Frightened grasshoppers can affect their environment
New Worlds: Grasshoppers under stress can behave like tense humans who overeat sweets.
Grasshopper Photo: Courtesy
To the layman’s eye, grasshoppers seem happy-go-lucky creatures, able to go
anywhere they want and have an adequate supply of food. In fact, according to
researchers at the Hebrew University of Jerusalem and Yale University,
grasshoppers tend to get frightened by spiders – and this can even affect the
productivity of our soil and our ecosystem.
A fearful grasshopper,
experiencing stress, will consume a greater quantity of carbohydrate-rich plants
– similar to humans under stress who might eat more sweets. This will, in turn,
cause chemical changes in the grasshopper and its excretions, affecting the
ecosystem it inhabits.
When a scared grasshopper dies, its carcass –
which contains less nitrogen as a result of its diet change – will have an
effect on the microbes in the ground, which are responsible for breaking down
animal and plant matter. With less nitrogen available, the microbes decompose
the hard-to-break-down plant materials in the soil at a slower rate. Thus, fear
of predation may slow down degradation of complex organic materials to the
simpler compounds required for plant growth.
Research on this biological/
ecological phenomenon, carried out by Dr. Dror Halwena of the department of
ecology, evolution and behavior at HU’s Alexander Silberman Institute of Life
Sciences, in cooperation with US researchers, appears in a recent issue of the
The scientists exposed grasshoppers to spiders to arouse
a stress reaction and compared the results with a control group of nonstressed
grasshoppers. They found the scared grasshoppers had a higher carbon-tonitrogen
ratio in their bodies than non-frightened grasshoppers. In further laboratory
and field tests, the researchers tested the influence of grasshopper remains on
soil. After the microbes consumed the grasshopper remains, the researchers added
plants to the surface.
They showed that the decomposition rate of the
plants in the areas where stress-free grasshopper remains were introduced
decomposed at a rate between 62 percent and 200% faster than those of the
In a further experiment, the researchers used
“artificial grasshoppers” – a mixture of sugar, protein and chitin, the organic
compound found in the grasshopper external skeleton – in varying
Here, too, they found that even the small amount of nitrogen
found in the protein added to the soil significantly increases the functioning
of the microbes responsible for breaking down the organic matter in
“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 has tremendous consequences for our ecological understanding
of the living world,” said Halwena. “We are gaining a greater understanding of
the necessity of conserving all of the component parts of the ecosystem in
general and of predators in particular. We are losing predators in nature at a
much faster rate than other species.”
He said he hoped the research help
scientists better predict changes in the biological system as a result of such
human-induced phenomenon as overfishing, hunting or global warming that can
undermine the entire ecosystem.
MARINE STOWAWAYS Marine scientists
studying life around deep-sea vents have discovered that some hardy species can
survive the extreme change in pressure that occurs when a research submersible
rises to the surface. The team’s findings, published recently in Conservation
Biology, reveal how a species can be inadvertently carried by submersibles to
new areas, with potentially damaging effects on marine ecosystems.
using the manned submersible Alvin to collect samples from the Juan de Fuca
Ridge under the northeastern Pacific Ocean, the team discovered 38 deep-sea
limpets (Lepetodrilus gordensis) among their sample. Intriguingly, this species
is believed to occur only in the vents of the Gorda Ridge, which are 635
kilometers south of the dive site.
“The big question was, how did they
get over 600 kilometers from their habitat?” said Dr. Janet Voight, from
Chicago’s Field Museum of Natural History. “We discovered that the individuals
must have been transported from the Gorda Ridge by our submersible.
though we clean the submersibles after sampling we had assumed that the extreme
pressure change would kill any species which are missed.”
introduction by humans of new species to an ecosystem – often inadvertently – is
a big challenge to conservation, as how a new species will react to new
surroundings and its effects are unpredictable.
Increases in deep-sea
drilling and submersible activity can raise the probability of introductions,
but until now hydrothermal vents have been considered too extreme and too
isolated to be a source of introduced species.
In coastal environments,
one of the biggest threats posed by invasive species to native species is
disease, as newly introduced pathogens and parasites can cause mass mortality.
Diseases that may exist in the extreme environments created by hydrothermal
vents have not been well studied.
“We’ve discovered that it is possible
to accidentally introduce a species, and any potential diseases it may carry,
from a deep-sea vent to a new location,” concluded Voight. “This has
implications for the future exploration of hydrothermal vents as it reveals the
potential risk of human-driven change to the ecosystem.”