Abstract
Rapid germination or flexible germination cues may be key traits that facilitate the invasion of exotic plant species in new environments. We investigated whether robustness or plasticity in response to environmental cues were more commonly exhibited by exotic than native species during germination, evidenced by (1) exhibiting consistently greater germination rate under a variety of conditions (robustness), or (2) increasing germination rate more strongly than native species in response to favorable conditions (plasticity). We conducted growth chamber germination trials of 12 native and 12 exotic species common to coastal sage scrub, a shrub-dominated Mediterranean-type ecosystem in California. Time to germination and percentage germination were recorded in response to variation in three environmental cues: temperature, day length, and soil moisture. Exotic species, especially annuals, displayed consistently higher germination percentages and more rapid germination than native species. Exotic germination percentages also responded more strongly when conditions were favorable (warm temperatures and high soil moisture), and germinated earlier than natives when conditions were indicative of typical growing season conditions in Mediterranean ecosystems (short day length and cool temperatures). Exotic species had more rapid and prolific germination across a variety of environmental cues and in response to increased resource availability compared with native species, indicating both germination plasticity and robustness. These traits may enable colonization of novel environments, particularly if they allow exotic species to establish earlier in the growing season than native species, setting the stage for seasonal priority effects.



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Acknowledgments
We wish to acknowledge the Kohn Lab and Roy Lab at the University of California, San Diego, for providing growth chamber space for this study. We also wish to thank the Kamprath Seed Company for their generous donation of seeds. This work was supported by a Mildred E. Mathias Graduate Student Research Grant from the University of California Natural Reserve System and an Educational Grant from the California Native Plant Society.
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Wainwright, C.E., Cleland, E.E. Exotic species display greater germination plasticity and higher germination rates than native species across multiple cues. Biol Invasions 15, 2253–2264 (2013). https://doi.org/10.1007/s10530-013-0449-4
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DOI: https://doi.org/10.1007/s10530-013-0449-4


