Population Density and Fluctuations of Pikas (Ochotona princeps) in Colorado

Southwick, Charles H.; Golian, Steven C.; Whitworth, Molly R.; Halfpenny, James C.; Brown, Richard N.

doi:10.2307/1381011

Cited by 19 publications

(13 citation statements)

References 18 publications

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“…Pikas have exhibited stable population size in a core portion of their range (Southwick et al. ), but can also suffer high mortality (Kreuzer and Huntly ) and high turnover in occupancy (Jeffress et al. ).…”

Section: Discussionmentioning

confidence: 99%

Distribution of a climate‐sensitive species at an interior range margin

2016

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Advances in understanding the factors that limit a species’ range, particularly in the context of climate change, have come disproportionately through investigations at range edges or margins. The margins of a species’ range might often correspond with anomalous microclimates that confer habitat suitability where the species would otherwise fail to persist. We addressed this hypothesis using data from an interior, climatic range margin of the American pika (Ochotona princeps), an indicator of relatively cool, mesic climates in rocky habitats of western North America. Pikas in Lava Beds National Monument, northeastern California, USA, occur at elevations much lower than predicted by latitude and longitude. We hypothesized that pika occurrence within Lava Beds would be associated primarily with features such as “ice caves” in which sub‐surface ice persists outside the winter months. We used data loggers to monitor sub‐surface temperatures at cave entrances and at non‐cave sites, confirming that temperatures were cooler and more stable at cave entrances. We surveyed habitat characteristics and evidence of pika occupancy across a random sample of cave and non‐cave sites over a 2‐yr period. Pika detection probability was high (~0.97), and the combined occupancy of cave and non‐cave sites varied across the 2 yr from 27% to 69%. Contrary to our hypothesis, occupancy was not higher at cave sites. Vegetation metrics were the best predictors of site use by pikas, followed by an edge effect and elevation. The importance of vegetation as a predictor of pika distribution at this interior range margin is congruent with recent studies from other portions of the species’ range. However, we caution that vegetation composition depends on microclimate, which might be the proximal driver of pika distribution. The microclimates available in non‐cave crevices accessible to small animals have not been characterized adequately for lava landscapes. We advocate innovation in the acquisition and use of microclimatic data for understanding the distributions of many taxa. Appropriately scaled microclimatic data are increasingly available but rarely used in studies of range dynamics.

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Section: Discussionmentioning

confidence: 99%

Distribution of a climate‐sensitive species at an interior range margin

2016

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“…Despite these tendencies, genetic analyses suggest that rare longer-distance dispersal events do occasionally happen and that genetic neighborhoods can extend as far as 4.2 km, although dispersal is more limited in hotter and drier contexts [72,63,73,74]. …”

Section: Methodsmentioning

confidence: 99%

Predictors of Current and Longer-Term Patterns of Abundance of American Pikas (Ochotona princeps) across a Leading-Edge Protected Area

et al. 2016

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American pikas (Ochotona princeps) have been heralded as indicators of montane-mammal response to contemporary climate change. Pikas no longer occupy the driest and lowest-elevation sites in numerous parts of their geographic range. Conversely, pikas have exhibited higher rates of occupancy and persistence in Rocky Mountain and Sierra Nevada montane ‘mainlands’. Research and monitoring efforts on pikas across the western USA have collectively shown the nuance and complexity with which climate will often act on species in diverse topographic and climatic contexts. However, to date no studies have investigated habitat, distribution, and abundance of pikas across hundreds of sites within a remote wilderness area. Additionally, relatively little is known about whether climate acts most strongly on pikas through direct or indirect (e.g., vegetation-mediated) mechanisms. During 2007–2009, we collectively hiked >16,000 km throughout the 410,077-ha Glacier National Park, Montana, USA, in an effort to identify topographic, microrefugial, and vegetative characteristics predictive of pika abundance. We identified 411 apparently pika-suitable habitat patches with binoculars (in situ), and surveyed 314 of them for pika signs. Ranking of alternative logistic-regression models based on AICc scores revealed that short-term pika abundances were positively associated with intermediate elevations, greater cover of mosses, and taller forbs, and decreased each year, for a total decline of 68% during the three-year study; whereas longer-term abundances were associated only with static variables (longitude, elevation, gradient) and were lower on north-facing slopes. Earlier Julian date and time of day of the survey (i.e., midday vs. not) were associated with lower observed pika abundance. We recommend that wildlife monitoring account for this seasonal and diel variation when surveying pikas. Broad-scale information on status and abundance determinants of montane mammals, especially for remote protected areas, is crucial for land and wildlife-resource managers trying to anticipate mammalian responses to climate change.

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“…Although other factors, including edaphic conditions, may also vary across this 10‐m gradient, we attribute the single greatest influence to pikas, based on several observations. First, most evidence indicates that pika populations show low population variability compared with other northern small mammals, low adult dispersal rates and high recolonization rates of vacated sites ( O. princeps : Southwick et al . 1986; O. collaris : Franken 2001; D. Hik, unpublished data), thus occupancy of established boulderfields is consistent and high.…”

Section: Methodsmentioning

confidence: 99%

Grazing history versus current grazing: leaf demography and compensatory growth of three alpine plants in response to a native herbivore (Ochotona collaris)

McIntire

Hik

2002

Journal of Ecology

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Summary 1We measured leaf births, leaf deaths and leaf length of three alpine perennial species, Kobresia myosuroides , Erigeron humilis and Oxytropis nigrescens , from sites with different grazing histories (strong or weak) in response to two levels of current season grazing (present or absent) by collared pikas ( Ochotona collaris ), a small lagomorph, in the south-west Yukon. 2 All three species appeared to tolerate the removal of 58-61% of summer leaf production under natural conditions. Grazing history, which was defined by the location of plants located either < 2 m or > 6 m from boulderfields with a history of occupation by pikas, was the most significant factor determining shifts in leaf births and leaf deaths following herbivory. 3 The only detectable influence of current season herbivory for any measured species was a reduction of leaf length of Kobresia . 4 A comparison of historically grazed with historically ungrazed plants indicated several changes in leaf demography and morphology. Kobresia leaves were generally shorter and had higher rates of production of new leaves. Oxytropis had higher rates of new leaf production. Erigeron had fewer leaf births throughout the summer, but showed a large and highly significant delay in the timing of leaf senescence. 5 These responses can be largely understood as strategies to avoid the predictable intensive late season foraging that is characteristic of pikas. Morphological mechanisms allow these species to tolerate and, more importantly for the herbivore, persist under heavy and chronic grazing.

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Population Density and Fluctuations of Pikas (Ochotona princeps) in Colorado

Cited by 19 publications

References 18 publications

Distribution of a climate‐sensitive species at an interior range margin

Distribution of a climate‐sensitive species at an interior range margin

Predictors of Current and Longer-Term Patterns of Abundance of American Pikas (Ochotona princeps) across a Leading-Edge Protected Area

Grazing history versus current grazing: leaf demography and compensatory growth of three alpine plants in response to a native herbivore (Ochotona collaris)

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