A life lived in fear leads to a less-productive death

You remember the nutrient cycle from high school? How organic matter breaks down and spreads throughout the ecosphere? Now it looks like the role of animals in this cycle may be larger than previously thought, and far more direct.

When the herbivorous grasshopper Melanoplus femurrubrum is under the stress of being in the presence of predator spiders, it does more than just freak out and escape. It undergoes major metabolic and chemical changes — and after the grasshopper dies, these alterations have a major influence on the surrounding soil.

In a new study, Israeli researchers raised one group of grasshoppers stress-free, and another exposed to simulated predator spiders. Once they were dead, the two different groups biodegraded at the same rate — but had significantly different effects on the biosphere around them.

Through laser analysis of the conversion from organic carbon to inorganic carbon in the decomposition of dead plant material, they found that the stressed-out insects notably slowed the rate in the areas around them. The plots with the remains of the frightened grasshoppers had slower decomposition and slower nutrient cycling.

We've never seen evidence before that animals have such a direct influence on the nutrient cycle. And this reveals another wrinkle in the complexity of an already labyrinthine cycle — and shows how important predators can be to maintaining the biosphere at every level.

Image: The herbivore grasshopper Melanoplus femurrubrum, courtesy of Dror Hawlena