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Western Population : Scientists Concerned

There are two geographically distinct Monarch populations in North America. The eastern population overwinters in Mexico and breeds east of the Rocky Mountains. The western population overwinters along the California coast and breeds in areas west of the Rockies. Contact between eastern and western Monarchs is minimal suggesting that there is little exchange, or what scientists call gene flow, between these populations. In recent years, several people have transplanted migrating Monarchs between east and west to determine, if for example, western Monarchs introduced in the east would be found in Mexico. Many scientists are concerned about this practice and cite numerous reasons, such as the potential introduction of diseases from one population into another which is why this practice should be stopped immediately.

Under the leadership of Dr. Lincoln Brower, 14 scientists have coauthored an article which appeared in the September 1995 issue of BioScience and outlines numerous reasons for not mixing eastern and western Monarch populations. Teachers may find this article useful for class discussions. The question "why should transfer between eastern and western Monarch populations be discouraged?" could be presented to the class. The article could then be used as a guideline to lead students by questioning, through many of the same biological and practical considerations presented by the scientists. If you would like to have a copy of this article, please send us a self-addressed stamped envelope and we will forward a copy of it.

For individuals living west of the Rockies and interested in Monarch conservation, check out our page on Other Monarch Programs

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