Diet breadth and macronutrient regulation reveal how generalist herbivores coexist

Coexisting species of generalist grasshoppers within the same genus have been shown to differ in their regulation of protein and carbohydrate intake (intake target). These species-specific nutrient requirements could represent different nutrient niches, which would explain the observed stable coexistence of multiple generalist herbivores. To investigate this hypothesis we compared host plant use to macronutrient intake targets among dominant grasshopper species in Central Texas (Balcones Canyonlands National Wildlife Refuge). In 2011 and 2012 we collected grasshoppers from the field and either conducted microscopic analysis of gut content, or reared them in the laboratory and subjected them to artificial diet experiments to determine the macronutrient intake target. We found that grasshoppers with broadly overlapping diets had significantly different nutritional requirements lending support to the nutrient niche hypothesis. Similar to other grasshopper communities, diets varied from monophagy to polyphagy. However, many of the most damaging rangeland grasshoppers had broad, overlapping diets. Interestingly, intake targets did not consistently reflect the nutrient composition of host plants for each respective taxa. For instance, many grasshoppers which only feed on protein-rich forbs had carbohydrate-biased intake targets.