Sierra Nature Notes, Volume 3, December 2003

Persistence of pikas
Continued, page 4 of 5

In contrast to our relatively clear understanding of the climatic effects on pika distribution, the exact extent to which human-related activities such as livestock grazing, altered fire regimes, clear-cutting of adjacent forest cover, and other influences on lava habitats affect pika population dynamics remains in need of clarification. While the systems of caves and lava tubes have undoubtedly facilitated persistence of pikas in the monuments, other factors that may contribute to their persistence in these low-elevation areas include: extensiveness and connectivity of lava habitats, relatively close proximity (30–80 km [18.6–49.7 mi]) to other known pika strongholds (Hafner 1994; J. Villegas, 2001, personal communication), physical complexity of lava formations, relative inaccessibility for humans, and wilderness management. Although Hell’s Half Acre possesses extensive lava flows, amounts of vegetation comparable to that of Craters, proximity (<130 km [80.7 mi]) to three other pika populations, and is relatively inaccessible over much of its area, it has fewer caves and lava tubes, a less convoluted lava structure, and a hotter, drier climate than Craters; and it is managed as a multiple use recreational area.

This research does not allow conclusive understanding of to what degree the effects of wilderness management, habitat extent, and physical structure of habitats have contributed to persistence of monument populations of pikas while other low elevation (interior Great Basin) populations have suffered extirpation. Although manipulative experiments, which provide stronger inference about cause-effect relationships, are not feasible within the monuments, two avenues of observational research may prove fruitful. Broad sampling for pikas in numerous caves and tubes within and around the monuments would afford greater understanding of the range of conditions (with respect to temperature, humidity, cave size and habitat extent, isolation from other populations, and human activity) that support pika populations. During sampling, collection of tissue samples from individual pikas would allow comparison of genetic differences among known pika populations and would suggest relative rates of gene flow among them. Correlation of genetic results with potentially isolating features (e.g., roads, surrounding non-talus habitat, different systems of lava tubes) and management actions (livestock grazing, fire frequency) would provide a basis for generating hypotheses as to which factors, if any, have constrained pika distribution.

Table 2. Estimated climatic conditions at areas in the interior Great Basin where pikas remained extant and where they were extirpated during the 20th century, and at two low-elevation national monuments adjacent to the Great Basin that still contain pikas.

Site(s)	Elevation range*	Average annual precipitation  (cm/yr ± 1 SE [standard error])	June maximum temperatures (°C)	July maximum temperatures (°C)	August maximum temperatures (°C)
Sites (N = 18) in the interior Great Basin with extant pika populations	1,798–3,612 m (5,900–11,850 ft)	58.9 ± 6.2	19.3 ± 0.7	24.7 ± 0.6	24.8 ± 0.5
Sites (N = 7) in the interior Great Basin with extirpated pika populations	1,680–2,877 m (5,512–8,600 ft)	47.4 ± 7.0	21.3 ± 0.5	26.6 ± 0.6	26.7 ± 0.5
Lava Beds National Monument	1,230–1,650 m (4,036–5,414 ft)	36.1	23.6	28.6	28.2
Craters of the Moon National Monument	1,590–1,990 m (5,217–6,529 ft)	38.8	23.5	29	28.1
Hell’s Half Acre	1,400–1,630 m (4,593–5,348 ft)	28.1	24.4	30.1	29.0

*Represented are the lower end of talus at the lowest sites in each category (lowest elevation currently with pikas, for the lowest site with an extant population in the interior Great Basin ), and the highest elevation of talus habitat within 3 km of the location of the historic record of pikas (among all sites in the group).

  **Average of daily maximum temperatures for days in June (values indicate average ± 1 SE when >1 site).

Management Implications
Persistence of pikas, at least in the interior Great Basin, appears to be a function of extent of habitat, distance to primary roads, and maximum elevation of habitat to which pikas can migrate (which should dictate pikas’ ability to respond to climate change) (Beever 1999; Beever et al. forthcoming). Additionally, pika population size relates to the presence of livestock grazing in some cases (Beever 1999; Beever et al. forthcoming). Therefore, management actions may hold great importance for pika persistence. For most species, persistence depends critically on the amount, spatial distribution, and quality of appropriate habitat. Although removal or physical degradation of lava and talus habitats are not likely over ecological time scales, habitat quality for pikas may be compromised by the following: consistently higher ambient temperatures (e.g., due to climate change); altered composition of forbs and grasses in and adjacent to lava flows (e.g., because of altered fire regimes, exotic species, or uncharacteristically intense levels of grazing at flow margins); and significant fragmentation of lava habitats (e.g., road construction). Pika persistence at low-elevation sites may also be affected by disturbance or alteration of pika habitats by humans or livestock (e.g., nutrient deposition by livestock in large caves [J. Villegas, 2001, personal communication], human disturbance of hay piles). Because human disturbance of lava flows to this point has been confined primarily to areas near roads or trails during warmer months, these latter influences probably have been minimal.

Isolation of Great Basin pika populations from the Sierra Nevada or Rocky Mountains is one of few variables that does not predict persistence in the Great Basin. This phenomenon probably occurs because talus habitats in the Great Basin are separated by vast areas of non-talus habitat that usually lie at low elevation, and pikas are unlikely to traverse these areas under current climatic conditions. In contrast, the recent nine-fold expansion of Craters’ area creates the possibility for promoting pika persistence across the more continuous lava habitats along the Great Rift, to the extent that the monument explicitly manages for vertebrate conservation. Although connectivity among volcanic habitats may not change with monument expansion, changes in management in the area may alter effective connectivity. Thus, although Newmark (1995) concluded that national parks in western North America are too small to support viable populations of large mammals, actions such as monument expansion and others described earlier may help prevent loss of noteworthy pika populations from these low elevation monuments.

Continued: Acknowledgements and Literature Cited