Variation in the strength of local and regional determinants of
herbivory across the Neotropics
Abstract
Insect herbivory can vary from an inconsequential biotic interaction to
a factor that contributes substantially to the diversity of plants and
animals and overall interaction diversity. 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 characterize patterns of herbivory on
plants in a species rich and abundant tropical understory genus (Piper)
across forests spanning 44° of latitude in the Neotropics. We modeled
the effects of geography, climate, resource availability, and Piper
species richness on the median, dispersion, and skew of generalist and
specialist herbivory. By examining these multiple components of the
distribution of herbivory, we were able to determine factors that
increase biologically meaningful herbivory at the upper ends of the
distribution. Site level variables such as latitude, seasonality, and
maximum Piper richness explained variation in herbivory at the local
scale (plot level) better for assemblages 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 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 responded differently to abiotic and biotic
factors, illustrating the need for careful studies to explore
distributions of herbivory and their effects on forest diversity.
Nevertheless, we observed a roughly two-fold increase in median
herbivory in humid compared to seasonal forests, and this finding aligns
with the hypothesis that precipitation seasonality plays a critical role
in shaping interaction diversity within tropical ecosystems.