Unpopular ecological opinions: on what ecological topics are you skeptical of the conventional wisdom?

Time to share your unpopular opinions about ecology: are there any widely-held ecological ideas that you’re skeptical of? Ideas that many other ecologists think are well-established, but that you think are still open questions, or even false? And what are you doing about your skepticism, if anything? Have you used it as the basis for a grant application, for instance, or does it affect how you teach the idea in question? Tell us in the comments!

Here are some examples to get you started:

  • I’m skeptical of the intermediate disturbance hypothesis, to the point of calling it a “zombie idea” (a widely-held idea that should be dead, but isn’t).
  • I’m skeptical of the idea that there’s community-level selection for stable communities, because unstable ones won’t persist. Although I have no idea how many people believe that idea so maybe it’s not a good example.
  • Jeff Ollerton and Angela Moles are skeptical that species interactions always are stronger and more specialized in the tropics.
  • Ambika Kamath and Jon Losos are skeptical of the idea that Anolis lizards are territorial–and now they have the data to show they were right to be skeptical. That paper is a great case study of how an idea can get established on shaky grounds, and then never get unestablished because subsequent generations of researchers just take it for granted. This is why science needs contrarians.
  • Our own Brian McGill was part of a working group that was skeptical of the idea that local species richness is declining everywhere. They compiled the data to show that it’s not, a result that proved controversial.
  • Can’t find it now, but Stephen Heard has said here that he’s skeptical of the consensus that insect herbivores don’t much affect plant population dynamics, feeling the question is ripe for further research.
  • Charley Krebs is skeptical of the value of microcosm experiments in ecology, which as best I can tell has long been a minority view.

p.s. The premise of this post is that professional disagreement is a normal part of science and worth talking about. Disagreement arises because science is hard and nobody’s infallible (very much including me).

 

 

71 thoughts on “Unpopular ecological opinions: on what ecological topics are you skeptical of the conventional wisdom?

  1. Rats, I was going to come and leave “I’m skeptical that insect herbivores don’t affect plant population dynamics” but you’ve worked that right into your post. Anyway, the reason you can’t find it is that I’ve had 1/2 of a blog post written about it for almost a year. Got to finish that one some time! In the meanwhile, there’s this paper: https://www.sciencedirect.com/science/article/pii/S0006320711002461 (paywall, but if anybody can’t get a copy let me know and I’ll send you one.)

  2. I’m skeptical that co-occurrence matrices and correlation networks tell us anything useful about interspecific interactions.

    • +1000. That makes at least two of us!

      I’d be curious how many ecologists share this skepticism. Many of my friends do. But they’re a small biased sample of ecologists obviously.

    • Dave, is it fair to interpret this as saying that you don’t believe that interspecific interactions have an effect on the co-occurrence or correlation of species in a community?

      • I won’t pretend to speak for Dave, but personally I’d say that they have effects–often big ones!–but that you can’t back those effects out of the co-occurrence or correlation matrix.

        Inferring causes from effects often is impossible.

        If you haven’t done so yet, I highly recommend Alison Barnier’s recent Ecology paper, linked to an earlier comment, and the other paper from another rocky intertidal group in the same issue. They both tested a range of standard co-occurrence/correlation-based approaches in circumstances in which those approaches have *the best possible chance of working*. And those approaches failed *completely*.

      • Hi Jeff, I definitely think that interactions can influence species coexistence and resulting correlations. Like Jeremy writes, the problem with these approaches is analogous to non-identifiability in parameter estimation. There are often two or more mutually-exclusive explanations for the observed pattern.

      • Dave and Jeremy, I’ve only had a quick look at Alison’s paper and will have a closer look at it but, if species interactions have major effects on co-occurence and correlations then how can co-occurence and correlation matrices not be useful in examining the effects of species interactions? Are your arguments more than ‘correlation doesn’t imply causation’? Because, if that’s the totality of the argument (and it may not be) then the implications of your position extend far beyond correlation or co-occurrence matrices… they extend to the utility of observational studies.

        It seems that the logical arguments here are – (Inferring causes from effects often is impossible + something analogous to non-identifiability in parameter estimation) = co-occurrence/correlation matrices tell us nothing about species interactions. That doesn’t seem to be true to me. Shouldn’t the the right hand side of that equation be “co-occurrence/correlation matrices can’t tell us everything about species interactions”? If so, that’s a much different conclusion.

        Conclusively inferring cause from effects is often impossible but that doesn’t mean that effects don’t tell us anything about causes. While it’s true that correlation doesn’t imply causality it’s also true that causality does imply correlation. Judea Pearl has developed a pretty impressive logical structure demonstrating how to infer causality from observational data. Further, if we were constrained to controlled experiments to draw conclusions about cause and effect, doctors wouldn’t advise people to avoid smoking if the want to reduce their chance of getting lung cancer.

        The position that co-occurrence and correlation matrices don’t ‘ tell us anything useful about interspecific interactions’ is, in my mind, a too extreme response to some ecologists taking the position that all we need to know about species interactions can be found in co-occurrence and correlation matrices. Neither position seems warranted by logic or the empirical evidence. Jeff

      • This probably isn’t the response you were expecting Jeff, but would you be willing to look at a draft book chapter on this and give me feedback?

      • Hi Jeff, my point wasn’t that causality can’t be derived from observational data. Of course it can. In the case of these specific frameworks, however, the effects of species interactions (which are typically never characterized beyond being positive or negative) are confounded with a variety of other factors including things like predation, disease, habitat heterogeneity, demographic stochasticity, competition-environment covariance, etc. Tacked on top of this is the often nonlinear nature of interspecific interactions. For instance, species’ responses to competitors can be flat across much of the range of their competitors’ densities, but then spike at a particular threshold. Such an effect could feasibly result in a correlation of zero between these species when surveyed at certain densities and lead a researcher to conclude that they do not interact. If, as in the case of your smoker analogy, a large amount of high-quality data were available to control for these factors, then perhaps the approach would be more fruitful.

    • Hi Dave, I agree with the points you make about confounding effects and nonlinear effects but when they result in zero correlations despite inter-specific competition likely occurring, that information is useful. The information shouldn’t be used to make inferences about the existence of inter-specific interactions but they can be used to make inferences about the relative importance of inter-specific interactions. And the criticism that we may not see evidence of a real driver causing an effect in observational data because (1) other drivers are more important or (2) that driver wasn’t important at the time or the level at which the data were collected is true of any inferences from any observational data set. We need to pay attention to these caveats, we need to try and identify additional or alternative data that will distinguish among hypotheses that co-occurrence matrices can’t distinguish among but we also need to understand that co-occurrence and correlation matrices may have very important contributions to make to questions about species interactions.
      I suspect we aren’t as far apart on this as I initially thought and the whole discussion has forced me to crystallize my thoughts on it – so, thanks for throwing it out there.

  3. I’m kind of skeptical about the idea that species diversity inevitably depletes as you ascend a latitudinal gradient from the equator. Reason being, at least for large animals, we are already living ina depauperate world relative to the late Pleistocene, early Holocene. I admit that I have not done a lot of research on this – not my area – but was the late Pleistocene diversity of fauna that much lower on the great plains than in the grasslands of the tropics? Perhaps the evidence is stronger for tree diversity, since no temperate or boreal forest could compete with the 300 – 400 trees per hectare that you get in the tropics. But we do know that the Ice Ages were an enormous filter on species diversity in the northern hemisphere, and that tree diversity, certainly in Europe, was quite a bit higher.

    • Interesting! Not my area either. I vaguely recall reading somewhere that for most groups for which there’s a decent fossil record, the latitudinal diversity gradient goes back 10s of millions of years at least, indicating it’s not just a post-Pleistocene transient, at least not entirely. But my memory could be *totally* wrong. Perhaps my mammalian paleontologist colleague Jessica Theodor will see this thread and comment.

    • Yeah – the latitudinal gradient goes back 100s of millions of years in diverse organisms. It tends to flatten out more when seasonality is less extreme (due to orbital variations) but it is always there.

    • I was waiting for someone to say that. 🙂

      That’s another for which I’d be very curious to know the distribution of opinion. Is there a broad consensus in favor of the generality of the dilution effect? Or is it more that there are two opposing camps, each comprised of a substantial fraction of ecologists with an opinion on the matter?

      • There’s definitely two camps, but I don’t know about the distribution between them. One interesting aspect of this controversy that sometimes gets overlooked: This is not a debate between dilution effect proponents and amplification effect proponents. (Most) everyone agrees that biodiversity protects against infectious disease in some cases. The debate is about the generality of the phenomenon.

  4. I have a problem with nutritional ecology of “woodeaters”.

    The activity of digestive tract symbionts is known to play a role in balancing the diet of insects that utilize suboptimal plant resources as their food, and in this context, xylophagous insects are believed to survive and thrive utilizing polysaccharides as either a direct food source or as a resource for their digestive tract symbionts. However, according to the law of the conservation of mass, this is insufficient because the constituent atoms of nutrients cannot be created by organisms from the available biomass. Therefore, the elemental composition of wood limits the available nutrients, although symbionts are able to increase the digestibility of woody matter and synthesize important organic compounds from nutrients furnished by dead wood. Polysaccharides and lignin, even when split into atoms, are a source of only three chemical elements (C, H and O). This is not enough to enable the growth, development and functioning of a living organism. Even considering the ability of symbionts to directly assimilate the fourth essential element (N) from the atmosphere this is still not enough, since a source of other micronutrients is required to synthesize physiologically essential organic molecules (e.g., RNA, metalloproteins, enzymes, structural proteins, phospholipids, nucleotides and vitamins). Therefore, wood alone may not be an appropriate food source for many saproxylic insects, even considering the activity of their digestive tract symbionts.

    • Interesting! Way outside my field so I have no idea if you’re right. But FWIW your argument makes total sense to me.

      Have you made this argument to other people in your field? If so, how have they responded?

    • A bit of a similar story with hummingbirds that are thought of as nectar feeders which is just sugar water. But in fact hummingbirds eat a fair amount of insects especially during growth and reproduction.

      I wonder if the fungi in wood could be an alternate source of nutrients?

      • Oh yes, fungi act as “transfer pumps” relocating nutrients from outside sources to dead wood and making this system nutritionally appropriate for xylophages. And they relocate specific nutrients in specific proportion.

        I get the impression that in terrestrial ecology in general the main focus is on adult organisms, which functionality is mainly limited by energy and only a little attention is paid to the fact that the ability of an organism to build a fully functional adult body is influenced by the availability of body-building nutrients during the juvenile stage. And this juvenile limitation may shape communities, populations, flow of nutrients in ecosystem, etc.

      • Re “I get the impression that in terrestrial ecology in general the main focus is on adult organisms, which functionality is mainly limited by energy”

        Definitely the story in the hummingbirds. Only in the brief times a hummingbird is a juvenile or a mom has juveniles in a nest are insects a notable fraction of the diet.

        But in forest ecology, undue attention is instead paid to the seedling and sapling stages as these are “limiting” stages. Which mistakenly led ecologists in the 1970s to conclude saguaros were going extinct because there were no juveniles even there were a multitude of healthy adults. Turned out later they are just episodic recruiters that only successfully recruit ever 20-30 years (usually during an El Nino).

        I think the real underlying truth is we study what stages are tractable and easiest, and spin stories about why that is OK. But we certainly miss

  5. Thanks again, Jeremy, for the link to our work! I have shameless plug for an empirical paper on mating systems in Anolis sagrei that, I hope, helps go beyond simply being contrarian and tries to refocus the trajectory of science on what the animals in question are actually doing. Here’s a blogpost about it: https://ambikamath.wordpress.com/2018/03/12/territoriality-attempting-a-one-two-punch/
    And, very excitingly, we’re also in the process of responding to two rebuttals to our historical review, that I think together have the chance to carry forward this debate about territoriality and mating systems in a way that I hope will be lasting–they should all be published in the next few months, so if this is your kind of thing, keep an eye out!

  6. Regarding the controversy around local declines in species richness, the latest salvo is here:
    “Is local biodiversity declining or not? A summary of the debate over analysis of species richness time trends” Cardinale et al 2018
    https://www.sciencedirect.com/science/article/pii/S000632071732089X

    with an accompanying editorial
    https://www.sciencedirect.com/science/article/pii/S0006320717321286

    Vellend discusses the original rejection of their 2013 PNAS paper in a chapter in the book
    “Effective conservation science: Data not Dogma” Kareiva et al ed. 2018.

  7. Via Twitter:

  8. I’m skeptical of the idea that there’s community-level selection for stable communities, because unstable ones won’t persist.

    And, despite usually people don’t express this idea so clearly, it is implicitly included in several statements. For instance, it is very common that authors uses the stability of ecological networks as explanation for the emergence of network-level features (e.g. nestedness and modularity). I am really skeptical with this idea. I can’t see how the evolution of the species involved in each interaction could be driven by the global stability of the network. This seems group selection (and teleological evolution) for me.

    • “And, despite usually people don’t express this idea so clearly, it is implicitly included in several statements. For instance, it is very common that authors uses the stability of ecological networks as explanation for the emergence of network-level features (e.g. nestedness and modularity).”

      Yep, exactly.

      There’s a very good Am Nat modeling paper on this in a food web context, that unfortunately has been little noticed as far as I can tell (sorry, blanking on the author just now). It’s from several years ago. Looks at how the structure of randomly-generated food webs differs from those that are constrained to exhibit “permanence” (roughly, that means every species bounces back if it ever gets too rare, rather than going extinct). Turns out that selecting for stable food webs by imposing a permanence constraint has basically no effect on food web structure. Permanent food webs don’t look any different than randomly-generated ones. I wouldn’t say this paper’s the last word by any means, but it’s the sort of thing we need a lot more of before we should take vague, implicit community-level selection arguments very seriously.

  9. I’m skeptical that autocorrelation is something to go gray over. I’ve used it as more of an opportunity for learning and representation of the world as it is. However, I’ve been raked over the coals for saying/doing so.

  10. I am skeptical that adding ecology to agriculture, as in agroecology, can improve what agronomy/soil science/crop science achieves. Not that we ignore ecology, but what we call crop or production ecology is mainly autecology and simple interactions. This is why I, as an agronomist, lurk here reading your very interesting blog posts.

    • Interesting! I know nothing about agronomy or agroecology, so I’d be interested to hear about some examples if you’d like to comment further. Are you thinking of stuff like managing the farm and surrounding land to ensure crop pollination by native bees vs. having to truck in commercial honey bees?

      • No, more like what Vandermeer and Perfecto propose in their book, Ecological Complexity and Agroecology, which has chapters on the Turing mechanism and geometric pattern, chaos, and coupled oscillators. Not being an ecologist, I am not sure where these topics stand within ecology, but they don’t seem promising for agriculture.

      • Ah, ok, I’m with you now, more or less. John Vandermeer started out in fundamental theoretical ecology, he wrote a textbook on it. He’s done some great stuff; his PhD dissertation involved a classic protist microcosm experiment, really ahead of its time. I’m not familiar with his agroecological work though. But judging solely from that book title, yes, I can see why one might be skeptical that that sort of work would translate into practical ecological advice for farmers (which in fairness may not have been the main goal?)

  11. I’m skeptical of most of the projected impacts of climate change on species distributions using either correlative and/or mechanistic models. For several reasons but the big ones are (1) extrapolation outside the data range (2) extreme publication bias due to fear of misinterpretation of a study somehow refuting that climate change is in general real and bad and (3) various assumptions and lack of data to parameterize convincing mechanistic models. But I also think there is an opportunity for progress given increased availability of open data these days. I think Brian has been on a few very cool papers pushing the boundary in this field, but in general I’m skeptical of mostly all current approaches.

    • Yes! If your standard is to predict which 1/4 of a continent a species will live in when it invades, these models work pretty well, but for any finer grained or more precise predictions, test after test after test shows pretty severe limits. It seems to me the rate of negative publications in this area is accelerating. It will be interesting to see where the field heads.

    • Yes! I’m especially wary due to the publication bias you mention and the lack of large-scale and detailed mechanistic models. Unfortunately I think developing the latter is highly limited by current computing power and lack of wide spread, repeated studies (also related to publication pressures).

  12. I’m sceptical to the argument that considering more and more ecosystem functions should make biodiversity become more and more important.

    For example, the title of the article “Multiple functions increase the importance of biodiversity for overall ecosystem functioning” (https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/06-2091.1) is misleading. I have a feeling the conventional wisdom is just as the title of that Ecology paper, and that this idea about biodiversity and multifunctionality has the potential to become a zombie idea.

    But I may of course be wrong.

    • Interesting.

      Random aside: did you only realize that the title of your Ecology paper was misleading after you published it? Why did you choose that title originally? Just curious.

      • Yes, I started realising it was misleading years after it was published, around three years ago (if my memory is correct).

        I/we chose the title at the time, beacuse I/we really thought we were on the right track, and we thought we were on to something really cool. And I spent much time and energy on the subject the following years. I will do my best to assist in revising the field.

    • A lot of people I really respect and who creative and diligent research work on biodiversity-ecosystem multifunctionality research — but all the same, I can’t think of a sub-sub-niche of ecology that I’m more wary of!

  13. Here is a cheeky one that might be more of a “Hot Take” and not even be unpopular.

    “Species Diversity causes/drives (ecosystem) function X” is always wrong in a technical sense, because species don’t interact with the world via their names, but via their traits.

    Logic: If you can manipulate x and it has no effect on y, then x is not a cause of y (with caveats).

    Thought Experiments:
    a) taxonomist splits/lumps a set of species all of which are present in the system. When the paper is published, Diversity has changed, Function has not.

    b) If we were able to physically manipulate species diversity (by altering composition) in such a way that the composition of the functional trait(s) was unchanged, would function be affected? (No)

    c) If we were able to physically manipulate composition of the functional trait(s) (by altering composition) in such a way that the species diversity/richness was unchanged, would function be affected? (Yes)

    Conclusion: Species diversity (sensu stricto) does not drive ecosystem function

    If by “Species Diversity causes/drives function X”, what we really mean is that “ecosystem function x is determined by the interaction of environmental conditions and traits (identities or values) associated with more than one species, such that if we changed species composition in a way that alters the distribution of the “functional” traits, then ecosystem function X would change”, a more correct, interesting and meaningful summary of this result would be “Function X is sensitive to changes in aspects of species composition (via changes in the distribution of functional trait(s) Y)”

    extra spicy corollary: while there is often a “species richness correlation”, there is no such thing as a “species richness effect”.

    • That is cheeky. 🙂 Like all good trolling*, it raises an important point: what exactly do we mean by “effect of species richness on ecosystem function” (or on anything else)? For instance, in my work applying the Price equation to BEF (Fox 2006 Ecology), part of what I’m up to is redefining the effect of species richness on ecosystem function. If each species contributes some amount of function to the total, then by definition total function equals mean function per species multiplied by species richness S. So in the Price equation, “effect of species richness” just means “the change in ecosystem function that would occur if you changed species richness but didn’t change mean function per species”. Which of course kind of ignores/avoids/dodges your point, because the Price equation is silent on the mechanistic reasons why those S species have whatever mean function per species that they have.

      *”Good trolling” is a rare beast!

      • Yep, the Price equation is mathematically silent, but the language used to name the mathematical entity implies a cause (i think). I interpret “species richness effect” to mean “the effect of species richness” which suggests that species richness is the cause (i.e. the thing that leads to the effect).

        important side note: You make a clear case for the possibility of the non-causal interpretation in the text of the paper (even offering a alternative grouping of entities!). All the same, I still have a hard time not interpreting the name as clearly implying causality, which might(?) be misleading.

  14. Via Twitter:

    Random aside: without wanting to criticize anyone who chooses to comment via Twitter–I’d much rather have folks comment via Twitter than not at all!–I often find myself wishing that folks tweeting their responses to the post title would comment here rather than just tweeting. I don’t know enough about the very brief tweeted responses like this one to fill in the missing background information and context. So I can’t really respond except to ask “Can you elaborate?” Which I suppose I should do if I really cared about fostering discussion. But I find it hard to carry on substantive discussions one tweet at a time. It’s a pain to ask someone to elaborate, then have to ask again because I still didn’t follow everything in the tweet-length elaboration, and so on. Plus, I tend to assume (probably correctly in some cases, incorrectly in others) that anyone who really wanted to elaborate would’ve either commented here or written a threaded series of tweets in the first place.

    In fairness, anyone who just wants to comment briefly and not get involved in an extended conversation might well consider it a pain to be asked to elaborate! Different strokes for different folks, obviously.

  15. I’m sceptical that species distribution models as they are commonly applied can tell us much very meaningful about the niche of the species. For me, the problem lies with the fact the data used to paramerise the SDMs is the result of a ‘realised’ process whilst we often interpret the predictions as the result of a ‘fundamental’ process and say things like “this is the potential distribution of the species”. The fact that there is now a whole subdiscipline of biogeography that goes on use the outputs of SDMs to estimate ‘niche overlap’ and perceived ‘niche shift’ in key species makes me worry that are building towering intellectual structures on foundations of sand.

    • Interesting. SDMs coming in for a fair bit of criticism on this thread. Not really my field, but there are at least some SDM folks who worry about this issue, right?

      I know William Godsoe has been thinking about it, but more from a theoretical angle.

  16. I’m skeptical of the idea that interactions between plants and light ought to be understood primarily in terms of light limitation and competition for (scarce) light. In many plant communities, excess light — leading to declines in photosynthetic efficiency, and changes in temperature and water relations — could be a major driver of community structure, but (with a few exceptions) we’ve done a poor job of testing that. This is probably most important in places where something else (temperature, water, soil nutrients) limits photosynthetic rates, but I suspect (without clear proof) it’s really quite common even in some systems we normally think of as highly productive.

    I don’t many people would dispute this idea if pressed, but it’s not something a lot of people think about.

  17. Just to clarify, Jeremy, it’s truer to say that “Jeff Ollerton and Angela Moles are skeptical that species interactions are *always* stronger and more specialized in the tropics.” Sometimes they are, sometimes they are not.

    A postdoc and myself are writing up a study using a plant family-level dataset that shows that (in this case) tropical species have more specialised interactions with pollinators than those at higher latitudes. That’s the opposite of what I found with a different plant family. Although some may interpret that as evidence against what I’ve previously written, in fact it’s not, it just shows that the idea that “tropical plant-pollinator interactions are *always* more specialised” is a zombie idea. There are similar examples with regard to strength of interactions, as Angela has shown.

  18. Via Twitter:

    Yep:
    https://dynamicecology.wordpress.com/2012/10/09/can-the-phylogenetic-community-ecology-bandwagon-be-stopped-or-steered-a-case-study-of-contrarian-ecology/
    https://dynamicecology.wordpress.com/2012/10/19/another-attempt-to-stop-or-steer-the-phylogenetic-community-ecology-bandwagon/

    This is another one where I’d be especially curious to know the mix of opinion in the field as a whole.

  19. Pingback: Poll results: here’s what our readers think about some of the most controversial ideas in ecology | Dynamic Ecology

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