The strength of complexity

Whether you look at a square centimeter or at a square kilometer, nature always reveals the most interesting patterns. It is this complexity at all spatial scales that makes nature different from many if not all human creations. Our latest research on mussel beds reveals that this many-scale complexity actually makes ecosystems very strong and resilient. Read more about it in the (Dutch) press release or in the actual paper!


Consumer fronts trigger runaway degradation in ecosystems

Consumer fronts, a common phenomenon in nature that occur in many different ecosystems, can trigger runaway ecosystem degradation and regime shifts. My latest review paper, together with Brian Silliman, just appeared in Annual Review of Ecology, Evolution, and Systematics; click here.

Theory of Albert Einstein confirmed with … mussels!

Do ecologists have to read the work of Einstein? Yes, it appears! Einstein’s theory with which he explained Brownian motion in molecules is equally valid for animals. This is the result of the work of Monique de Jager, one of my PhD students, and has just appeared in the Proceedings of Royal Society B.

See here a direct link:

Mussels confirm theory Albert Einstein

Mussels in dense mussel beds move in a similar fashion as molecules. Hereby, they confirm the theory for Brownian motion proposed by Albert Einstein in 1905. Monique de Jager of the NIOZ Royal Netherlands Institute of Sea Research explains the movements of mussels in mussel beds in the Proceedings of the Royal Society B, published today.

Albert Einstein theorized in 1905 that the movements of dust particles suspended in water was the result of collisions with water molecules. Research by Monique de Jager shows that the movements of individual mussels in mussel beds is similarly caused by collisions with conspecifics. Interactions with other mussels limit the freedom of movement of mussels and make mussels in dense mussel beds move in a similar fashion as molecules. These results emphasize the generality of Einstein’s theory and provide a new, different view on animal movement in their natural habitats.

“Many animals seem to move differently in dense environments than when they are alone,” says Monique de Jager, first author of the paper. “Mussels, for example, use a so-called ‘Lévy walk’, where long moves are alternated with small steps, mostly when they are alone. Mussels in dense mussel beds, however, behave totally different: they tumble around in the little space that they have left. This type of movement is very similar to ‘Brownian motion’ as found for instance in dissolved dust particles. Our research shows that this difference in movement pattern is not because mussels use a different movement strategy in different environments, but because of collisions with other mussels.”

“The mechanisms behind Brownian motion was a big scientific mystery in the 19th century,” says Johan van de Koppel, supervisor of Monique de Jager and honorary professor at the University of Groningen. “Why did the pollen particles that Robert Brown was trying to examine under the microscope shake so much? Einstein solved this puzzle in 1905 by showing that the pollen’s movements were caused by collisions with water molecules. Our research demonstrates that the Brownian movements of mussels are similarly the consequence of collisions, this time with other mussels.”

Also for other animals
The results of this study emphasize that ecologists have in the past ignored an important mechanism affecting the movement and dispersal of organisms. In most ecological studies, an observed movement pattern is believed to be an animal’s basic movement strategy.

The research led by Monique de Jager shows that interactions between organisms, such as collisions with conspecifics or interactions with predators, can be an important factor influencing the observed movement patterns. These interactions, rather than the intrinsic search and movement strategy of the organisms themselves, explain Brownian movement that we observe in many species.

Our mussel study therefore explains the change in movement that we observe when Tuna move from the open ocean to the continental shelf. It also clarifies why travelling to work is more time-consuming in New York or Tokyo than in a small village. Einstein’s theory on Brownian motion provides a universal explanation for all these phenomena.

Mussel beds are “as strong as steel”

Mussel beds are not a random clustering of mussels, but they contain patterns that resemble the arrangement of molecules and atoms in materials like bronze, steel or polymers. PhD student Quan-Xing Liu, myself, and a team of ecologists and mathematicians revealed their findings in the journal Proceedings of the National Academy of Science (PNAS) of July 1st.

Direct link:

“In our study we discovered that mussels form a pattern based on the mathematical principle behind phase separation, a process unknown within ecology,” highlights drs. Quan-Xing Liu of the NIOZ, currently working at the University of Amsterdam. Phase separation, where molecules and atoms of different types separate out to form spatial patterns, is an important physical process explaining the strength of alloys like bronze or steel, or polymers like polystyrene.

Until now, ecological models explain regular, self-organized spatial patterns, based on spatial differences in birth and mortality rates of organisms. The phase separation principle is solely based on movement and therefore deals with animal behaviour. “This is therefore a fundamentally different process of ecological pattern formation,” Liu adds.

Classroom experiment
“This discovery was made with a very simple experiment that can be done in any school classroom,” says prof. dr. Johan van de Koppel of the NIOZ, who is the supervising author of this article. “We spread out mussels in an aquarium and using a camera, we watched them move around to form strings that become regularly spaced on the aquarium bottom. The strings then form a net shape, very similar to that found in the field. In these strings, local mussel density is high enough for the mussels to attach to each other together using byssus threads. Because of the net-shaped patterns, the mussels are well protected against the pounding of waves and the snatching by predators such as gulls that threaten them in the real world.”

Quan-Xing Liu then made a mathematical description of the movement of mussels that he integrated into a model. To his surprise, this model was very similar to the classical model for phase separation developed by John Cahn and John Hilliard in 1958. Phase separation leads to the formation of honeycomb-shaped structures within materials that make polymers and alloys such as bronze and steel very strong. These results highlight that the same process makes mussel beds robust. Mussel beds are, so to say, ‘as strong as steel’.

A unifying principle
The results of this study extend well beyond the ecology of mussels. Aggregation and pattern formation is common to many animals. By demonstrating in their analysis the potential of applying phase separation models to ecological systems, they alert colleagues in their field to the possibility of using the results and models from the physics community in applications to ecological phenomena. Potential applications include aggregation in foraging birds, and mound building in social insects.

Moreover, it highlights that even in the 21st century, scientists can discover unifying principles that explain common phenomena in seemingly unrelated fields such as material science and ecology.

This study was financially supported by The Netherlands Organisation for Scientific Research (NWO) through the National Programme Sea and Coastal Research: the Project WaddenEngine, and by the Mosselwad Project, funded by the Waddenfonds and the Dutch Ministry of Infrastructure and the Environment.

Quan-Xing Liu, Arjen Doelman, Vivi Rottschäfer, Monique de Jager, Peter M.J. Herman, Max Rietkerk, Johan van de Koppel. Phase separation explains a new class of self-organized spatial patterns in ecological systems. PNAS July 1 2013.

A paper on Early Warning Signs in Science as coauthor with Marten Scheffer

Anticipating Critical Transitions
Marten Scheffer, Stephen R. Carpenter, Timothy M. Lenton, Jordi Bascompte, William Brock, Vasilis Dakos, Johan van de Koppel, Ingrid A. van de Leemput, Simon A. Levin, Egbert H. van Nes, Mercedes Pascual, John Vandermeer

Tipping points in complex systems may imply risks of unwanted collapse, but also opportunities for positive change. Our capacity to navigate such risks and opportunities can be boosted by combining emerging insights from two unconnected fields of research. One line of work is revealing fundamental architectural features that may cause ecological networks, financial markets, and other complex systems to have tipping points. Another field of research is uncovering generic empirical indicators of the proximity to such critical thresholds. Although sudden shifts in complex systems will inevitably continue to surprise us, work at the crossroads of these emerging fields offers new approaches for anticipating critical transitions.

You can find more at the Sciencemag website:

Oil spill triggers cliff erosion on southern US marshes

The BP Deepwater Horizon oil spill temporarily worsened existing manmade problems in Louisiana’s salt marshes such as erosion, but there may be cause for optimism, according to a new study.

A study appearing online Monday in the Proceedings of the National Academy of Sciences found the 2010 spill killed off salt marsh plants 15 to 30 feet from the shoreline and this plant die off resulted in a more-than-doubled rate of erosion along the marsh edge and subsequent permanent marsh habitat loss. Vegetation farther from shore was relatively untouched by the incoming oil.

“Louisiana is already losing about a football field worth of wetlands every hour, and that was before the spill,” said Brian Silliman, a University of Florida biologist and lead author of the study. “When grasses die from heavy oiling, their roots, that hold the marsh sediment together, also often die. By killing grasses on the marsh shoreline, the spill pushed erosion rates on the marsh edge to more than double what they were before. Because Louisiana was already experiencing significant erosive marsh loss due to the channelization of the Mississippi, this is a big example of how multiple human stressors can have additive effects.”

(From the University of Florida Press release)

For the paper, look here:

For the English press release, see:

For the Dutch press release, see:

For a US newspaper article about our work, see:

For some Dutch newspaper article, see:

See also vroege vogels: