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Loose screws in the Ecosystem

Bill Meredith

"Never look to see for whom the bell tolls; it tolls for thee." John Donne, Meditation XVII

There seems to be no limit to the variety of questions people ask you when the word gets out that you are a biologist. My latest example came from a friend who reported that he was sitting in a lawn chair, peacefully reading a book when a beetle flew down and landed on the page before him. It was small, even as beetles go, and quite beautiful, with a metallic green body and white wings with narrow brown stripes. It seemed to find the book interesting; it crawled back and forth across the page, as if reading line by line. My friend had never seen a specimen like it; he found it more interesting than the book, so he watched it for several minutes. Eventually it flew away, but it left an important question for him to ponder.

The question began trivially, with, "What if I had closed the book and squashed the beetle? Except for making a messy splotch on the page, would it have mattered?" To this, I answered, "Probably not; although you have never seen one like it, no doubt there are many more of its kind, and no doubt many of them die in various ways every day. I’m glad you didn’t squish it, but in the biological sense it wouldn’t have mattered." But the follow-up was more profound: "What if I somehow wiped out its entire species? Would that matter?" The answer to this was not so easy, for it raises the central problem of biodiversity in ecosystems.

Biodiversity is the word used for the variety of different species of plants and animals that live in a particular ecosystem. When you begin counting things, you always find a lot of beetles; biologists estimate that there may be as many as a million different species of them in the world… more than any other kind of animal. Someone once asked J. B. S. Haldane, one of the most brilliant and controversial biologists of the 20th century, what he thought God was like, and he replied, "Well, He must have an inordinate fondness for beetles." But biodiversity involves more than just the number of species; it involves a pattern. In any well-balanced ecosystem there are only a few native species that are very abundant, and many species with fewer individuals. All of them, numerous or rare, are involved in complex relationships with each other. Some eat plants, some eat other animals; some are parasites or cause diseases; some recycle dead materials to enrich the soil; some pollinate plants, some modify the habitat so other kinds can find a place to live; and so on. These relationships become so complex and entangled that ecologists have not been able to work out all of them for even simple ecosystems.

Although the entire picture is not yet understood, we have known at least since the 1950s that when an ecosystem is disturbed by removing rare species and thus diminishing biodiversity, that ecosystem becomes unstable. For example, a species whose predators are removed may undergo a population explosion and destroy its food supply; other species that shared that food supply in happier times may become extinct. A domino effect follows; other plants and animals that were held in check by the extinguished species then go out of control. Removing a common species is even worse; recall how the destruction of bay grasses in Chesapeake Bay by overdevelopment and runoff from nitrates and other pollutants has affected crab and oyster populations. And introducing new species which do not fit into the web of relationships of an ecosystem can be equally devastating; think of the effect of gypsy moths on Maryland’s forests.

All of this went whizzing through my head when my friend asked if exterminating his beetle mattered. I knew I could not give a clear-cut answer to his question without explaining every function that beetle plays in the ecosystem, and I do not have that information… nor does anyone else. Somewhere there probably is a specialist who knows the Latin name of that little green, white and brown beetle, and knows what it eats, and what eats it, and a lot of other facts about it; but even such an expert doesn’t know all of its relationships with all the other components of the ecosystem. And I also knew my friend didn’t have several hours to spend listening to a lecture on biodiversity and niche differentiation. So the best I could do was to offer an analogy.

If you were driving down the road and a screw fell out of your car, would it matter? Clearly, it would depend on the function of the screw. If it held down the floor mat in the back seat, the answer would be, "No." But if the screw connected two vital parts of the brake or steering mechanism, its loss could be fatal to the driver, to passengers, and to anyone the car might hit when it careened out of control. All screws are not equally important; and likewise, any ecologist would admit that all species of animals are not equally important. The trouble is that it’s a lot easier to tell with screws. A good mechanic would be able to tell you the precise function of any screw in a car, be it a Model T Ford or the latest Mercedes. By comparison, an ecosystem is vastly more complex than any automobile, or, for that matter, any other man-made structure. So since we don’t know what that little beetle does, prudence suggests that we shouldn’t do anything to hasten its demise.

When the Endangered Species Act became law in 1973, rare species got some recognition by the public as well as some protection, but increasingly they are threatened by the loss of habitat. This is a critical issue in Maryland right now; the state government appears to be looking for ways to turn land that had been set aside as wildlife preserves over to developers. In order to make this palatable to voters, the Governor has called these areas "Surplus Land," implying that they are expendable. The rationale for this action is that it will raise revenue to offset budget imbalances; but this is a false pretext. As revenue, the sale of this land would be a small, one-time drop in the state’s deficit bucket; but it would be a permanent blow to biodiversity, and a guarantee of disruption to an ecosystem that is already under stress. Once started, the process of selling off protected land will snowball, and the effect on biodiversity will be clearly predictable. It will be like randomly removing screws from the car as you speed down the highway; sooner or later, a vital species will be lost and the ecosystem will crash.

John Donne had it right 400 years ago: "If a clod be washed away by the sea, Europe is the less." Once extinct, species do not come back. The bell that tolls for them also tolls for us.

Read other articles by Bill Meredith