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Stressed grasshop­pers affect whole ecosystem

pub­lished 24 June 2012 | mod­i­fied 05 Decem­ber 2012

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.

grasshopperGrasshop­pers 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.

Under stress­ful con­di­tions they go to dif­fer­ent parts of the gro­cery store and choose dif­fer­ent foods, chang­ing the makeup of the plant community
co-​author Oswald Schmitz, Yale School of Forestry & Envi­ron­men­tal Studies »

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.

So 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, 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.”

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. 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
co-​author Dror Hal­wena, Hebrew Uni­ver­sity of Jerusalem »

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.

(Sources: Yale School F&ES, 14.06.2012; Alpha­Galileo, 14.06.2012)

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