Great Basin Naturalist


The purpose of this study was to observe the dynamics of a meta-population of Mimulus guttatus. Changes in size and location of 16 original populations and the new populations established in their vicinities in Big Cottonwood Canyon, Salt Lake County, Utah, were observed for 25 yr. Twenty-three new populations appeared. Seven original populations and 13 new populations had become extinct by the end of the observation period in 1996. Many populations died out and were reestablished, often repeatedly, during the observation period. Altogether there were 54 population disappearances and 34 reappearances. Many populations changed sized as much as 100-fold or more from year to year. There were spectacular examples of populations expanding to fill newly available, large habitats.

Frequent extinctions were due overwhelmingly to the canyon drying trend, which led to the drying up of most Mill D North drainage springs, creeks, and ponds. Precipitation and minimum temperatures increased moderately during the observation period. The growing season lengthened almost 50%, a typical consequence of global warming. The drying trend, lengthened growing season, and disappearance of Mimulus populations in Big Cottonwood Canyon appear to be a clear, local example of global warming.