Cascading effects of soil type on assemblage size and structure in a diverse herbivore community.

Soil type is understudied as a driver of herbivore community size and structure across host plants. This study extends predictions of resource availability hypotheses to understand how soil types of different resource levels alter plant resistance and structure of herbivore assemblages. In this 2-yr study we use seven dominant chaparral shrub species that grow across a natural mosaic of low and high resource soils to explore effects of soil type on plant resistance, and relate these soil-based differences in resistance to the abundance and diversity of the larval lepidopteran community. We show that growing on low-resource soils increases plant resistance, as measured by herbivore performance, both within and across host plant species, and that resistance may be driven by variation in plant nutritive and defensive traits. We then show that more resistant plants on low-resource soils host less abundant and less diverse herbivore assemblages across a natural soil mosaic in the field.