Print PagePlant defensive traits drive patterns of herbivory and herbivore diversity among plant species. Over the past 30 years, several prominent hypotheses have predicted the association of plant defenses with particular abiotic environments or geographic regions. We used a strongly supported phylogeny of oaks to test whether defensive traits of 56 oak species are associated with particular components of their climatic niche.
Results/Conclusions
Climate predicted both the chemical leaf defenses and the physical leaf defenses of oaks, whether analyzed separately or in combination. Using phylogenetically corrected linear regression, we found that plant defenses tended to be greater in oak species that occur in regions with low temperature seasonality, mild winters, low minimum monthly precipitation, and high precipitation seasonality. An Ornstein-Uhlenbeck modeling approach supported the hypothesis that selection for oak leaf defenses differed among abiotic environments, but suggested that plant defenses track the abiotic environment slowly over macroevolutionary time. The pattern of association we observed between oak leaf traits and abiotic environments was consistent with a combination of a seasonality gradient (which may relate to different herbivore pressures) and the resource availability hypothesis, which posits that herbivores exert greater selection on plants in resource-limited abiotic environments. Independent surveys of herbivorous insects in a common garden of 60 oak species also suggested that increased leaf longevity increased overwintering success of herbivores on oak leaves, even though evergreen leaves were less palatable to those herbivores.
