Title: Causes of Amphibian Declines
1Causes of Amphibian Declines
- Julie Robertson
- Biol 402
- November 18, 2008
Pacific treefrog
2(No Transcript)
3- One-third to one-half of the worlds 6000 known
amphibian species could vanish in our lifetime,
resulting in the single largest mass extinction
since the disappearance of the dinosaurs. - -Vancouver Aquarium Marine Science Center
4Overview
- Trends in Amphibian Populations
- Global Status
- Threats to Amphibians
- Complex Causes of Amphibian Declines
- The Effect of Trematode Infection on Amphibian
Limb Development and Survivorship - Conclusions
- 2008 Year of the Frog
- Questions
5Trends in Amphibian Populations
- Declining throughout North America and Europe
Houlahan (2000)
6IUCN Red List Assessment for all 5,918 Known
Amphibian Species
EX Extinct EW Extinct in the wild CR
Critically endangered EN Endangered VU
Vulnerable NT Near threatened LC Least
concern DD insufficient information
7Threats to populations
IUCN 2008
8 Broad Causes of Declines
- Embryo Mortality with S. ferax
- Complex causes of amphibian population declines.
- (Kiesecker et al 2001)
- Reduced Fitness with Ribeiroia
- The effect of trematode infection on amphibian
limb development and survivorship. - (Johnson et al 1999)
9Background
- Knew that S. ferax outbreaks, in connection with
UV-B radiation, were correlated with high
amphibian embryo mortality. - Disease outbreaks on several species occurring
simultaneously - Believed that ozone depletion was causing
increased UV-B radiation, leading to increases in
mortality. - Wanted to know if it was Climate change that was
increasing UV-B radiation, rather than ozone
depletion.
10Methods
- Oregon Cascade Mountains between 1990 and 1999
- Measured 3 variables
- Number of embryos deposited
- Percent of S. ferax related mortalities
- Depth at which embryos developed
- Conducted field experiment
- Manipulated depth at which embryos were raised
- Embryos were subjected to either full UV-B
exposure, or completey shielded. - Collected summer S.O.I. data and winter
precipitation data
11Southern Oscillation Index
- Air pressure difference between Tahiti and Darwin
is recorded - The monthly fluctuations in this air pressure
difference is used to calculate the Southern
Oscillation Index (S.O.I) - Sustained negative values of S.O.I. are
associated with El Nino events
12Southern Oscillation Index
13Climate Change Affects Depth
- Knew that El Nino events are increasing in
frequency and intensity due to climate change - As S.O.I. increases, precipitation in the North
Cascades increases
14Climate Change Affects Depth
- Showed that depth of water column at oviposition
sites was a function of S.O.I.
15UV-B Radiation
White Shielded from UV-B Grey Exposed to UV-B
16Saprolegnia ferax
- Infected eggs easily detected
- Infected eggs do not hatch
17Saprolegnia ferax
- Acts synergistically with UV-B radiation
- Increases embryonic mortality
- Complex transfer from infected fish through soil
Black UV Blocking filter
18Saprolegnia ferax
- More than 50 of embryos that developed in
shallow water became infected - Less than 19 of embryos that developed in deep
water became infected - No UV-B influence on S. ferax related mortality
in deep waters
19CLIMATE CHANGE
REDUCED POOLS
UVB EXPOSURE
PATHOGEN OUTBREAKS
EMBRYO MORTALITY
20 Broad Causes of Declines
- Embryo Mortality
- Complex causes of amphibian population declines.
- (Kiesecker et al 2001)
- Reduced Fitness
- The effect of trematode infection on amphibian
limb development and survivorship. - (Johnson et al 1999)
21Reduced Fitness
- Number of reported deformed amphibians increasing
since early 1990s - Causes thought to include
- UV-B radiation
- Biocide contamination
- Parisite infection
- retinoids
22Methods
- Surveyed 35 ponds in Santa Clara County,
California - Focused on Pacific tree frogs (Hyla Regilla)
- Egg masses were collected from Eel River
- Six treatments
- Control
- Light
- Intermediate
- Heavy
- Alaria mustelae
- Alaria mustelae and Ribeiroia
23Results
- 85 of tadpoles exposed to Ribeiroia developed
severly abnormal limbs - Tadpole survival declined with increasing
parasite density - High survival rates in control group
- High rates of abnormalities in Heavy treatment
group - Alaria infected tadpoles, but had no effect
24Ribeiroi spp.
- Survivorship frequency decreases with increasing
Ribeiroia density - Abnormality frequency increases with increases
Ribeiroia density
- Survivorship and abnormality frequencies
unaffected by Alaria infection - Survivorship frequency significantly lower after
Ribeiroia treatment - Abnormality frequency significantly higher after
Ribeiroia treatment
25Infection to Death
- Direct mortality
- Indirect mortality
- Few abnormal adults found in the field
26Recent Increases
- Limb abnormalities shown to be caused by
Ribeiroia - Recent increases could be caused by
- Host species
- Accelerated eutrophication
- Removal of predators
- Further research needed
27Conclusions
- Amphibian populations declining drastically
- Complex interactions between abiotic and biotic
factors, on global and local scales - Climate change, depleting ozone layer (and other
factors?) leaving amphibians more vulnerable to
disease outbreaks
282008 Year of the Frog Campaign
- http//www.youtube.com/watch?v2hBdHydtF1I
- http//www.amphibianark.org/online-petition.php
29Questions?
30Literature Cited
- Houlahan J.E. (2000). Quantitative evidence for
global amphibian population declines. Nature 404
752-755. - Johnson P.T.J., Lunde K.B., Ritchie E.G. Launer
A.E. (1999). The effect of trematode infection on
amphibian limb development and survivorship.
Science 284 802-804. - Kiesecker J.M. Blaustein A.R. (1995). Synergism
between UV-B radiation and a pathogen magnifies
amphibian embryo mortality in nature. Proceedings
of the National Academy of Sciences of USA
92(24) 11049-11052. - Kiesecker J.M., Blaustein A.R. Belden L.K.
(2001). Complex causes of amphibian population
declines. Science 410 681-684. - Kiesecker J.M., Blaustein A.R. Miller C.L.
(2001). Transfer of a pathogen from fish to
amphibians. Conservation Biology 15(4)
1064-1070. - Pounds A.J. (2001). Climate and amphibian
declines. Nature 410 639-640. - Vanaqua.org
- Wikipedia.org
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