Iowa State University

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Born to be bad?
by
Bob Hartzler

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Sept. 2, 2004 - The study of invasive plants has increased dramatically in recent years due to the increased potential for plant movement with the global economy, and an increased appreciation of the value of natural habitats.   A recent article in Science (Science.  2004.  Vol. 305:1100-1001) summarized information presented at the 2004 meeting of the Ecological Society of America regarding the origins of invasiveness.

It has long been assumed that a primary reason for an introduced plant being invasive is that it is simply placed in a favorable environment and is released from the natural enemies (insects, diseases, etc.) that suppress it in its native land.  However, ecologists recently proposed that species may evolve to become invasive after they have been placed in a new environment.   It is proposed that when a plant is removed from its natural enemies it will no longer need the defense mechanisms it had developed to protect it against them.  Since protective mechanisms require energy, the plant would have additional resources available when these mechanisms are lost.  These resources could be directed toward making the plant more competitive with neighboring plants.

Several studies were cited that provide evidence of a loss of defensive mechanisms in species removed from their native habitat, including Chinese tallow tree, garlic mustard, and St. John's wort.  The loss of these defense mechanisms was found to enhance the competitiveness of Chinese tallow tree, but not the other two species.  One of the scientists said the lack of supporting evidence in two of the species does not disprove the hypothesis, but rather that the real world is complicated and that it may not always be a simple tradeoff between defense mechanisms and growth.

Thus, it may be that some plants are born to be bad, but others may need to grow into the role of villain.

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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