On the Balance of Nature
Old ideas of balance and harmony need to be put aside if we are to save a natural world in constant flux.
…The stability of this ancient yew woodland, capable of rebuffing storms, insect outbreaks and other moderate disturbances, embodies an original tenet of ecology going back to the late 19th century. I’m talking about the so-called ‘balance of nature’. Henry David Thoreau coined the word ‘succession’ to describe the predictable and progressive development of vegetation from the weedy colonisation of newly exposed rocks to the stable and balanced state of a mature system. Bare ground is colonised by a few hardy plants. These give way to a new suite of species, which in turn can be superseded by yet more species. At last, mature vegetation (forest trees, for instance) establishes itself and persists, generation after generation. Succession was ecology’s first significant conceptual scaffolding. Upon this, the young scientific discipline was built. Nature in this view of things is stable and balanced until humankind, that agent of derangement, interferes with it, after which it can wither away.
The term ‘balance of nature’ raised the hackles of some scientists as early as the first decades of the 20th century. The Oxford ecologist Charles Elton forcefully claimed in his book Animal Ecology (1927) that ‘the balance of nature does not exist, and perhaps has never existed’. Nonetheless, it remained central to the highly influential systems thinking of the late and celebrated American ecologist Eugene Odum. Think of an ecosystem as something like an individual organism: the adult develops in an orderly, predictable way from the child. Similarly, Odum argued, the trajectory of natural systems was preordained too.
Perhaps it says unflattering things about me that I felt bored, impatient even, in these minutes waiting for my demise
In the mid-20th century, Odum modernised the concept of succession, so central to early ecology. He turned it into a mechanistic account of how organisms and their environments interact to produce orderly and predictable results. He identified 24 trends that might be expected to develop as ecosystems mature, each of which was like a physiological marker of a functioning organism. One of these was ‘overall homeostasis’ — the ability to retain equilibrium in the face of change, just as our bodies keep a stable internal temperature. The ‘development’ of a mature ecosystem led to a stable whole. When severely disturbed, the system would simply rebound to balance.
One of Odum’s favourite catchphrases was that ‘the whole is greater than the sum of its parts’. Complex ecosystems contain surprises just as living organisms do — this explains some of the force of the superorganism analogy. Due to its complexity as a system, a living body has qualities that its constituent parts cannot have. If you can’t imagine emergent properties, think of a carcass that has lost the body’s lustre and, with it, the emergent properties of the living.
Odum was explicitly committed to the idea of a balance of nature. Stability and equilibrium were at the heart of his ecological thinking. But it hovered in other, less obviously philosophical, ecological thinking too — such as the theory of island biogeography posited in 1967 by Robert MacArthur and EO Wilson. This theory predicts that the number of species on an island will be the outcome of a dynamic balance; an equilibrium, that is, between immigration to an island and extinction rates of those populations.
The trouble was, an attachment to ideas of balance and stability didn’t seem to match the messy dynamic reality of nature. And, increasingly, ecologists were troubled by what it all meant. Daniel Simberloff, a former graduate student of EO Wilson’s, was the one to pull the old ‘balance of nature’ idea to pieces. His work in community ecology, looking at the distribution and diversity of species, led him to see it as hardly a scientific idea at all.
