A constructionist perspective on the structure of ecological complexity, follow-up questions

It would be interesting to investigate why the constructionist perspective on ecological complexity (see below) is overlooked. One answer is that people haven’t come across what has been written on that perspective by me and others. But I’m more interested in why hasn’t it been discovered and enunciated by others for themselves and why they don’t discuss its implications once they know about it. This post presents the idea again (quoting from a 2010 post, which draws from Taylor 2005, 3-17) then reviews Robert May’s response to it over the last 30 years.

Robert May’s theoretical work in the 1970s [is often cited–I mean often] as showing that, because “the more complex a randomly built food web, the less stable it is… real networks must have some contrasting, nonrandom structures that allow them to persist despite their complexity.” [M]ore attention [could be given] to lesser-known theoretical work from the 1970s and 80s that showed that, whereas stable systems may be extremely rare as a fraction of the systems being sampled (May’s result), they can be readily constructed over time by the addition of populations from a pool of populations or by elimination of populations from systems not at a steady state. Under such a “constructionist” perspective: stable complex ecosystems need not be weakly interlinked modules of populations—they can be more richly interactive; the range of mathematical possibilities that modelers can consider is extended; persistence of complexity does not necessarily require devious strategies (ongoing turnover of populations may be all that is needed); complexity can be constructed in ecological time without shaping of interactions by natural selection; complexity constructed in ecological time depends on its spatial context; and complexity might be better conceived in terms of intersecting processes, not well-bounded systems.

If you follow the links to my 2000 letter to Science on this issue, you’ll see a reply from Robert May saying that his “1973 book expresses exactly Taylor’s sensible argument that real ecosystems ‘develop’ by adding, and losing, species over time, not by randomly sampling ecological possibilities.” It was nice to have his endorsement of my argument, except that my reading of his 1973 book is different. We agree that “Nature represents a small and special part of parameter space” (1973, 75), but he sees this having been “[shaped ultimately by evolutionary forces acting on individuals]” (2010 reply). It is evolution that creates the “devious strategies which make for stability in enduring natural systems” (May 1973, p. 174).

In the early 1980s, after a presentation I gave to the Population Biologists of New England conference as a PhD student on the construction of stable model ecosystems over time, May spoke to me explaining that evolution for him included the development over time I had described. Given that most people hear “evolution” as natural selection, I thought it was helpful to distinguish between the ecological time scales of ecosystem construction and the longer evolutionary time scales of fine-tuning inter- and intra-specific interactions.

Fast forward to 2000 and the exchange of letters (see above), then fast forward to an article of his I only read this week, his 2009 review of “Food-web assembly and collapse: mathematical models and implications for conservation.” Here May reviews the complexity begets instability result, then remarks:

as strongly emphasized at that time (May 1973), real food webs are most certainly not randomly assembled. They are ultimately the winnowed products of evolutionary processes. In short, this work… refocus[ed] the agenda to address the question of what are the structural mechanisms whereby real food webs and ecosystems reconcile complexity… with persistence in the face of environmental buffetting (p. 1643).

He goes on to review the “empirical data and theoretical ideas about how food webs are assembled and structured” (p. 1644), but makes no mention of the idea that the “winnowing and “evolutionary processes” could be as simple as the “addition of populations from a pool of populations or by elimination of populations from systems not at a steady state.”

In relation to my question “why hasn’t [the constructionist perspective] been discovered and enunciated by others for themselves?”, let me note that this perspective is obscured by the ambiguous term assembly, which is used in ecology to describe patterns of linkage and species co-occurrence without reference to data about trajectories of construction over time. Perhaps the patterns will point to elucidation of processes of “assembly” over time–or at least exclude some hypotheses about processes–but the pattern-process connection is not a simple one in ecology (see, e.g., Austin 1987). Noting that May does not distinguish the pattern from the process meanings of “assembly,” and taking into account the other exchanges dating back 30 years, my other question seems relevant” “Why they don’t discuss its implications once they know about it?”

Again, this is not a complaint about people not reading my work clothed as a question–I freely concede that I have not stuck with the issue and tried to build recognition and support for the constructionist perspective. It is a genuine question, which, if explored, might show us something about the way conceptions tend to be shaped in non-historical ways by the modeling and data analysis tools that ecological theorists use. Perhaps there is also something to look at about the decline in confidence that society is well-ordered that became evident on the streets in the 1960s and in the social sciences since the 1970s? Or….? — suggestions and insights welcome

Austin, Michael P. 1987. Models for the analysis of species’ response to environmental gradients. Vegetatio 69: 35-45.
May, Robert M. 1973. Stability and Complexity in Model Ecosystems. Princeton, NJ: Princeton University Press.
—-. Food-web assembly and collapse: mathematical models and implications for conservation. Philosophical Transactions of the Royal Society B 364: 1643–46.
Taylor, Peter J. 2005. Unruly Complexity. Chicago: University of Chicago Press.


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 )

Google+ photo

You are commenting using your Google+ 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 )


Connecting to %s