Competitive interactions among insect herbivores with variable diet breadth: Novel insights from a community of grasshoppers

Coexistence of multiple generalist herbivores utilizing the same host plants seems to violate Gause's postulate, however coexistence is common in grasshopper communities where 20 or more species can coexist. Diet breadth of these grasshoppers overlaps broadly although species tend to be in different functional feeding groups: oligophagous feeders that primarily consume either grass or forbs and polyphagous species that consume both. Coexisting species are also known to have tightly regulated species-specific nutrient intake targets that could represent nutrient niches. We investigated whether diet breadth (grass or polyphagous) or nutrient target differences correlated with competitive interactions in diverse grasshopper communities in a restored mixed-grass prairie at the Balcones Canyonlands National Wildlife Refuge, Texas. Using field cage experiments we demonstrate that there was little difference between intra- and interspecific competition even at high densities. Competition among species in the same functional feeding groups was equal to that between species from different groups. No correlation existed between survival and differences between species' nutrient intake targets. These experiment demonstrate that community assembly rules for these herbivores are likely highly complex and not fully explained by classic competition theory.