The Ecosystem is a Unicorn: Does A Balance of Nature Exist?

A unicorn is described as having the legs of a deer, the tail of a lion, the head and body of a horse. It possesses a single horn which is white at the base, black in the middle and red at the tip.  Its body is white, its head red, and its eyes are blue.  Clearly, the only thing unreal about a unicorn is in the combination of its parts.  That is, a unicorn is less than the sum of its parts, assuming, that is (with a prayerful nod to Anselm of Canterbury), that existing in reality trumps existing in the mind, or in this case existing in the mind as in a series of disarticulated parts that are themselves very real.  

When an ecosystem is described as greaterthan the sum of its parts, as it was in Eugene Odum’s holistic conception of it, what is meant is that when the biotic components of ecological communities interact with the abiotic realm (that is, the formerly living and the never-alive), certain properties of the whole emerge that cannot be readily predicted from an analysis of the component parts.  This claim, made on behalf of the larger units of nature, was persuasive to generations of ecologists influenced by Odum’s textbook, first published in 1953 and now in its posthumously published 5^th edition (2005).[1]  However, in as much as Odum’s notion of the ecosystem manifests a Balance of Nature perspective it has almost universally fallen out of favor in ecology and, like the unicorn, is emphatically relegated to myth and fancy.

Read on at 3quarksdaily 

On Balance, a Battle: Simberloff (vs. Grene) vs. Odum on the Greek Roots of Ecosystem Ecology’s Enduring Appeal

[Recently I wrote about Eugene Odum’s ecosystem concept.  Its motto is that “the whole is greater than the sum of its parts.”  Odum’s view that natural ecosystems were integrated wholes which developed in a manner that parallels the development of an individual organism or human societies (a harkening back to the largely discredited views of Frederic Clements) was regarded with great suspicion by ecologists who saw the Balance of Nature view as obsolete and unhelpful.  I discuss one especially influential critique of Odum’s ecology in this post.  Since this is a rough draft of what will be a more comprehensive essay please feel free to comment if you think I stand in need of correction: no doubt I do!)]

Daniel Simberloff (1942 - ), an iconoclastic American ecologist, visited a variety of Irish zoological institutions in the early 1990s to examine collections of mustelid skulls (weasels, martens, stoats and so on).  He was doing so in order to test ideas about a phenomenon called ecological release – that is, changes in the anatomical characteristics of animals predicted to emerge in circumstances of reduced competition.  Ireland, a relatively small moist rock off the European coastline, has 20 terrestrial mammal species, compared to 42 in relatively larger island of Britain, and 134 on the European continental mainland.[1]  Therefore, one might expect that some anatomical characteristics of these mammals would differ between the Irish populations and their British and European counterparts, since in Ireland there are fewer species competing for resources in the same place at the same time. The size and shape of predators’ skulls, an aspect of these animals associated with that most ecological of characteristics, feeding, seemed an excellent feature to examine.  Consistent with the expectations of theory Simberloff confirmed that in many important respects these Irish mammals differed significantly from their British counterparts.[2]  I remember his visit well, not only because my friend John Lynch, then a brash young evolutionary biologists, now at Arizona State University (not quite as youthful, but still, thankfully, brash!) hosted him.  Simberloff had a comprehensive knowledge of the Irish fauna, and indeed was very familiar the work of most contemporary Irish naturalists; though some of them did not know him!

It should not have been a surprise to find Simberloff in Ireland since from the earliest days of his career he had been embroiled in an important controversy about the composition of island biotas.  In particular, Simberloff had been one of the first to experimentally test hypotheses about the so-called equilibrium theory of island biogeography which made predictions about the number of species likely to be found on islands of different sizes and located at increasingly distances from the continental mainland.

The theory of island biogeography is an equilibrium theory – a theory of balance, though balance meant here in a milder sense than in the holistic ecosystem concept of Gene Odum.  In 1967 in one of ecology’s more famous monographs, Simberloff’s mentor at Harvard, E O Wilson speculated along with mathematical ecologist Robert McArthur, that the number of species on an island was related to the geographical extent of the island, and emerged as a dynamic equilibrium between immigration and extinction rates.  Large islands and those closer to a continental shore enjoyed higher immigration rates – they are easier to find and colonize by species from the mainland, and in turn, by virtue of the larger populations which they can support, larger island experience lower extinction rates.  The equilibrium between these rates therefore predicted higher species richness on such large and/or close islands. 

To test this theory Simberloff and Wilson censused invertebrates on five mangrove islands off the Florida coast and then controversially chopped them up to create archipelagos of smaller islands.  They also defaunated some of them using methyl bromide (CH3Br) and observed the recolonization of insects in the years that followed.  In all cases they expected that the islands would re-equilibrate in a manner predicted by the theory.  Although the results of this audacious project confirmed many aspects of theory, nevertheless Simberloff urged caution both in interpreting these results as tests of the equilibrium theory and in extending these insights into conservation practice in mainland situations.[3]

There is much to be said about this work, its implications and the controversies that surround it, but let me just make the following remark: Simberloff’s commentary on the research showed a willingness to exercise caution in the interpretation of his own work, a commendable scholarly trait.  His prudence regarding the extrapolation of island biogeography to make general conservation prescriptions was noticeable[4].  Simberloff did not propose a “strategy of island faunal development”, and did not enter into discussion of whole faunas being in any way greater than the sum of its parts, that is, there is simply no attempt in his work at a holistic ecology of islands. 

Later, commenting on island biogeography he noted that both species number and species composition emerges as equilibria in several factors operating at the same time.  And these equilibria are frequently disrupted as a result of capricious events such as introductions or geological changes. Thus the equilibria are ultimately what he called “quasiequilibria” and are subject to long-term change. “‘Equilibrium’ in this sense is synonymous with "compromise," he said, “and the realization that island communities represent compromises parallels a Dawinian view that individual species are compromises.” Simberloff was prepared to argue an analogy between the equilibrium in species richness on islands and the optimizing of evolutionary forces, however, he did not succumb to a temptation to extend the analogy of island communities to organisms.  Though islands biotas might be balancing acts they are not superorganisms.  Patterns of species richness on island could be understood based upon the probabilistic outcomes of the comings and goings of individual biological populations.

I have dallied a little on island biogeography not only because it illustrates that ecology can propose theories of balance that do not make a commitment to holism but also because Simberloff  later became the most spirited critic of the Odum conception of the ecosystem.  There may be a balance in nature – ecological patterns emerging as a temporary balancing of forces – but there is no Balance of Nature.

The Last Great Balancing Act: Eugene Odum and the Strategy of Ecosystem Development

There was a small bust of Eugene (Gene) Odum in the lobby of the Institute of Ecology at the University of Georgia which bore the inscription “The whole is greater than the sum of its parts”.  It used to entertain me to see Odum, that spritely giant of ecology, pass by his own bust most days without remarking it much at all.  Lesser men might have glanced.  I showed it to my father once when he visited me in Georgia while I worked there in the 1990s.  His response after he read it was merely a shrug and he wondered whether the phrase actually meant anything.  My father was not the only one to wonder this.

In fact, the epigram was central to Odum’s holistic understanding of ecology.  In the mid 1960s he wrote that there were two types response to discussions about ecology as a system’s science.  One group of responders would affirm, he thought, that “any school child knows that the whole is not a sum of the parts”, but another “remains unconvinced that there is anything really new or different at ecological levels that can not be ultimately explained either by the reduction of the whole into even smaller parts…”[1]  Identifying the most appropriate unit of analysis was critical to humanity adequately addressing of its environmental problems.  Odum recognized the ecosystem as that unit of analysis.  As he defined it, a definition that remains serviceable in contemporary ecology, the ecosystem was

“made up of all the organisms in a given area (that is, “community”) interacting with the physical environment so that a flow of energy leads to characteristic trophic structure and material cycles within the system.”[2]

Asserting that the ecosystem whole was greater than the sum of its parts meant that ecological analysis restricted to another ecological level – individual organisms or biotic communities, for instance, would fail to capture the dynamics of nature in a way that permitted us to ameliorate our impacts. 

The attributes of ecosystems, properties which for the most part could not, according to Odum’s adage, be predicted from an examination of the components constituting the ecosystemic whole include the following: community energetics (production, standing biomass, nutrient cycling, and overall metrics of ecosystem stability).  In his list of 24 ecosystem attributes Odum includes metric of biotic community structure, life history and strategy since lower ecological levels may not add up to the properties of the whole, nonetheless the whole may constrain the parts.

By defining the ecosystem in a holistic fashion, one with characteristics such as balance, integration, the possession of emergent properties, stability, equilibrium, attainment of a steady-state, and homeostasis, Odum tied his ecology to a venerable tradition, one that dates to the earliest Greek conceptions of the natural order known as the Balance of Nature.  The Balance of Nature defined in the most general terms is where the interrelated components of a system operate in harmony, thereby reflecting a stable equilibrium of traversing forces.  This dynamic harmony persists unless disturbed by external interventions.  Odum’s unit of concern is primarily the ecosystem, but since his ecosystem is the upper-level entity that constrains those levels below it in the ecological hierarchy, therefore where he expresses a Balance of Nature perspective it ramifies throughout the entire system.