Modeling Contemporary Range Contraction in Great Basin Pikas

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1 Boundary Peak, White Mountains, Nevada Modeling Contemporary Range Contraction in Great Basin Pikas Jennifer Wilkening

2 Alpine species particularly vulnerable, what about pikas? Crane Mountain, Warner Mountains, Oregon Global Climate Change Rising temperatures, changing precipitation patterns, increased frequency of extreme weather events

3 Located only in mountains surrounded by sagebrush areas Relictual populations from cooler climates Dispersal is difficult Habitat Islands susceptible to biogeographic patterns of extinction Mount Jefferson, Toquima Range, Nevada

4 Several in the Great Basin have become extirpated during the 20 th century (Beever et al. 2003) Occurred at lower elevation sites, hotter and drier Other factors Amount of talus habitat Distance to a primary road However, single strongest determinant of persistence was elevation of nearby habitat

5 Direct thermal stress Hyperthermia and death from high temperatures in the C range Survival declines during extremely cold winters with less insulating snow cover, increased freeze-thaw events Lava Beds National Monument Photo by Chris Ray Indirect thermal stress Higher temperatures limits activity during the day Changes in vegetation plant communities

6 Acute or chronic heat stress: pikas no longer occur where mean daily summer temperature and the amount of time above a temperature threshold are high Cold stress: pikas no longer occur where amount of time below a temperature threshold is high Vegetation: pikas no longer occur where there are less forbs and graminoids, more xeric adapted species Combinations: Pikas no longer occur where high mean summer temperatures combined with low forbs/grams Pikas no longer occur where high amounts of time below a temperature threshold combined with low forb cover

7 25 Field sites located in Nevada, Oregon, California Site Classification Sites of persistence vs. sites of extirpation(n = 20) Site level analysis Transitional (n = 5), lower occupancy limit > than 200 meters upslope Desatoya Range, Nevada Sub-site level analysis

8 Temperature Methods Thermochron ibuttons 5-8 per site Placed adjacent to hay piles, scat (extirpation sites), GPS locations (transitional sites) Recorded temperature readings every 4 hours Placed inside the talus at a depth between meters Multiple localities within each site (n = 191) Varying aspects, elevations (none below historical site elevation

9 Toiyabe Range, Nevada Desatoya Range, Nevada Toiyabe Range, Nevada Line-point-intercept method 4-5 Vegetation Surveys per site randomly selected A 50 meter long transect with the data logger location as center point, one additional 50 meter long transect both above and below Vegetation was placed into 1 of 6 life form categories: Forbs (herbaceous, flowering plants, excluding cushion plants), Graminoids (grasses and grass-like plants such as sedges and rushes), Shrubs (woody plants), Trees, Cushion Plants (low, mat forming plants), and Non-Vascular Plants (including lichen)

10 Steens Mountain, Oregon 7 Predictor Variables Logistic Regression Various models composed of different combinations of temperature and vegetation factors R was used to model pika persistence as a function of predictor variables Relative support for each model and predictor were calculated using AICc Welch two-sample t-test used to compare mean value of each predictor variable Predictors based on temperature Mean summer temperature Number of days above 26 C Number of days above 28 C Number of days below -5 C Number of days below -10 C Predictors based on vegetation Relative cover of forbs Relative cover of graminoids Sources: 1) Beever et al ) Smith and Ivins ) Smith ) Hafner ) Tapper ) Smith 1974a 7) MacArthur and Wang ) Dearing 1995, 1996, 1997a 9) Huntly et al ) Sundby ) Ray and Beever ) Dearing 1995, ) Kreuzer and Huntly 2003

11 Model: Predictor (effect sign) AIC C ΔAIC C Akaike weight SITE LEVEL DaysBelow-10 C (+), MeanSummerTemp (-) MeanSummerTemp/RelForbCov er (-) Mean SummerTemp (-) SUB-SITE LEVEL Null model (intercept only) DaysBelow-10 C/RelForbCover (-) MeanSummerTemp/RelGramCo ver (-) MeanSummerTemp/RelForbCov er (-) RelGramCover (+) RelForbCover (+)

12 Predictor Akaike weight Mean Akaike wt/model Sign of effect SITE LEVEL MeanSummerTemp Neg (3) MeanSummerTemp/RelForbCover Neg (1) DaysBelow-10 C Pos (2), Neg (1) RelForbCover Pos (2) DaysAbove28 C Neg (2), Pos (1) RelGramCover Neg (2) DaysBelow-10 C/RelForbCover Neg (1) MeanSummerTemp/RelGramCover Pos (1) SUB-SITE LEVEL DaysBelow-10 C/RelForbCover Neg (1) MeanSummerTemp/RelGramCover Neg (1) MeanSummerTemp/RelForbCover Neg (1) RelGramCover Pos (2) RelForbCover Pos (2) DaysAbove28 C Pos (4) MeanSummerTemp Neg (4) DaysBelow-10 C Neg (4) Photo by Shana Weber

13 Persistence observed (dots) and modeled (line) The best model (ΔAIC c = 0) of persistence at the site level Hays Canyon Range, Nevada C H (a) Duffer Peak, Pine Forest Range, Nevada D Linear predictor: f(mean summer temp., Days below -10 C)

14 Disease Relationship between intestinal bacteria and other endoparasites Species interactions Reduced dispersal Reduction in the amount of available forage time Night time activity? Sites of persistence mean summer temp (17.04 C) vs. sites of extirpation (11.74 C), p = 0.00 Photo by Chris Ray

15 Mean number of days above 28 C at sites of persistence was 1.23, at sites of extirpation it was ( p = 0.02) Hyperthermia and death can occur from even brief exposure to moderately high temperatures ( C; MacArthur and Wang, 1973, 1974; Smith, 1974) Behavioral thermoregulation, access to cooler temperatures? Hart Mountain, Oregon

16 Ruby Mountains, Nevada White Pine Range, Nevada Pika survival declines during harsh winters; shallow snowpack, ice barrier, etc. However, number of days below -10 C was positively correlated to persistence, possibly due to: Two year time series represents a limited period of time. Pika mortality resulting from harsh winters may occur only periodically. Long term pika persistence may be less affected by colder winter temperatures.

17 Highly variable Consume grasses immediately (smaller, less toxic) Store forbs (herbaceous, flowering plants) for winter consumption (larger, toxic secondary compounds) Toiyabe Range, Nevada Hart Mountain, Oregon

18 Hay piles sometimes contain more than enough plant material for winter survival (Dearing 1997) OR Hay piles do not always contain sufficient quantities of vegetation to provide an exclusive food source for the winter (Millar and Zwickel 1972) OR Pikas may forage outside of the hay pile (Conner 1983) OR Hay piles are not always necessary (Simpson 2001) HOWEVER Most likely hay piles function as an adaptive response to environmental unpredictability Photo by Chris Ray Kiger Gorge, Oregon

19 Hay pile presence may be more important in the Great Basin Haying food resources may be more important than grazing food resources Essential nutrients found only in forbs Forbs contain preservatives (Dearing 1997) Moisture content of forbs Sites of persistence relative forb cover (28.79) vs. sites of extirpation (8.61), p = 0.00

20 Future of pikas in the Great Basin? Arc Dome, Toiyabe Range, Nevada