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The Ruby Mountains, a major Great Basin range, appears to harbor only half as many small animals as were found there in the 1920s, according to a new study by Utah Museum of Natural History researchers.

Climate change, grazing and fire suppression have altered the vast basin-and-range province between the Wasatch and the Sierra Nevada, considered one of the most threatened landscapes in North America. But "significant declines" among small mammals across the mountain range's habitat types and elevation zones are cause for renewed concern, said University of Utah biologist Rebecca Rowe, lead author of two recent studies based on modern "resurveys" of sites investigated 80 years ago by a University of California ecologist, Adrey Borell.

"A lot of people say the Great Basin is in trouble. This is another indication that the area may really be in trouble," said Rowe, a postdoctoral research fellow at the museum. "We think it's a region-wide problem. ... We don't know unless we have something we can compare it to."

Instead of focusing on just a handful of species, Rowe and her colleagues examined properties of entire animal communities, comparing overall numbers, the animals' collective biomass and energy use against what Borell recorded. Under all three measures, furry little critters are half as prevalent as they used to be, according to Eric Rickart, curator of the Utah museum's vertebrates collections.

The decline in these prey animals indicates something is amiss with the plant communities that form the ecosystem's resource base. And the effects could be rippling up the food chain, said Rickart, the co-author of the study published in the June edition of the journal Ecology. Also contributing was Rebecca Terry, a paleontologist at Stanford University.

In an earlier paper, Rowe and colleagues documented something they didn't anticipate in the Rubies. High temperatures, on average, have increased by about one degree Fahrenheit, but the ranges of heat-tolerant species are not moving upslope in response to the warming.

Livestock and fire suppression "have changed the habitat so that even though the climate at the upper elevations is suitable, the habitat is no longer suitable," said Rowe, who is leaving Utah this month to take a faculty position at the University of New Hampshire's department of natural resources and environment.

Rowe's two studies are the first to emerge from the museum's ongoing Great Basin Resurvey Project, a National Science Foundation-funded effort to reconstruct ecological surveys of mountain ranges conducted in the early decades of the 20th century. The Rubies, one of five ranges in the study, form an 80-mile-long glaciated mountain range 200 miles west of Salt Lake City in northeast Nevada.

The resurvey project, which is tackling the Toiyabe Range this summer, targets small mammals because they exhibit great diversity, with big populations from numerous species and several families, according to Rickart. Some species are generalists in habitat choice and diet, while others eat just bugs, leaves or seeds and live exclusively in dry or wet areas.

Using spring traps set out overnight, the Borell survey recorded 19 species of mice, voles, woodrats, shrews, chipmunks and other small mammals, while the modern team, using identical trapping techniques, recorded 17 species at Borell's nine sites in the Rubies. The historic survey yielded 1,408 animals from 7,103 trap-nights, while the Utah team caught 592 from 6,539 trap-nights.

Borell surveyed the Rubies when more sheep and cattle were roaming the Great Basin, so less grazing should have translated into more resources for native animals, Rickart observed. Instead, there appear to be fewer resources for these creatures.

The best explanation is the extent to which human activity has rearranged plant communities. Grazing has ensured woody shrubs dominated areas formerly covered in grasses, while fire suppression has allowed pinyon-juniper woodlands to spread. Meanwhile, invasive cheat grass has displaced many native grasses in lower elevations.

The environmental changes seem to favor generalist species like the deer mouse (Peromyscus maniculatus) at the expense of specialists, like the xeric-adapted canyon mouse (P. crinitus) and moisture-dependent water shrew (Sorex palustris). And omnivores fared better than granivores and herbivores, Rickart said.

Great Basin Resurvey Project

Biologists at the Utah Museum of Natural History are returning to mountain ranges in the Great Basin that were surveyed by ecological scientists 80 years ago. Their work in the Ruby Mountains has documented troubling reductions in the landscape's ability to support animal life. The project moves to the Toiyabe Range this summer and will resurvey Pine Forest, Tushar and Snake ranges in the years to come.