COS 48-6 - The impact of small vertebrate consumers on community assembly in degraded California sage scrub

Background/Question/Methods

Native consumers have been found to influence plant recruitment and community assembly, depending on what species they prefer. In California sage scrub, little is known about the preferences of small vertebrate consumers, although their feeding behavior may affect interspecific competition between native and invasive plant species. Moreover, there is an unexplored opportunity to investigate which plant functional traits are preferred by small herbivores in the sage scrub community. We established caged and uncaged native restoration plots in degraded sage scrub to investigate the effects of consumers on community assembly. Thirteen native species were hand-seeded into research plots dominated by invasive grasses and forbs. Three community types were created using different seed treatments (dominated by a preferred species (Stipa pulchra), dominated by a less preferred species (Salvia mellifera), or control with species included in equal abundance). Plant recruitment and growth were monitored in experimental communities while motion activated trail cameras recorded consumer activity. In addition, consumer preference trials for common native and invasive plant seeds and seedlings were conducted.

Results/Conclusions

During the first year of data collection, consumer exclosures had a positive effect on native plant recruitment but no significant effects on invasive plant recruitment in experimental communities. Native abundance was highest in caged plots across all seed treatments. The granivorous bird Melozone crissalis (California towhee) was the dominant animal present after seeding, followed by Sylvilagus audubonii (desert cottontail). Monthly seed preference trials showed that granivorous birds preferred to eat native seeds over invasive seeds. Thus, the presence of granivores may explain the differences in native and invasive plant establishment observed between caged and uncaged restoration plots. Furthermore, preliminary analysis of functional traits showed that a large seeded native annual, Lupinus bicolor, was favored by consumers. Following year two of the experiment, overall community functional diversity will be examined. These results suggest that small mammals and birds negatively influence native plant establishment in a degraded California sage scrub. Habitat restoration efforts should focus on protecting vulnerable native species from consumers in addition to invasive species control.