Do habitats show a different invasibility pattern by alien plant species? A test on a wetland protected area

Biological invasions are deemed as the second most important global driver of biodiversity loss right behind habitat destruction and ragmentation. In this study, we aimed at testing if community invasibility, defined as the vulnerability to invasion of a community, could be associated with the characteristics of a given habitat, as described by the composition and structure of its native species. Based on a probabilistic sampling of the alien flora occurring in the temperate wetland Lake Doberdò (Friuli Venezia Giulia region, NE Italy) and using a null model-based approach, observed occurrence of Invasive Alien Species (IAS) within sampling units were randomized within habitats. While testing the degree of invasibility for each habitat within the wetland, our null hypothesis postulated that habitats are equally invaded by IAS, as IAS can spread homogeneously in the environment thanks to their plasticity in functional traits which make them able to cope with different ecological conditions. The results obtained comparing observed IAS frequencies, abundance and richness to those obtained by the null model randomizations, showed that for all habitats invasion was selective. Specifically a marked preference for habitats with an intermediate disturbance level, a high nutrients level and a medium-high light availability was observed while an avoidance was detected for habitats characterized by lower levels of nutrients and light availability or extreme conditions caused by prolonged submersion. This method allows us to provide useful information using a simple-to-run simulation, for the management of the IAS threat within Protected Areas. Moreover, the method allows us to infer important ecological characteristics leading to habitat invasion without sampling the environmental characteristic of the habitats, which is an expensive operation in terms of time and money.