incomplete because their interaction with other factors remains poorly studied. We contributed to filling this knowledge gap, by analysing temporal trends in pathway importance, pathway-specific differences in the invaded niche, and the effect of pathways on invasion success. We used the non-native flora of Catalonia (NE Spain) as a study system. The contribution of pathways to the non-native flora interacted with time: from before 1500 to the present, gardening replaced agriculture as the main donor of new plants, while the contribution of unintentional introductions fluctuated without a consistent trend. Among neophytes (plants introduced after 1500), introduction pathways influenced differences mainly in habitat type, and secondarily in elevation: natural habitats and high elevation promoted invasion by gardening plants over unintentionally introduced ones. These nuances were unrelated to interactions between environmental variables. Among neophytes, invasion success was unrelated to pathways and interactions between pathways and traits, but was positively related to minimum residence time: older introductions achieved greater area of occupancy, habitat range, and invaded climatic niche breadth. Our results suggest that non-native plants diversified their niches over time (1500-present), a process that resulted in similar area of occupancy and niche breadth across plants with different introduction pathways. This was accompanied by pathway-specific nuances in the type of invaded environmental conditions.