Hi My Friends: A VUELO DE UN QUINDE EL BLOG., 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.
Credit: Dror Hawlena
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Credit: Dror Hawlena
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Credit: Copyright AAAS 2012
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Study of grasshoppers' diets shows that animals are an important part of organic matter decomposition
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.
"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.
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."
Other co-authors are Michael Strickland of Yale, and Dror Hawlena of the Hebrew University of Jerusalem.
-NSF-
Dave DeFusco, Yale University (203) 436-4842 david.defusco@yale.edu
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receives over 50,000 competitive requests for funding, and makes about
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professional and service contracts yearly.
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