Evidence for reductions in physical and chemical plant defense traits in island flora

Reduced defense against large herbivores has been suggested to be part of the “island syndrome” in plants. However, empirical evidence for this pattern is mixed. In this paper, we present two studies that compare putative physical and chemical defense traits from plants on the California Channel Islands and nearby mainland based on sampling of both field and common garden plants. In the first study, we focus on five pairs of woody shrubs from three island and three mainland locations and find evidence for increased leaf area, decreased marginal leaf spines, and decreased concentrations of cyanogenic glycosides in island plants. We observed similar increases in leaf area and decreases in defense traits when comparing island and mainland genotypes grown together in botanic gardens, suggesting that trait differences are not solely driven by abiotic differences between island and mainland sites. In the second study, we conducted a common garden experiment with a perennial herb—Stachys bulla..., Study 1: Chaparral Shrub Sampling
We selected five pairs of taxa characteristic of the chaparral plant community that occur on both the California Channel Islands and the nearby southern California mainland. Pairs were chosen because they are common representatives of the chaparral flora and also to match the taxa sampled in Bowen and Van Vuren (1997). Sampling consisted of either congeners or conspecifics from three plant families: Rosaceae (Cercocarpus, Prunus, Heteromeles), Papaveraceae (Dendromecon), and Rhamnaceae (Ceanothus). We collected leaf tissue in February and March of 2016 for use in morphological and chemical analysis. In total, we sampled 291 individual plants from five taxonomic pairs across six sites (three island, three mainland), for an average of approximately 10 plants per site.
We collected leaf tissue for morphological analysis from focal plants by clipping branches containing variable numbers of leaves. When possible, we collected a branch from both the lower (&l..., , # Evidence for Reductions in Physical and Chemical Plant Defense Traits in Island Flora

[https://doi.org/10.5061/dryad.51c59zwgj](https://doi.org/10.5061/dryad.51c59zwgj)

This dataset consists of three primary data sources:

(1) Morphological and chemical measurements of leaf traits, collected from five taxonomic pairs of chaparral shrubs (*Ceanothus megacarpus*, *Cercocarpus betuloides*, *Dendromecon rigida/harfordii*, *Heteromeles arbutifolia*, *Prunus ilicifolia*) at three sites on the California Channel Islands (Santa Rosa, Santa Cruz, Santa Catalina) and three sites on the California mainland.

(2) Morphological and chemical measurements of the same leaf traits from the same species, but this time measured from plants growing at botanic gardens

(3) Morphological, chemical, and biomass data from a common garden experiment with *Stachys bullata*, with genotypes from two islands (Santa Rosa, Santa Cruz) and four mainland locations

In addition, our analysis also includes bioclimati...