Ruth and I watched a very moving movie last night at our local art house. “The Serengeti Rules” is a beautifully produced story of the discovery of a very important feature of ecosystems. Seen through the eyes, mouth, and work of six ecologically oriented scientists, the film focuses on the role of “keystone species” as the glue that sustains the integrity of ecosystems. The film is the work of Sean B. Carroll, himself a biological scientist. For those that cannot find the film, he has written a book with the same title that tells the story.
Classic models of ecosystems were largely built on a hierarchical model with ascending trophic levels, beginning at the bottom with plant species that rely on solar energy and produce their own food through photosynthesis. Moving toward the top level are, first, herbivores that consume stuff from level 1; then, carnivores that eat the herbivores; and, finally, bigger carnivores (sometimes called predators) that eat the lesser ones.
Seeking to understand why some rich ecosystems become barren or monocultures, Robert (Bob) Paine discovered a different kind of relation among the species in a stable, rich ecosystem. His lifework is summarized in a memoir written by his colleague and admirers. Rather than try to capture its importance I have extracted a paragraph.
What Bob meant by this phrase was shown in his first demonstration that certain species were ecological keystones. It occurred when he experimentally manipulated distributions of the carnivorous purple (or ochre) sea stars, Pisaster ochraceus, [shown in the image] along the rocky coast of Mukkaw Bay at the westernmost tip of Washington State, across the Juan de Fuca Strait from Canada’s Vancouver Island. At low tide, these starfish grip the rocky shoreline with thousands of tube feet. Bob pried Pisaster off the rocks with a crowbar and pitched them into the sea. Within two years after Bob and his team removed starfish from a stretch of shoreline, California mussels (Mytilus californianus) started to monopolize primary space of the rocky substrate that had formerly supported a rich biota of tunicates, anemones, sponges, mussels, barnacles, chitons, limpets, and various seaweeds. Pisaster feeds extensively on mussels, along with other prey, including barnacles, limpets, chitons, and snails. But lacking Pisaster, mussels are the competitive dominate for primary space. Where starfish were extirpated, mussels established a near mono-culture, and local species diversity of the primary space occupiers collapsed. Along control shoreline areas where the starfish were not removed, the original diverse community persisted. Five years after the experiment began, when starfish removal was discontinued, the mussel-dominated community persisted, as mussels had escaped in size from starfish predation. Bob had discovered that one keystone species, the purple sea star, kept the diverse structure of its community from collapsing.
The story continues with the other scientists finding similar “keystone” species in a variety of ecosystems ranging from small ponds to the huge Serengeti plain. Another example shown was deforestation on isolated islands caused by the absence of army ants which allowed their normal prey, leaf-cutting ants, to defoliate, weaken and eventually kill all the trees. The deterioration of the Yellowstone park ecosystem, after the grey wolves were removed, may be more familiar to many of my followers.
Ecosystems remain rich and stable as long as the keystone species is present to prevent other species from taking over or to provide some other critical function. In the Serengeti, the keystone species is the wildebeest, whose dung provides the nutrients that support the grasses that, in turn, nourish other species, and so on and on. During years that the wildebeest population was decimated by rinderpest, the system languished. After the rinderpest scourge was brought under control, the herds eventually recovered and have grown to a stable size that holds the complex ecosystem together. The story of the Serengeti is, itself, worth finding and watching the film. Having been there some year ago, the film brought back memories of the extraordinary impact of seeing nature in full bloom.
Side-by-side photos of ecosystems in their barren and rich states transformed the film’s scientific importance into an existential lesson. We humans are really connected to the natural world; certainly, in fact, but, importantly, also in spirit. Photos of barren places, created by human encroachment, jar the senses and emotions. The explosion of deer populations, resulting from the removal of keystone predators, has turned into a widespread nuisance in many suburban areas. The film ended, however, on a positive note, with stories of the potential restoration of ecological richness by human interventions.
There is another important story here, but not one that is part of the explicit words and pictures. Rich, that is stable, flourishing, sustainable, ecosystems are highly interconnected, complex systems. The hierarchical, mechanistic models of earlier ecological theory could not describe the phenomena that these scientists were observing. Human societies and their institutions are complex in the very same way.
Paine and his colleague discovered these relationships in these complex ecosystems through careful observation, not by applying theories. Indeed, their work pointed to the limits of those theories. They lived with their systems, playing with them over long times, until they were able to come to new powerful truths. Their frame was pragmatic, as opposed to the conventional scientific methodology. They examined the whole, not isolated parts taken out of context. Human societies are also complex ecologies. A visitor from another planet would see humans merely as another life form among many others. We should be following the lead of Paine and his colleagues whenever we try to understand how our own cultures, another name for our human ecosystems, work. Only then can we avoid what Whitehead called the fallacy of misplaced concreteness and the terrible unintended consequences that follow.
The Earth, now that we are moving into the Anthropocene epoch, is increasingly becoming more and more barren. Restoring its health seems possible if we begin to replace the current top predator, Homo economicus (modern human beings), with a closely related species I call, Homo curitans, the caring human being. Both species share the same body; they differ according to which brain hemisphere is the master. Imagine the immense difference we humans can make in restoring the Planet to flourishing, simply by altering the balance in the structure of our brain. It can be done!
ps. The word sustainable, can be properly used in reference to these rich, stable, flourishing ecosystems, but not to unstable, ever growing human settlements.