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.

The Butterfly of Doom: Everything connected?

It is a banality of the ecological sciences to state that everything is connected. That ebullient Scot, and eventual stalwart of the American wilderness movement, John Muir, claimed, "When we try to pick out anything by itself, we find it hitched to everything else in the universe." And if such statements are employed to sponsor a notion that individual organisms cannot be regarded in isolation from those that they consume, and those that can consume them, or furthermore, that as a consequence of the deep intersections of the living and the never-alive, that there can been unforeseen consequences flowing from species additions or removals from ecosystems, then few may argue with this. However, just as the ripples of a stone dropped in a still pond propagate successfully only to its edges (though they may entrain delightful patterns in the finest of its marginal sands), not every ecological event has intolerably large costs to exact. True, if the dominoes line-up and the circumstances are just so, a butterfly’s wing beat over the Pacific may hurl a typhoon against its shores, but more often than not such lepidopterous catastrophes do not come to pass. Ecosystems, energized so that matter cycles and conjoins the living with the dead, have their lines of demarcation, borders defined by their internal interactions being more powerful than their external ones.  They are therefore buffered against many potentially contagious disasters.  This, of course, is the essence of resilience - the capacity of a system to absorb disturbance without disruption to habitual structure and function.  Ecology is as much the science investigating the limits of connections as it is the thought that everything is connected.

Decomposing Thought

Living things are born and die.  And living things rely for their living on the dying of other living things.  This is a central ecological thought – the decomposing thought.  A thought compelling enough to sustain an enduring research program: investigations of decomposition of dead organic matter (DOM) remain at the core of ecosystem ecology. These studies have promoted an understanding of the importance of the upper 5cm of soil – Earth’s tumultuous rind – where the roiling community of decomposers consume and transmute the apparent uselessness of dead flesh into the currency of ecosystems.  Input: DOM.  Process: decomposition by microbes regulated by the tiny champing of soil fauna – mites, springtails, and their divers kind. Output: energy for decomposers and the mineralization of the organic into nutrients available to the living. 

The God of Disruption – Is Genesis an ecological fable?

In the beginning was the disturbance: God disrupted the pristine formlessness of the deep and created the heavens and the earth. Literally in a flash. With His utterance, the darkness was relegated to Night; the light He called Day. Waters were separated from waters by an expanse, and the expanse was called Heaven. Vegetation, and their seed, sprouted from the Earth and then, the Good Ecologist provisioned vegetation with light to distinguish day and night, to separate the seasons, and to mark the passage of time. God started on the largest imaginable scale, and then He attended to the ecological details. On the fifth day the earth pullulated with creatures: birds in the air and the great sea swarmed with life. On the sixth day God successfully propagated the terrestrial surface with creeping things, beasts, and livestock. And then He made man and in giving him dominion over the creatures, explained the ecological services that each could provide – for instance, the plants He told him make good eating. When He rested, His creation was stable. That which He created in a cataclysm persisted in the aftermath.

When He was adequately restored, He resumed His labor. His tasks were now ones of governance rather than creation. The largest entities of all were stably in place – the heavens and the earth, the stars in the firmament, the day separated from the night, the seasons, the seas and the land, the vegetation and the creeping beings, the livestock and mankind. The world that God created though it persisted was an imperfect one. His creature, Man, fell and God expelled Adan and Eve from his Garden. The children of the first man and women fought and Cain slew Abel. The descendents of Adam were numerous; the very old gave way to the young; but God saw the wickedness of man and was sorry that He made him. In surveying the earth God thought it corrupt and was determined to disrupt it by ending all flesh. He commanded Noah, a righteous man, to build an ark, and on that ark Noah brought his family: his wife, his sons, his sons’ wives, and seven pairs each of all clean animals, and a pair each of unclean animal, and seven pair of each species of bird. And then God unleashed his Disturbance in the form of a flood. The flood remained for 40 days and the water persisted for 150 days. All flesh upon the earth died – beast and man. The sacrifice that Noah made of some parts of the clean animals and the clean birds pleased him and God made a covenant with man and with the animals. He determined never again to destroy all flesh.

Introducing the Rules of the Ecological Game: The descent of a flock of hierarchy theories in Manhattan, circa 1986

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).

From the universe as a whole down to the atoms: distinctions between community and ecosystem ecology

Tools of the trade: ecosystem ecology

In one of the more nerve-wracking moments of my early career I was informed that the ecosystem concept was “putting food on the family table.”  I was to stick to the methods of ecosystem ecology and not to waste time with community level questions.  By this I understood that I should not indulge an interest in individual organisms nor attempt to identify these to the species level – certainly this was consuming a lot of my time. I should not, I was told, become overly interested in species diversity, another community-level phenomenon.  Though ecology is rapidly changing, nevertheless as recently as a decade and a half ago you picked your favourite flavour early – if you chose chocolate it is frowned on if you started adding dollops of vanilla.

The ecosystem, as we have discussed, is a compound constituted by all the organisms of a region interacting with the non-living environment – soil, water, and atmosphere.  In modern ecology the ecosystem concept has become the foundation for functional studies of the environment, often at the landscape scale, where ecologists study the processes contributing to the flow of energy (primarily starting with the photosynthetic “fixing” of the sun’s energy by plants) and the cycling of nutrients.  For instance, a present-day ecosystem ecologist might be interested in how the rates of leaf litter decomposition in a woodland affects the availability of nutrients in the soil, thus influencing subsequent plant growth.  This functional interpretation of the ecosystem is contrasted with the approach taken by population and community ecologists who study the interaction of individual organisms, the growth of populations and the interactions that occur between individual of multiple species coexisting in the same place at the same time.