Invasive grasses do not always exhibit superior and faster plant life-history traits in the introduced range than in the native range

Many invasive plants are larger, and produce more seeds in populations from the introduced range compared to those from their native range. Annual invasive plants might also benefit in their introduced range from fast germination, early seed production and shorter life cycles. Using three species of annual grass native to Spain and invasive in California ( Avena barbata , Bromus hordeaceus and Brachypodium distachyon spp. complex), we tested the hypothesis that plants from the introduced range are not only larger and more fecund, but they also have faster life cycles than plants from the native range. Additionally, these plant traits are expected to vary along climate gradients, both in the introduced and in the native populations. Hence, we collected seeds from introduced and native populations across different climate conditions and then grew them all under a common outdoor condition. In support of our hypothesis, we found that Avena plants from the introduced range were larger, more fecund and had a shorter lifespan than from the native range. By contrast, Bromus plants invested less biomass in reproduction in the introduced range. In Brachypodium , seeds from the introduced range germinated later and flowering was delayed compared to the native range. These plants also produced fewer seeds and had a shorter lifespan in the introduced range. Genome size analysis indicated that Brachypodium plants from the introduced range are tetraploid while, in the native range, diploid and tetraploid individuals co-occur. We found some trait variation could be explained by climate differences amongst populations, but this was mostly within the native range, suggesting that our study taxa are not yet locally adapted to climatic conditions of their introduced range. Overall, our common garden experiment indicated that the invasion success of these annual grasses is not clearly associated with superior biomass, reproduction or fast plant life-history traits. For Brachypodium , polyploidy may play a role in its invasion success.