Broad patterns in the distribution of herbivory are elusive due to the
importance of local scale variation and differences between specialist
and generalist herbivores
Abstract
Insect herbivory is a critical top-down force structuring plant
communities, and quantifying the factors that mediate damage caused by
herbivores is fundamental to understanding biodiversity. As herbivory is
the result of numerous ecological and evolutionary processes, including
complex population dynamics and the evolution of plant defense, it has
been difficult to predict variation in herbivory across meaningful
spatial scales. In the present work, we characterized patterns of
herbivory on plants in a speciose and abundant tropical understory genus
(Piper) across forests spanning 44° of latitude in the Neotropics. We
modeled the effects of geography, climate, resource availability,
species richness and top-down pressure from parasitoids on the mean,
dispersion, and skew of generalist and specialist herbivory. By
examining these multiple moments of the distribution of herbivory, we
were able to determine factors that increase biologically meaningful
herbivory at the upper ends of its distribution. The strongest pattern
that emerged at a large spatial scale was a roughly two-fold increase in
herbivory in humid relative to seasonal forests. Site level variables
such as latitude, seasonality and maximum Piper richness explained
variation in herbivory at the local scale (plot level) better for
communities of Piper congeners than for a single species. Predictors
that varied between local communities, such as resource availability and
diversity, best explained the distribution of herbivory within sites,
dampening any broad patterns across latitude and climate and
demonstrating why generalizations about gradients in herbivory have been
elusive. The estimated population means, skew, and dispersion of
herbivory respond differently to abiotic and biotic factors,
demonstrating the need for careful studies to explore the distributions
of herbivory and their effects on forest diversity.