Invaders and Natives show different variability in Hawaii

Displacement of native plant species by non-native invaders may result from differences in their carbon economy, yet little is known regarding how variation in leaf traits influences native-invader dynamics across climate gradients. In Hawaii, one of the most heavily invaded biodiversity hotspots in the world, strong spatial variation in climate results from the complex topography, which underlies variation in traits that likely drives shifts in species interactions. Andrea Westerband and colleagues set out to understand how invading species interact with climate by tracking leaf traits in plants across the largest four Hawaiian islands.

“In Hawaii, climate is highly variable spatially, due to extreme topography resulting from the volcanic origin,” write the authors. “Elevational gradients may thus represent a good proxy for climate variability, with considerable reductions in temperature and significant but region-specific shifts in rainfall as elevation increases. The Hawaiian Islands also vary in age, such that islands with similar climates may still express significant variation in soil nutrient concentrations.”

Westerband and colleagues detected significant differences in trait means, such that invasives were more resource-acquisitive than natives over most of the climate gradients. However, they also detected trait convergence and a rank reversal (natives more resource-acquisitive than invasives) in a subset of conditions. There was significant intraspecific variation (ITV) in leaf traits of natives and invasives, although invasives expressed significantly greater ITV than natives in water loss and photosynthesis. Species accounted for more trait variation than did climate for invasives, while the reverse was true for natives. Incorporating this climate-driven trait variation significantly improved the fit of models that compared natives and invasives. Lastly, in invasives, ITV was most strongly explained by spatial heterogeneity in moisture whereas solar energy explains more ITV in natives. 

The authors conclude that their study, “…clarifies the extent to which climate drives trait variation in native Hawaiian species, and the extent to which invasives vary in their trait expression within the same environments. We detected similar ITV in natives and invasives but these were constrained by distinct climate variables. Furthermore, in a subset of the climate space, natives expressed more resource-acquisitive traits than invasives, which is contrary to many previous studies.”