Stressed Grasshoppers Binge on Carbs, Destroy Soil

By Chelsea Whyte on June 18, 2012 9:40 PM EDT

grasshopper
Little bug, big appetite: Stressed out grasshopper binge eat on carbs, affecting their body chemistry and the entire ecosystem. (Photo: Dror Hawlena)

A little bug's life can have a big impact on the Earth. A study published in the journal Science finds that grasshoppers stressed while being hunted by spiders will gorge on high-energy carbohydrates, leaving behind an altered plant ecosystem and creating more carbon when they eventually die.

"Under stressful conditions they go to different parts of the 'grocery store' and choose different foods, changing the makeup of the plant community," said Oswald Schmitz, a co-author of the paper and an ecologist at Yale University. Grasshoppers usually feast on nitrogen-rich grass which stimulates their growth and reproduction.

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But when spiders are on the hunt for the long-legged creatures, they shift their diets toward carbohydrates to cope with the stress of fear. This change in their body composition leads the critters' carcasses to decompose more slowly and deprives the microbes in the soil beneath them of the nitrogen required to break down plants and animals.

"It only takes a slight change in the chemical composition of that animal biomass to fundamentally alter how much carbon dioxide the microbial pool is releasing to the atmosphere while it is decomposing plant organic matter," said Schmitz. "A clever suite of experiments shows that the dark hand of predation extends all the way from altering what prey eat to the nutrients their decomposing bodies contribute to soil."

The researchers exposed grasshoppers to spiders in order to observe their stress reaction. They then compared the carbon-to-nitrogen ratio in their bodies to a control group of non-stressed grasshoppers.

They then used the remains of the grasshoppers to test the effect on soil in the laboratory. After sprinkling tubes of soil with ground up grasshopper carcasses from environments known to have or lack grasshopper predators, they found that the microbes in the soil digested plant matter at a rate between 62 and 200 percent faster when fed with un-stressed grasshoppers.

"We were surprised at how big the effect was," ecologist and study co-author Dror Hawlena of the Hebrew University of Jerusalem told Nature News. "The traditional view is that plants and microbes are the main players linking the biotic and the abiotic world, but here we have shown that predators can actually regulate microbes by affecting the chemical composition of their own prey."

"This has tremendous consequences for our ecological understanding of the living world," said Hawlena, according to The Daily Mail.

"We are dealing here with an absolutely new kind of mechanism whereby every small chemical change in a creature can regulate the natural cycle, thus in effect affecting the ecology in total, such as the amount of carbon dioxide released into the atmosphere through decomposition) and field crop productivity."

This surprising finding suggests that even the smallest insects can have huge effects on entire ecosystems. 

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