By Ellen Welti, a community ecologist working on grassland insects and plants. She is part of the Great Plains Science Program, based in the prairies of north central Montana. She runs observational monitoring targeting grasshoppers, dung beetles, wolf spiders, plant composition, and plant biomass. Her research topics include the function of insects in grasslands, plant-insect interactions, ecological time series, and plant and insect responses to altered biogeochemistry. Originally published by The Conversation.
More than one-third of all animals on Earth, from beetles to cows to elephants, depend on plant-based diets. Plants are a low-calorie food source, so it can be challenging for animals to consume enough energy to meet their needs. Now climate change is reducing the nutritional value of some foods that plant eaters rely on.
Human activities are increasing atmospheric carbon dioxide levels and raising global temperatures. As a result, many plants are growing faster across ecosystems worldwide.
Some studies suggest that this “greening of the Earth” could partially offset rising greenhouse gas emissions by storing more carbon in plants. However, there’s a trade-off: These fast-tracked plants can contain fewer nutrients per bite.
I’m an ecologist and work with colleagues to examine how nutrient dilution could affect species across the food web. Our focus is on responses in plant-feeding populations, from tiny grasshoppers to giant pandas.
We believe long-term changes in the nutritional value of plants may be an underappreciated cause of shrinking animal populations. These changes in plants aren’t visually evident, like rising seas. Nor are they sudden and imminent, like hurricanes or heat waves. But they can have important impacts over time.
Plant-eating animals may need more time to find and consume food if their usual meal becomes less nutritious, exposing themselves to greater risks from predators and other stresses in the process. Reduced nutritional values can also make animals less fit, reducing their ability to grow, reproduce and survive.
Rising Carbon, Falling Nutrients
Research has already shown that climate change is causing nutrient dilution in human food crops. Declines in micronutrients, which play important roles in growth and health, are a particular concern: Long-term records of crop nutritional values have revealed declines in copper, magnesium, iron and zinc.
In particular, human deficiencies in iron, zinc and protein are expected to increase in the coming decades because of rising carbon dioxide levels. These declines are expected to have broad impacts on human health and even survival, with the strongest effects among populations that are highly dependent on rice and wheat, such as in East and Central Asia.
The nutritional value of livestock feed is also declining. Cattle spend a lot of time eating and often have a hard time finding enough protein to meet their needs. Protein concentrations are falling in grasses across rangelands around the world. This trend threatens both livestock and ranchers, reducing animals’ weight gains and costing producers money.
Nutrient dilution affects wild species too. Here are some examples.
Dependent on Bamboo
Giant pandas are a threatened species with great cultural value. Because they reproduce at low rates and need large, connected swaths of bamboo as habitat, they are classified as a vulnerable species whose survival is threatened by land conversion for farming and development. Pandas also could become a poster animal for the threat of nutrient dilution.
The giant panda is considered an “umbrella species,” which means that conserving panda habitat benefits many other animals and plants that also live in bamboo groves. Famously, giant pandas are entirely dependent on bamboo and spend large portions of their days eating it. Now, rising temperatures are reducing bamboo’s nutritional value and making it harder for the plant to survive.
Mixed Prospects for Insects
Insects are essential members of the web of life that pollinate many flowering plants, serve as a food source for birds and animals, and perform other important ecological services. Around the world, many insect species are declining in developed areas, where their habitat has been converted to farms or cities, as well as in natural areas.
In zones that are less affected by human activity, evidence suggests that changes in plant chemistry may play a role in decreasing insect numbers.
Many insects are plant feeders that are likely to be affected by reduced plant nutritional value. Experiments have found that when carbon dioxide levels increase, insect populations decline, at least partly due to lower-quality food supplies.
Not all insect species are declining, however, and not all plant-feeding insects respond in the same way to nutrient dilution. Insects that chew leaves, such as grasshoppers and caterpillars, suffer the most negative effects, including reduced reproduction and smaller body sizes.
In contrast, locusts prefer carbon-rich plants, so rising carbon dioxide levels could cause increases in locust outbreaks. Some insects, including aphids and cicadas, feed on phloem – the living tissue inside plants that carries food made in the leaves to other parts of the plant – and may also benefit from carbon-rich plants.
Uneven Impacts
Declines in plant food quality are most likely to affect places where nutrients already are scarce and animals struggle now to meet their nutritional needs. These zones include the ancient soils of Australia, along with tropical areas such as the Amazon and Congo basins. Nutrient dilution is also an issue in the open ocean, where rapidly warming waters are reducing the nutritional content of giant sea kelp.
Certain types of plant-feeding animals are likely to face greater declines because they need higher-quality food. Rodents, rabbits, koalas, horses, rhinoceroses and elephants are all hind-gut fermenters – animals that have simple, single-chambered stomachs and rely on microbes in their intestines to extract nutrients from high-fiber food.
These species need more nutrient-dense food than ruminants – grazers like cattle, sheep, goats and bison, with four-chambered stomachs that digest their food in stages. Smaller animals also typically require more nutrient-dense food than larger ones, because they have faster metabolisms and consume more energy per unit of body mass. Smaller animals also have shorter guts, so they can’t as easily extract all the nutrients from food.
More research is needed to understand what role nutrient dilution may be playing in declines of individual species, including experiments that artificially increase carbon dioxide levels and studies that monitor long-term changes in plant chemistry alongside animals in the field.
Over the longer term, it will be important to understand how nutrient dilution is altering entire food webs, including shifts in plant species and traits, effects on other animal groups such as predators, and changes in species interactions. Changes in plant nutritional value as a result of rising carbon dioxide levels could have far-reaching impacts throughout ecosystems worldwide.
Remembering the human cost (from 2017):
> Gonnella Baking Co – which supplies the buns to Major League Baseball’s Wrigley Field – faced an unusual problem in October when flour from this year’s U.S. wheat harvest arrived at their factories containing low levels of protein… That meant bakers couldn’t produce bread with the airy texture customers demand
CO2 levels are over 20 ppm higher since then.
>> We believe long-term changes in the nutritional value of plants may be an underappreciated cause of shrinking animal populations.
Not just the primary effects, from decreased protein and mineral uptake in food. Weak trees fall easier and entire biomes are altered. While new niches are created, established niches are destroyed too quickly for any evolutionary response within-species. Invasive species are the tautological winners. Jellyfish eaters will do well.
And you agree with the author that climate change alone, actually increasing CO2levels, are the sole cause of lowered plant nutrients? I find this conclusion breathtakingly simplistic and likely wrong. To me, a far more important problem is industrial agriculture destroying the soil structures, nutrients, living processes that foster healthy growth. Take a walk in a commercial potato field- the soils have been destroyed by excess ploughing, stripping of organic material by not replacing it, indiscriminate spraying of glyphosate and other herbicides that kill off the healthy soil fauna.
This blaming all ills on CO2 is just wrong. And it’s resulting in bad policy by ignorant politicians for whom simple solutions are about all they’re intellectually capable of.
In general what you say certainly plays a role but I doubt, if the chart above is accurate, it seems that climate change has a major role to play here.
The issue is what is causing climate change. I don’t doubt the climate is changing- I just doubt the one size fits all demonization of CO2 as the one, The only causal factor. We’re dealing with a massively complex system and the models being used to drive policy are simplistic and exclude solar forcing, and the effects of the polar excursion, for example. Of course, simplistic models are loved by politicians who push this anti-CO2 religiosity. How many solar panels has that fraud Al Gore on the roof of his 40,000 sq ft mansion? Look it up -NONE!
I am not impressed by this attempt at fossil fuel industry-based bullFUD hasbara. This seems like one of those attempts by the fossil fuel industry brainwar spokesfolks to set up a decoy velcro tarbaby by the side of the road to trick people into wasting their time and energy engaging with it.
” How many solar panels has that fraud Al Gore on the roof of his 40,000 sq ft mansion? Look it up -NONE!” . . . may be correct. It is also irrelevant.
I understand your frustration with this stereotypical “oh the climate is too complicated to model” agnotology. But the tone of your comment is out of line.
This article is addressing lowered nutrient densities in wild-growing plants across non-agricultural ecosystems which are not being agricultured at all. So examples taken from the field of active agriculture are irrelevant to the topic of this article.
(They are certainly relevant to the topic of declining nutrient levels in farmed food in agricultural settings, which is where this comment would be usefully offered when such a posting next appears.)
Indeed the most limiting nutrient in plants is usually nitrogen (then others like phosphorous), so if carbon fixation improves there can be an increase on overall biomass but relatively poorer in N, P etc. and that may go up the feeding chain somehow… or not, or depends. This does not affect equally woody biomass, herbaceous biomass, grass,straw depending also on C3/C4 metabolism plant types etc. More detailed analysis of the feedstocks would be necessary. Would a relative increase of C,H,O over N,K,P, Ca… have a negative effect on biomass digestion and uptake of the most essential components? Would the new “diet” be less healthy? Unclear that. Yet the effects might indeed be uneven as the article states. Whether noticeable or not it is quite unpredictable and with what we know we can only speculate. This is all speculative but merits an interest.
Do you doubt that industrial chemical big ag is unhealthy? How much evidence do you need?
You’re the only mention of BigAg in this article, why are the rest of us are required to address your pet peeve?
Besides, the article is talking about the nutritional content of wild animals’ plant foods. What does BigAg have to do with micronutrients in wild bamboo forests in China?
Beyond the obvious of contributing to the rise in atmospheric CO2.
I object to the one size fits all demonization of CO2 as the one, the only, cause of what ails the planet. And if you read Ignacio’s comment, it directly relates to Ag nutrients – in particular, the limiting factors in nutrient takeup. You don’t have to agree with, or even read my comment – but clearly you didn’t read the article anyway as it also mentions agricultural issues – declining nutrients in cattle feed. Try improving your reading and comprehension skills instead of just attacking based on your unshakeable belief in the CO2 is bad religion.
” if carbon fixation improves ”
How big is the IF in carbon fixing? Us humans seem to do the opposite .
Simply because the relative amount of atmospheric CO2 is greater. RUBISCO, which catalyses CO2 fixation, and is probably one of the most abundant proteins on Earth, can bind both O2 and CO2. The higher the ratio [CO2]/[O2] the more efficient the process.
Animal biomass is much richer than plant biomass in N (and other components). Besides, C is more reduced in animals (C+H content) thus more “energetic”, compared with O, more abundant in plant biomass (more oxidised). Most of plant biomass (90%) is lost in the food chain. Because the energy is taken basically from the CHO component of plant biomass this means that we can (must?) waste more energy to obtain the same of other components in the nutritional ladder.
C2H5OH for the win.
Lol. Yes, there does seem to be some drinking before commenting going on here.
I begin to wonder whether this dilution of nutrients in plants growing under a higher ambient CO2 airload would happen even if the climate weren’t changing at all. That is to say, if we were skydumping the very same amount of carbon anyway, but the climate were magically not changing at all the least bit, would the greater carbon skyload still drive greater growth in plants with the same problem of more dilute nutrients in the phytomass?
Because if it would, and if it does, then this phytomass nutrient dilution is a totally separate and completely direct effect of carbon skyflooding. Which would mean that even if there were zero global warming happening due to the carbon skyflooding, this problem of phytomass nutrient dilution would still be a direct problem and consequence of carbon skyflooding. And carbon skyflooding would need to be reduced and reversed for that parallel reason alone.
And if the rising carbon skyloads would acidise the ocean just as much as it already is, even if it caused zero global warming, then we would still
need to address the survival problems caused by ocean acidation.
And that would mean that lame efforts to pretend to dispute the role of carbon skyflooding in climate change are even lamer and more totally irrelevant to the separate parallel problems of phytomass nutrient dilution and ocean acidation than I at first thought.
And that would also mean that global dewarming through geo-engineering would still be utterly irrelevant to the problems of phytomass nutrient dilution and ocean acidation, even if they magically addressed the problem of carbon skydumping driven global warming. And there would be no escaping the need to drain-down the skycarbon levels.
Fancy! I don’t disagree at all that the energy feast has to end at some point. But I think it will rather be caused by civilisational destruction than by forcing everyone to get an electric car and heat pumps, presto, problem solved! MOther Nature bats last – the current polar excursion is troubling, it could result in all kinds of consequences including destroying all electronics, volcanic eruptions, earthquakes, tsunamis and so on. DO some research – the north pole has moved from somewhere near Baffin Island to Siberia (according to NASA) in the last ten years. If there is a God, and I hope there is, He/she has to be unhappy with the mess we are making of our lovely green planet. The climate chaos which is increasing has many causes, not least of which is the disruption of the magnetosphere caused by the polar excursion. This allows more radiation to enter the biosphere, with many effects, including geologic.