Theory indicates that variability and skew in species interactions can have a major influence on ecology and evolution. Ecologists have long remarked that interactions between plants and herbivores are strikingly variable in space and time and hypothesized about causes and consequences. The field, however, has lacked the large datasets needed to assess the macroecology and macroevolution of variability in plant–herbivore interactions. The Herbivory Variability Network is a global collaboration, started in mid 2019, that aims to describe and understand how and why patterns in plant–herbivore interactions vary across the tree of life and around the world. As of early 2020, our 150+ collaborators (https://herbvar.org/collaborators) have completed >190 standardized surveys of >160 plant species from >60 plant families on 6 continents. In this talk, we focus on describing variation in herbivory within plant individuals and how the magnitude of variability varies with plant phylogeny, plant growth form, ecosystem type, latitude, and other ecological variables.
Results/Conclusions
We found that herbivore damage was distributed highly unevenly among leaves within plants (Gini index of inequality = 80.8±4.4% [mean±SE]). This result indicates that most leaves escape herbivore damage, except for a small number of leaves with high levels of damage. The unevenness in herbivory among leaves within plants was even greater than the unevenness in herbivory among plant individuals within species, which was also substantially large (Gini index= 65.9±4.4%). Moreover, variability at these two scales was strongly correlated (ρ = 0.80). In other words, plant species with high variation in herbivory among individuals within populations also had high variation in herbivory among leaves within plants. We found that the few plant species with even distributions of herbivory among leaves were consistently small plants with few leaves that occurred at low local densities. Overall, our results indicate that patchiness and variability in the distribution of herbivore damage within plants is a pervasive feature of plant–herbivore interactions that has likely played a key role in the evolution of plant resistance and tolerance.