Thinking eco-logically and the food web of a bluebird
From Gene Logsdon (1999)
Garden Farm Skills
I believe my great backyard sphexes [cicada-killer wasps] have evolved like other creatures. But watching them in the October light as one circles my head in curiosity, I can only repeat my dictum softly: in the world there is nothing to explain the world. Nothing to explain the necessity of life, nothing to explain the hunger of the elements to become life, nothing to explain why the stolid realm of rock and soil and mineral should diversify itself into beauty, terror, and uncertainty. To bring organic novelty into existence, to create pain, injustice, joy, demands more than we can discern in the nature that we analyze so completely… The equation that can explain why a mere sphex wasp contains in his minute head the ganglionic centers of his prey has still to be written. There is nothing below a certain depth that is truly explanatory. It is as if matter dreamed and muttered in its sleep. But why, and for what reason it dreams, there is no evidence. ~Loren Eiseley, “Coming of the Giant Wasps,” Audubon, September, 1975
When you consider which plants, insects, and animals you ideally would like to share your backyard garden with, you think immediately of the most beautiful and beneficial creatures—perhaps bluebirds, luna moths, fiery searcher beetles, barn owls, bluegills, and foxes. You reject “ugly” or “harmful” creatures—pine voles, rosy apple aphids, starlings, and hognose snakes. This kind of thinking, perfectly logical when applied to a totally man-made environment like a house, won’t work when applied to nature. You can select and reject, to a certain extent, what enters your house: furnishings, pets, appliances, and friends. But you can’t choose between “friends” and “enemies” in a natural setting. The owls and the foxes must have the voles to dine on. The bluebird enjoys rosy apple aphids. The voles eat the luna moth pupae in their cocoons.
Even these simple observations about the food chain, or food web, as ecologists prefer to call it, in no way approach an accurate notion of the complicated interdependency of living things. Nature is a tremendous banquet table at which sits the eating being eaten. If each eater ate only one other species, then the human mind could map out some logical and more or less easy-to-follow graph of what was going on, but such is not usually the case. The everglade kite (Rostrhamus sociabilis) is a bird that lives almost exclusively on the apple snail, and the sharp-tailed snake (Contia spp.) lives on slugs, but most creatures eat a variety of other creatures, including in some cases, as with the praying mantis, its own kind. Snakes eat frogs and birds, among other things. Some bullfrogs and some birds eat snakes. Snakes, frogs, and birds eat spiders and wasps. Spiders eat wasps and wasps eat spiders. Crows will rob nests of other birds but, strangely enough, often will not molest nests close to their own. Foxes normally will avoid skunks, but when hungry enough, a gray fox has been known to climb a tree and drop upon a skunk from above. Meanwhile, within each of these creatures another food web is interacting: Parasites, along with bacteria and other microorganisms, interrelate with their hosts and with each other.
All this competition for survival depends upon causally unrelated factors such as favorable weather, the absence of which can have a greater effect on the population of any segment of the food web than the predator-prey process. Weather is an unpredictable phenomenon. So is, in any particular instance, wildlife road kill. Such factors introduce the element of chance into an already terribly complex system. Chance is not a concept that either the logician or the scientist cares to account for in his deductions. But an ecologist must try. He brings to his imperfect science a unique vision. He must seek truth eco-logically, rather than logically. He must seek explanations that transcend the cause-effect relationships the human mind uses to understand reality. For example, the human mind learns how a motor works by considering causal relationships. The battery “causes” the spark, which “causes” the gasoline vapors to burn and explode, which “causes” the piston to move, which “causes” the crankshaft to revolve, which “causes” the transmission to turn the wheels. Aha, says the human mind, now I understand how a piston engine works! And, for practical purposes, there is understanding. Equipped with that kind of knowledge alone, says the Dumb Farmer, “the dumbest teenager in town can keep a car running long enough to get to his girl friends house. It’s a matter of sheer logic.”
Such cause-effect, logical thinking isn’t nearly as helpful in trying to “fix” a natural environment. What “causes” an apple? Sunlight and water? The tree it grows on? The man who plants the tree? The apple seed? The soil it grows in? The nutrients that feed it? The microorganisms that break down the nutrients into a form the tree roots can use? The mycorrhizal fungi that allow the roots to absorb the nutrients? The pollinating bee? The bluebird that eats the aphids that would otherwise have withered the branch before the apple formed? Photosynthesis? Plant tissue? Protoplasm? Evolution? God? Philosophers have tried to overcome this “logical” problem by defining various kinds of cause, such as essential cause, first cause, approximate cause, instrumental cause, and so forth. But labeling causes does not help us to understand the apple, much less how to repair a damaged environment. In fact, long ago mankind unconsciously admitted the limitations of causal knowledge applied to the real world with the classic joke: which came first, the chicken or the egg? The question is unanswerable within a logical, causal framework.
Cause and effect are, of course, at work in the food web—or what we humans consider to be cause and effect. The process is not simply linear, however, as we suggest by using the phrase “food chain,” nor is it even geometric, as when we say “food web.” The interaction is explosive, implosive, exponential, and simultaneous, and therefore four-dimensional. As skilled as we are in marshaling numbers in our computers, the food web defies adequate programming. Introduce the factor of chance, and the computer can only run simulations. For example, if you kill a pair of mice in your house, the computer can quickly tell you not only how many millions of mice you theoretically “caused” not to be born in the next 50 years, but also how many of that number would have survived, given a “normal” mouse environment. What is normal? It is possible that by killing one pair of mice in your house, you allowed another pair to produce more healthy offspring than the two pairs would have produced together, if a shortage of food or habitat prevailed.
Attempts are being made to subject the food web to mathematical analysis in hope of finding keys to unravel the complexities of predator-prey interactions. Biologists such as Joel E. Cohen of Rockefeller University (Food Webs and Niche Spaces) are pioneering methods of reducing complex food web information into simple one-dimensional “interval graphs” that can be plotted on straight lines. Then they further convert the data into tables that can conveniently be fed into computers for analysis. Results are interesting to trained ecologists, although backyarders without backgrounds in mathematical analysis will have difficulty understanding the graphs, much less using the information practically in their gardens.
The Food Web of a Bluebird
Consider, for example, the bluebird and how to convert its small food web domain to meaningful analysis. About 80 percent of its food is insects, worms, and other small creatures. It also eats some wild fruit and weed seeds. Its predators—squirrels, raccoons, opossums, and skunks—mostly take young birds and/or eggs. The eggs, incidentally, are usually light blue, though they can be white. Some hawks and the great horned owl will eat adult bluebirds occasionally. The starling kills nestly bluebirds if it can get its head far enough into the nest. The house sparrow drives out the bluebirds and builds its own nest on top of the bluebird eggs. The larvae of a bloodsucking fly, hatching in the bluebird’s nest, can kill young bluebirds, too. Though rarely, lice and mites may be troublesome enough to cause nestling mortality.
While availability of food and nesting sites are the main problems for bluebirds, they also must contend with adversities somewhat incidental to their food web. Bluebirds enter stovepipes or downspouts and die when they can’t get out. They used to enter the aeration flues of old-time tobacco-curing barns, become trapped, and starve. Thousands of songbirds, bluebirds included, die during their migration, colliding with TV power boosting towers, tall buildings, monuments, and other structures jutting into the sky.
A bluebird mother may lay three eggs or seven or any number between. She may raise one brood or two, sometimes three. If she dies, the male may raise the hatched chicks. Or, he may not. Where there are no tree hollows to nest in, the bluebird adapts to holes in old corner posts of farm fences. When the old fencerows are bulldozed away, as commonly happens now, the bluebird adapts to holes in old corner posts of farm fences. When the old fencerows are bulldozed away, as commonly happens now, the bluebird may not be able to find suitable nesting sites at all.
A small lot owner, by the name of Smith, is surprised that one bluebird in his backyard ignored prevailing scientific theory and nested in a very un-bluebird type of box. The back of a conventional bluebird house had rotted away, making the nest more attractive to birds that nest on open shelves, such as phoebes and robins. Yet, this bluebird raised two broods on the shelf without being the worse for wear.
In the face of such complexities (and the enumeration above hardly brushes the surface), what chances are there to practice an exact science of ecology? As Smith explained while he erected yet another bluebird house on his property, “My bluebird houses are prayers of faith and hope, not acts of scientific certitude. Faith will save nature long before science will.”
Perhaps. Science pursues knowledge about nature in several ways. In its early days, science mostly involved identifying and classifying. Then researchers went on to study individuals and their parts in great detail, applying the knowledge gained to manipulate nature or to develop new products, all for the seeming benefit of man. Ignored, or at least often overlooked, in the process were the interrelationships between individuals and their environment, the study of which is called ecology. Overlooking these interrelationships scientists then assumed that by understanding individuals and their parts, they could understand adequately the whole of the environment—the communities of plants and animals and the soil water, air, and weather they depend on for survival. Such science easily spawned TV towers that kill thousands of birds annually, or developed a toxic chemical like DDT.
Identification and classification are essentially a logical process of deduction and induction. Smith sees in the woods for example, a black furry creature with a white stripe down its back and a bushy tail, rooting up a yellow jacket nest. Only one creature fits that description—the common skunk. Therefore, the creature must be a skunk, scientific name, Mephitis mephitis, which freely translates into “a godawful smell.” Applying the knowledge gained from studying individual skunks, and their parts led scientists to conclude that the odor of M. mephitis is not only nasty but amazingly enduring. If the cause of the bad odor could be separated from the cause of the endurance, then the skunk oil might make a good base for perfumes. And, indeed it does!
But the deduction and induction by which this kind of knowledge is acquired have limitations in all science, especially ecology. Deduction and induction can guide a person to build a proper “scientific” bluebird house, but whether a bluebird will actually nest in the house is another matter altogether. In the case of the skunk, deduction and induction can help one take skunks apart to make fur coats and perfumes but won’t help a bit in putting together used skunk parts into a living skunk again.
For ecology, and really for all science there is another kind of thought process that transcends deduction and induction, that is based more upon a vision than it is upon logically deduced or induced facts. This vision is aware of the sacredness of the life principle running through all living things, existing elusively beyond the most powerful microscope, extending to all living creatures, and possessed by none of them individually. The life of the tree from which the apple falls extends to the life of the soil; to the life of the bluebird that nests in the tree; to the life of the yellow jacket that eats the fallen apple; to the life of the skunk that eats the yellow jacket; to the life of the whole backyard that is linked biologically to the next backyard, extending at last to all living creatures. The fallen apple, though pronounced dead, teems with all kinds of creatures turning that deadness back into nutrients that will spark new life in plants and animals and begin again the long slow interwoven journey back through the explosive, implosive, cascading web of life. In a very real sense, no creature loses life, but instead is constantly reabsorbed into other forms of life. Real death can come only through a final, fatal disruption of the food web itself. This is the vision, the place of ecology: to witness and defend the sacredness of the natural web of life. It is a vision that is neither totally scientific nor religious, but one that combines both the pragmatism of the former and the solace of the latter. There is a way in which we can live forever, says the ecologist, if we will but preserve the inviolability of the web of life.
See also Gene’s A Death In The Family
Gene and Carol Logsdon have a small-scale experimental farm in Wyandot County, Ohio.
Gene is author of The Mother of All Arts: Agrarianism and the Creative Impulse (Culture of the Land),
The Last of the Husbandmen: A Novel of Farming Life, and All Flesh Is Grass: Pleasures & Promises Of Pasture Farming