Insect functional traits reveal processes that shape niche differentiation patterns.

Abstract

Functional traits allow ecologists to infer processes that structure ecological communities and quantify interactions between trophic levels. Insects are a ubiquitous group that exhibits a variety of functional traits, and studying these traits could prove useful for understanding insect community assembly. We use insect trait measurements, community sampling along a disturbance gradient, and a cafeteria-style feeding assay to elucidate the mechanisms that govern insect herbivore community assembly processes. Using a trait principal component analysis, we first identified life history trade-offs between herbivore feeding and nutrition based on 3 traits measured on 14 grasshopper species collected across 30 pine savanna field sites. In the field, we tested hypotheses regarding how competition or environmental filtering might structure communities by examining dispersion patterns of functional traits. We found that grasshopper incisor strength and C:N ratio were consistently under-dispersed, patterns that indicate trait-clustering resulting from environmental filtering. Using mesocosms, we tested the hypothesis that grasshopper species should exhibit differentiation in their feeding niches based on the traits of the plants they consume and that feeding traits should correlate with traits of consumed plants. We demonstrated that grasshopper species strongly differentiated their feeding niche based on the traits of plants incorporated into their diets. We also found linkages between herbivore incisor strength and plant leaf dry matter content, and between grasshopper C:N ratio or body size and plant C:N ratio. This study revealed likely mechanisms that govern the interactions between insect herbivores, the plants they feed on, and how they partition resources to coexist.