Abiotic and biotic factors shape the invasion success of the alien plant species Senecio inaequidens (Asteraceae) in northern Italy

Invasive alien species threaten global biodiversity and ecosystems. Understanding the context-dependency of invasion dynamics is crucial for uncovering the processes driving the establishment and spread of alien species. This study investigates how abiotic (soil characteristics) and biotic factors (resident vegetation diversity and similarity to the invader) affect the invasion success of Senecio inaequidens (South African ragwort) across high- and low-productivity habitats in northern Italy. Our results revealed that abiotic and biotic factors affect S. inaequidens success. We found evidence of biotic resistance from resident plant communities, driven mainly by diversity and cover. However, a negative relationship between S. inaequidens performance and both phylogenetic and functional similarity to resident species was found, indicating better performance when growing with more similar species. We additionally observed stronger resistance in more nutrient-rich environments, highlighting the context-dependent nature of such relationships. Our results suggest that S. inaequidens is more susceptible to competition than adverse abiotic conditions, making it as a good colonizer rather than a strong competitor. These findings emphasize the complexity of invasion dynamics and the importance of considering both biotic and abiotic factors in developing management strategies for invaded ecosystems.