Mark Denny discusses Ecological Mechanics

According to Mark Denny, the time is right for biomechanics to be folded into the broader study of ecology. In Ecological Mechanics, Denny explains how the principles of physics and engineering can be used to understand the remarkable ways plants and animals interact with each other and their surroundings, and how this controls where species can survive and reproduce. Recently, Denny shared some thoughts on the emerging discipline and his new book:

Ecological MechanicsEcological mechanics is not something I’ve heard of. Is it a new field of study?

MD: Yes and no. Biomechanics, the field in which I was raised, has traditionally focused on trying to understand how individual plants and animals work: how they are shaped to perform certain functions, what materials they are constructed from, how they interact with wind and moving water. But this biomechanical perspective has matured to the point where it can now be productively applied to questions of how individuals interact. In other words, the time is right for biomechanics to be folded into the broader study of ecology. That’s the basic idea of the book: to reveal to ecologists can they benefit from incorporating some physics and engineering in their approach, to challenge biomechanics to extend their expertise beyond the individual, to bring two well established disciplines together.

Can you give me a good example of ecological mechanics in action?

MD: I’d be delighted to! Let’s take coral reefs. They are an iconic example of how an assemblage of plants and animals interact to build a community that can grow and persist in a physically stressful environment, in this case the wave-beaten shores of tropical islands. But coral reefs exist in a delicate balance. Fish that shelter among branching coral colonies eat the seaweeds that otherwise would outcompete corals for space on the reef. If too many of the branching corals are broken by waves, the fish population declines, and the seaweeds take over. So, the state of the reef is a complex interaction between fluid mechanics (which governs wave forces), solid mechanics (which governs the ability of corals to resist those forces), and ecology, (which accounts for the community-wide consequences of coral breakage). But ecologists have had no way to predict how these interactions will play out as climate changes. Fortunately, ecological mechanics can now provide the answer. By taking into account both the predicted increase in intensity of tropical cyclones and the reduction in strength of corals due to ocean acidification, we can use the principles of engineering to accurately predict the change in species composition on a reef, and, from that, to use ecological principles to predict the change in competitive interactions between corals and seaweeds.

What’s the scope of the subject matter?

MD: Broad! In the first section we cover basic concepts from the physics of diffusion to fluid mechanics. We then use those concepts to understand the forces that plants and animals encounter both on land and in water, how animals move, and how the environment affects the temperature of everything, both living and dead. Then there’s a section on the mechanics of materials: how the chemical composition of a structure determines its stiffness and strength, how the shape of the structure affects the forces imposed on materials, and how structures interact in dynamic fashion with their surrounds. We then finish up by tying together the information from the previous sections. We explore how variation in the environment affects the plants’ and animals’ performance, and how that variation changes through time and space. We delve into the statistics of extremes (which can be used to predict the likelihood of ecological catastrophes), and we see how physics causes ecological patterns to emerge even in physically uniform habitats. There’s plenty here for both terrestrial and aquatic biologists, at scales ranging from the molecular to the global.

What tools will I take away from reading Ecological Mechanics?

MD: Great question. In a nut shell, you should come away with enough practical knowledge not only to understand the ecomechanics literature, but also to start working as a practicing ecomechanic. The chapter on thermal mechanics, for instance, teaches you how to construct a head-budget model for an organism that you can use to predict body temperature in any environment. The chapter on scale transition theory provides a recipe for predicting how the average performance of a population will change as the population spreads through space.

Sounds pretty technical, though. How much of a background in physics, math, and engineering would one need?

MD: Not much, actually. If you’ve had a course in basic physics somewhere along the line, and remember a reasonable amount of the algebra you learned in high school, the ideas presented here are should be easy to absorb. My own formal background in math and physics is absolutely minimal. Most of what I know about engineering I learned by explaining it to myself, and I think that has put me in a good position to explain this material to others. Readers are likely to be pleasantly surprised at how far a little bit of mathematics and basic physics can take them.

Given the scope and level of the discussion, what do you see as the audience for Ecological Mechanics?

MD: I wrote this text with several audiences in mind. First, there are ecologists and biomechanics actively involved in research, everyone from undergraduates on up. I feel certain that the breadth of information presented here will provide them with new perspectives on their subjects, new ways of thinking about the ways in which plants and animals interact with each other and with their environment, and the tools to explore those thoughts. The text can also be used as the basis for an upper-level undergraduate course. Combining as it does biomechanics and ecology, it could easily fit into a general curriculum in biology. It could equally well provide accessory information for other courses; various chapters could be used in isolation in a general biomechanics course, for instance, or a general course in ecology. And lastly, I hope there is an audience among folks who are just interested in science. Ecological mechanics involves such a compelling mixture of physical and biological science; I’m hoping that people will pick up this book just to scratch the itch of curiosity.

How did someone with little background in math and physics end up in a field like ecological mechanics?

MD: Pure serendipity. Like so many people, I went to college planning to go to medical school. I majored in zoology, avoided math, and put off taking physics until my senior year, and even then I took it pass/fail. But I found that physics offered a different (and intriguing) way of thinking about the world. And that really clicked into place when, in my final semester, I took a biomechanics course from Steve Wainwright and Steve Vogel. They showed me how the physics perspective could be applied to biology, and I’ve been riding that wow!! feeling ever since. I’d love to pass that excitement along to others, and books like this are best way I know to do that.

Mark Denny is the John B. and Jean DeNault Professor of Marine Sciences at Stanford University’s Hopkins Marine Station in Pacific Grove, California. His books include Biology and the Mechanics of the Wave-Swept Environment, Air and Water, and How the Ocean Works.