TAKE HEED YE YOUTHFUL SCHOLARS: books discovered in your tender years will influence your thinking for decades to come. In 1987 while surfing the stacks of the library of CUNY Graduate School in Manhattan, I plucked off the shelves a copy of Hierarchy: Perspectives for Ecological Complexity by T. F. H. Allen and Thomas Starr (1982). Shortly after this I picked up a copy of a monograph by R.V O’Neill and his colleagues (including T.F.H. Allen) entitled A Hierarchical Concept of Ecosystems. I recall that this volume was regarded with a measure of scorn, albeit a bemused rather than a vicious scorn, by several of the ecologists who taught me at the time (primarily population and community ecologists). It was this book, placing the ecosystem into the framework of a more general systems theory, that ultimately had the longest lasting influence on me in terms of my conception of how the complexities of nature can be made tractable.
Hierarchy theory was in the air back them. Perhaps one should say “hierarchy theories” since the observation that many of the complexities in the world can be resolved into structures comprised of parts within parts within wholes is not only a commonplace observation; it is one that has been theorized in many disciplines. Herbert Simon, a leading figure in developing this perspective, was an economist, Ilya Progogine, a chemist, Howard Pattee, a theoretical biologist, Jean Piaget a developmental psychologist. Hierarchy theory draws upon more general systems theory developed by luminaries such as Ludwig von Bertalanffy and James Grier Miller, both theoretical biologists. These early students of complex systems developed ways of thinking about commonalities between disciplines whose objects were structured as nested sets of parts within wholes (in more mathematical terms, hierarchies are a partially ordered set).
In the 1980’s it was not only ecologists who were discovering the usefulness of this body of thinking. Around the time that I discovered the Allen and Starr book I attended a lecture at Queens College, given by Stan Salthe, an evolutionary biologist from Brooklyn College, who was promoting his book Evolving Hierarchical Systems: Their Structure and Representation. Salthe not only looked like a wizard, but had accumulated a bewitched following for his book. The graduate student who introduced him, assured Stan that his was the first book he had consumed in one sitting since William Peter Blatty’s The Exorcist. Consoling, no doubt. Over at the Field Museum, Niles Eldredge the paleontologist and co-proposer of punctuated equilibrium (a pattern of rapid evolutionary shifts after long periods of stasis), had just published Unfinished Synthesis: Biological Hierarchies and Modern Evolutionary Thought. I spent quite a bit of time working with this material. A number of months later I gave a seminar on hierarchy theory to the Zoology Department (as it was then), at University College Dublin. My good pal John Lynch, now at Barrett Honors College at Arizona State, reminded me recently of how incomprehensible this seminar was. I suppose some ideas need to be digested slowly. So here (and in the next post), a quarter of a century later is why I think this is useful.
IN RECENT POSTS I HAVE BEEN DISCUSSING THE ECOSYSTEM CONCEPT named over 75 years ago by Arthur Tansley. The concept was proposed in the context of debates about the development of vegetation systems (towards a so-called climax state) and about the identification of the ecological structures that exist along a scale from the universe to the atom. Hierarchy theory is appealing to ecologists and evolutionary biologists because it usefully contributes to thinking in the most fundamental terms about the complexity of nested systems and the behavior of system parts as they interact with one another. In evolutionary debates hierarchy theory has been applied by those looking for a salve to evolutionary perspectives taking a very gene-centric view of the process, since wholes can constrain parts as much as parts contribute to the whole. Salthe concluded his opus by suggesting that “it nothing short of myopic to believe we can understand how this hierarchy of taxa [species, genus, family etc.] was produced by trying to construe it as having been only by way of organism level (or even demic level [population]) processes!” In his preface Salthe approvingly cites van Valen’s maxim, and a very Darwinian one it is too, that “evolution is the control of development by ecology.” Therefore, in examining the usefulness of hierarchical thinking in understanding the persistence and dynamics of the ecosystem, one should be able to draw not only upon the regional versions of this thinking developed by ecologists, but upon insights into hierarchies drawn from across those disciplines that have applied it.
In my next post I will briefly outline the utility of viewing the ecosystem as a hierarchical system. If this strikes you as useful for the problems upon which you personally ponder, I refer you to the book-length treatments of the topic alluded to above.