UC Riverside

Biodiversity can be maintained or disrupted by disturbance. With human activities drastically altering natural disturbance regimes in ecosystems, understanding the factors that most impact recovery is vital. California coastal sage scrub (CSS) is a fire-prone system with many endemic plant species, including fire-following forbs and shrubs. However, increased fire and plant invasions have impacted native recovery, which may have implications for plant-pollinator interactions. As biodiversity continues to be threatened, investigating post-disturbance recovery may help to predict outcomes of climate change and altered disturbance regimes across trophic levels.

In Chapter 1, I investigated how a wildfire influenced CSS plant composition at four- to six-years post-fire. I found cover and species richness metrics were influenced not only by fire, but also by site characteristics and seasonality. Overall, native annual forbs and invasives grasses contributed largely to composition patterns. I also found a positive association between increased precipitation and both fire-follower richness and floral resource richness. These results highlight the importance of employing multiple metrics and species-level investigations to assess post-fire plant composition more accurately.

In Chapter II, I assessed host plant suitability of CSS species by quantifying larval development and survival for commercially sourced painted lady butterflies (Vanessa cardui). Overall, larval survival was extremely low (0.1%), as was successful pupation and survival to adulthood. This contrasted with 63% survival for wild sourced larvae. These findings broaden our understanding of V. cardui ecology and host plant suitability for supporting complete development of larvae.

In Chapter III, I leveraged community science observations of V. cardui butterflies throughout California shrub/scrub ecosystems during and outside of irruptive migrations. I identified visitation to 329 plant species of various functional types and native status. 195 of the plants in my dataset had not previously been identified as V. cardui nectar plants. These findings broaden our understanding of the diverse floral resources supporting this butterfly.

The goals of this dissertation were to 1) explore the factors driving post-fire plant composition, 2) assess the suitability of various putative host plants for V. cardui larval survival, and (3) quantify migratory butterfly nectar plant use throughout a geographic range.