A Deadly Disease in a Changing
Climate Causes Tough Times for
Montane Frogs
Karen Pope, Jonah Piovia-Scott, Monty Larson, Janet Foley
U.S. Department of Agriculture
Pacific Southwest
Research Station
Science that makes a difference
MtnClim Topics
Climate
modeling
Climate
refugia
Paleoclimatology
Range shifts
Adaptation
Amphibians
Why are amphibians important in
mountain environments?
Threats to Amphibians
* Land use change – habitat alteration/loss
* Exotic species – predators/competitors
* Over-exploitation
* Pesticides and other toxins
* Infectious disease
* Climatic change
(Collins and Storfer 2003)
Trout introduced into most
mountain lakes
Remove trout and frogs recover
(Knapp et al. 2007)
Global Amphibian Epidemic Chytridiomycosis
“the most spectacular loss of vertebrate biodiversity due
to disease in recorded history”
Skerratt et al. 2007
Vredenburg et al. 2010
Lips et al. 2006
Batrachochytrium dendrobatidis (Bd)
•Flagellated
zoospores
•No dormant
stage
From Rosenblum et al. 2008
Bd is highly sensitive to temperature
Raffel et al. 2013. Nature Climate Change
Cascades frog (Rana cascadae)
Klamath Range
Southern
Cascade Range
What we know about Bd and Cascades frogs
• Bd is widespread
• Life stages
– Young frogs more
infected
• Seasonality
– Young frogs do not
clear infections
• Survival decreases
adult
juvenile
metamorph
Genome equivalents (log-transformed)
Bd prevalence and loads vary by site
and year
4
3
2
All sites
Carter Meadow
Colby Creek
Nelson Creek
Old Cow Creek
Screwdriver Creek
1
0
2008
2009
2010
Year
2011
2012
Objectives
• Understand why effects of Bd vary
• Assess the influence of microhabitat variables,
individual characteristics, and climatic
variables on infection dynamics
• Develop methods to improve chances of
survival with Bd
•
•
•
•
•
Methods
Repeat sampling
Local habitat characteristics
Frog measurements and marking
>2000 skin swabs
Temperature data from Daymet (http://daymet.ornl.gov)
Analysis
• Multistate Population Models
• GLMs
– 3 global models for climate, microhabitat,
individual characteristics
– Variable reduction
– Combine best models and reduce to composite
model
– Assess variables using model-averaged coefficients
and 95% confidence intervals
Variables to predict Bd status (+/-)
Climate (preceding 4wks)
• Mean of max daily
• Days >28°C
• Days<23°C
• MaxDrop
• DayDrop
• MaxMax
• MinMax
• Precipitation
• Easting, Northing
Microhabitat
• Water temperature
• Onshore veg type
• % cover
• % aquatic vegetation
• Flow
• Substrate
• Water depth
• pH
• Aq. Habitat type
Frog characteristics
• Length
• Weight
• Life stage
• Sex
• Julian day*Length
-Also Site, Year, Day
Variables to predict Bd status (+/-)
Climate (preceding 4wks)
• Mean of max daily
• Days >28°C
• Days<23°C
• MaxDrop
• DayDrop
• MaxMax
• MinMax
• Precipitation
• Easting, Northing
Microhabitat
• Water temperature
• Onshore veg type
• % cover
• % aquatic vegetation
• Flow
• Substrate
• Water depth
• pH
Frog characteristics
• Length
• Weight
• Life stage
• Sex
• Julian day*Length
-Also Site, Year, Day
Important climatic variables
Precipitation preceding 4 wks
Mean of max daily temp from
preceding 4 wks
Important habitat and life history
variables
Frog length
Local water temperature
Conclusions
• Short-term climatic variables influence disease
risk
• Local water temperature matters
• Juvenile frogs are most susceptible
• Year differences strong – climate?
40
61
68
75
82
89
96
103
110
117
124
131
138
145
152
159
166
173
180
187
194
201
208
215
222
229
236
243
250
257
264
271
278
285
292
299
306
313
320
327
334
341
348
355
362
30-day running average of daily temp (degrees C)
45
28 per. Mov. Avg. (2008)
28 per. Mov. Avg. (2009)
28 per. Mov. Avg. (2010)
28 per. Mov. Avg. (2011)
28 per. Mov. Avg. (2012)
28 per. Mov. Avg. (2013)
35
30
25
20
15
10
5
0
day number
Mean monthly temperature difference
from the 2008-2013 average
Difference from mean monthly max
temperature (°C)
6
4
2
2008
2009
2010
0
2011
2012
2013
-2
-4
-6
mar
apr
may
jun
jul
Month
aug
sep
oct
nov
Difference from mean monthly max
temperature (°C)
6
4
2
2008
2009
2010
2011
2012
0
-2
-4
-6
mar
apr
may
jun
jul
Month
Bd Prevalence, Spring
0.9
0.8
0.7
aug
Adult
survival
sep
oct
nov
Frog Recruitment
800
700
600
0.6
500
0.5
400
0.4
300
0.3
0.2
200
0.1
100
0
0
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
Implications
• Three threats – nonnative fish, disease, climate change interact to reduce survival of montane frogs
• Affect life stages differently
– Fish preclude breeding in most stable aquatic habitats (lakes)
– Bd most deadly to post-metamorphic frogs following cold
periods
– Recruitment rates (from tadpole to frog) highest following cool,
wet springs
• Results in strong annual shifts in life stage demographics
• While warming may be “good” for fighting disease, climate
variability is likely “bad”
• “Treatments” likely necessary to prevent extinction
• Climate : Disease forecasting needed
Acknowledgements
Melanie McFarland
Ryan Foote
Garth Hodgson
Cathy Johnson
Chris Mayes
Kevin Aceituno
Betsy Bolster
Josh Mell
Heather Rowe
Sherilyn Munger
Sharon Lawler
Erica Mittermaier
Cheryl Bondi
Jen Brown
Jon Stead
Alison Sanger
Almanor fish crew
Bennett Hardy
Marina de Leon
Joel Smith
Adam Clause