UC Irvine

In this study, we utilized a suite of plant trait-based approaches towards understanding plant-arthropod interactions from an ecological perspective. Through laboratory and field-based assays on 14 species of woody shrubs native to the Coastal Sage Scrub ecosystem, we compared variance in plant resistance to herbivory and in non-defensive plant traits to variance in components of associated arthropod communities. Our analyses revealed the following: (1) plant resistance to herbivory assessed in a lab bioassay was overall a poor predictor of herbivore density in the field though it did provide insight into arthropod herbivore dynamics for several plant species and over time; (2) plant species varied strongly in predator abundance but this did not correlate with herbivore densities, suggesting a limited role for predators as a from of indirect defense for plants ; and (3) variance in non-defensive plant traits strongly correlated with variance in associated arthropod density and community composition. Taken together, our findings indicate that plant-arthropod interactions on ecological time scales in realistic ecological are driven more by traits presumably evolved for other purposes than by aspects of direct and indirect defense that are tyically the focus of studies on plant-herbivore evolutionary ecology. While these other traits may be the dominant drivers of herbivore abundance, we speculate that aspects of plant defense may still have weaker, hard to detect effects that act to mediate these interactions over evolutionary time scales. While these other traits may be the dominant drivers of herbivore abundance, we speculate that aspects of plant defense may still have weaker, hard to detect effects that act to mediate these interactions over evolutionary time scales.