Endemic Castilleja grisea support diverse floral-visitor assemblages with implications for promoting local plant communities

Jo'lene Saldivar; C. Sheena Sidhu; Erin Wilson Rankin

doi:10.26786/1920-7603(2026)891

Authors

Jo'lene Saldivar Department of Botany and Plant Sciences, University of California Riverside, Riverside, CA 92521 https://orcid.org/0000-0002-2694-9631
C. Sheena Sidhu Department of Entomology, University of California Riverside, Riverside, CA 92521
Erin Wilson Rankin University of California, Riverside https://orcid.org/0000-0001-7741-113X

DOI:

https://doi.org/10.26786/1920-7603(2026)891

Keywords:

California Channel Islands, endemic, Plant-pollinator networks, pollination

Abstract

Castilleja grisea, the San Clemente Island paintbrush, is endemic to San Clemente Island (Los Angeles County, California). This bushy hemiparasitic perennial was once threatened by livestock and feral herbivore grazing, but occurrences have increased since island-wide non-native herbivore removal. Recently declassified as a federally endangered species, C. grisea remains state listed (California Rare Plant Rank: 1B.3), and a subset of the population is surveyed annually as part of its post-delisting monitoring plan. We investigated the flower-insect interactions of C. grisea and its neighboring plant community at six locations during early, mid, and late in the flowering season. A total of 23 insect taxa were observed visiting 12 species of plants, with 74% of the floral-visitor taxa observed actively visiting C. grisea flowers. Moreover, plots with blooming C. grisea boasted nearly 50% higher insect species richness than areas where the paintbrush was absent or not flowering. Plant-floral-visitor networks changed over time, becoming significantly less connected and exhibiting lower interaction evenness. Our findings suggest that C. grisea supports a diversity of floral visitors and may be an indicator of habitat health and high plant community diversity. As a potential keystone species, conservation planning and management strategies promoting C. grisea may have far reaching benefits for this island ecosystem.

Author Biographies

Jo'lene Saldivar, Department of Botany and Plant Sciences, University of California Riverside, Riverside, CA 92521

Current address: Department of Entomology and Nematology, University of California, Davis, Davis, CA 95616

C. Sheena Sidhu, Department of Entomology, University of California Riverside, Riverside, CA 92521

Current address: Jasper Ridge Biological Preserve, Stanford University, Stanford, CA 94305

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