Plant size, latitude, and phylogeny explain within-population variability in herbivory

Interactions between plants and herbivores are central in most ecosystems, but their strength is highly variable. The amount of variability within a system is thought to influence most aspects of plant-herbivore biology, from ecological stability to plant defense evolution. Our understanding of what influences variability, however, is limited by sparse data. We collected standardized surveys of herbivory for 503 plant species at 790 sites across 116° of latitude. With these data, we show that within-population variability in herbivory increases with latitude, decreases with plant size, and is phylogenetically structured. Differences in the magnitude of variability are thus central to how plant-herbivore biology varies across macroscale gradients. We argue that increased focus on interaction variability will advance understanding of patterns of life on Earth. Herbivory is a major selection pressure on plants, which have evolved many different physical and chemical adaptations to prevent animals from eating their tissues. However, herbivory pressure can be highly variable, even between plants in the same population. The Herbivory Variability Network consortium used standardized surveys to compare herbivory variability within populations at 790 sites across five continents. They found that the weak increase in mean herbivory at lower latitudes was accompanied by lower variation between individuals. Smaller plant species had higher herbivory variability, which also showed a phylogenetic signal. These findings highlight how variation in species interactions can influence eco-evolutionary outcomes. —Bianca Lopez Smaller plants at lower latitudes show higher variation in herbivory pressure among individuals.