Neutrality in plant–herbivore interactions

Understanding the distribution of herbivore damage among leaves and
individual plants is a central goal of plant-herbivore biology. Commonly
observed unequal patterns of herbivore damage have conventionally been
attributed to the heterogeneity in plant quality or herbivore behavior or
distribution. Meanwhile, the potential role of stochastic processes in
structuring plant-herbivore interactions has been overlooked. Here, we
show that based on simple first principle expectations from metabolic
theory, random sampling of different sizes of herbivores from a regional
pool is sufficient to explain patterns of variation in herbivore damage.
This is despite making the neutral assumption that herbivory is caused by
randomly feeding herbivores on identical and passive plants. We then
compared its predictions against 765 datasets of herbivory on 496 species
across 116° of latitude from the Herbivory Variability Network. Using only
one free parameter, the estimated attack rate, our neutral model
approximates the observed frequency distribution of herbivore damage among
plants and especially among leaves very well. Our results suggest that
neutral stochastic processes play a large and underappreciated role in
natural variation in herbivory and may explain the low predictability of
herbivory patterns. We argue that such prominence warrants its
consideration as a powerful force in plant-herbivore interactions.