Effects of prescribed fire on mediating coexistence between grasshoppers

Rapid environmental change is reshaping patterns of biodiversity in unpredictable ways. Modern coexistence theory (MCT) offers a useful framework for predicting these patterns, and insects serve as an ideal study system due to their diversity and complex interactions. However, few studies have applied MCT to examine how insect taxa respond to environmental disturbances. We examined how two co-occurring grasshoppers with contrasting diet breadths, Aptenopedes sphenarioides (mixed feeder) and Achurum carinatum (grass specialist) respond to disturbances. As a natural disturbance in grasslands, the main habitat for grasshoppers, fire was predicted to influence plant nutritional quality and thereby impact the potential coexistence of these two species. We quantified the strength of niche and fitness differences between the two species by manipulating their frequencies and densities in burned and unburned plots using field cages in old-pasture habitats. I hypothesized that 1) intraspecific competition will be stronger than interspecific competition in recently burned habitats, thus promoting coexistence through niche differences and that 2) Aptenopedes will face competitive exclusion from Achurum, the presumed superior competitor, in unburned plots because the plants will be lower quality, and competition will be more intense. Our results suggest the grass specialist Achurum experienced stronger intraspecific competition than interspecific competition, potentially promoting coexistence with Aptenopedes in burned plots. Additionally, we found that Aptenopedes faced exclusion from Achurum, against certain environmental conditions. Our findings help identify environmental factors that stabilize or disrupt insect coexistence, broadening the conceptual framework of biodiversity maintenance in insect communities.