Which ecological and evolutionary theories are widely misunderstood even by experts?

Economics blogger Tyler Cowen recently listed prominent economic theories that are widely misunderstood even by economists. I thought it would be interesting to ask the same question for theories in ecology and evolution.

Only well-known theories are candidates for this list. A theory can’t be misunderstood if nobody’s heard of it. And I’m not talking about loosely-defined verbal theories about which there is legitimate disagreement as to exactly what the theory says or means. I’m talking about cases where many people are confused or wrong about what the theory says or means.

Some opening bids:

Modern coexistence theory as developed by Peter Chesson and colleagues is definitely an example. Take my word for it, there are a lot of really sharp ecologists, including people who do mathematical modeling themselves, who just don’t get it. A while back I had a go at trying to explain some (not all!) of modern coexistence theory in an accessible yet precise way; starts here. I think understanding of modern coexistence theory is slowly increasing, thanks to an increasing number of empirical studies grounded in this theoretical framework, and thanks to accessible explanatory papers from folks like Peter Adler, Jon Levine, Janneke Hille Ris Lambers, and others (e.g., Adler et al. 2007). But it’s going to be a long haul.

“Optimism” and “pessimism” in animal behavior. Houston et al. (2012) argue cogently that lots of current work on this topic rests on misunderstandings. But then again, they suggest that many of these misunderstandings arise from the use of imprecisely-defined verbal models, so maybe that’s not a great example here.

The Price equation. Misunderstood from the get-go; Richard Lewontin famously dismissed it as trivial when George Price first wrote to him about it, only to later change his mind and write to Price apologizing for failing to get it. And I once had a conversation with a very good theoretician who said to me “The Price equation…yeah, I’ve never been able to get that.” The Price equation is much better and more widely understood than it used to be, thanks to the tireless efforts of Steven Frank and others. But even in his latest paper Frank is still at pains to refute unfounded criticisms of the Price equation. And reviewers ask to have explanatory appendices or text boxes added to pretty much every paper I write on the Price equation. Then again, maybe this isn’t the greatest example, because the Price equation still isn’t widely known?

Zombie ideas about the IDH. The three zombie ideas I listed in my original post on the intermediate disturbance hypothesis all are misunderstandings about how disturbance and environmental fluctuations can affect species coexistence. Note that I’m referring here to those three specific theoretical claims, not to broader disagreement or confusion about what ideas define the IDH.

The “portfolio effect” and its relationship to other mechanisms affecting the diversity-stability relationship. I was talking with a colleague recently who dug into the literature on diversity-stability relationships, and who asked me, “So, what’s the portfolio effect, exactly? And how does it relate to “mean-variance scaling”, “statistical averaging”, and “density compensation”? Because I’ve been reading all these papers and I can’t pin it down.” And I demurred because I’m not exactly sure either! I may do a post on this at some point, as an excuse to try to clear up my own embarrassing confusion. Feel free to explain it to me in the comments–and hope that nobody else replies that you’ve misunderstood! 🙂

Limiting similarity. I think confusion about what models of limiting similarity assume and predict is the longest-standing and most important theoretical misunderstanding in ecology.

R* theory, resource ratio theory, and dynamic energy budget theory. Actually, I don’t think any of those are widely misunderstood. But Marquet et al. made me wonder a little…

Just looking at the above list, I don’t see any obvious reason why these theories are widely misunderstood. It’s not as if they use especially advanced mathematics, for instance. Indeed, if anything the Price equation is hard to get because it’s so simple mathematically that it seems trivial. And it’s not inevitable that any popular theory will be widely misunderstood. For instance, I don’t think the theory of island biogeography is widely misunderstood. Perhaps some patterns will emerge with more examples, but I’m guessing not. The causes of misunderstanding are just too diverse for that.

You will note that I did not try to summarize any of the theories that in my view are widely misunderstood. I figured that exposing my own misunderstanding of any of those theories would undermine my point! But now it occurs to me that it might’ve strengthened my point. 🙂

23 thoughts on “Which ecological and evolutionary theories are widely misunderstood even by experts?

  1. It’s perhaps worth distinguishing between theories which are themselves misunderstood, and theories for which the evidence required to test them has been misunderstood (sometimes wilfully). For example, there is a special place in biogeography hell for authors who claim that finding reduced species richness on islands with increased isolation and lower area supports the Equilibrium Model of Island Biogeography. The whole point of EMIB was to explain these well-known patterns, and instead the assumptions and dynamic processes (colonisation, extinction, turnover) need to be examined. Plopping out another pair of graphs illustrating the pattern doesn’t add any support for the theory itself. Likewise when unexplained variation in community dynamics is attributed to ‘neutral’ processes. No, it’s just unexplained variance. Just because your predictors didn’t account for everything doesn’t mean the rest must be stochastic. I could go on but I’m told it’s bad for my stress levels.

  2. I’d be curious to see your list of which ecological & evolutionary theories are least misunderstood too (perhaps that’s different from most widely understood, since some are better known than others…) Obviously would make an interesting starting point for asking why…

    • Good question. If you’re trying to do a comparative analysis of the sources of misunderstanding, you obviously need to include well-understood theories.

      Hard to say, though, because I think the distribution is sort of bimodal, without much variation within each mode. Either the experts all understand the theory, or a lot of them don’t.

      I dunno, what do you think? What are the least misunderstood theories in ecology and evolution?

  3. Other candidates: Adaptive dynamics theory of J.A.J. Metz et al. and Harte’s MaxEnt Theory of Ecology – though Ethan White is doing a lot to make that approach clearer.

    I would even extend Carl’s question from above and say what is to stop us from the scary null hypothesis of:

    H_0: All theories in ecology and evolution are largely misunderstood.

    • Yeah, I thought about MaxEnt as a candidate. What do you think are the widespread misunderstandings about it?

      Same question for adaptive dynamics sensu Metz et al. I’m surprised to hear someone suggest that, I’d have thought that was sufficiently technical and of sufficiently narrow interest that it wouldn’t be widely misunderstood. You either know enough math to understand it, or you’re not much aware of it.

      Your H0 is too depressing to contemplate! Fortunately, I don’t think it’s actually true.

      • I also thought about MaxEnt – the misunderstandings I think are mostly philosophical. Why would you want a model with no mechanism? What does it tell us? What doesn’t it tell us? Why would you ever want a model when you know the assumptions are wrong (many similar understandings about neutral theory – although I think neutral theory ahd a lot of confusion about what was and wasn’t included as well)

        I am curious to hear what Drew has to say about Adaptive Dynamics. In my mind the actual tool is pretty clearly understood (other than those who reject any phenotypic model). Its the implications for e.g. speciation (disruptive selection as a mode of speciation) that are what people are confused about. And certainly in the larger evolution community there is misunderstanding of the whole optimization approach of which adaptive dynamics is a specific instance.

      • @Brian:

        “Its the implications for e.g. speciation (disruptive selection as a mode of speciation) that are what people are confused about. ”

        Hmm…confused about, or disagree about? I’d have said the latter–that people disagree on the plausibility of sympatric speciation via disruptive selection, or more broadly about the plausibility of speciation in the face of substantial gene flow. That people all understand what alternative models predict and why, and just disagree on which models are the best approximation of reality. But I don’t know this literature well so maybe I’m seeing disagreement where really there’s confusion and misunderstanding?

      • I think with this topic as with group selection the debate has gotten so heated and emotional it goes beyond the level of which model is a better fit to very over the top incorrect statements made about opposing models (probably with some degree of willful ignorance). I’ll let you decide whether that fits your category!

      • Yeah, group selection/kin selection/inclusive fitness is a hard case, for precisely the reason you describe.

        My hope is that some of that debate fades into irrelevance as new theoretical and empirical work reframes existing questions and asks new, better questions. See Hammerschmidt et al. 2014 Nature (one of the best papers I’ve ever read in my life!)

  4. I think it would be worth distinguishing theories which are “not-well understood” by the average ecologist from theories which are incorrectly-specified in literature attempting to address them. Coexistence theory is one that I know many people don’t fully grasp, which is fine if it doesn’t apply to your research…but are there a lot of papers explicitly addressing the theory that are completely off-base? I’m not so sure. But if so, why aren’t these papers getting shot down by reviewers and by post-pub letters?!

    Oh, and if this kind of misunderstanding pervades the literature, I think the conflation of neutral with stochastic dynamics wins hands-down. Or it is the most obvious error to me, anyway.

    • Re: coexistence theory, I listed it in the post because I’ve shot down, or attempted to shoot down, two papers by very prominent people that were specifically about coexistence theory, and that got it very badly wrong. And I had a conversation with a third top person who admitted that he didn’t really get it. So I confess I’m extrapolating from those three anecdotes, but I think it’s a reasonable extrapolation. What are the odds that the only three people who misunderstand coexistence theory even though it applies to their research happen to have talked to me or had me as a reviewer?

  5. Well, thats not exactly about misunderstood theories, but I think you mentioned an important point in the second paragaph:
    “But then again, they suggest that many of these misunderstandings arise from the use of imprecisely-defined verbal models, so maybe that’s not a great example here.”
    A lot (maybe a lot is a little to much) of terms that are used in ecology and evolution are imprecise defined, which could lead to confusion and misunderstundings.

    Like generalization and specialiazition where I always have to think twice what people are talking about. Or even terms like “behaviour”. One of the most popular books (in Germany) on animal behaviour (“Animal Behaviour: An evolutionary approach” by John Alcock) doesn’t even have a definition of behaviour in it. An apparently even experts don’t agree what behaviour really is (http://www.sciencedirect.com/science/article/pii/S0003347209001730).

  6. I would have said I understood the portfolio effect…but then I didn’t think it was widely misunderstood so maybe I’m in the group that is missing something. But here goes – I would say the portfolio effect refers to the the fact that if species in two communities, A and B, with the same total abundance have the same population-level temporal variability (e.g. on average the species fluctuate +/- 10 %) the community-level temporal variability in the more species-rich community will be lower than in the less species-rich community. So, there will be a negative relationship between species richness and community-level variability even without invoking interactions among species that cause negative covariance and it doesn’t even really require that species respond differently to fluctuations in the environment – as long as there is some stochasticity in the common response to the environment (i.e. all species aren’t perfectly correlated in their population changes) there will be some portfolio effect. It’s been represented as a “non-biological” explanation for the negative relationship between temporal variability in community abundance and species richness but when it is modeled the models usually assume zero correlation in abundance among different species and buried in that null is some biology, in my opinion. It assumes that species are responding independently to environmental fluctuations and I think this implies something about how communities are constructed.
    Of the three concepts mentioned (mean-variance scaling, statistical averaging and density compensation) i would have said that only statistical averaging is really relevant. The mean:variance relationship usually refers to population level mean:variance relationships and even if those are identical in the two communities the more species rich community will show lower community-level variability. Density compensation ( and I’m assuming that means either density-dependent growth rates at the population level and/or inter-specific competition resulting in increases in one species being compensated for by decreases in another) also doesn’t need to vary among the two communities to get the negative relationship between richness and temporal variability. Statistical averaging is what drives this – because the species aren’t perfectly correlated some of the increase in one species will be offset by a decrease (or even a smaller increase) in another species and so, all else being equal and species not being perfectly correlated. more species rich communities will have lower community-level variability.
    I would be interested to hear if other have a different take on the portfolio effect. Best, Jeff H

    • Hi Jeff – I agree with your understanding the portfolio affect as referring to one of the three components of decomposing the formula for community stability (or coefficient of variation): overyielding, covariances/compensation and sum of variances. This last is the portfolio effect. And it is a mathematical fact that statistical averaging (a result of the central limit theorem) says that when you sum or average a set of random variances the variance of that sum or average goes down as the the number of variables go up. Weaker versions of the CLT don’t require the variables to be uncorrelated or identically distributed – just not perfectly correlated as you note. This was first applied to portfolios of stocks in the stock market (hold a diversified portfolio to reduce variance/risk) and hence the name.

      However the Doak & Tilman exchange in AmNat in 1998 around that same 3rd term (sum of variances) focusing on the mean-variance scaling relationship of individual populations and what the exponent is (which I am NOT going to summarize here!) have got a lot of people thinking that is the portfolio effect. While I think this is an interesting subject (even have a paper on it coauthored with Greg Mikelson), it requires a lot of assumptions to get tractable math. Greg & I used portfolio effect generically to refer to anything that involves that third term (the sum of the population variances) which could include the statistical averaging argument (always increases stability with diversity) or the mean-variance argument (may increase or decrease stability depending on assumptions). From this distance I think I like the term portfolio effect referring just to the statistical averaging argument though.

  7. Bet hedging. Although that may be gradually changing.

    One sign that an idea is widely misunderstood (or perhaps just unfamiliar and so not widely understood): lots of people are able to publish review/perspectives-type pieces explaining the idea. There’ve been numerous reviews of bet hedging over the past decade or so. Same for modern coexistence theory and the Price equation.

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