All that is green is not nutritious or, The importance of peeing earnestly

Grasshopper chewing on leave. Woodcut by Dr. Ellen Welti.

Grasslands can be zen places: hectares of rolling prairie. But to an herbivore, all that is green is not nutritious. In a recent paper led by NSF REU Katerina Ozment mentored by Dr. Ellen Welti of OU_Biology we reveal how drought & Bison combine to create a nutritional patchwork.

The paper (PDF: began as a 2018 study of Bison Lawns at

@KonzaLTER, patches revisited by the big herbivores, where they eat, poop, and pee. The bison get a dependable, high nutrient food supply; the local grasshoppers do too. Win:Win!

But 2018 was also a *big* drought year. Enter Nutrient Dilution: where lotsa plant biomass dilutes with carbs the other essential nutrients in a bite of grass *and visa versa*. 2018 nitrogen supplies *off* bison lawns were like those of bison lawns in *normal* years.

So Ellen and I revisited the same 10 bison lawns in 2019, a normal rainfall year that would 1) reduce nutrient densities with the increased biomass, and 2) exacerbate (we predicted) the consequences for grasshoppers of *not* taking advantage of Bison pee-supercharged grass.

Combined, the 2 years tell a story of grasshoppers minding their nutrients. In the wet year (triangles) bison lawns were ‘hopper hotspots in a green desert; in the drought year, where nutritious grass was everywhere (just less of it), grasshoppers were less discriminating.

Katerina’s honors project revealed the interaction of subtle (rainfall) and not so subtle (bison) factors in generating a prairie patchwork for grasshoppers, and the counter-intuitive result that a lush green prairie may not necessarily be a herbivores cup of tea.

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