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!

Self-organization in deep time

I gave an Evening Keynote talk about ecological self-organization at the Autogenic Dynamics Conference of the Society for Sedimentary Geology. We discussed possible signs of self-organization in the geological record. See an example in the poster image, of a deposit with stromatolite-like shapes found in the book cliffs, Colorado, where we went for a field visit.

Spatial ecology papers catch two prizes at the NAEM Meeting

On 12 February, two papers from the Spatial Ecology lab in Yerseke received the 2nd and 3rd price in the ‘Best Paper Award’ category at the Netherlands Annual Ecology Meeting (NAEM). This concerns the papers by Monique de Jager et al. (‘Mussels confirm theory of Albert Einstein’) and Quan-Xing Liu et al. (‘Musselbeds are as strong as steel‘).

Links to the full papers:

Monique de Jager et al.:

Quan-Xing et al.:

Talk at Studium Generale Zeeland

I am going to give a talk for the Zeeuwse Studium Generale in Middelburg on Februari 5, 2014, in the Zeeuwse Bibliotheek, starting at 19:30. My talk will provide a popular angle to my work on the spatial ecology of intertidal systems. The talk will be in Dutch.

Title (in Dutch): Ruimte! Essentieel voor getijdenatuur.

See link:–ruimte!-essentieel-voor-getijdenatuur.html

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.

I gave a lecture and a masterclass within the Wageningen ecology & evolution series (WEES lectures) on Sept 19, 2013.

On september 19, 2013, I gave giving a lecture entitled “The ecology of animal movement: can we learn from physics?”, and before the lecture interested PhD and Master students joined a Master class.



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.