In the sky islands of southern Nevada, climate change may be forcing two species of chipmunks into conflict.
It’s an example of how far-reaching the potential ripples of climate change have on all species great and small, and on ecosystems that rarely get the spotlight -- especially if you’re first reaction to that lead sentence was “where and what?”
“Sky islands” are what ecologists call the tree-lined oases found on mountain peaks rising above the Basin and Range Province of southwestern North America -- the series of alternating highlands and flatlands stretching between the Rockies and California’s Sierra Nevada, and south into Mexico.
If these coordinates bring to mind arid high plains and scorching hot deserts, you would be right. And it’s also why the snow-packed, alpine forests on these 11,000-foot-plus peaks host such unique ecosystems, given their relative isolation from each other -- and from the vastly different flora and fauna of the basins that isolate them.
It’s an ecosystem that has caught the attention of state and federal researchers, like ecologist Chris Lowrey of the USGS Western Ecological Research Center.
The bristlecone pine forests preferred by the Palmer's chipmunk. Image credit: Chris Lowrey/USGS.
“In recent geologic time, a lot of these higher elevation habitats would have been interconnected, since previous temperatures would have made the temperature differences less severe between the basin and range,” says Lowrey, who works out of the WERC Las Vegas Field Station with Kathy Longshore. “Now that they are isolated, sky islands make for really interesting living laboratories to study how species diverged, how they occupy distinct niches and elevations, and how predator and prey species interact within a bounded environment.”
In the sky islands west of Las Vegas, Lowrey has been studying two species of chipmunks -- Palmer’s chipmunk (Tamias palmeri) and the panamint chipmunk (Tamias panamintinus).
Both have the big eyes and striped back that so well-known from their cartoon counterparts, although the Palmer’s is slightly larger than the panamint. Palmer’s chipmunks only occur on one sky island -- the Spring Range -- whereas panamint chipmunks are found in other Nevada and California ranges.
Lowrey’s surveys have shown that the two species occupy separate niches. Palmer’s chipmunks prefer fir and bristlecone pine forests higher than 2,500 feet, while panamint chipmunks prefer mixed forests of Ponderosa and pinyon pine lower than 2,600 feet.
In that narrow strip where the two species overlap, Lowrey is discovering that relationships between the two rodents might not be cute and cuddly.
A map of the elevation distributions of Palmer's and panamint chipmunks in the Spring Range of Nevada. The upper boundary of panamint chipmunks are in red, while the lower boundary of Palmer's chipmunks are in yellow. Image credit: Chris Lowrey/USGS.
“In the presence of Palmer’s chipmunks, we’re finding that panamint chipmunks are less likely to occupy those mixed forests they prefer, and more likely to be forced into less productive habitat,” says Lowrey. “In these overlapping areas, we believe the Palmer’s chipmunk may be excluding the panamints from areas of potentially suitable habitat.”
Just another day in chipmunk world of the sky islands. But that could change with future climate patterns, causing temperature zones along mountain elevations to shift upwards.
“Animals and plants adapted to certain temperatures and resources may be forced to climb to higher elevations just stay in their comfort zone,” says Lowrey. “But that would raise the chance of interspecies interactions. It might be that as panamint chipmunks move towards higher elevations, they’ll increasingly come into Palmer’s chipmunk territory and simply get out-competed for food and resources, and lose out in the end.”
Much ado about chipmunks, one might say. However, both species anchor the sky island food web. Chipmunks are adept at distributing and caching plant seeds, and they are also the most populous mammal prey there, feasted on by coyotes, bobcats, weasels, skunks, raptors and other species.
“These chipmunks are the perfect rations up there -- little fur-covered dumplings, if you will -- and offer good calories for the predators,” says Lowrey. “Palmer’s chipmunks often run in groups across the landscape. It’s not like gazelles on the Serengeti or anything, but they’re all over the place, doing their thing, hidden in the background.”
Would a shift in chipmunk species affect vegetation seeds and predator dynamics? Questions like these are always on the minds of ecologists, who seek to understand how seemingly isolated changes could have domino effects throughout an ecosystem.
Lowrey and Longshore’s research is conducted in cooperation with the Nevada Department of Wildlife, University of Nevada-Las Vegas, U.S Fish and Wildlife Service, U.S. Forest Service and Clark County, Nevada. Lowrey will be presenting a poster on his sky island research at The Wildlife Society 2012 Conference in Portland, Oregon, this October.
-- Ben Young Landis
A Palmer's chipmunk being examined by biologists. Image credit: Chris Lowrey/USGS.