Opportunistic Species Gain In Battle for the Backyard
By WILLIAM K. STEVENS
Published: March 1, 1994
JUST outside the kitchen windows of suburbia, nature's wild, desperate dance of life and death takes place almost unnoticed, veiled by the tame surroundings. But as the suburbs continue their relentless expansion into formerly wild habitats, a complex new order of ecological conflict is playing itself out.
At the struggle's center is a hardy, opportunistic group of native North American species with both the intelligence to adapt quickly to suburban surroundings and the eclectic appetite to take advantage of the wide variety of foods that suburbanites wittingly and unwittingly serve up. Crow and blue jay, mallard duck and Canada goose; squirrel, cottontail, skunk and white-tailed deer: together they and other seemingly innocuous species are emerging as collective winners in give-no-quarter combat with a much larger number of more sensitive and less adaptable species that include many songbirds and uncommon plants.
Scientists fear that as the adaptable victors proliferate and spread, the less flexible species will be driven out and suburban ecosystems -- which now display more biological diversity than do many rural areas -- will become impoverished and unstable.
If the situation is not dealt with, ecologists say, the results could be catastrophic. In the current issue of the journal Conservation Biology, three ecologists wrote that the populations of many native species that thrive in environments altered by humans "will increase and overwhelm more sensitive species, predictably leading to biotic impoverishment and threatening the ecological integrity of many communities, ecosystems, landscapes and regions."
"In turn," they added, "many of these overabundant species will come into conflict with humans."
The article, by Dr. Robert A. Garrott and P. J. White of the University of Wisconsin and Dr. Callie A. Vanderbilt White of the University of California at Davis, is an attempt to aim a spotlight on a largely neglected area of study and action. While conservation biologists have lavished much attention on plants and animals from abroad that run wild and crowd out native species in America, they have given relatively little thought to native species that act the same way, the authors said.
Few areas of the country actually remain pristine, and to the extent that they are disturbed by humans, they favor the spread of these native dominators. For this reason, Dr. Garrott and his colleagues wrote, controlling and manipulating populations of disturbance-loving native species will become increasingly important as the populations grow and spread in seminatural areas.
The suburbs are the focus of this developing struggle because that is where humans have provided especially attractive and nourishing environments for animals that thrive in disturbed areas, because people come into contact with wild animals more often there and because the suburbs are home to a greater variety of wild species than either the city or the farm. The city has much less green habitat, while the farm's domination by a handful of crops and grazing animals makes it too simple an ecosystem. Many other disturbed stretches of rural landscape, like logged areas, are also poorer in species than are the suburbs.
The suburb is a relatively new and highly distinctive ecological form characterized by an equally distinctive wildlife community. Humans have quite unintentionally determined the makeup of the community, and to the extent that some species become dominant and others weaken, people are acting much like an instrument of natural selection. Changing the Landscape
On one hand, they have taken away some landscape features that favor certain species, said Dr. Larry W. VanDruff, an ecologist at the State University of New York at Syracuse who has studied the suburbs. People, who seem to like open, savannalike surroundings, reduce tree cover that is home to some birds. Cavity-dwelling species like woodpeckers find a paucity of nesting places as old, dead trees are eliminated, although some of these species continue to frequent the suburbs for the seed and suet people leave out.
People also eliminate the brushy understory of woodlands to create lawns and other open spaces. With the understory goes a variety of insects on which birds like flycatchers and swallows depend, and so their numbers dwindle. Mowing and insecticides wipe out still other bugs on which particular bird species depend.
Fish and amphibians tend to lose out as well because of water pollution and alterations of aquatic habitats that make them unfit for breeding.
On the other hand, these manmade landscapes favor certain other animals -- the adaptables. For these, people produce a whole new array of potential dwelling places: ledges, crevices, holes, storm sewers, bushes, chimneys and countless others.
Garden vegetables and flowers make succulent meals for many omnivores, as does the food people put out not only on purpose, in bird feeders, but also inadvertently, in the garbage. Suburbia is easy street for creatures like the raccoon, which will eat almost anything (except onions), the crow, whose diet includes some 600 items, and gulls, which have been known to snatch french fries out of the hands of children at fast-food restaurants, according to Dr. David M. Bird, a wildlife biologist at McGill University who works at Ste. Anne de Bellevue, Quebec.