Amphibian
population declines at Savannah River Site are linked to climate, not
chytridiomycosis
P. DASZAK,1,5 D. E. SCOTT,2 A. M. KILPATRICK,1
C. FAGGIONI,3 J. W. GIBBONS,2 AND D. PORTER4
1Consortium
for Conservation Medicine, 460 West 34th Street, 17th Floor, New York,
New York 10001 USA
2Savannah River Ecology Laboratory, University of Georgia,
Aiken, South Carolina 29802 USA
3College of Veterinary Medicine, University of Georgia, Athens,
Georgia 30602 USA
4Department of Plant Biology, University of Georgia, Athens,
Georgia 30602 USA
Abstract
Amphibian populations at the Savannah River Site (SRS), South Carolina,
USA, have been censused consistently for 35 years, and this provides a
time series to examine the causes of population fluctuations. We examined
archived museum specimens of 15 anuran species collected at wetlands on
the SRS for the presence of the causative agent (Batrachochytrium
dendrobatidis) of chytridiomycosis, an emerging disease associated
with population declines elsewhere. Infections were present in three out
of 137 (2.18%) individuals; the pathogen was detected in two Rana
catesbeiana and a single Rana sphenocephala, all collected
between 1978 and 1981. Lesions were not consistent with the later stages
of fatal chytridiomycosis. Analysis of population trajectories of nine
amphibian species over 26 years at SRS showed that four species declined
significantly over this period, including R. sphenocephala. However,
we demonstrate that these declines are more likely caused by an increase
in the number of years with insufficient rainfall and a shortened hydroperiod
at the breeding site than by chytrid epidemics. This pattern appears to
be linked to a drying trend at SRS through the 1990s, although it is unclear
whether this was caused by climate change. This study demonstrates that
the presence of B. dendrobatidis in amphibian communities where
some species are declining does not always implicate chytrids as a cause
of the decline. Like many other emerging pathogens, the outcome of infection
can vary among individuals and populations, depending on life history
traits, environmental conditions, and virulence factors of the pathogen.
Our report also demonstrates the usefulness of archived museum specimens
and long-term population monitoring in studying the host–parasite
ecology of emerging diseases.
Key
words: amphibian population declines; Batrachochytrium dendrobatidis;
chytridiomycosis; climate change; disease ecology; host–parasite
ecology; hydroperiod; Savannah River.
5 E-mail: daszak@conservationmedicine.org
SREL Reprint #2909
Daszak, P.,
D. E. Scott, A. M. Kilpatrick, C. Faggioni, J. W. Gibbons and D. Porter
2005. Amphibian population declines at Savannah River Site are linked
to climate, not chytridiomycosis. Ecology 86:3232-3237.
