Why are some ecological ideas controversial?

Why are some ideas in ecology much more controversial than others? You might be tempted to say that “Ideas which apparently conflict with other ideas, or with empirical data, will be controversial.” But I think that’s wrong—in ecology there seems to be very little correlation between the amount of criticism or controversy surrounding an idea, and the theoretical and empirical support for that idea.

Just off the top of my head, here’s a list of some ecological ideas that were, at least for a time (perhaps a long time), very controversial, but for reasons largely or entirely unrelated to the available evidence:

• Interspecific competition. Debate over the importance of competition, and how to test for it (the “null model wars”), was famously intense in the late ’70s and early ’80s. This despite the fact that there are good theoretical reasons to expect competition (see any introductory ecology textbook), and the fact that, when you do a removal experiment to look for interspecific competition, you usually find it (Schoener 1983, Gurevitch et al. 1992).

• Density dependence. Intense as it was, the debate in community ecology over interspecific competition was nothing compared to the debate in population ecology over density dependence. But here again, you would have a hard time arguing that the debate was driven primarily by data, or even by conventional theoretical considerations—it was ultimately a reflection of very deep-seated conceptual commitments (Cooper 2007).

• Trophic cascades. As a grad student in the mid-’90s, I lived through the “top-down vs. bottom-up wars”, as they were sometimes called, although the issues actually went beyond the question of whether communities are “mostly” structured by top-down or bottom-up forces (see the special feature in the June 1992 issue of Ecology). Even just 20 or so years later, it’s hard to understand why there was so much fuss. The most basic question—Are top-down and bottom-up effects common?—has a clear-cut answer. When we look for trophic cascades, in both aquatic and terrestrial systems, we mostly find them: removing predators causes their prey to increase, which causes the prey of those prey to decrease (Shurin et al. 2002). When we look for bottom-up effects, we mostly find them too. As for pretty much every other question, such as those about the determinants of the strength of top-down and bottom-up effects, either all the proposed answers are either unimportant or wrong, or else the available data are totally inadequate to test them (Borer et al. 2005). So rather than having silly arguments about particular cases (see, e.g., the amusingly contrasting views of Pace et al. 1999 and Chase 2000 on the implications of Spiller and Schoener 1994), we ought to be either coming up with better answers, or better data. NutNet is leading the way on the latter.

• Neutral theory. Evolutionary biologists enjoyed the neutralist-selectionist debate so much that community ecologists decided to refight the debate themselves. And just for fun, they decided to fight it using a particular kind of data (relative abundance distributions) which evolutionary biologists had already found to be inadequate to the task of distinguishing neutrality from non-neutrality.*

Contrast the above—intense controversies that arose and often persisted in the absence of much data, or even despite a pretty clear-cut empirical consensus—with the history of the intermediate disturbance hypothesis, which has never been a very controversial idea despite a horrible empirical track record (much worse than that of trophic cascades, density dependence, interspecific competition, or neutral theory), and being based on outright logical fallacies. Or think of keystone predation, the prevalence of which has been the subject of active research and ordinary scientific discussion, but never vociferous debate, even though the empirical evidence could hardly be considered to be more clear-cut than that for, say, trophic cascades.

The same question about the origin of controversies could be asked in other fields as well.** I’m no expert, but as far as I know sexual selection and sexual conflict was a pretty well-developed body of evolutionary theory, well-integrated with a fair bit of data (Arnqvist and Rowe 2005). Not a topic that would seem ripe for a big controversy about fundamentals—until Joan Roughgarden created one pretty much single-handedly.

And that’s probably part of the answer. If someone really prominent says something controversial, lots of people often pay attention. In ecology, Don Strong had a prominent role in the controversies over both interspecific competition and trophic cascades, and Steve Hubbell pretty much single-handedly kicked off the neutral theory debate. In evolution, Gould and Lewontin single-handedly created controversy over the “adaptationist programme”. But personal fame isn’t sufficient. In evolution, I don’t think many people paid much attention to Lynn Margulis’ stranger claims about “symbiogenesis” as an alternative to natural selection. And in ecology, Hal Caswell proposed a version of neutral theory in 1976 but as far as I know failed to kick off anything like the recent controversy over Hubbell’s neutral theory.

So, when this blog makes me massively famous and influential, what controversy would you like me to create? Because with great power comes great responsibility. 😉

*I actually think it’s very valuable that ecologists now collectively have a much better sense of what sort of dynamics distinguish neutrality from non-neutrality. I just think we learned it the hard way.

**And in fact it has. But I haven’t read the enormous social science literature on this. You get the background research you pay for on this blog.