Boundary Peak, White Mountains, Nevada
Modeling Contemporary Range
Contraction in Great Basin Pikas
Jennifer Wilkening
Crane Mountain,
Warner Mountains, Oregon
Global Climate Change
Rising temperatures,
changing precipitation
patterns, increased frequency
of extreme weather events
Alpine species particularly vulnerable,
what about pikas ?
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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
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Several in the Great Basin
have become extirpated
during the 20th century
(Beever et al. 2003)
Occurred at lower
elevation sites, hotter
and drier
Other factors
◦ Amount of talus habitat
◦ Distance to a primary road
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However, single
strongest determinant of
persistence was elevation
of nearby habitat
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Direct thermal stress
Lava Beds National Monument
◦ Hyperthermia and
death from high
temperatures in the
25.5-29.4°C range
◦ Survival declines
during extremely cold
winters with less
insulating snow cover,
increased freeze-thaw
events
Photo by Chris Ray
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Indirect thermal stress
◦ Higher temperatures
limits activity during the
day
◦ Changes in vegetation
plant communities
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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
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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
Desatoya Range, Nevada
meters upslope
 Sub-site level analysis
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 0.5-1
meters
◦ Multiple localities within
each site (n = 191)
◦ Varying aspects,
elevations (none below
historical site elevation
Toiyabe Range, Nevada
Desatoya Range, Nevada
Toiyabe Range, Nevada
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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)
Steens Mountain, Oregon
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7 Predictor Variables
Logistic Regression
Various models composed
of different combinations
of temperature and
vegetation factors
R 2.6.2. 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. 2010 2) Smith and Ivins 1983 3) Smith 1978 4) Hafner 1993
5) Tapper 1973 6) Smith 1974a 7) MacArthur and Wang 1973 8) Dearing 1995, 1996, 1997a
9) Huntly et al. 1986 10) Sundby 2002 11) Ray and Beever 2007 12) Dearing 1995, 1996
13) Kreuzer and Huntly 2003
Model: Predictor (effect sign)
AICC
ΔAICC
Akaike weight
SITE LEVEL
DaysBelow-10 C (+),
MeanSummerTemp (-)
17.381
0
0.529
MeanSummerTemp/RelForbCov 19.473
er (-)
2.093
0.186
Mean SummerTemp (-)
19.843
2.463
0.154
16.363
0
0.282
DaysBelow-10 C/RelForbCover 17.976
(-)
1.613
0.126
MeanSummerTemp/RelGramCo 18.109
ver (-)
1.746
0.118
MeanSummerTemp/RelForbCov 18.185
er (-)
1.822
0.113
RelGramCover (+)
18.433
2.070
0.100
RelForbCover (+)
19.281
2.918
0.066
SUB-SITE LEVEL
Null model (intercept only)
Predictor
SITE LEVEL
MeanSummerTemp
MeanSummerTemp/RelForbCover
DaysBelow-10 C
RelForbCover
DaysAbove28 C
RelGramCover
DaysBelow-10 C/RelForbCover
MeanSummerTemp/RelGramCover
SUB-SITE LEVEL
DaysBelow-10 C/RelForbCover
MeanSummerTemp/RelGramCover
MeanSummerTemp/RelForbCover
RelGramCover
RelForbCover
DaysAbove28 C
MeanSummerTemp
DaysBelow-10 C
Akaike
weight
Mean Akaike
wt/model
Sign of effect
0.722
0.186
0.536
0.066
0.058
0.016
0.004
0.000
0.241
0.186
0.179
0.033
0.019
0.008
0.004
0.000
Neg (3)
Neg (1)
Pos (2), Neg (1)
Pos (2)
Neg (2), Pos (1)
Neg (2)
Neg (1)
Pos (1)
0.126
0.118
0.113
0.100
0.066
0.075
0.071
0.071
0.126
0.118
0.113
0.050
0.033
0.019
0.018
0.018
Neg (1)
Neg (1)
Neg (1)
Pos (2)
Pos (2)
Pos (4)
Neg (4)
Neg (4)
Photo by Shana Weber
The best model (ΔAICc = 0) of persistence at the site level
1.0
H
(a)
0.2
0.4
0.6
0.8
C
D
0.0
Duffer Peak, Pine Forest Range, Nevada
Persistence observed (dots) and modeled (line)
Hays Canyon Range, Nevada
-5
0
5
10
Linear predictor: f(Mean summer temp., Days below -10 C)
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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
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Mean number of days above 28°C at sites of persistence was
1.23, at sites of extirpation it was 10.42
( p = 0.02)
Hyperthermia and death can occur from even brief exposure
to moderately high temperatures (25.5-29.4°C; MacArthur
and Wang, 1973, 1974; Smith, 1974)
Behavioral thermoregulation, access to cooler temperatures ?
Hart Mountain, Oregon
Ruby Mountains, Nevada
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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:
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White Pine Range, Nevada
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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.
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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
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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
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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
Future of pikas in the Great Basin?
Arc Dome, Toiyabe Range, Nevada