Are there general laws in ecology?

John Lawton. Oikos 84(2): 177-192. Are there general laws in ecology?

Dunbar harbour (Will Pearse, 2006)

Dunbar harbour (Will Pearse, 2006)


Will Pearse

Will Pearse

This week Lynsey and I are trying something different, and we’re covering the single most-important paper I’ve read, because it made me study ecology. Hence the picture above these words is one I took a few years beforehand, during an internship where I was doing a lot of marine biology.

While natural history was always interesting to me, ecology seemed very dull. Everything depended on very specific details (“this leaf miner eats this particular plant when there has been that much rain in November”) and with so little generality I never saw the point. When Lawton almost gleefully noted that he “can summarise twenty years of work on bracken at Skipwith in a short paragraph”, it was a breath of fresh air. Apparently there were these people called macroecologists who asked questions so simple I had always naively assumed we already knew the answer. I decided, almost as soon as I finished the paper, that I wanted to be one of those people who asked extremely (hopefully embarassingly) simple questions, and as such started to understand generalities among systems. I saw Lawton’s focus on contingency as almost a call to arms – if things are contingent, figure out why they’re contingent, and how the rules of that contingency operate.

Reading it again now, I notice that, part-way down page 180, Lawton notes that examining “taxonomic relatives” might provide “some progress” in dealing with this overwhelming sense of contingency. I try and work phylogeny into ecology precisely because I feel it is the only way of generalising across, and finding links among, profoundly different systems with no species in common. I am always struck by the work on network motifs, and have a great hope that one day I will uncover some grand unifying repeating motif in the phylogenetic structure of assemblages. Indeed, if community phylogenetics is an attempt to link wider source pool dynamics (how did those species evolve and migrate to form a source pool) into community ecology, then perhaps the field is a response to Lawton’s call for more people to listen to Rickleffs. I’m reading ‘Maximum Entropy and Ecology’ at the moment, and I’m struck by how much of the book seeks to find a mechanistic underpinning for the nine ‘general laws’ that Lawton laws out at the end of the article. Long may the search for an understanding of these laws continue.


Lynsey McInnes

Lynsey McInnes

Will and I decided we were getting a bit lax with our PEGE commentaries so we thought we’d shake things up a bit with some classics. Will wasted no time in choosing this paper by John Lawton, so off we go.I never thought of myself as an ecologist until I joined a department of population geneticists and realised I definitely wasn’t one of them….yet. So I’ve spent the past 6 months honing my ecology skills, hoping to merge them into some population genetics as and when…I enjoyed this paper a lot. I hadn’t read it before, so it was a fun read. I took too major points away from it, one, community ecology really is a bit dodgy and two, why macroecology can be exciting (but doesn’t appear to have moved on much since 1999).

The enthusiasm Lawton has for ecology and ecological patterns and processes is infectious and I felt like I had to say thank you to him for really driving home the message that general patterns are exciting when found, mostly because they are damn hard to find, especially in that mesoscale of community ecology, less so in the fuzzy, broad brush scale of macroecology.

I’ve always been dubious of community ecology, especially of its latest incarnation meshed with phylogenetics. Conclusions always seem to depend on how you circumscribe the question and few communities appear genuinely comparable. So, if patterns are hard to detect, processes are even harder to ascribe to these shadowy patterns.

And then you have macroecology which is all about patterns. Satisfying ones too, most clades follow latitudinal diversity gradients, Bergmann’s rule, Rapoport’s rule, exceptions make sense, its all great. But all these patterns were already known when Lawton wrote his paper, and 14 years later it doesn’t seem like macroecology has moved on much. We are still finding more and more patterns, the hypotheses on the underlying processes are proliferating, the methods to detect these things are getting more and more jazzy, but it doesn’t feel like we know anything much more than we did then. Why is that?

I kind of feel like macroecology, perhaps just like community ecology, doesn’t work because it’s all at one scale. Patterns don’t just come about at a single macro scale. They are built up from individuals, populations, even communities. Lawton seemed really keen on revelling in the really clear patterns he could see at the macro scale, but if we want to get at process maybe we have to delve down into that murky world where general laws and even general patterns most certainly don’t exist. I know for sure this is not a new idea! The Razgour et al. paper we covered a couple of weeks ago is just one example of a paper that brings together all sorts of data from the population to the macro level to understand the fate of a single species. The Ferri et al paper from a few weeks earlier took a comparative look at niche evolution by splitting up multiple species’ ranges into cold and hot extremes. This is definitely the way I think advances can be made, go below the species level to find out stuff emergent above the species level.

I still reckon Lawton’s conclusions will remain unchanged. General laws are damn hard to find, their pursuit can be self-defeating (but also a lot of fun) and they are mega exciting to stumble upon.

Advertisements

About will.pearse
Ecology / evolutionary biologist

4 Responses to Are there general laws in ecology?

  1. jeffollerton says:

    Lynsey writes that “14 years later it doesn’t seem like macroecology has moved on”. I have to disagree because new techniques and data availability is allowing us to address questions we were not able to do so before, e.g. the role of current versus past climate in determining present day community patterns. See for example [shameful plug warning]:

    http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0025891

    We simply could not have done this 14 years ago.

    • lynsey83 says:

      HI Jeff,
      You are right, techniques and data have both proliferated in the intervening 14 years. I guess my point was it is surprising (perhaps it’s actually not surprising given Lawton’s thesis) that despite this proliferation I don’t feel like we have progressed THAT far in really understanding emergent macroecological patterns. Maybe we never will and the fun to be had is in the trying?

  2. dmcglinn says:

    Great discussion Will and Lynsey! Just found out about your blog via the Ecobloggers aggregator. The Lawton paper is an especially timely classic paper to discuss because it seems like the search for general laws is slowing down and progress is now being made on testing and unifying general patterns in ecology. Brian McGill’s Unification of Unified Theories is a good example of how some of this unification is taking place. David Storch and colleagues provide a nice visual example illustrating a better conceptual unification (http://mcglinn.web.unc.edu/files/2013/09/storch_etal_2008_fig1.png) of general laws in ecology. Will mentioned John Harte’s METE which is another great example of how we are developing predictions not for a single pattern but for a whole suite of patterns, see for example (my own shameless plug):

    http://arxiv.org/abs/1308.0731
    and
    http://arxiv.org/abs/1308.0655

    Another important direction that the research appears to be taking is that we are developing a better understanding how biology or context dependence can be built into these general models to make more nuanced predictions (e.g., Pawar et al (2012) http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature11131.html).

    Thanks for the great post and keep the ideas rolling.

  3. lynsey83 says:

    Hi Daniel,

    Thanks for commenting, glad you like our blog! Thanks also for all the links. The Storch et al. fig isn’t exactly ‘nice’, but looks really useful…As an aside, the Pawar et al. Fig.1 is brilliant – looks like a great paper too.

    I agree that progress within the field of ecology in general is being made by these cool studies integrating across scales, merging generalities and context dependencies. I’m happy to be shot down, but I still don’t think this constitutes progress within the field of macroecology, more a step away from it following a full on acknowledgement that assigning processes to such broad patterns might be impossible?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: