Sierra Nature Notes, Volume 3, December 2003

Persistence of pikas in two low-elevation national monuments in the western United States

The American pika (Ochotona princeps) © WWF / J. MacKENZIE/ www.pikaworks.com

By Erik A. Beever, Ph.D.
Ecologist with the U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR 97331.

Editor's Note: This article was first published in Spring of 2002 by the National Park Service. Last spring, Dr. Beever followed up this paper with PATTERNS OF APPARENT EXTIRPATION AMONG ISOLATED POPULATIONS OF PIKAS (OCHOTONA PRINCEPS) IN THE GREAT BASIN (Erik A. Beever, Peter F. Brussard, and Joel Bergera in the Journal of Mammalogy: Vol. 84, No. 1, pp. 37–54 (abstract only). In this paper, disturbing evidence was presented that suggests pikas may be among the first mammal species for which scientists have empirical data that demonstrate rapidly altered distributional patterns across a bioregion during the current period of global climate change. His paper received wide press coverage and summary articles can be read on the World Wildlife Fund website (interview); and The Daily Telegraph (London) among many others. As a result of this research, Sequoia and Kings Canyon scientist Dr. David Graber asked backcountry rangers to begin recording all pika sightings while on patrol in the high country. As with a similar request 15 years ago to record the Mountain yellow-legged frog (now listed as endangered), this will establish a critical baseline to determine if Sierra populations are being affected.

Introdution
Although national parks act as island reserves for animals and plants, recent research has highlighted the dramatic changes (e.g., local extirpations, invasions of exotic species) that can occur in flora and fauna even on lands where the primary management mandate is resource conservation (Svejcar and Tausch 1991, Newmark 1995). The legacy of past disturbances, influences from adjacent lands, and climate change, in addition to the isolation and relatively small size of park units may all affect persistence of species within parks. In the western United States, pikas (Ochotona princeps) represent a model system that may help ecologists to understand these timely and complex relationships, as well as their implications for management in at least two units of the National Park System.

"pikas may be early sentinels of biological response to global climate change such as increased temperatures"

Relicts of a cooler time
Pikas are small (100–175 g [4–6 oz]) mammals typically found in talus and other rocky habitats such as lava formations and mine tailings (fig. 1). Paleoecological evidence suggests that pikas were far more widespread during the late Pleistocene in western North America than they are today (Grayson 1987). Climatic warming during the past 10,000 years led to the extirpation of most low-elevation pika populations, producing the modern-day relictual distribution of the species. In the intermountain West currently pikas generally inhabit high-elevation areas and are considered montane mammals. However, temperature appears to limit their distribution more than elevation per se (Hafner 1993). For example, high temperatures (25.5–29.4°C) [77.9 to 84.9° F] ambient shade temperature) can be lethal to pikas in as little as six hours, if they are caged on the surface of talus and thus deprived of their behavioral mechanisms to avoid stressful temperatures (Smith 1974). Consequently, pikas may be early sentinels of biological response to global climate change such as increased temperatures, although to date little fieldwork has been done on response of terrestrial vertebrates to climatic changes. Pikas’ vulnerability to high temperatures partly results from the thick fur that insulates them against severe cold, because it also inhibits evaporative cooling during warm periods. A mystery remains, however, in whether acute (i.e., short-term) thermal stress, from high maximum temperatures, or chronic thermal stress over a pika’s lifetime (resulting from living in hotter, drier climates) most affects pika persistence. Furthermore, as is true for most mammals, we know little about how thermal stresses interact with other potential stresses to pika populations such as small habitat area, catastrophic fires, human disturbance, and livestock grazing.

“Climatic warming during the past 10,000 years led to the extirpation of most low-elevation pika populations....”

 

 

 

 

 

 

 

Figure 1. Often heard but not seen, pikas typically inhabit high-elevation talus slopes in the western United States. However, the unusual occurrence of low-elevation pika populations in two western U.S. national monuments prompted the author to investigate their persistence and to evaluate implications for management of the species.

Figure 2. Pika surveys took place at 25 locations in the internally drained (interior) Great Basin; at Craters of the Moon and Lava Beds National Monuments where low-elevation populations of pikas persist; and at Hell’s Half Acre, a low-elevation site near the monuments that lacks pikas but has similar habitat.

In the Great Basin (where precipitation drains internally rather than to an ocean; fig. 2), persistence of pika populations during the 20th century was significantly correlated with habitat area, elevation, longitude, distance to primary roads, latitude, grazing status, and management jurisdiction (wilderness vs. non-wilderness), but not with isolation of populations from the Sierra Nevada or Rocky Mountains (Beever 1999). Island biogeography theory predicts greater rates of extinction on islands (which may be oceanic or island-like pockets within continents) that are smaller in area and more isolated from the mainland, but does not make direct predictions about the other factors. Thus, the fact that isolation from Sierra Nevada or Rocky Mountain “mainlands” is not important in pika extirpations suggests that migration of pikas between mountaintop islands is not occurring currently. Rather, it appears that extirpation of populations from montane areas across the Great Basin is occurring without any concomitant colonization events. Average temperatures generally decrease with increasing latitude and elevation, thus latitude must be accounted for when assessing persistence at different elevations.

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