Subspeciation in the Meadow Mouse, Microtus montanus, in Wyoming and Colorado

In the high, moisture‑rich valleys of Wyoming and Colorado, a modest rodent—the meadow mouse—offers a window into evolution in action. This study follows months of summer fieldwork, during which the researcher collected over a thousand specimens across the Rocky Mountain range. By mapping where these tiny mammals thrive, the work reveals how isolated patches of suitable habitat shape their numbers and behavior.

Back in the lab, the specimens undergo meticulous analysis: twenty‑seven body measurements, skull dimensions recorded to the nearest tenth of a millimeter, and careful notes on coloration and subtle skeletal features. Statistical comparisons across dozens of local populations let the author test how selection, drift, and environmental moisture drive variation. The results suggest that, despite dramatic fluctuations in population size, the meadow mouse shows only modest subspecific divergence in this part of its range.