Grasshoppers are gorging themselves on the equivalent of ‘junk food’ as rising levels of carbon dioxide in the atmosphere make plants less nutritious, a study has found.
Experts studying a grassland preserve in Kansas discovered that its grasshopper numbers have fallen by more than 30 per cent over the last two decades.
Increasing levels of atmospheric carbon dioxide are diluting nutrients like nitrogen, phosphorus and sodium in plants — make life harder for the grasshoppers.
The findings — the latest piece of evidence indicating that many insect groups are on the decline — also raises concerns for the future nutrient value of our crops.
Scroll down for video
Grasshoppers are gorging themselves on the equivalent of ‘junk food’ as rising levels of carbon dioxide in the atmosphere make plants less nutritious, a study has found. Pictured, a plains lubber grasshopper, Brachystola magna, seen in the Konza Prairie reserve in northeast Kansas
Ecologist Ellen Welti of the University of Oklahoma and colleagues have been studying grasshoppers in the Konza Prairie — a protected reserve located in the northeast of Kansas — for nearly three decades.
‘One surprise was that grasshopper abundances in this large native tallgrass prairie reserve are declining,’ Dr Welti said.
‘This grassland appears to be a stable and prime habitat for grasshoppers and yet even here, we are seeing two per cent annual declines.’
Grasslands are important because they cover almost a third of the Earth’s landmasses — and are the source of the majority of our food crops.
‘This decline in plant nutrient concentration poses a challenge for all animals that consume plants, including humans,’ she added.
In the study, Dr Welti used tools originally developed by geologists to study orbital cycles in order to identify repeating patterns in the grasshopper data — and reveal how climate oscillations such as El Niño help to shape the insect’s numbers.
‘Where some folks look at these data — with their wide yearly swings in grasshopper numbers — and see only noise, Dr. Welti had the tools and the insight to reveal the music in the data,’ said her colleague and fellow paper author Michael Kaspari.
This, the Oklahoma University biologist added, ‘consisted of five-year cycles in precipitation and temperature that drove changes in grasshopper numbers, as well as the plants they feed on.’
Experts studying a grassland preserve in Kansas discovered that its grasshopper numbers have fallen by more than 30 per cent over the last two decades
Alongside these cycles, however, the team also spotted that — even as plant growth doubled — plant quality has seen a steady decline.
‘The greenhouse gas carbon dioxide is heating the Earth and acidifying its oceans, but it is also the main ingredient in the sugars, starches, and cellulose of plants,’ Professor Kaspari said.
‘When we pump the atmosphere full of CO2, we build more plants. But, with no additional nutrients to fertilise them, the nutritional value of each bite is diluted.’
‘Mouthful by mouthful, the prairie provides less and less food to the grasshoppers. Hence, their decline.’
‘The mechanism of grasshopper declines that we propose in this study — declining plant quality with increasing atmospheric CO2 — is expected to be global in scope and pose the largest challenge to herbivores,’ added Dr Welti.
‘It is notable that a large number of previous studies documenting insect declines were on another herbivorous group — butterflies and moths — but few of these papers identified a mechanism causing declines.’
The finding also raises complications for commonly-touted plans to combat rising carbon dioxide levels in the atmosphere.
‘Of late, much has been made of “greening the Earth” as a tool to fight climate change,’ noted Professor Kaspari.
‘We show that while growing plants may indeed help scrub CO2 from the atmosphere, those same plants are likely becoming and less nutritious.’
‘It is as if, by burning fossil fuels, humans are transforming all of our kale into iceberg lettuce: still edible, but less and less sustaining.’
The full findings of the study were published in the journal Proceedings of the National Academy of Sciences.