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Subject: [permaculture] Predators have outsized influence over habitats |
        Science Codex
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Predators have outsized influence over habitats | Science Codex
http://www.sciencecodex.com/predators_have_outsized_influence_over_habitats-93424

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 research results published
this week in the journal 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,
scientists have found.

"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.

The high-energy, carbohydrate diet also tilts a grasshopper's body
chemistry toward carbon at the expense of nitrogen.

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.

Grasshoppers' diets while being hunted may affect how soil releases
carbon dioxide.

(Photo Credit: Dror Hawlena)

"This study casts a new light on the importance of predation in
natural communities," said Saran Twombly, program director in the
National Science Foundation's Division of Environmental Biology, which
funded the research.

"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."

Microbes in the soil require a lot of nitrogen to function and to
produce the enzymes that break down organic matter.

"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.

"This shows that animals could potentially have huge effects on the
global carbon balance because they're changing the way microbes
respire organic matter."

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, a co-author of the study and also an ecologist at Yale.

This image shows field experiments underway at the Yale Myers forest
research site.

(Photo Credit: Dror Hawlena)

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."

The researchers took soil from the field, put it in test tubes and
ground up grasshopper carcasses obtained from environments either with
or without grasshopper predators.

They then sprinkled the powder atop the soil, where the microbes digested it.

When the grasshopper carcasses were completely decomposed, the
researchers added leaf litter and measured the rate of leaf-litter
decomposition.

The experiment was then replicated in the field at the Yale Myers
Forest in northeastern Connecticut.

"It was a two-stage process where the grasshoppers were used to prime
the soil, then we measured the consequences of that priming," said
Schmitz.

The effect of animals on ecosystems is disproportionately larger than
their biomass would suggest.

"Traditionally people thought that animals had no important role in
recycling of organic matter, because their biomass is relatively small
compared to the plant material that's entering ecosystems," Schmitz
said.

"We need to pay more attention to the role of animals, however. In an
era of biodiversity loss we're losing many top predators and larger
herbivores from ecosystems."