Thursday, January 16, 2025

Dung data: manure can help to improve global maps of herbivore distribution

University of New South Wales

image:
Dung is actually an important resource for millions of people worldwide. Photo: Professor David Eldridge studies herbivore dung on a field trip to Fowler's Gap
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Credit: Prof. David Eldridge

Researchers have used dung records to create high-resolution maps of herbivore distribution around the world. Their new study, recently published in Nature Food, reveals a strong positive relationship between dung presence and grazing pressure, meaning the amount of dung found in a particular location could help us understand approximately how many herbivores live there.

Many people consider dung simply as the manure left behind by horses and cows at country shows, or something to be avoided when you visit the cousins’ farm. But dung is actually an important resource for millions of people worldwide.

Dung also acts a biological footprint – it can tell us a lot about our environment, such as what animals are grazing where, and what this might mean for environmental health.

Now, scientists from Australia, Spain, China and Saudi Arabia, led by Professor David Eldridge from UNSW Sydney, have produced the first global assessment of dung produced by livestock and native grazing animals in drylands – arid and semi-arid environments that occupy about 40% of the world’s land area.

The research revealed hotspots of dung production, but also highlighted that broadly speaking, livestock and wild herbivores – animals like horses, cows and kangaroos that only eat vegetation – don’t occupy the same spaces on earth.

“Understanding where herbivores are distributed is important for a number of reasons,” says Prof. Eldridge. “It helps us to improve our understanding of the grazing industry, like the spread of bovine diseases. If we have a better understanding of where animals are, we've got a better understanding of where we might need to target particular land management practices.”

Estimating livestock density

Current assessments of livestock density are based on crude estimates of environmental variables such as mean annual rainfall, temperature, and some soil variables. These environmental variables are broad indicators of habitats that are likely to be occupied by herbivores, because more productive systems generally have more grass and therefore support more herbivores.

International organisations such as the United Nations Food and Agriculture Organisation (FAO) need to know where livestock are concentrated, and in what numbers. To do this they use relatively coarse computer models.

Improving these existing methods of predicting herbivore distribution is central to a number of agricultural industries. So, Prof. Eldridge and his team set out to solve some of these challenges with a somewhat unusual solution.

Dung – a byproduct of meat production, a source of nitrogen and phosphorus fertiliser – is used in building construction, and as a fuel for cooking by millions of people around the world. “Measuring and mapping dung could be a useful resource to help these organisations fine tune coarse predictions of animal distribution,” says Prof. Eldridge.

Methods & findings

The research team assembled 50 global datasets that included the mass of dung produced and measures of grazing pressure by different herbivores, including antelopes, sheep, and kangaroos.

Their analysis showed that all but one of these datasets showed strong positive relationships between dung production and grazing pressure.

“These data show a strong positive correlation, or positive relationship, between the amount of dung produced and animal grazing pressure,” says Prof. Eldridge. “If we know how much dung there is, then we can predict where the animals are distributed.”

The team also combined livestock and wild herbivore dung mass data from surveys at 760 dryland sites worldwide, representing independent measurements of herbivory, to generate high-resolution maps.

“The surprising thing that we found is that when you model where native herbivores are and where livestock are, there's some overlap, but in general, there are a lot of areas where they don't interact,” says Prof. Eldridge. “This could be due to direct competition for resources or avoidance by wild herbivores of potential livestock-borne parasites and diseases.”

The researchers located hotspots of dung production in central Africa, northern and eastern Australia, the Eurasian grasslands, east central India, and the west coast of the United States of America. Dung production was shown to be lower in north-central Africa and west-central China.

Dung as a scientific tool

Global assessment of livestock distribution is critically important for land use planning, for estimating gross methane emissions, predicting global meat production, or predicting where livestock may be at risk from pests and diseases such as brucellosis.

It also improves the ability of organisations to predict trends in global food production and the impacts of drought and natural disasters on food security.

Counting dung can often be easier and more efficient than counting animals, Prof. Eldridge explains.

“For example, one paper shows how dung counts often give us a better estimate of elephant densities than aerial surveys of the animals themselves. Dung counts are also efficient ways of studying habitat preference of elusive herbivores that are hard to detect or occur in very low numbers,” he says.

But dung can also help researchers at more local scales. “Knowing the location of dung in different paddocks can tell us about the habitat preference of different herbivores and how they interact. This could provide farmers with better information on where to place fences, watering points and other infrastructure to improve livestock production,” says Prof. Eldridge.

Assessments of dung are not without their complexities, Prof. Eldridge explains. “Many farmers in Asia and Africa collect dung, reducing the potential field assessment and therefore potentially underestimating the amount of dung produced by animals.”

Some animals such as deer bury their dung, and in many tropical countries, dung beetles and termites break this dung down in just a few days, making regional assessments more difficult.

“These and other issues make it difficult to come up with robust assessments of animal densities,” says Prof. Eldridge. “However, even when we accounted for areas where people collected dung, there was still strong relationships with grazing pressure.”

Despite the challenges, this research provides a world-first, comprehensive global map of the dung of livestock and wild herbivores in drylands, and paves the way for organisations to incorporate dung data into livestock maps and models.

Journal

Nature Food

DOI

10.1038/s43016-024-01112-9

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Dung predicts the global distribution of herbivore grazing pressure in drylands

Article Publication Date

14-Jan-2025

Volcanic eruption caused Neolithic people to sacrifice unique "sun stones"

Archaeologists and climate scientists from the University of Copenhagen can now show that ritual sacrifices of sun stones coincided with a large volcanic eruption hat made the sun disappear throughout Northern Europe.

University of Copenhagen - Faculty of Humanities

Throughout history, volcanic eruptions have had serious consequences for human societies such as cold weather, lack of sun, and low crop yields. In the year 43 BC when a volcano in Alaska spewed large quantities of sulphur into the stratosphere, harvests failed the following years in the countries around the Mediterranean, causing famine and disease. This is well-documented in written sources from ancient Greece and Rome.

We do not have written sources from the Neolithic. But climate scientists from the Niels Bohr Institute at the University of Copenhagen have analysed ice cores from the Greenland ice sheet and can now document that around 2,900 BC a similar volcanic eruption took place. An eruption that must have had equally devastating consequences for the Neolithic peoples who lived in Northern Europe at the time and who were deeply dependent on agriculture.

This new insight into a climate episode in the Neolithic period has led archaeologists from the University of Copenhagen, the National Museum of Denmark and the Museum of Bornholm to view their findings of so-called "sun stones" from the Neolithic Vasagård site on Bornholm in a new light, and they have just published a scientific article on the phenomenon in the journal Antiquity:

"We have known for a long time that the sun was the focal point for the early agricultural cultures we know of in Northern Europe. They farmed the land and depended on the sun to bring home the harvest. If the sun almost disappeared due to mist in the stratosphere for longer periods of time, it would have been extremely frightening for them,” says archaeologist Rune Iversen from the University of Copenhagen, who has participated in the excavations at the site led by the Museum of Bornholm and the National Museum. He adds:

“One type of find that is completely unique to Bornholm is the so-called sun stones, which are flat shale pieces with engraved patterns and sun motifs. They symbolized fertility and were probably sacrificed to ensure sun and growth. Sun stones were found in large quantities at the Vasagård West site, where residents deposited them in ditches forming part of a causewayed enclosure together with the remains of ritual feasts in the form of animal bones, broken clay vessels, and flint objects around 2,900 BC. The ditches were subsequently closed.”

Rune Iversen and his colleagues believe that there is a very high probability that there is a connection between the volcanic eruption, the subsequent climate changes and the discovery of the ritual sun stone sacrifices.

“It is reasonable to believe that the Neolithic people on Bornholm wanted to protect themselves from further deterioration of the climate by sacrificing sun stones – or perhaps they wanted to show their gratitude that the sun had returned again.”

Major cultural changes
As if an acute climate deterioration around 2,900 BC was not enough, Northern European Neolithic cultures were also affected by other disasters; New DNA studies of human bones have shown that the plague was very widespread and fatal.

During the same period when the Neolithic people were affected by both climate change and disease, archaeologists can also document a shift in the traditions they had held on to for a long time. The so-called Funnel Beaker Culture, which had been dominant until about 5,000 years ago with its characteristic ceramics and passage graves, was gradually disappearing.

“At the causewayed enclosure we have excavated on Bornholm, we can also see that, after the sacrifice of the sun stones, the residents changed the structure of the site so that instead of sacrificial ditches it was provided with extensive rows of palisades and circular cult houses. We do not know why, but it is reasonable to believe that the dramatic climatic changes they had been exposed to would have played a role in some way, Rune Iversen concludes.

Sun stones to be exhibited in Copenhagen
Four of the sun stones from Vasagård on Bornholm can be experienced from 28 January in the prehistoric exhibition at The National Museum of Denmark in Copenhagen. They probably exemplify one of the earliest depositional practices connected to a Neolithic sun-cult in South Scandinavia, which are also known from the Nordic Bronze Age with objects like the sun chariot.

"The sunstones are completely unique, also in a European context. The closest we get to a similar sun-cult in the Neolithic is some passage graves in southern Scandinavia or henge structures like Stonehenge in England, which some researchers associate with the sun. With the sun stones, there is in my mind no doubt. It is quite simply an incredible discovery, which demonstrates that depositions honouring the sun is an ancient phenomenon, which we encounter again in South Scandinavia during the climate disaster caused by a volcanic eruption in the year 536 AD, where several large gold hoards were deposited as sacrifices,” says Lasse Vilien Sørensen, who is senior researcher at The National Museum of Denmark and co-author of the research paper.

Volcanic eruption 2,900 BC
The researchers can document reduced radiation from the sun and consequent cooling, which can be traced in both the United States and Europe around 2,900 BC.

Dendrochronological analyses of fossil wood show signs of frost in the spring and summer months both before and after 2,900 BC.

And ice cores from the Greenland ice cap and the Antarctica contain sulphur, which is a sign of the occurrence of a strong volcanic eruption.

The archaeological site Vasagård is located on Bornholm in the Baltic Sea

Credit

University of Copenhagen