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Invasion of the ecosystem.

Invasion of the ecosystem

While geneticists and ecologists are arguing about the likelihood of small genetic changes influencing the impact of an organism on its environment, Peter Vitousek of Stanford University proposes that it may be more useful in the long run to consider what happens when a totally foreign species moves into a new habitat. Genetic engineers, he says, hope eventually to make many changes in organisms--for example, to create a "supercrop' by adding to a plant species genes for nitrogen fixation, disease- and pest-resistance, higher productivity and easier harvest.

The addition or deletion of a single species can change important properties of an ecosystem, influencing the regulation of energy flow and the cycling of chemicals, Vitousek reports after considering examples of deliberate and accidental species introductions. "These can be a major nuisance, an economic problem or even cause extinctions,' he says. Ecosystem upset is more likely with an introduced animal than with a plant, and domestic animals can be especially destructive.

"It is not easy to find clear examples of plant invasions altering system properties,' he reports. "The invader must have access to resources not available to the natives or else must be more efficient in their use.' In one identifiable case, he points to a deep-rooted, fast-transpiring tree that, when introduced into southwestern wetlands, turned them into a desert. When the U.S. Park Service eliminated the trees, the wetlands returned.

In contrast, it is not difficult to demonstrate altered ecosystems in response to animal invasions, Vitousek says. For example, feral pigs, now present in 11 states and spreading rapidly, drastically change the characteristics of ecosystems by their rooting in the soil. In the Great Smoky Mountains of North Carolina and Tennessee, he reports, regions examined that are not inhabited by pigs have no bare ground, while in comparable regions with pigs 88 percent of the ground is bare. The pigs also change the levels of calcium, phosphorus and nitrogen in the soil. "Changes in soil fertility result in changes for every species in the ecosystem,' Vitousek says.
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Title Annotation:effects of introducing new species to an ecosystem
Author:Miller, Julie Ann
Publication:Science News
Date:Jun 29, 1985
Previous Article:Gene travel: plasmids around the world.
Next Article:Lessons from biological pest control.

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