Losing contact

Natural History, Nov, 2007 by Stephan Reebs

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Agriculture, development, and logging are often blamed for habitat fragmentation. Now we can blame global warming, too. Worldwide, a combination of rising temperatures and fire suppression by foresters is causing mountain tree lines to climb. The trees are creeping into alpine meadows and carving them to pieces; along the way, animal populations are being carved up as well.

Take Jumpingpound Ridge in the Rocky Mountains of Alberta. There, trees now live some 650 feet higher up the mountainsides than they did forty years ago. Each year from 1995 through 2005, Jens Roland of the University of Alberta in Edmonton and Stephen F. Matter of the University of Cincinnati surveyed the number of Apollo butterflies, Parnassius smintheus, living in a series of alpine meadows on the ridge. After counting each meadow's butterflies for eleven summers and comparing the fluctuations in their numbers, Roland and Matter discovered that the broader the swath of forest between two adjacent meadows, the less in synch were the ups and downs of the two butterfly populations. In other words, populations divided by thick forest fall out of touch and become increasingly independent.

The encroaching forests, the ecologists conclude, prevent the Apollos (and quite possibly other organisms) from dispersing and thus mixing their genes. That could be bad news for the butterflies and other locals: isolated populations are more vulnerable to being wiped out than are connected populations. (PNAS)