Abstract:
Non-indigenous species are a major conservation threat in the sub-Antarctic islands whose small size and low diversity render them vulnerable to biological invasions. However, what determines whether alien arrivals become successful invaders or not has not been well-explored for the region. We used a trait-based approach to understand whether the success of invasive plant species can be explained by differences in functional traits between indigenous and alien plant species. Average values for number of functional traits of all alien and indigenous higher plant taxa on sub-Antarctic Marion Island were collected from across the island using a stratified sampling design. To test whether native, non-invasive alien and invasive species differ in their functional traits, general linear models were performed for height, leaf area, specific leaf area (SLA), and electrolyte leakage as an indicator of frost sensitivity. Our findings showed that only SLA differed significantly between the three status groups. However, when phylogeny was accounted for by fitting a phylogenetic generalised least-squares model, all of the four traits analysed differed significantly for native, non-invasive alien and invasive species. Our results suggest that invasive species have a capacity for faster growth rates and enhanced resource acquisition but low frost tolerance. This suggests that invasive species are strong competitors who invest little in leaf defences against the cold. The consequences of these findings are of concern, given that Marion Island has become considerably warmer. With temperatures expected to increase into the future, invasive species are likely to spread and become competitively superior to native species. In summary, understanding which functional traits favour invasion success and potential may provide a useful tool to minimise future invasions.
