COS 30-7
Are native and invasive species functionally similar in low-resource ecosystems? A functional trait comparison across five Mediterranean-climate ecosystems
It is difficult to identify a suite of general traits explaining invasiveness because traits of invaders depend on characteristics of the invaded habitats. Specifically, the mechanisms allowing exotic species to invade low-resource ecosystems are likely to be very different from those allowing species to invade high-resource ecosystems. Invasive species tend to be located on the fast-return end of leaf economic spectrum (LES), displaying low leaf mass per unit area (LMA), high rates of carbon assimilation, high leaf nitrogen (N) content, and short leaf lifespan while native species occupy the slow-return end of the LES. However, it is unclear if these functional differences exist in low-resource ecosystems where theory suggests plant species should benefit from traits characterized by the slow-return end of the LES.
In this study, we measured functional traits from native and invasive species occurring in eight vegetation communities across the five Mediterranean-climate ecosystems (MCEs). MCEs are characterized by cool, wet winters and hot, dry summers. Woody species native to these regions have developed traits that allow them to thrive in this climate, including LMA and small evergreen leaves or drought deciduousness, while annual species germinate and flower early in the wet season to avoid hot, dry summers. Understanding invasion dynamics in these systems is critical due to their status as biodiversity hotspots.
Results/Conclusions
We collected functional trait data from the most common invasive (5-9 species per site) and native (7-47 species per site) species in California (serpentine grassland, coastal sage scrub), Chile (sclerophyll woodland), South Africa (acid-sands fynbos, Renosterveld), Spain (coastal grassland), and Western Australia (banksia woodland, coastal banksia woodland). Traits included leaf N and P content, LMA, photosynthetic capacity, water use efficiency, photosynthetic nutrient use efficiency, root depth, specific root length, nutrient acquisition strategy, height, seed mass, and life form. Traits differed more strongly across the eight sites than between native and invasive species. Despite differences in LMA, root depth, and life form, native and invasive species were similar with respect to rates of carbon assimilation and resource use efficiency. Overall, our data suggest that invasive species are functionally similar to native species in MCEs although there is significant variability across regions and across sites within regions resulting from different environmental pressures and land-use history.