How do coexisting animals find enough to eat? Biologists unlock insights into foraging habits in Yellowstone

Brown University ecologists teamed with National Park Service scientists in Yellowstone to answer a vexing question about how different wildlife species find enough to eat

Brown University

 

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Bison are seen grazing in a meadow in early winter at Yellowstone National Park. 

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Credit: Photo courtesy of Bethan Littleford-Colquhoun

PROVIDENCE, R.I. [Brown University] — Ecologists have long sought clarity on the dietary habits of different animal species. For scientists at Brown University and the National Park Service, it wasn’t obvious how herbivores in Yellowstone National Park, who subsist on grasses, wildflowers and trees, could compete for enough of those foods to survive the winter.

Over two years, with the aid of cutting-edge molecular biology tools and GPS tracking data, the researchers were able to determine not only what herbivores in Yellowstone eat, but also what strategies the animals use to find food throughout the year. The team published its findings in Royal Society Open Science.

“In Yellowstone, we know vegetation changes across seasons, but until now, we didn’t know how these seasonal changes influenced what animals eat or how they sustained themselves when options were limited,” said lead study author Bethan Littleford-Colquhoun, a postdoctoral research associate at Brown. “It turns out that while species eat similar categories of food, their diets differ from one another in cryptic and nuanced ways. And an animal’s body size plays an important role in how this is achieved.”

For decades, ecologists have debated how wildlife should confront challenges with their food supplies, said co-author Tyler Kartzinel, an associate professor of ecology, evolution and organismal biology at Brown.

Some experts argue that animals should diversify their diets to satisfy their taste preferences when they have the most freedom to select their favorite foods in summer, Kartzinel said. Others have posited that animals should diversify what they eat when they’re forced to accept whatever happens to be available — such as in a hard winter when they may have to compete for even undesirable foods to survive.

“These opposing predictions couldn’t both be true, so it wasn’t at all clear how Yellowstone's assemblage of herbivore species — with such a diversity of foraging behaviors — could succeed in finding enough food throughout the year,” Kartzinel said.

Seasonal specialization

For the study, the researchers used two years of GPS tracking and dietary DNA data to elucidate dietary variation across times of resource limitation and resource abundance for five of Yellowstone’s best-known species: bison, elk, deer, bighorn sheep and pronghorn antelope.

Scientists and staff at Yellowstone tracked the animals. Researchers at Brown, many of them undergraduate students overseen by Littleford-Colquhoun, analyzed fecal samples using a sophisticated molecular technique called metabarcoding, which helped to identify what foods the animals had consumed.

They found that all species capitalized on the seasonal abundance of wildflowers in summer, and that each species consolidated its foraging efforts around the subset of plant types that it was best prepared to compete for in winter. But the researchers discovered that feeding behaviors depended on the animal’s body size.

Members of the smallest species, such as deer and sheep, tended to fan out across summer meadows and dramatically expanded their diets before gathering in protected valleys where they survived the winter on leftover plants, according to the study. Larger animals like bison tended to do the opposite: In the winter, they were large enough to avoid competing for dwindling resources, so they instead ventured out into deep snow to find unique food reserves inaccessible to smaller deer and sheep.

“The study showed that these species can feed far more adaptably than anyone had previously assumed,” Littleford-Colquhoun said. “All species switch the ways they search for food, but the opportunities an individual bison has to fuel its migration or survive a hard winter might only work for it because it’s big. Meanwhile, other species might need to group together for protection in winter because they’re small.”

So when should animals search for unique foods to diversify their diets — summer or winter? Kartzinel said it depends on the kind of animal.

“Because of the variety of ways animals behaved in our study, we learned that both hypotheses about how animals fuel their migrations were right, but in different ways and at different times,” Kartzinel said. “So the question that biologists should have been bickering about for the past generation shouldn't have been, ‘Which foraging strategy is right?’ but rather, ‘When does each strategy work best for a given group of animals?’”

Kartzinel hopes the more nuanced insights about foraging behavior will help scientists take a more customized approach to wildlife conservation.

“If we want to help wildlife populations thrive,” Kartzinel said, “we should be maintaining a diversity of habitats and plant resources across their migratory corridors so that many animals, each with their own preferences, personalities and needs, can find what's best to fuel their journey.”

The study was supported by the National Science Foundation (DEB-525 2046797, OIA-2033823) and the National Park Service Cooperative Research and Training Program (P22AC00332, P23AC00378).

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Journal

Royal Society Open Science

DOI

10.1098/rsos.240136 

Method of Research

Observational study

Subject of Research

Animals

Article Title

Body size modulates the extent of seasonal diet switching by large mammalian herbivores in Yellowstone National Park

 

Are cows pickier than goats?

Uppsala University

 

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Håkan Rydin, Professor Emeritus of Plant Ecology, Uppsala University.

Photo by Märta Gross Hulth

 

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Credit: Märta Gross Hulth

To answer this question, Linnaeus collected 643 different plant species that were then fed to horses, cows, pigs, sheep and goats. The results were carefully compiled but not analysed until now, 275 years later, when they are also published by the Linnean Society in London.

“It may have been the first experiment in what would only later become the subject of ecology in the late 19th century. By today’s standards, it was a huge experiment involving an impressive number of plants,” notes Håkan Rydin, Professor of Plant Ecology at Uppsala University and one of the researchers who carried out the analysis.

Carl Linnaeus’ thesis, Pan Svecicus, describes 2,325 experiments involving 643 different plant species. It was published in 1749 and defended by his student, Nils Hesselgren. Earlier, Linnaeus and his disciples had travelled around Sweden collecting information from farmers about the best pastures for their animals.

Although the thesis was translated into German and English and was known among contemporary botanists in Europe, the results were never analysed. Now, however, Rydin has worked with other researchers to compile and analyse the data.

The results show that pigs were the most selective, eating 32 percent of the 204 plant species tested on all the animals. This was followed by horses at 59 percent, cows at 66 percent, sheep at 82 percent and goats at 85 percent. The animals generally preferred legumes and grasses.

“Pigs were probably the pickiest eaters because they are omnivores and do not solely eat plants. Somewhat surprisingly, the animals were not very good at avoiding the toxic plants. Cows and horses were the best in that regard,” explains Rydin.

The thesis contains numbers and references to Flora Svecica, Linnaeus’ list of Swedish flora. According to the researchers, this was one of the first times Linnaeus used the now common naming convention, which has also allowed them to identify the species involved in the experiments.

“Carl Linnaeus laid the groundwork for future scientists to analyse this area. It was about 200 years before biologists started using statistics. What is also absolutely fascinating is that all the data is documented. If this had been done in more recent times, the researchers probably wouldn’t have saved the raw data,” adds Rydin.

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Journal

Biological Journal of the Linnean Society

DOI

10.1093/biolinnean/blae084 

Method of Research

Data/statistical analysis

Subject of Research

Animals

Article Title

Are cows pickier than goats? Linnaeus’s innovative large-scale feeding experiment

Article Publication Date

18-Sep-2024

 

Play it forward: lasting effects of pretend play in early childhood

Psychologist cautions how modern society ignores best way to educate young children

Florida Atlantic University

 

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Pretend play is associated with a host of enhanced cognitive abilities such as executive function, language and perspective taking, which are important to education, making the minimization of pretend play unwise.

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Credit: Florida Atlantic University

From developing social skills to fostering creativity, pretend play in young children is likened to being a “metaphoric multivitamin” in an editorial published in the journal Neuroscience and Biobehavioral Reviews by Florida Atlantic University’s David F. Bjorklund, Ph.D.

As the school year kicks into full gear, Bjorklund, associate chair and professor in the Department of Psychology within FAU’s Charles E. Schmidt College of Science, highlights the plethora of robust benefits of pretend play on cognitive, social and emotional development in children and cautions how “learning through play” has changed with the demands of contemporary society.

Given natural selection’s shaping of childhood for the acquisition and refinement of species-adapted social-cognitive skills – much through pretend play – Bjorklund says it is unfortunate that modern culture is ignoring the evolved wisdom of how best to educate young children.

“Throughout our species’ history and prehistory, and in hunter-gatherer and traditional cultures today, young children acquired important cultural knowledge and skills through play and observation, with much adult behaviors being imitated during play,” said Bjorklund. “Pretend play is associated with a host of enhanced cognitive abilities such as executive function, language and perspective taking, which are important to education, making the minimization of pretend play unwise.”

He explains that direct teaching of children by adults is rare in traditional cultures, and likely was for our hunter-gatherer ancestors. However, with the advent of increasingly complex technologies such as reading and mathematics and the need for universal education, formal schooling became necessary, and this has recently extended to early childhood.

“The prevalence of preschool education has increased over the decades in many developed countries, and unlike earlier days when ‘learning through play’ described the basic curriculum, contemporary preschool education instead often emphasizes direct instruction, characteristic of pedagogy designed for older children,” said Bjorklund. “This reflects an evolutionary mismatch between young children’s evolved learning abilities and the demands of contemporary society.”

Pretend play occurs voluntarily and spontaneously, especially when the individual is relaxed and not under stress and typically lacks any immediate practical purpose.   

“In the context of pretend play, skills encompass imagination, the ability to think about possibilities that differ from reality, mental time travel, and imitation, among other symbolic capabilities,” said Bjorklund.

He explains that pretend play functions as an experience-expectant process, enhancing the brain’s readiness for focused learning.

“It’s not clear whether the extended period of childhood and juvenile development created more opportunities for play or if this playfulness emerged as a result of that extended period,” said Bjorklund. “However, this evolution of childhood, along with the prolonged neural plasticity it brings, may have been a crucial adaptation for the development of the modern human mind.”

He says pretend play likely plays a crucial role in developing and refining psychological skills rather than being solely necessary for their emergence.

“Advanced pretend play is most evident during the extended juvenile stage in humans,” said Bjorklund. “This extension has led to a distinct childhood stage, lasting until about age 7, characterized by greater independence and social interaction.”

During this time, children engage in more complex play while their cognitive abilities continue to develop. Bjorklund emphasizes that this prolonged juvenile period and its neural plasticity are essential for fostering our unique social-cognitive skills.

Research comparing play-based preschool curricula to those focused on direct instruction has consistently shown that while direct instruction may yield immediate benefits, play-based approaches offer more significant long-term advantages in both academic performance and students’ attitudes toward school.

“One of the most comprehensive studies on the long-term effects of direct instruction for preschoolers from low-income backgrounds found that although there were initial academic gains, these benefits diminished over time,” said Bjorklund. “By third grade, children in the control group outperformed those in the direct-instruction program, and this gap widened by sixth grade.”

These findings led the researchers to reevaluate the effectiveness of heavily drilling children on basic skills and to consider the potential benefits of play-oriented preschool programs, particularly for children at risk of intellectual challenges.

Bjorklund says recess and opportunities for free play for older school-aged children also have been declining in developed countries, sometimes replaced by adult-directed play, again at odds with what is known about children’s evolved learning abilities.

“These practices may not only make learning more arduous, but negatively impact children’s sense of autonomy with respect to learning,” said Bjorklund. “Pretend play evolved to enhance children’s acquisition and refinement of important cultural knowledge and skills during an extended juvenile period. The abilities needed by modern children have changed and may require new means of learning, but we should not lose sight of the substantial benefits that pretend play can still afford our species’ youngest members.”

- FAU -

About Florida Atlantic University:
Florida Atlantic University, established in 1961, officially opened its doors in 1964 as the fifth public university in Florida. Today, the University serves more than 30,000 undergraduate and graduate students across six campuses located along the southeast Florida coast. In recent years, the University has doubled its research expenditures and outpaced its peers in student achievement rates. Through the coexistence of access and excellence, FAU embodies an innovative model where traditional achievement gaps vanish. FAU is designated a Hispanic-serving institution, ranked as a top public university by U.S. News & World Report and a High Research Activity institution by the Carnegie Foundation for the Advancement of Teaching. For more information, visit www.fau.edu.

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Journal

Neuroscience & Biobehavioral Reviews

DOI

10.1016/j.neubiorev.2024.105805 

Method of Research

Commentary/editorial

Subject of Research

People

Article Title

The evolution of pretend play and an extended juvenile period and their implications for early education

New research reenvisions Earth’s mantle as a relatively uniform reservoir

Earth’s mantle more chemically uniform than previously thought

University of British Columbia

Lavas from hotspots—whether erupting in Hawaii, Samoa or Iceland—likely originate from a worldwide, uniform reservoir in Earth’s mantle, according to an evaluation of volcanic hotspots published today in Nature Geoscience.

The findings indicate Earth’s mantle is far more chemically homogenous than scientists previously thought—and that lavas only acquire their unique chemical “flavours” enroute to the surface.

“The discovery literally turns our view of hotspot lavas and the mantle upside down,” said Dr. Matthijs Smit, associate professor and Canada Research Chair at the University of British Columbia’s Department of Earth, Ocean and Atmospheric Sciences. “In a way, Earth’s lavas are much like humankind itself—a beautifully diverse population with a common ancestor, which developed differently wherever it went.”

Research of Earth’s mantle has been complicated by the fact that it can’t be sampled directly. Scientists instead have to engage in a bit of geoscientific detective work; they study this important part of our planet through trace-element and isotope analysis of lava that comes from the mantle and is erupted at oceanic volcanoes around the world. The vast differences in composition of these lavas, along with the assumption that the isotope composition of magma doesn’t change between its source and the surface, has led to the general view that the mantle contains distinct reservoirs of different age, located in different regions, and formed by different processes. The observations made by Dr. Smit and co-author Dr. Kooijman of the Swedish Museum of Natural History’s Department of Geosciences indicate that the reality may be quite different.

“By looking at a specific set of elements, we were able discern the chemical effects of various processes that act on magma melts on their way to the surface to discover that all hotspot lavas actually share the same starting composition,” said Dr. Smit. “The lavas only come out differently because the magmas interact with different types of rocks as they ascend.”

Earth’s mantle is a seething layer of molten and semi-molten material comprising about 84 per cent of the planet’s volume, which lies between the iron core and the surface crust. When magma derived from the mantle penetrates the crust and erupts onto the surface it is called lava.

Knowing what the mantle is made of is central to our understanding of how our planet formed and how the mantle has developed over time. It may also provide clues as to why the mantle behaves the way it does, how it drives plate tectonics, and what its role is in the global cycle of elements.

Besides shedding entirely new light on hotspot lavas in oceanic parts of the world, the analysis also revealed an exciting new link to basaltic lavas on the continents. These melts, which contain diamond-bearing kimberlites, are fundamentally different from magmas found at oceanic hotspots. They nevertheless prove to have the same magma “ancestor”.

“The discovery is a game-changer when it comes to models for Earth’s chemical evolution and how we look at global element cycles,” said Dr. Smit. “Not only is the mantle much more homogeneous than previously thought, it likely also no longer contains “primordial reservoirs”—entities that were once needed to explain the data, but could never really be reconciled with the concept of mantle convection.”

“This model explains the observations in a simple way and permits a myriad of new hypotheses for global geochemical research going forward,” said Dr. Kooijman.
 
Financial support for this research was provided by the National Science and Engineering Research Council of Canada.

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Journal

Nature Geoscience

DOI

10.1038/s41561-024-01538-7 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

A common precursor for global hotspot lavas

Article Publication Date

19-Sep-2024

 

Global warming leads to drier and hotter Amazon: reducing uncertainty in future rainforest carbon loss

A new study narrows the uncertainty in future Amazon carbon cycle predictions and reveals that future climate change may reduce the Amazon rainforest’s ability to act as a carbon sink by making it drier and hotter

National Institute for Environmental Studies

 

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In the Eastern Amazon flooded forest, trees stay partly covered by water due to the rainy season that typically lasts from February to June. Photo is taken in early August when the water levels start going down.

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Credit: NIES

The Amazon, often called the "lungs of the planet", is the world’s largest tropical forest, playing a crucial role in the global climate system due to its vast carbon storage. While it is typically warm and humid all year round, continued climate change poses the threat of more frequent and severe droughts and heat extremes. A new study, published in Nature Communications delves into future projections of the Amazon carbon cycle, focusing specifically on the impacts driven by climate change.

Scientists use the latest generation of Earth system models from the Coupled Model Intercomparison Project which contributed to the IPCC's Sixth Assessment Report. In the study framework, the climate change impacts are isolated from other factors such as land-use changes, including deforestation, and the CO2 fertilization effect on photosynthesis. An advanced technique known as Emergent Constraints that allows reducing uncertainties in future predictions using past observations is employed.

The study shows that future climate change may lead to hotter and drier conditions in the Amazon rainforest that reduces the Amazon carbon sink, in other words carbon dioxide absorption by plants. The lead author Dr. Irina Melnikova, a research associate at NIES, said that “this happens because global warming is accompanied by a phenomenon known as polar amplification—greater warming in polar regions compared to others”. It causes the intertropical convergence zone, a tropical rain belt crucial for the Amazon's climate, to shift northward. Such a shift would make Amazon drier and warmer, reducing the rainforest's ability to absorb carbon dioxide through photosynthesis while increasing carbon dioxide emissions through plants and soil respiration. Combined with the increased risk of droughts and fires in the hotter and drier conditions, this results in a net loss of carbon from the rainforest.

The new study also reveals that Earth system models, which estimate higher past global temperature trends, are more likely to predict a hotter, drier Amazon under a high-emission scenario compared to other models. The study concludes that the models that can reproduce past observational global warming trends have higher reliability in predicting the future Amazon climate change-driven carbon sink. "By refining our projections with emergent constraints, we can provide more accurate predictions of future climate impacts, which are essential for informed policymaking," stated Melnikova.

This research successfully reduces uncertainties in predicting the Amazon's response to climate change, enhancing our understanding and highlighting the critical role of accurate climate models in shaping future conservation strategies and global climate policies. The findings also reveal the potential for further warming to trigger large-scale atmospheric circulation changes, leading to a drier and hotter Amazon climate and increased carbon emissions from the rainforest. The authors caution that “While our study provides a more nuanced understanding of the Amazon's future, it also underscores the urgency of mitigating climate change to prevent the worst-case scenarios. The Amazon's fate is not just a regional concern but a global one.”

  

Schematic representation of the physical mechanisms of the climate-driven changes in carbon cycle in the Amazon forest region.

The horizontal axes represent past global trends in surface air temperature (1980–2014) in °C per year. The vertical axes show future projections for the Amazon: (a) surface air temperature change (°C), (b) precipitation change (%), and (c) climate change-driven carbon sink (GtC per year) as estimated by the CMIP6 models. Pearson’s correlation coefficients and p-values are indicated at the bottom of each panel. Horizontal box plots display the mean (white line), 17–83% range (box), and 5–95% range (horizontal bar) of observed global temperature trends from HadCRUT4 (light blue). Vertical box plots provide the same information but for raw CMIP6 models (black) and the constrained ranges using observations (teal). The emergent constraint is estimated for 120–139 year means under the 1pctCO2 scenario and for 2072–2091 under the SSP5-8.5 scenario, both corresponding to an intermodel mean of 4.4 °C warming relative to preindustrial levels. The figure is adapted from Figs. 2 and S11 of Melnikova et al. (2024).

Credit

NIES

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Journal

Nature Communications

DOI

10.1038/s41467-024-51474-8 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Emergent constraints on future Amazon climate change-induced carbon loss using past global warming trends

Article Publication Date

19-Sep-2024

 

Insights into South African population history from 10,000-year-old human DNA

Thirteen ancient human genomes from the Oakhurst rock shelter in South Africa provide new insights into human history in the region

Max Planck Institute for Evolutionary Anthropology

 

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Cape Point promontory, Cape Point Nature reserve, South Africa

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Credit: © R. Gibbon

A team of researchers from the University of Cape Town (South Africa) and the Max Planck Institute for Evolutionary Anthropology in Leipzig (Germany) have analysed human remains from the Oakhurst rock shelter in southernmost Africa and reconstructed the genomes of thirteen individuals, who died between 1,300 and 10,000 years ago, including the oldest human genome from South Africa to date.

“Oakhurst rock shelter is an ideal site to study human history, as it contained more than 40 human graves and preserved layers of human artefacts, such as stone tools, going back 12,000 years,” says Victoria Gibbon, Professor of Biological Anthropology at the University of Cape Town and co-senior author of the study. “Sites like this are rare in South Africa, and Oakhurst has allowed a better understanding of local population movements and relationships across the landscape over nearly 9,000 years.”

Long history of genetic stability in southernmost Africa

The successful genetic sequencing of thirteen individuals from the site was not without its challenges, as Stephan Schiffels, co-senior author of the study, explains: “Such ancient and poorly preserved DNA is quite difficult to sequence, and it took several attempts using different technologies and laboratory protocols to extract and process the DNA.” The ancient genomes represent a time series from 10,000 to 1,300 years ago, providing a unique opportunity to study human migrations through time and the relationship to the diverse groups of people living in the region today.

A key finding was that the oldest genomes from the Oakhurst rock shelter are genetically quite similar to San and Khoekhoe groups living in the same region today. This came as a surprise, as Joscha Gretzinger, lead author of the study, says: “Similar studies from Europe have revealed a history of large-scale genetic changes due to human movements over the last 10,000 years. These new results from southernmost Africa are quite different, and suggest a long history of relative genetic stability.” This only changed around 1,200 years ago, when newcomers arrived and introduced pastoralism, agriculture and new languages to the region and began interacting with local hunter-gatherer groups.

In one of the most culturally, linguistically and genetically diverse regions of the world, the new study shows that South Africa’s rich archaeological record is becoming increasingly accessible to archaeogenetics, providing new insights into human history and past demography.

Rock art at Oakhurst rock shelter, Oakhurst farm, near Hoekwil, South Africa

Credit

© V. Gibbon

Journal

Nature Ecology & Evolution

DOI

10.1038/s41559-024-02532-3 

Article Title

9,000 years of genetic continuity in southernmost Africa demonstrated at Oakhurst rockshelter

Article Publication Date

19-Sep-2024

 

Aversion to inequality drives support for redistribution

Experimental economic research

University of Zurich

Traditional economic theories assume that individuals only care about their own income when it comes to supporting redistribution policies. However, an international team of researchers from the University of Zurich (UZH), the University of Lille and the University of Copenhagen now challenges this view.

The results of their study show that people’s preferences towards inequality per se play a major role. “By taking into account for how much people dislike inequality, we can better predict who will support policies aimed at reducing the income gap,” says Ernst Fehr, corresponding author and director of the UBS Center for Economics in Society at the Department of Economics at UZH.

Attitudes towards inequality vary

People’s aversion to inequality comes in two forms: While some dislike being worse off than others, known as “disadvantageous inequality aversion”, others dislike the existence of poorer individuals, termed “advantageous inequality aversion”. These attitudes vary widely among people, and the understanding of how these preferences shape political support for redistribution policies remains limited.

In the study involving roughly 9,000 Danish participants aged 20 to 64, the researchers measured individuals’ aversion to inequality with a behavioral experiment. They then linked the results to individuals’ support for politically enforced income redistribution, i.e., policies that reduce income differences, and for charitable giving through documented real-life charitable donations that reveal their private redistribution preferences.

Inequality aversion influences support for redistribution

“Our empirical results show that people who have a stronger dislike of both advantageous and disadvantageous inequality are more likely to support political redistribution,” says Fehr. However, when it comes to charitable giving, those with a stronger dislike of advantageous inequality are more generous while those with a stronger aversion for disadvantageous inequality are less generous.

“Our findings support the theory of inequality aversion which suggests that many people dislike inequality per se, and that this dislike has important economic and political consequences – both at the societal and the personal level,” Ernst Fehr concludes.

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2401445121 

Method of Research

Experimental study

Subject of Research

People

Article Title

Inequality aversion predicts support for public and private redistribution

Article Publication Date

18-Sep-2024