Grow with the flow
Learning from nature to build efficient, resilient transportation networks

There is much we can learn from nature on how to build efficient, adaptive transportation networks. An Oxford study, published in Proceedings of the Royal Society B, helps shed light on one such natural network.

In the study, the researchers looked at how fungi transport water and nutrients in a way that is robust and resilient, while maximising growth. The research, conducted by members of the CABDyN Complexity Centre, the Institute for Science, Innovation and Society (InSIS) and the Oxford Centre for Integrative Systems Biology, aims to contribute to our understanding of how to optimise other transport systems in nature and society to transport resources in the most efficient way possible.

According to Eduardo López, a Research Fellow in Complex Systems at CABDyN and InSIS, similar patterns already exist between train networks and networks of fungi, which suggests that both humans and nature are aiming for the same goal — efficient distribution of resources. But, how do the solutions arrived at by humans and nature differ from one another?

“In mathematics, there is a family of problems for which it is believed that optimal solutions are exponentially hard to discover. When trying to solve these problems, we often settle for solutions that are ‘good enough’, and an entire industry has been developed around methods to derive the ‘best available’ solution. At the core of this lies the idea that people have limited time and resources to explore alternatives and build improvements,” says López. “Nature has limited time too, but considerably more.”

Fungi are particularly relevant natural systems for study because they collect water and nutrients from a few central points, and then form extensive networks to efficiently transport these nutrients to all corners of the system. These networks have been found to be robust and resilient to breakage, as well as providing wide coverage of relatively large areas. While our understanding of other natural transport systems, such as vascular system in animals and plants, is fairly well developed, much less is known about fungal transportation mechanisms, particularly over long distances, which makes this a productive area of research.

“There has been relatively little research on fungal systems that has focused on their network structure,” says Nick Jones from Oxford’s Physics Department and the Oxford Systems Biology Centre. “This Complex Systems approach aims to look at how the underlying network architecture brings different parts of systems together to interact,” he said.

The study focused on the relationship between the growth of the organism and the flow of water and nutrients throughout the network. Since water is often collected far from the points of growth, the researchers hypothesised that the network’s growth was linked to water flow into these areas. Though it might be expected that the organism requires nutrients in order to grow, the research team found that the opposite is also true. It must continue to grow in order to draw nutrients from the regions where its food sources are located to the areas of growth.

To study how these networks operate, the researchers developed a model, based on electrical circuits, which was used to estimate the speed of these flows inside the fungus. The team then measured the growth of the fungal network through time-lapse photography, taking pictures every three days over several weeks, and running the results through an image analysis program. By incorporating the assumption that all sources of fluid can be accounted for, the team set up calculations that could be used to estimate fluid flows over the entire fungus. Once these estimates were obtained, they were then compared with the growth itself.

“Our core observation was elementary: if a fungus grows, that increase in volume must come from somewhere,” says Jones. “If the source of new volume is distant from the growth then this must create flows in the network. Because the volume is mostly water, which here is effectively incompressible, growth in one part of the network will be rapidly coupled to the rest,” he said.

The results showed that the growth of the organisms were consistent with the team’s estimates, and in areas where there were faster flows, they also observed a thickening of the ‘cords’ or pathways in the network, while less used pathways became thinner.

The study of efficient networks in biology has implications for how society builds and optimises transportation networks going forward. As cities continue to grow and face increasing challenges, by looking to nature, we may be able to devise roads and railways that channel resources more efficiently, potentially providing better coverage and better connections at lower cost.

10 June 2010