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Thesis Abstract – Meadors (2018)

Title:

Salvia apiana Seed Dispersal Patterns and Seed Predation: Implications for Population Establishment and Recovery

Author and college:

Savannah R. Meadors, Pomona College

Date:

April 2018

Degree:

Bachelor of Arts in Biology

Advisor:

Frances Hanzawa, Department of Biology, Pomona College

Abstract:

Seed dispersal patterns and seed predation can inform patterns of seed and seedling survivorship, and ultimately of recruitment of new individuals. The connection between survivorship and dispersal success in the early life stages and eventual population establishment and recovery post-disturbance is important to consider in California sage scrub (CSS), an endangered habitat. CSS is a well-studied Southern California habitat type characterized by a Mediterranean climate that holds an abundance of endemic species, including Salvia apiana, commonly known as white sage. S. apiana is a native shrub that is closely associated with CSS, but the seed dispersal patterns of and rates of predation on S. apiana are not well understood. Using seed dispersal simulations, camera trapping, seed depot experiments (with vertebrate and invertebrate exclosures), and soil seed bank sampling, I studied dispersal patterns of S. apiana and the implications of seed predation on future population establishment and regeneration post-disturbance. Dispersal is limited to a 2 meter radius range around the parent plant, where 40-55% of seeds typically land within 1 meter of the flowering stalk/parent plant. Evidence of vertebrate and invertebrate predation was found, and vertebrates are the main drivers of predation. Relatively low rates of avian and rodent seed predation were observed, but 9 species, the most reliable of which were native species, were observed predating seeds. The highest rates of predation were observed in CSS recovering from a 2013 fire, and all predators observed in that habitat type, and some were observed in multiple habitat types. Soil seed bank samples showed that the distribution of seeds in the soil follows a pattern similar to expected dispersal, but in 2013 recovering CSS, predation seems to be greatest from the canopy edge to 1 m, resulting in a slight increase in recovered seeds and decrease in the proportion of damage on recovered seeds. These results imply that S. apiana is likely more susceptible to habitat fragmentation and increased frequency of disturbance due to slow recolonization and increased predation in recovering areas. This is important for future conservation policy justification for S. apiana and CSS as a habitat, but because this area of research is very limited, further studies characterizing the demography of this plant, particularly the seed and seedling life stages are much needed to better understand this important CSS shrub.

For more information:

Contact Frances Hanzawa – frances.hanzawa@pomona.edu