Let’s identify all the zombie ideas in ecology!

As regular readers know, I worry a lot about zombie ideas–ideas that should be dead, but aren’t. Zombie ideas are the most important failures of science’s self-correction mechanisms: they’re big, widespread errors or misconceptions that aren’t recognized as such. Over the years, I and our guest posters have identified several zombie ideas in ecology:

The intermediate disturbance hypothesis

r/K selection

Species interactions are stronger and more specialized in the tropics

Humped diversity-productivity relationships

“Neutral” = “dispersal-limited”

“Neutral” = “drift”

Local-regional richness relationships (specifically, the ideas that linear ones are ubiquitous, and that linear ones show that colonization not local species interactions controls local community membership)

And we’re starting to see folks identify other candidate zombie ideas in other venues. For instance, Luke Harmon thinks the notion of ecological limits on continental scale species richness is a zombie idea. I don’t agree, but I can see the argument. Peter Abrams thinks ratio-dependent predation is a zombie idea, though I’d call it a lost cause. Terry McGlynn just listed a couple from his own fields of entomology and tropical biology (three-toed sloths are Cecropia specialists; canopy ants are dominant because of their high-sugar diet).

Here’s my question to you: Is that it? Are those the only zombie ideas in ecology? Or are there others, shambling around unrecognized, eating the brains of the next generation of students even as we speak?* Tell us in the comments: What are the other zombie ideas in ecology?

Remember, zombie ideas are widespread errors. We’re not looking for personal criticisms of individual scientists here, and no such criticism is implied by discussion of zombie ideas. Having proposed or supported a zombie idea doesn’t make anyone a bad scientist. Science is hard and we all get things wrong sometimes.

p.s. I can’t believe I never thought of this post idea before!

*Textbooks are a refuge for zombie ideas.

43 thoughts on “Let’s identify all the zombie ideas in ecology!

  1. How about ‘Global Warming’?

    1. Sure, most scientists recognize that more than temperature is changing, but temperature is certainly the focus of must climate change studies. Precipitation gets some attention, but little effort is directed towards snow depth, ice phenology, wind speed or other aspects of climate change.

    2. Warming may be the pattern of annual average temperature, but that rise in avg temperature is often because winters and nights are getting less cold, not days getting hotter.

    • Hmm…interesting suggestion. But do lots of ecologists actually have mistaken beliefs about which variables matter (e.g., mistakenly thinking mean temperature matters way than mean nighttime low, or mean winter temp or snow depth or etc.)? Or is this suboptimal distribution of research effort for some other reason besides false beliefs?

      • Maybe I don’t fully understand what a zombie idea is. Based on your definition (“…big, widespread errors or misconceptions that aren’t recognized as such), I don’t think my suggestion is a stretch. A couple weeks ago an ecologist that looks at warming effects wrote to me that she didn’t associate changes in wind or UV light as climate change. That is something I run into a lot.

        I don’t know how to judge which variables a scientist values (i.e., “which variables matter”) other than with the assumption that they study the ones they think are important. With that in mind, my experience suggests increasing daytime highs matter a whole lot more than than nighttime lows.

        Zombie idea or not, it irks me!

      • Hi Brandon,

        I guess I was wondering to what extent people do experiments manipulating mean temperature (as opposed to nighttime lows, or wind, or winter snowfall, or etc.) just because it’s easy to do and has been done a lot before. Experimenters following the path of least resistance and studying what’s easiest to study. Or studying what they think everyone else wants them to study. Or studying some environmental variable for reasons that don’t have to do with climate change, but then spinning it as having to do with climate change. Peter Adler has a great guest post on that: https://dynamicecology.wordpress.com/2012/12/10/ecological-forecasting-why-im-a-hypocrite-and-you-may-be-one-too/

  2. Adult survivorship is the most important life history trait for increasing persistence.
    It is often the most sensitive parameter in a structured population projection matrix, but trying to increase it may not give the most bang for your buck.

    • So, is the zombie idea that adult survivorship is what matters? And it’s a zombie because everybody is looking at sensitivities when they should look at elasticities?

      Assuming I’m not misunderstanding you, I’m surprised by this suggestion. I’d have thought the sensitivity/elasticity distinction was totally standard in the structured population modeling world. Heck, I teach it to undergrads in my population ecology class!

      • Yes – it is standard, but not without problems. Take as example a long-lived bird, that lives about 30 years and whose reproduction – but not survival – is highly dependent upon variable food resources (common case). Elasticity or sensitivity analysis will tell you that the elasticity of the population growth rate to adult survival is the highest, yet achieving 10% more adult survival is much more difficult than achieving 10% more reproduction, because there’s one vital rate which is rather constant, adult survival, and one which is highly plastic, upon which you/the environment can act. It’s related to “environmental canalization” of fitness components that have large effects on PGR, I think.

      • @Fred and @atiretoo: Ah, ok, I’m with you now. FWIW, I actually teach this point in population ecology as well. So I’d be surprised if it was *that* unfamiliar.

        Without wanting to pick on anyone, can you give some citations of people making mistakes by ignoring this point? Say, recommending completely infeasible conservation interventions in the discussion sections of their papers?

      • What Fred said. It isn’t about sensitivity vs. elasticity, but the cost of changing a given life history trait as well as the scope over which that trait can move. Can’t have more than 100% survival, for example.

        And this: http://www.ace-eco.org/vol6/iss2/art2/

        Which lead to the widespread abandonment of nest exclosures on beaches up and down the east coast. Turns out that even if nest exclosures increase adult mortality, they increase chick survival so much that they are still helpful. And when they aren’t the sites are so bad that regardless of what is done the local population is probably a sink. Here’s a report from the NCTC workshop we did on this:
        a revised version of which is a paper that is currently in revision.

        I don’t have a full list; would be a useful thing to review systematically. The main difficulty is what Fred mentioned, that the people actually making the decisions are not publishing or even referring to the published literature to make their decisions.

        So is it still a zombie idea if academic ecologists ‘get it’, but many practioners/decision makers don’t?

      • “https://dynamicecology.wordpress.com/2012/10/11/in-praise-of-pre-publication-peer-review-because-post-publication-review-is-an-utter-failure/”

        Good question, to which I don’t know the answer. What zombie ideas about ecology are prevalent only among managers and other decision-makers, but not among academics?

    • I’m not sure this is really a zombie idea per se – more like a misunderstanding of finer points of demographic analyses and what sens/elast are/mean/do.

      Besides, couldn’t adult survivorship still be the most “important” for persistence because while it can’t be increased, it can be reduced and reductions can dramatically lower lambda? In other words, the logic is wrong but the conclusion is correct. Of course that could still lead to incorrect management actions – trying to enhance adult survival rather than prevent increases mortality – but I still think this is a misunderstanding, not a zombie.

      One ? For clarification based om this and follow up comment below: my experience is mostly with plants, where juvenile/recruit vital rates usually have the highest sensitivity, not reproductive adults (who instead have the highest elasticity) . Does one often find in animals that the same vital rates have the highest sensitivities *and* the highest elasticities?

  3. what about zombie methods? I know I’m a broken record but…partial regression coefficients as estimates of causal effects using observational data have much (much!) larger error than typically estimated (unless explicitly modeled) and consequently the idea that we can make appropriate management or conservation decisions using the analysis of observational data is an illusion. So the belief that the coefficients approximate the true causal effects is the zombie idea. Or, the idea that any kind of variable importance ranking will closely approximate the most important variables for intervention is a zombie idea.

  4. I have two for you that are a bit different than the ones above.
    1. Acid rain damages trees directly. It’s effects are broad, but the papers that proposed that it damaged leaves directly have been proven wrong. Its effects are mediated through the soil.
    2. Centaurea diffusa and C. maculosa are allelopathic, and this explains their invasions. The articles have been largely retracted or are still being retracted (after an investigation by NSF) but e.g. wikipedia has not been fully corrected yet, and it is still found in some ecology textbooks.

    • Thanks Ruth. I always like hearing about zombie ideas totally outside my own field, it’s an interesting window into what other ecologists worry about. Not knowing anything about acid rain or knapweed, I had no idea that there might be zombie ideas about them.

  5. @Jeremy Common issues with elasticities have been studied, e.g., http://doaklab.org/pdf/Mills_1999_Conservation_Biology.pdf (and there’s more). I can’t point to any “big” decisions made based on them (perhaps because few management decisions are truly based on models, or because people prefer projections, or I just know too little about real management!).

    Regarding the list of zombie ideas, what about “more/less complex systems will be more stable”, given it has been showed repeatedly that it depends on the specifics (what network, what complexity measure, what stability, what variance of intraspecific interaction strengths…)

    • It’s as if every commenter on elasticity/sensitivity has taken population ecology at Calgary! When I teach this topic, I have the students read Mills 1999.🙂

      Full disclosure: all of my teaching of this topic is stolen shamelessly from Ed McCauley’s prep, back from the mid-oughts when he taught this course at Calgary. Which explains why the coverage is so good–Ed McCauley is good!🙂

  6. Jeremy, I am pleased to see this zombie ideas in ecology meme lift off again. Subfields, such as fisheries, are probably not relevant to the whole endeavour. But a nasty zombie idea in fisheries is that larger-bodied fishes have higher fecundity and hence must have higher capacity to sustain mortality and recover from overfishing. The reality is that rmax is negatively related to body size and hence while larger-bodied species lay more eggs their rmax is lower. Again related to the death of r/K larger fishes are just spread-betting in the planktonic lottery. This has been rebutted regularly over the past 15 years yet still gets wheeled out, particularly by agencies, but also in the academic literature.

  7. “zombie ideas–ideas that should be dead, but aren’t”

    Well applying the definition strictly: the assertion that the intermediate disturbance hypothesis is a zombie is itself a zombie (should be dead but apparently isn’t). I won’t repeat all the arguments here as we’ve done that to (near) death already (e.g., https://dynamicecology.wordpress.com/2013/09/03/a-thumbs-up-for-the-intermediate-disturbance-hypothesis-guest-post/ ).

    Would such a zombie-zombie be a meta-zombie or a zombie^2? Maybe we need a new term.

    • Douglas, the fact that I didn’t link to your post in the original wasn’t intended as a slight. I didn’t link to many posts of my own on the IDH. Including the recent one where I go beyond both your previous arguments and mine and suggest that it’s a “ghost” rather than a “zombie”.

  8. Maybe best seen as a rare, endangered and restricted range zombie/ghost-zombie. Sounds like it requires a conservation plan.

    • I may have to drop the whole zombie/ghost/lost cause/Buddy Holly ideas thing if we’re going to be having conservation-style debates. I don’t want to have a debate about whether some “subspecies” of zombie is an “ideologically significant unit”!🙂

  9. Hi Jeremy; I think there are several separate issues here. I will mention 2.
    First is ..whose acceptance of an idea constitutes Zombieization ( is this a word?)? Many folks in ecology, and particularly out of ecology, accept r/K selection, but few who actually work on life history evolution [ they use age structured models, W/WO density dependence and stochasticity]. Stearns ( 1977) raised all the classical issues about r/K, and many people over the yrs have critically examined the issues; r/K is critically reviewed in all the basic technical books on LHs [ charlesworth, stearns, roff]. Do I really care if someone who has never really looked at LH evolution just parrots back simplistic notions? sure do wish they would think more carefully about the issues, but … you tell me how to get people to do this? maybe I should care if they are part of a gov agency and make decisions based on the wrong notion [ a nod to N Dulvy].
    But a more important issue is not to label r/k a zombie, but to take from it WHAT IS PART of modern LH theory; I submit that question is …..what is the role of density dependence in LH evolution?( I usually assume non-growing pops, put DD in survival of the pre-reproductives, and end up using Ro as fitness). Some recent work from the larry Lawler [ U Arizona] lab shows that DD is needed to account for the LH of desert annuals; if ever a beast would be a candidate for a small role for DD, it would be annuals! Yet DD is needed even here. r/k was the early incarnation of this important LH concept. so in a real sense r/k lives…it just got evolved. most concepts in science are this way; their origins lie on the wrong side of the track, so to speak.
    I must confess that I am not a fan of labels{ like Zombie}, which may/may-not aid our thoughts.Labels sometimes take on a life of their own.

    • “whose acceptance of an idea constitutes Zombieization…Do I really care if someone who has never really looked at LH evolution just parrots back simplistic notions?”

      Good question. One characteristic of many zombie ideas in ecology is that they’re in the textbooks, widely taught to undergrads, and vaguely remembered and believed by researchers who don’t work on the topic, but are widely (not universally) disbelieved by researchers working on the topic. r/K selection is a great example. The IDH is another.* So one way to rephrase your question is to ask “Why should we care what’s taught to undergrads, or about the views of researchers on topics on which they aren’t specialists?” Rephrased that way, the question has some obvious answers! Related post here: https://dynamicecology.wordpress.com/2013/09/17/teaching-controversial-or-contrarian-ideas/

      “so in a real sense r/k lives…it just got evolved. most concepts in science are this way; their origins lie on the wrong side of the track, so to speak.”

      The question is whether older versions of the idea were basically on the right track, or basically off base but maybe with some kernel of truth. Which is a difficult judgment to make, particularly when older versions of the idea were presented verbally. So there’s often scope for reasonable disagreement. Is Darwin’s theory of how selection can drive diversification (“Principle of Divergence”) more or less the modern theory (as I think David Reznick would say, though I may be wrong about that)? Or is it subtly but importantly unmodern and wrong, as I’d say? Is Connell’s original version of the IDH basically just a correct summary of competition-colonization trade-offs, as Doug Sheil and David Burslem think? Or is it a difficult-to-parse intermingling of valid and invalid theories that in practice has mostly led ecologists astray, as I think? Is Hutchinson’s notion of overlapping n-dimensional hypervolumes basically a good theory of the niche, as many ecologists apparently think given that they’re happy to teach it to students? Or is it a seriously misleading metaphor, as I and Mathew Leibold (see Leibold 1995 Ecology) and many others think?

      “a more important issue is not to label r/k a zombie, but to take from it WHAT IS PART of modern LH theory”

      That’s a common criticism of zombie ideas rhetoric–that it risks throwing the baby out with the bathwater. I don’t buy that criticism, for a couple of reasons. First, because zombie ideas don’t get killed off. There’s no risk of throwing the baby out with the bathwater if there’s no risk of throwing out the bathwater. Second, nothing prompts people to revisit old ideas and try to separate what’s right vs. wrong about them like serious criticism of those ideas. Third, if what matters is correct ideas, not the labels we slap on them, why should anyone care if we stop using the r/K selection label, or the IDH label? Fourth, there are grains of truth in lots of old ideas in science that aren’t currently taught or used in research. You can explain the history of work on a topic and give credit where it’s due without actually teaching work that perhaps has an important grain of truth but has now been superseded. Chemists don’t teach Democritus’ atomic theory to students. And if they did, it would deserve to be called a zombie idea.

      “I must confess that I am not a fan of labels{ like Zombie}, which may/may-not aid our thoughts.Labels sometimes take on a life of their own.”

      I think rhetoric like zombie ideas is helpful to calling attention to widespread, important errors that seem to resist correction. But the term has been co-opted already (https://dynamicecology.wordpress.com/2015/04/09/peter-abrams-on-ratio-dependent-predation-as-a-zombie-idea/). I have an old post on the pros and cons of rhetoric in scientific writing: https://dynamicecology.wordpress.com/2011/11/08/on-rhetoric-in-scientific-writing/

      *Not all zombie ideas in ecology fit this pattern. For instance, a fair number of researchers working on species interactions in the tropics believe species interactions are stronger and more specialized in the tropics.

  10. I think it is premature to say that “species interactions are stronger in the tropics” is a zombie idea, in part because it hinges on how you define stronger.

    As for specialization, it certainly appears to be the case in some interactions, maybe not in others, and some we din’t know because we have no data.

  11. The first thing that popped into my mind from my field is the idea of “pollination syndromes”. I’m hoping Jeff Ollerton will chime in because he’s much more versed in the topic and I’m not even convinced that this fits entirely as a zombie idea. Wikipedia defines them as such: “Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic (wind and water) or biotic, such as birds, bees, flies, and so forth.” and that isn’t a bad working definition. Flowers are complex organs so viewing them as a suite of traits is useful however it is clear the ideas that 1. floral traits are shaped by pollen vectors alone and 2. floral traits can predict the pollen vectors are often false (and maybe zombie?). These two ideas pop up again and again in the plant-pollinator literature without the accompanying evidence although that is changing. But these ideas definitely hang out in textbooks! I think the attractiveness of pollination syndromes is that they intuitively make so much sense and simplify these complex traits and interactions. “Do you want to know about natural selection on floral traits? Look to the pollinators.” That is a much more simple idea then the one that other biotic and abiotic agents might drive selection on flowers and the suite of traits we see is a compromise of all of these agents. It is also a much easier approach to deciding who the important pollinators are than actually observing and testing all the visitors to the flowers. Jeff? You’re a zombie expert, should we add pollination syndromes to the zombie list?

    • Hmm, that could be a good one! My impression is that some researchers have recognized this and are trying to collect data to confirm if pollination syndromes are a thing, so it’s not a total zombie. But I can ask Lawrence Harder here at Calgary and report back.

      • I’d be really interested to hear what he has to say! My feeling is that there are elements of the idea that are good (with data to support in some but not all cases) but as a blanket concept it is too simple and often wrong.

  12. If pollination syndrome (viewed critically) is a zombie idea, then so is convergent evolution. Pollinators comprise components of the pollination environment of plants, as do abiotic conditions, herbivores, etc. Consequently, pollination by the same or functionally similar vectors (not just animals) would reasonably impose similar selection on unrelated species. To the extent that other aspects of the pollination environment have weaker effects on selection, this should generate phenotypic similarity. The possibility of such convergent evolution supports cautious reverse logic (similar phenotype suggests similar vectors). Such logic underlies the famed example of Darwin correctly predicting the existence of a hawk moth with a >12-inch proboscis in Madagascar after observing that Angraecum sesquipedale had a nectar spur of such length. However, reverse logic is a hypothesis and must be viewed as such until tested (as was Darwin’s prediction). The preceding characterization contains many caveats that should be recognized when considering pollination syndromes. For example, it is unreasonable to expect a single “bee-pollination” syndrome. There are >20,000 species of bees with very different morphologies and behaviors that would create very different pollination environments. Viewed judiciously, pollination syndromes are no more a zombie idea than is convergent evolution, both of which are hypotheses that need to be tested in an particular situation.

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