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Thesis Abstract – King (2012)


The Effects of Invasive Grasses on the Survival and Germination of Native Forbs

Author and college:

Rachel A. King, Scripps College


April 23, 2012


Bachelor of Arts in Biology


Diane Thomson, Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges


Invasive species are an increasingly severe conservation problem that can dramatically alter native plant communities. Although ecologists have proposed many mechanisms for the dominance of invasive species, superior competitive ability is one of the longest standing hypotheses. In winter annual plant communities, germination timing affects competition among plants. I hypothesized that grass invasion has changed the costs and benefits of early and late germination, and that species with flexible germination timing would compete better with invasives. Experiments at the Bernard Field Station in Claremont, CA and germinator trials in a controlled environment were used to examine the survivorship and germination rate of three native forbs in the presence or absence of invasive grass competition. Germinator trials revealed that most Clarkia purpurea var. quadrivulnera seeds germinated in fall conditions, though newer seeds had higher proportions germinate under winter conditions. Older seeds had a lower germination success, indicating a potential decrease in seed viability. In the field experiment, November germinants had higher survival rates than October germinants for Amsinckia menziesii var. intermedia and Phacelia distans, and both species had similar numbers of new germinants at each census. Removal of invasive grasses did not significantly affect the survival of either species, though a trend towards increased survivorship was observed in removal plots of November germinants, indicating that invasive grasses may affect the survivorship of late germinants. Taken together, these results show evidence for variation in germination timing and responses to environmental cues among native annual seeds, and also support the idea that germination timing has important consequences for survivorship, and potentially competitive interactions, with invasive grasses. Future experiments will continue examining variation in germination timing of natives in this community and its effects on competition with invasive plants.

Thesis availability:

Scholarship@Claremont – http://scholarship.claremont.edu/scripps_theses/136/

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