The empirical-theoretical divide in ecology
Sam Scheiner published a piece recently on ecology’s lack of engagement with theory. Frankly, the title pretty much tells you his conclusion “The ecological literature: an idea free distribution”, but if you want to know more, either read the original piece (it’s short) or EEB & Flow’s nice write up on it. The empirical-theoretical divide is a topic I’ve been pondering for a while. A long time ago (I was a postdoc), in a galaxy far far away (New Mexico), I read an awesome book called “The Making of the Atomic Bomb”*. It’s a wonderful history on the discovery of the atom and the race to harness its energy in the midst of World War II. In the book, a tight interaction between theorists and empiricists is portrayed, with empiricists pouring over the latest theories trying to figure out how to test them and theorists pouring over the latest results trying to understand what they might mean theoretically. It’s a gripping tale. In contrast to the scientific process portrayed in the book, ecology lacks the same tight integration between theoretical development and empirical testing. What is going on in ecology that might be impeding this scientific give and take? I have some ideas, though they are admittedly from the perspective of an empirical ecologist.
1) Empiricists and math literacy. This is the one that will have the theoreticians nodding vigorously. In ecology, empiricists often lack a basic level of comfort and literacy with math. In my graduate level class, we read a lot of primary literature. Some of those papers are math heavy. Without fail, my students see an equation and freeze up. They don’t even know how to think about what that equation might mean. And – let’s be honest here – it’s not just students that this happens to. As I tell my students, math is another language. You don’t necessarily need to be able to speak it fluently, but to be a literate scientist you at least need to be able to ask where the bathroom is. I’d say that right now, many empiricists can’t ask for the bathroom. If we’re going to bridge the empirical-theoretical divide, empiricists need to get more comfortable with seeing and interpreting equations.
2) Theoreticians and ecological literacy. This is the one that will have the empiricists nodding. Theory papers are often more focused on the mathematical aspects of the theory than the ecological meaning of the assumptions, variables, parameters, and predictions. I don’t think it’s a coincidence that some of the theories that have received the most empirical attention were formulated by people with a strong empirical component to their research; examples include: R* coexistence theory (Tilman, long-term field experiments at Cedar Creek), Metabolic Theory of Ecology (Brown, long-term field experiments at Portal), neutral theory (Hubbell, long-term research at Barro Colorado Island), and Chessonian coexistence (Chesson, long-term field experiments in SE Arizona)**. These authors have tried to communicate their theories in biological terms. Given the limited math literacy of empiricists, we need theorists to be better at communicating the ecology captured by the math in order to get empiricists engaged with the theory. Even though the most precise and concise way of providing directions to the bathroom is to provide a latitude, longitude, and datum, it’s really better to tell someone to take a left on the Champs Elysees.
3) Communication between empiricists and theoreticians. Given the two points above, it should come as no surprise that we have relatively limited communication between the groups. All sorts of pathologies can arise when two groups don’t know how to communicate to each other. For example, we have separate theory sessions at the annual Ecological Society of America meetings! I’ve always found that odd. Like theory is its own subdiscipline studying things of little relevance to the other population, community, and ecosystem ecologists at the meeting! If we are not communicating, then empiricists are unaware of relevant theories and theoreticians are unaware of new empirical developments that can improve existing theory or point towards the need for new theories. Without communication, our intellectual progress is severely hampered. We end up with piles of data that are only used for understanding a specific system at a specific point in time. We also end up with piles of theories that serve as little more than mathematical ornaments, because they have not been tested. Maybe I’m alone in this, but I think this is something that needs to be remedied.
4) Testing theories is hard. In ecology, testing theories is often hard. It’s rare that a theory will make predictions that simply require us to document that X impacts Y (e.g., does fire impact nitrogen levels in soils?). Coexistence theories like those developed by Peter Chesson are a great example of this problem. The storage effect and stabilizing vs. equalizing mechanisms for coexistence are big complex concepts that require a lot of thought and effort to test in useful ways. We need a class of creative empiricists, who can engage actively with theory, assess the key aspects of the theory that are testable, and figure out how to design those tests. We also need theorists who communicate broadly about the key predictions of their models, important underlying assumptions, and explicitly describe what good tests of their theories would entail, so that empiricists are correctly testing those models.
So, assuming that a better integration of theory and empirical research is desired, how do we accomplish it? Honestly, I don’t have a prescription for fixing this right now. But I do think there are some key elements that we need to be thinking about:
1) More context specific exposure to mathematics for our undergrads and grads. Shipping them off to Calculus 101 in the Mathematics Department and hoping they pick it up there is clearly not working.
2) Better communication between theorists and empiricists. There’s lots of ways to work on this. In our group, we house my empirically minded students with Ethan’s more quantitative students and also run joint lab meetings. We’ve been pleased with the results, but how to scale this up to whole programs is less clear to me. Another possibility is a series of workshops or even a center whose mission is to bring together theoreticians and empiricists interested in similar questions. The one thing I do know is that this isn’t something we can just fix through the literature. The current barriers are such that we will need venues for in-person exchanges as the two groups learn each other’s languages.
3) Broad conversations about how we test (and improve) theories. As a field, we’ve spent a lot of time talking about how to rigorously test cause-effect relationships and assessing whether patterns in nature are real or can be explained by null models. Our conversations about how to create a good dynamic for designing theory, rigorously testing it, and using the empirical results to improve the theory, has – as far as I am aware – not been very vigorous in ecology.
Addressing these key elements might not create a “Golden Age of Ecology”, but I steadfastly believe that no single approach is sufficient for addressing the complicated questions facing ecology. In that context, improving how theoreticians and empiricists interact can only be a plus.
* Note to the NSA, who undoubtedly had a red light go off somewhere when that precise combination of words crossed their giga-computers sucking in the internet: “The Making of the Atomic Bomb” by Richard Rhodes is a history book, not a how-to manual.
**I think the fact that all of them have long-term field programs is very very interesting, but a topic for another day.