Plant invasions are economically and ecologically costly. Research suggests a species may differ physiologically and ecologically between invasive and native ranges and these differences may enhance invasiveness. I examined biogeographical growth and defense differences of three aggressive invaders in Hawaiian forests: the tree strawberry guava (Psidium cattleianum), the shrub Koster’s curse (Clidemia hirta) and the herb cane tibouchina (Tibouchina herbacea). In quarantine in Volcano, Hawai‘i, I tested the Evolution of Increased Competitive Abilities (EICA) hypothesis, postulating individuals from invasive Hawaiian populations would be faster growing and less defended chemically and structurally than individuals from native South American populations. Seeds of focal taxa were collected in native Brazil and Venezuela and introduced Hawai‘i and grown in a growth chamber for 120-180 days. Plant height, mass and relative growth rates were quantified for 24 paired populations. Key structural traits leaf hair density and specific leaf mass were quantified and feeding trials with specialized insect pests are underway to compare plant defenses.

Results/Conclusions

I found strong support of my first hypothesis; Hawaiian populations grew significantly larger than South American conspecifics, consistent with field observations of larger and more abundant populations in the invasive range. Initial defensive data and feeding trials are mixed and do not conform to my second hypothesis; suggesting post introduction biomass allocation shifts are not complicit in these invasions. My findings warrant explanations divergent from EICA, while underscoring the importance of founder effects as determinants of invasive trajectories. Continued research of biogeographical differences has potential to strengthen theoretical knowledge and prediction of invasions and help develop more effective control strategies.