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Once a physicist: John Harte

John Harte is an ecologist in the Energy and Resources Group at the University of California.

John Harte

What attracted you to physics? I was always good at mathematics, and I liked the fact that you can write down simple equations that describe nearly everything, from the waves in the ocean to the structure of a crystal. When I later became interested in ecology, I think the same motivation applied – I approached it as a wonderful example of a complex system for which we really had no theoretical understanding, and I tried to apply patterns of reasoning from physics to come up with a theory that is relatively simple compared with the complexity of nature.

How did you get into ecology? I got my PhD in theoretical physics in 1965, and after that I was a postdoc at CERN for a year before I went to Berkeley to work with Geoffrey Chew and Stanley Mandelstam. That was the heyday of their "bootstrap" theory of elementary particles (which held that "elementary" particles are actually all made up of each other), and I found this theory very attractive. But then along came the quark model and knocked us all out of the water, and that was when I began to switch over to ecology. It seemed somehow fresher to me – there weren't many people doing theoretical ecology, whereas in physics I was just a small piece of a huge enterprise. Also, I have always been fascinated by natural history. As a child, probably my most intense hobby was birdwatching, and I loved walking through forests and staring into ponds. So I took a job as an assistant professor in the physics department at Yale, and I used my five years of job security there to turn myself into a real ecologist.

What skills did you need to learn? I pretty much already had the skills I needed to do theoretical ecology, but I wanted to do field work, too, so I had to learn how to do that. I was very interested in lakes as prototype ecosystems, so we did a lot of field studies on lakes in California, and we also created test lakes in the laboratory so we could study them under controlled conditions. I was looking through microscopes at plankton and measuring water chemistry, which got me interested in acid rain and its effects on ecosystems. That, in turn, led to a whole decade of research on the decline of frogs and salamanders.

What are you working on now? My theoretical work is about applying ideas from statistical mechanics and thermodynamics to understanding patterns in the abundance and distribution of species around the planet. We use a method called "max-ent" (short for "maximum entropy"), and it is remarkably accurate in describing the patterns we see in pristine ecosystems, but it works less well on ecosystems that have been disturbed by things like fire, grazing or climate change. We are trying to understand why that is and to figure out how to extend the theory so that it will work in disturbed ecosystems. For the field work, I operate a climate warming experiment in a meadow up at the Rocky Mountain Biological Laboratory in Colorado. We have overhead electric heaters shining heat onto a large area – there are 10 plots and each is 30?m2 – and we've been warming half the plots for 25 years now. This has told us a lot about how climate change affects ecosystems, and in particular about the feedback to the climate as the ecosystem responds to change. For example, as ecosystems are heated and change their character, they emit carbon dioxide to the atmosphere, which causes more warming.

Is it depressing to see change happening to a place you've studied for so long? Yes, but I've been aware of this since I was a child. I grew up in the suburbs of New York City, and when we first moved there, there were forests and fields around my house. By the time I went to university, most of that was gone, and as I've grown older, the pace of change has accelerated. There are places in the Colorado Rockies where, in the 1960s, you would not see any signs of humankind, but now they're overrun with trail bikers and trekkers on horseback. There's been a huge influx of people into the remotest areas of the US, and a lot of it has to do with population growth – there's twice as many of us now as there were back then.

How has your physics background helped you? I use some physics directly in my theoretical work, but I also think that studying it gave me confidence that I could understand mathematical concepts well enough to extend them to a new field. In biology, there's generally less motivation for students to learn quantitative skills. They do learn a lot of statistics, how to test for significance levels and do regressions, but my sense is there's a much broader range of quantitative skills that ecologists would find useful.

What advice would you give to a physicist who wanted to get into ecology? Extend your repertoire of quantitative tools. Stochastic processes, partial differential equations, game theoretic methods – all kinds of quantitative tools are applicable to many areas in the natural world. But I would also strongly recommend that you ask yourself, do you really love the topic? Do you enjoy plants and animals? Do you like walking through a forest and examining the patterns in nature? The grounding that I have in nature is really important, and I think that if you don't love the substance of the topic – if you're approaching it purely abstractly – then it might not be the right career. Don't go into a field because you think it's exciting. Go into it because you feel a passion for the subject.



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