Scale-dependent variation in leaf functional traits clarifies mechanisms of invasion

Comparing the functional traits of co-occurring native and invasive plant
species can offer insight regarding mechanisms of invasion. Previous
studies have failed to reach a consensus, indicating that the extent of
trait differences between native and invasives might depend on the
environmental context and on the spatial grain of the analysis. Here we
evaluate the scale-dependency of native-invader trait comparisons within
the Hawaiian Archipelago, a globally important region of high endemicity
and high invasibility. We evaluated trait (e.g. gas exchange, leaf
nutrient concentration, specific leaf area) differences locally and
regionally (i.e. within and across islands) and found that while invasives
are more resource acquisitive at the regional scale, native-invader
differences are highly idiosyncratic at localized scales, varying both in
direction and magnitude within islands. Our findings clarify how
region-wide species comparisons may fail to characterize interactions
happening at local scales, thereby misleading or obscuring the mechanisms
underlying invasion.