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Out of Control

If it is true that nature is fundamentally in constant flux, then instability may cause the richness of biological forms in nature. But the idea that the elements of instability are the root of diversity runs counter to one of the hoariest dictums of environmentalism: that stability begets diversity, and diversity begets stability. If natural systems do not settle into a neat balance, then we should make instability our friend.

Biologists finally got their hands on computers in the late 1960s and began to model kinetic ecologies and food webs on silicon networks. One of the first questions they attempted to answer was, Where does stability come from? If you create predator/prey relationships in silico, what conditions cause the virtual organisms to settle into a long-term coevolutionary duet, and what conditions cause them to crash?

Among the earliest studies of simulated stability was a paper published in 1970 by Gardner and Ashby. Ashby was an engineer interested in nonlinear control circuits and the virtues of positive feedback loops. Ashby and Gardner programmed simple network circuits in hundreds of variations into a computer, systematically changing the number of nodes and the degrees of connectivity between nodes. They discovered something startling: that beyond a certain threshold, increasing the connectivity would suddenly decrease the ability of the system to rebound after disturbances. In other words, complex systems were less likely to be stable than simple ones.

A similar conclusion was published the following year by theoretical biologist Robert May, who ran model ecologies on computers populated with large multitudes of interacting species, and some virtual ecologies populated with few. His conclusions contradicted the common wisdom of stability/diversity, and he cautioned against the "simple belief" that stability is a consequence of increasing complexity of the species mix. Rather, May's simulated ecologies suggested that neither simplicity nor complexity had as much impact on stability as the pattern of the species interaction.

"In the beginning, ecologists built simple mathematical models and simple laboratory microcosms. They were a mess. They lost species like crazy," Stuart Pimm told me. "Later ecologists built more complex systems in the computer and in the aquarium. They thought these complex ones would be good. They were wrong. They were an even worse mess. Complexity just makes things very difficult -- the parameters have to be just right. So build a model at random and, unless it's really simple (a one-prey-one-resource population model) it won't work. Add diversity, interactions, or increase the food chain lengths and soon these get to the point where they will also fall apart. That's the theme of Gardner, Ashby, May and my early work on food webs. But keep on adding species, keep on letting them fall apart and, surprisingly, they eventually reach a mix that will not fall apart. Suddenly one gets order for free. It takes a lot of repeated messes to get it right. The only way we know how to get stable, persistent, complex systems is to repeatedly assemble them. And as far as I know, no one really understands why that works."

In 1991 Stuart Pimm, together with colleagues John Lawton and Joel Cohen, reviewed all the field measurements of food webs in the wild and by analyzing them mathematically concluded that "the rate at which populations recovered from disasters...depends on food chain length," as well as the number of prey and predators a species had. An insect eating a leaf is a chain of one. A turtle eating the insect that eats the leaf makes a chain of two. A wolf may sit many links away from a leaf. In general, the longer the chain, the less stable the interacting web to environmental disruption.

The other important point one can extract from May's simulations was best articulated in an observation made a few years earlier by the Spanish ecologist Ramon Margalef. Margalef noticed, as May did, that systems with many components would have weak relations between them, while systems that had few components would have tightly coupled relationships. Margalef put it this way: "From empirical evidence it seems that species that interact freely with others do so with a great number of other species. Conversely, species with strong interactions are often part of a system with a small number of species." This apparent tradeoff in an ecosystem between many loosely coupled members or few tightly coupled members is nicely paralleled by the now well-known tradeoff which biological organisms must choose in reproduction strategies. They can either produce a few well-protected offspring or a zillion unprotected ones.

Biology suggests that in addition to regulating the numbers of connections per "node" in a network, a system tends to also regulate the "connectance" (the strength of coupledness) between each pair of nodes in a network. Nature seems to conserve connectance. We should thus expect to find a similar law of the conservation of connectance in cultural, economic, and mechanical systems, although I am not aware of any studies that have attempted to show this. If there is such a law in all vivisystems, we should also expect to find this connectance being constantly adjusted, perpetually in flux.

"An ecosystem is a network of living creatures," says Burgess. The creatures are wired together in various degrees of connectance by food webs and by smells and vision. Every ecosystem is a dynamic web always in flux, always in the processes of reshaping itself. "Wherever we seek to find constancy we discover change," writes Botkin.

When we make a pilgrimage to Yellowstone National Park, or to the California Redwood groves, or to the Florida Everglades, we are struck by the reverent appropriateness of nature's mix in that spot. The bears seem to belong in those Rocky Mountain river valleys; the redwoods seem to belong on those coastal hills, and the alligators seem to belong in those plains. Thus our spiritual urge to protect them from disturbance. But in the long view, they are natural squatters who haven't been there long and won't always be there. Botkin writes, "Nature undisturbed is not constant in form, structure, or proportion, but changes at every scale of time and space."

A study of pollen lifted from holes drilled at the bottom of African lakes shows that the African landscape has been in a state of flux for the past several million years. Depending on when you looked in, the African landscape would look vastly different from now. In the recent geological past, the Sahara desert vastness of northern Africa was tropical forest. It's been many ecological types between then and now. We hold wilderness to be eternal; in reality, nature is constrained flux.

Complexity poured into the artificial medium of machines and silicon chips will only be in further flux. We see, too, that human institutions -- those ecologies of human toil and dreams -- must also be in a state of constant flux and reinvention, yet we are always surprised or resistant when change begins. (Ask a hip postmodern American if he would like to change the 200-year-old rule book known as the Constitution. He'll suddenly become medieval.)

Change, not redwood groves or parliaments, is eternal. The questions become: What controls change? How can we direct it? Can the distributed life in such loose associations as governments, economies, and ecologies be controlled in any meaningful way? Can future states of change even be predicted?

Let's say you purchase a worn-out 100-acre farm in Michigan. You fence the perimeter to keep out cows and people. Then you walk away. You monitor the fields for decades. That first summer, garden weeds take over the plot. Each year thereafter new species blow in from outside the fence and take root. Some newcomers are eventually overrun by newer newcomers. An ecological combo self-organizes itself on the land. The mix fluxes over the years. Would a knowledgeable ecologist watching the fencing-off be able to predict which wildlife species would dominate the land a century later?

"Yes, without a doubt he could," says Stuart Pimm. "But his prediction is not as interesting as one might think."

The final shape of the Michigan plot is found in every standard ecology college textbook in the chapter on the concept of succession. The first year's weeds on the Michigan plot are annual flowering plants, followed by tougher perennials like crabgrass and ragweed. Woodier shrubs will shade and suppress the flowers, followed by pines, which suppress the shrubs. But the shade of the pine trees protect hardwood seedlings of beech and maple, which in turn steadily elbow out the pines. One hundred years later the land is almost completely owned by a typical northern hardwood forest.

It is as if the brown field itself is a seed. The first year it sprouts a hair of weeds, a few years later it grows a shrubby beard, and then later it develops into a shaggy woods. The plot unfolds in predictable stages just as a tadpole unfolds out of a frog's egg.

Yet, the curious thing about this development is that if you start with a soggy 100-acre swamp, rather than a field, or with the same size lot of Michigan dry sandy dunes, the initial succession species are different (sedges in the swamp, raspberries on the sand), but the mix of species gradually converges to the same end point of a hardwood forest. All three seeds hatch the same adult. This convergence led ecologists to the notion of an omega point, or a climax community. For a given area, all ecological mixtures will tend to shift until they reach a mature, ultimate, stable harmony.

What the land "wants" to be in the temperate north is a hardwood forest. Give it enough time and that's what a drying lake or a windblown sand bog will become. If it ever warmed up a little, that's what an alpine mountaintop wants to be also. It is as if the ceaseless strife in the complicated web of eat-or-be-eaten stirs the jumble of species in the region until the mixture arrives at the hardwood climax (or the specific climax in other climates), at which moment it quietly settles into a tolerable peace. The land coming to a rest in the climax blend.

Mutual needs of diverse species click together so smartly in the climax arrangement that the whole is difficult to disrupt. In the space of 30 years the old-growth chestnut forest in North America lost every specimen of a species -- the mighty chestnut -- that formerly constituted a significant hunk of the forest's mass. Yet, there weren't any huge catastrophes in the rest of the forest; it still stands. This persistent stability of a particular composite of species -- an ecosystem -- speaks of some basin of efficiency that resembles the coherence belonging to an organism. Something whole, something alive dwells in that mutual support. Perhaps a maple forest is but a grand organism composed of lesser organisms.

On the other hand, Aldo Leopold writes, "In terms of conventional physics, the grouse represents only a millionth of either the mass or the energy of an acre. Yet subtract the grouse and the whole thing is dead."