Researchers present a new model that links the rules of life at the individual and ecosystem level

Researchers at Michigan State University and the Carnegie Institution for Science have developed a model linking microscopic biology to macroscopic ecology, which could deepen our understanding of the laws of nature and create new opportunities in ecosystem management.

Report in the newspaper Science The team showed how microscopic relationships within plankton, for example between an organism’s size and nutrient consumption, extend to predictably affect food webs.

“Using data that other researchers have measured at the microscopic scale on these organisms, our model can predict what is happening at the scale of entire ecosystems,” said Jonas Wickman, a postdoctoral research associate at the College of natural sciences from MSU and first author of the new paper. .

“We can now show how lower-level rules of life fuel these higher levels based on ecological interactions and evolutionary considerations,” said Elena Litchman, a senior scientist in Carnegie’s Biosphere Science and Engineering Division. “Until now, people considered these levels in isolation.”

This new report will allow the team and their peers to design new experiments to test, refine and extend the model by extending it to other species and ecosystems. This could ultimately allow the model to inform ecosystem management strategies in diverse environments around the world.

Small organizations, global impact

The team also wants to know what more they can learn from their model and the plankton they study.

“We chose them as a model system for several reasons,” said Christopher Klausmeier, an MSU Research Foundation professor at the WK Kellogg Biological Station. He is also a faculty member in the Department of Plant Biology, the Department of Integrative Biology, and MSU’s Ecology, Evolution and Behavior, or EEB, program.

One reason is that plankton is the main research focus of the research group led by Litchman and Klausmeier.

“They are relatively simple organisms. If something has to follow the rules, plankton is a good candidate,” Klausmeier said. “But they are also important globally. They are responsible for about half of primary production on Earth and form the basis of most aquatic food webs.”

Primary producers use biochemical processes such as photosynthesis to transform Earth’s raw carbon and nutrients into compounds useful to organisms themselves and their predators. This means that plankton is an essential cog in the natural machinery that cycles the elements essential to life on the planet, including carbon, nitrogen and oxygen.

Having this scale model that describes plankton can therefore be useful to better understand these key processes, as well as whether and how these change with the planet’s climate.

The team did not include climate-related variables like temperature in this study, but the researchers are already planning their next steps in this direction.

“The effects of global warming could alter lower-level physiological processes,” Litchman said. “We could then use this framework to see how these effects propagate across different organizational levels.”

Stunning simplicity

Wickman wasn’t always a plankton ecologist. His undergraduate degree was in physics, but he shifted to ecology during his doctoral studies in Sweden before joining the Klausmeier-Litchman laboratory in 2020.

The team said its background in physics shaped its approach to developing this model, which Litchman described as “beautiful – stripping away everything but the essential processes.”

To begin, Wickman built himself from fundamental theories describing his system of interest. Only in this case the system wasn’t, say, quantum mechanical particles. They were tiny organisms connected by a simple food web.

Within this network, phytoplankton is the main producer and zooplankton is the predator.

“Well, definitely grazers,” Wickman said of the zooplankton. “We’re not in the habit of calling cows predators of grass.”

To fully appreciate how this important relationship works and its global implications, researchers have broken it down into its components governed by ecology and evolution.

For example, microscopic considerations such as the size of a phytoplankton affect its ability to compete for nutrients, which in turn influences the size of the cells and the likelihood that they become food for the zooplankton.

These microscopic factors are therefore linked to macroscopic variables, notably the distribution of nutrients and the density or rarity of the different plankton that populate their environments.

Over the past several decades, scientists have formulated mathematics that individually describe important relationships at the micro and macro scales. Attempts to bridge the differences, however, have left researchers wanting more, Wickman said.

That’s because previous attempts to make this connection have had to make compromises. Some previous models have chosen simplicity over precision and realism. Others have tackled this complexity with raw computational force, making them less accessible and more difficult to use.

“Our model includes real ecological and evolutionary mechanisms, but it is quite simple to use,” Wickman said.

The work began as pure theory, but Litchman suggested that it should be possible to test his predictions using existing data. “When I saw how well the model matched the observations, my eyes widened,” she said.

The team had been working on this problem for several years and had published an earlier paper expanding on the eco-evolutionary modeling techniques they relied on.

Today, the team demonstrated the potential of their model by uniting it with real-world data.

“The revelation that emerging patterns at the macroecological scale can be explained by properties of individual organisms at the microecological scale is as compelling as it is elegant,” said Steve Dudgeon, program director in the Biological Sciences Branch of the NSF, which helped finance the work.

“The study opens new avenues of research that could improve the prediction of how ecosystems and the relationships between the organisms within them will change with eco-evolutionary dynamics interacting in changing environments.”

Because of the natural variation in biological systems, the model and its results may seem complicated to someone accustomed to the precision of physics, but Wickman views them with enthusiasm.

“We’ve actually achieved pretty good accuracy in ecology,” he said. “We may not have the same level of theoretical elegance as physics, but that just means we have a lot more territory to explore.”