Assessing the impact of Antigonon Leptopus on Saba and St. Eustatius
The spread of invasive species globally has had acknowledged impacts on species extinction, biodiversity and ecosystem services. Gauging the type and magnitude of impacts from invasive species is an important consideration in the allocation of resources towards the prevention of their spread, management and efforts towards elimination. The focus of this research was the assessment of the impacts of the invasive species Coralita (Antigonon Leptopus) on the islands of Saba and St. Eustatius in the Dutch Caribbean. Although there was anecdotal information about its impacts available from prior studies, specific information was lacking. Whereas experimental or observational research would typically be used to assess impacts of this nature, this research attempted to identify impacts more remotely, based upon the application of a dual methodological approach. As such, whilst the main aim was to assess impacts of Coralita, the primary concern was the acquisition of information in order to make such an assessment.
Two complementary methodological frameworks were loosely applied to help guide the analytical approach. The first, the Environmental Impact Classification of Alien Taxa (EICAT), adopted by the IUCN to standardise invasive species impacts, was used to help focus the research on species and community level impacts. The analytical approaches associated with this methodology included an investigation of impacts associated with biodiversity richness, competitive exclusion and changes in species types over time and an approach to transfer the types of impacts noted for comparable species to the Coralita on the islands. The other approach was instead focussed on species characteristics (traits) and the impact that Coralita may have had on community averages, which could then be potentially linked to ecosystem function/services based on generalised relationships observed from research literature. Although these approaches were carried out separately, they were complementary, with findings from the EICAT methodology used to support those from the trait-based methodology and vice versa. Analysis included statistical testing and principal component analysis.
Overall, the impact of Coralita on individual species and communities was classed as moderate in terms of the EICAT classification level (i.e. 3 out of 5). This reflected potential impacts on biodiversity, likely impacts as a result of comparison with other invasive species and some limited evidence of competitive exclusion through analysis of co-occurrence. Trait-based evidence appears to show that Coralita has more in common with other invasive species than island species, and as such is likely to impact the structure of communities where it is found by changing average trait values. On the contrary, analysis associated with traits and levels of abundance used for this study suggest that Coralita is not having a substantial impact in the areas that it is found, at least based on the areas covered by this analysis. These somewhat conflicting findings, together with a lack of certainty in relation to these findings more generally, means that further research would be recommended to build sufficient confidence that Coralita is having a major impact. In particular, research into the implications of Coralita extent in more urban areas, where disturbance is a key driver of Coralita spread, is recommended in this regard.