Grasshoppers stressed by the proximity of predators such as spiders may affect the whole ecosystem.
A grasshopper’s change in diet to high-energy carbohydrates while being hunted by spiders may affect the way soil releases carbon dioxide into the atmosphere, according to Yale and Hebrew University researchers in Science.
Grasshoppers like to munch on nitrogen-rich grass because it stimulates their growth and reproduction. But when spiders enter the picture, grasshoppers cope with the stress from fear of predation by shifting to carbohydrate-rich plants, setting in motion dynamic changes to the ecosystem they inhabit.
The high-energy, carbohydrate diet also tilts a grasshopper’s body chemistry toward carbon at the expense of nitrogen. Microbes in the soil require a lot of nitrogen to function and to produce the enzymes that break down organic matter. So when a grasshopper dies, its carcass breaks down more slowly, thus depriving the soil of high-quality fertilizer and slowing the decomposition of uneaten plants.
“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.
The researchers found that the rate at which the organic matter of leaves decomposed increased between 60 percent and 200 percent in stress-free conditions relative to stressed conditions, which they consider “huge.” “Climate and litter quality are considered the main controls on organic-matter decomposition, but we show that aboveground predators change how soil microbes break down organic matter,” said Mark Bradford, also co-author of the study from Yale School of Forestry & Environmental Studies.
Schmitz added: “What it means is that we’re not paying enough attention to the control that animals have over what we view as a classically important process in ecosystem functioning.”
Schmitz said that the effect of animals on ecosystems is disproportionately larger than their biomass would suggest. “Traditionally people have thought animals had no important role in recycling of organic matter, because their biomass is relatively small to all of that plant material that’s entering ecosystems,” he said. “We need to pay more attention to the role of animals because in an era of biodiversity loss we’re losing many top predators and larger herbivores from ecosystems.”
The above news item is reprinted from materials available at Yale School of Forestry & Environmental Studies, and The Hebrew University of Jerusalem via AlphaGalileo. Original text may be edited for content and length.