Date of Award

Winter 12-12-2025

Degree Type

Honors Thesis

Major

Biology

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Sevan Suni

Second Advisor

James Sikes

Third Advisor

Brian Thornton

Abstract

Drought is becoming an increasingly dominant force shaping plant–pollinator interactions, yet we still know little about how nectar rewards respond to water limitation across species commonly used to support pollinators. We examined nectar volume and sucrose content in six flowering species relevant to California’s Mediterranean climate and quantified how drought alters these traits for four of those species. Under well-watered conditions, species differed in their nectar production, spanning more than two orders of magnitude. Perennial species such as Epilobium canum and Scrophularia californica produced the highest nectar volumes and sucrose amounts, suggesting that they contribute substantial carbohydrate resources when moisture is sufficient. Among the species for which drought treatments were implemented, water limitation significantly reduced nectar volume and sucrose availability overall, but these reductions varied among species. While Clarkia unguiculata and Phacelia tanacetifolia both showed declines under drought, Linaria purpurea’s nectar rewards increased under drought. These results reveal substantial interspecific variation in how floral rewards respond to drought and demonstrate that some species may continue to provision pollinators reliably even as water availability decreases. Identifying drought-resilient nectar sources will be critical for designing pollinator-supporting plantings in a warming, increasingly water-limited climate.

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