1. Amphibian Decline: Global Change By: Brandon Udy December 3, 2009

2. Causes of Amphibian Decline
Disease
Habitat modification
Killer fungus (Batrachochytriumdendrobatidis)

3. What Do These Have in Common?

4. Global Change

5. Hundreds are on the brink of extinction
The Global Amphibian Assessment
Lists:
427 species as “critically endangered”
122 species as “possibly extinct”

6. Reasons Why Global Change Causes Amphibian Decline
Climate-change has reduced water depth at oviposition sites which increases embryos’ exposure to UV-B radiation
Saprolegniaferax outbreaks due to increased UV-B exposure have been identified as a cause of high amphibian embryo mortality in the Pacific Northwest

7. Reasons Why Global Change Causes Amphibian Decline
Ozone depletion has caused an increase UV-B radiation that harms amphibians’ DNA and their eggs

8. Reduced Water Depth
El Nino: the warm phase of the periodic change in the atmosphere and ocean of the tropical Pacific region
Precipitation and water depth/ UV-B exposure are strongly linked to El Nino/ Southern Oscillation cycles
Amphibians, particularly those that breed in shallow montane lakes and ponds, may be quite susceptible to climate-induced changes in UV-B exposure

9. Experiment of Reduced Water Depth
The experiment was conducted at a natural oviposition site of Bufoboreas
The water depth at which embryos were placed was manipulated to 10, 50 or 100 cm
The exposure to ambient UV-B radiation was also manipulated (either exposed to the full complement of ambient UV-B or shielded from UV-B)

10. Experiment of Reduced Water Depth
The percentage of mortality associated with S. ferax infection was monitored in all manipulates

11. Experiment of Reduced Water Depth: Results
climate-induced fluctuations in the water depth influence the exposure of developing embryos to UV-B radiation
The percentage of mortality due to S.ferax was dependent on the water depth
The hatching success of B. boreasexposed to UV-B radiation was 33% less than that of their counterparts that were shielded from UV-B

12. Experiment of Reduced Water Depth: Results

13. Experiment of Reduced Water Depth: Results

14. Experiment of Reduced Water Depth: Results

15. Experiment of Reduced Water Depth: Conclusion
results suggest a complex series of interactions involving changes in both physical (water depth and UV-B exposure) and biotic (disease outbreaks) factors that alter mortality patterns
Changes that alter hydrology may be the precursor to other related mortalities in other population declines (not just B. boreas)
Supports that Pacific warming over recent decades is a common denominator for amphibian declines

16. Experiment of Reduced Water Depth: Conclusion
in aquatic ecosystems, climatic changes can increase the exposure of organisms to UV-B
Exposure of embryos to UV-B decreases the chances of survival of embryos
Increased frequency of El Nino events may increase the incidence of high embryonic mortality experienced by certain amphibians in the Pacific Northwest

17. Experiment of Reduced Water Depth: Conclusion
results suggest that in high mountain lakes, thefluctuation in water levels caused by global change could be of more concern with respect to UV-B exposure than depletion of stratospheric ozone

18. Chytridiomycosis
In the mountains of Costa Rica, seventeen years ago, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufoperiglenes)
The pathogenic chytrid fungus (Batrachochytriumdendrobatidis) is implicated
An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate

19. Chytridiomycosis Batrachochytriumdendrobatidiscauses chytridiomycosis
It is believed that amphibians die from this because of interference with skin functions including maintenance of fluid balance, electrolyte homeostasis, respiration and role as a barrier to infections

20. How Does This Have Anything To Do With Global Change?
At many high habitats, temperatures are shifting towards the growth optimum of Batrachochtrium, thus increasing outbreaks.

21. The Climate-Chytrid Paradox
shifts in temperature or related variables often influence disease dynamics
In fact, as temperatures rise, climate fluctuations may cross thresholds for certain pathogens, triggering outbreaks
However, Batrachochytrium, according to theory, becomes more pathogenic at lower temperatures.

22. 2 Solutions:
Warm or dry conditions may stress amphibians, thus increasing susceptibility to disease
“Lower temperatures benefiting the chytrid” may be and oversimplification of the pathogen’s response to climate.  warm years could favor the Batrachochytrium directly.

23. The Climate-Chytrid Experiment
assess large-scale altitudinal patterns of extinction risk
show that the timing of the widespread extinctions is strongly tied to large-scale temperature signals
explore local climate from a chytrid’s viewpoint to frame a solution to the paradox

24. 1. Assess large-scale altitudinal patterns of extinction risk
Bars indicate the number of species known per altitudinal zone, and the grey- shaded portions represent the estimated percentage of species lost from each.

25. 1. Assess large-scale altitudinal patterns of extinction risk
The percentage of species lost increases sharply at 200 m, and again at 1,000 m.
The percentage of species lost decreases, at 2,400 m, and thus peaks at middle elevations.
This suggests that low temperatures as well as high ones may limit the impact of Batrachochytrium

26. 2. Show that the timing of the widespread extinctions is strongly tied to large-scale temperature signals
Extinctions showed a positive correlation with warming
Around 80% of the species that have disappeared were seen for the last time right after a relatively warm year

27. 3. Explore local climate from a chytrid’s viewpoint to frame a solution to the paradox
Shielding them from excessive warmth and fostering moist conditions, cloud cover may promote the chytrid’ssurvival, growth and reproduction
increasing cloudiness therefore may increase amphibians’ susceptibility to infection
lowlands are often too warm for the chytrids during the day

28. 3. Explore local climate from a chytrid’s viewpoint to frame a solution to the paradox
highlands are often too cool for the chytridsat night
most Atelopus extinctions have occurred at elevations where the minimum temperature is shifting towards the growth optimum for this pathogen

29. The Climate-ChytridExperiment: Conclusion
Global climate change is already causing extinctions
Global climate change is moving towards the optimum temperature for chytrids

30. References
KieseckerJ.M., Blaustein A.R. & Belden L.K. (2001) Complex causes of amphibian population declines. Nature, 410,
Pounds, J.A. (2006) Widespread amphibian extinctions from epidemic disease driven by global warming.  Nature 439: 161
Stuart, S.N., J.S. Chanson, N.A. Cox, B.E. Young, A.S.L. Rodrigues, D.L. Fischman, and R.W. Waller Status and trends of amphibian declines and extinctions worldwide. Science306: