Grasshopper Declines and the perils of Nutrient Dilution

Grasshopper numbers at a tall grass prairie have declined ca. 2% per year. Ellen Welti leads in identifying a likely culprit: increasing CO2 is diluting plant nutrients, making each bite less and less nutritious over the years. This open access paper at PNAS earned the 2020 finalist for the Cozarelli Prize for the best PNAS paper in the Environmental Sciences.

This paper was a collaboration from three generations of the Joern Lab–Joern, Kaspari, Welti/Roeder, and the geographer de Beurs

An intensive program of sweep netting at @KonzaLTER revealed 37% decline over 22 years. This decadal decline is similar to those found for butterflies, suggesting a common cause. Konza-a large preserve-isn’t destroying habitat or using pesticides. But…

Locations of our Konza long-term sampling transects
Sweep netting grasshoppers in days gone by, and two of the blogger’s favorites: Aulocara and Dactylotusm.

Konza also harvests plants every season to measure production. We show over this time how grass production has ca. doubled. And with no corresponding added nutrients the concentration of nutrients is declining in dominant grasses: grasshopper food. Hence the Dilution Hypothesis.

Four of five nutrients critical to animal health are declining over the past 20+ years on Konza. =

We are left w the working hypothesis that 5-year fluctuations in climate combine with long-term accumulation of CO2 to reduce the capacity of this tall grass prairie to support a dominant herbivore. How common is Nutrient Dilution? And how do we fix it? Stay tuned.

A schema representing our best understanding of the drivers of grasshopper declines. A doubling of grass biomass driven by warmer temperatures and increasing CO2 is depleting critical nutrients that the grasshoppers need. The changes in climate also have a direct, if less understood, effect.

Originally tweeted 9 March 2020

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