Zombie ideas in ecology: a comment on my paper critiquing the IDH, and my reply

As some of you have already noticed, a few days ago Trends in Ecology and Evolution (TREE) published a letter from Douglas Sheil and David Burslem, commenting on my paper arguing for abandonment of the intermediate disturbance hypothesis (IDH). My reply was just published today.

Douglas Sheil and David Burslem kindly invited me to comment on a draft of their letter before they submitted it, and we had an amicable exchange of views which is still ongoing. I think their letter is very thoughtful and useful. Thanks for them to taking the time to write to TREE to share their views. There’s much on which we agree, though of course we don’t agree on everything.

For those of you without access to Trends in Ecology and Evolution, here’s a brief summary. Sheil and Burslem say that they “agree with [my] observations, but reject [my] conclusions” that the IDH should be abandoned. They argue that my critiques are directed largely against theoretical ideas that should not be considered part of the IDH. So that the IDH, defined in terms of successional niches and competition-colonization trade-offs (which is how they see Connell as having originally defined it), remains a valid hypothesis worthy of investigation. They suggest that the proper conclusion to draw from my critiques is that the IDH should be more precisely defined. They conclude by writing “Not all diversity–disturbance theories are correct, but neither are all of them the IDH.”

In response, I argue that in practice the IDH has been broadly defined by many authors, and that imprecision in its definition is inevitable given that it was originally formulated verbally. In light of this, I suggest it is appropriate to critique the broadly-defined IDH we have rather than the narrowly-defined IDH we might want. I also argue that a focus on substantive issues should take priority over a focus on definitional issues. Whether or not the ideas I critiqued are considered part of the IDH “sensu stricto”, they are widely-cited, influential ideas. I think the important thing is to separate valid from invalid ideas, whatever terms are used to refer to those ideas. It would be unfortunate if debate over definitional issues were mistaken for debate over substantive issues*. But if more widespread recognition of the distinctions between valid and invalid models of disturbance-diversity relationships encourages ecologists to narrow the definition of the IDH in the way Sheil and Burslem want, I’d be happy with that outcome.

In an old post, I speculated on the responses advocates of the IDH might make to my TREE paper, going so far as to list 10 possible responses. I see Sheil and Burslem’s letter as basically a combination of responses #5 and #7 from my list. Let me also say that, looking back, I don’t think I wrote that old post very well. It was unnecessarily combative and cynical about the sort of responses I thought I might receive. I put too much emphasis on the possibility of responses that, if made, would’ve reflected negatively on their authors (e.g., self-contradictory responses, or responses based on failure to understand my paper). I’m very glad that the first published response to my TREE paper is a productive and thoughtful one.

*In a recent comment on another blog, Jon Lefcheck describes Sheil and Burslem’s letter as a “rebuttal” of my paper. Which of course it is in a sense–Sheil and Burslem don’t agree with me that the IDH should be abandoned. But I worry that simply describing their letter as a “rebuttal” of my paper leaves the mistaken impression that they disagree with me on everything. Again, Sheil, Burlsem, and I actually agree on which ideas about disturbance-diversity relationships are valid and which ones aren’t. Our areas of agreement and disagreement can’t be captured by any brief summary, I don’t think. Brief summaries have their place, but I don’t know that this is it. I encourage interested readers to click through and read my paper, and the exchange of letters, fully and carefully, rather than relying on brief summaries. And if you want to tweet about this exchange of letters, maybe consider just tweeting that the exchange exists, rather than trying to summarize it in 140 characters. Just a suggestion. 🙂