IN THE BIOLOGICAL SCIENCES
Department of Biology
and extinction in a high-elevation population of Rana mucosa.
David F. Bradford. Environmental Science and Engineering Program, School of Public Health, University of California, Los Angeles, California 90024 USA.
Rana mucosa is one of several high-elevation amphibians that have
recently disappeared from seemingly pristine sites. The present study documents
an event of mass mortality among larval and metamorphosed R. mucosa
in a lake in Kings Canyon National Park, California, and the ultimate extinction
of the population. In 1979 metamorphosed individuals declined from ca.
800 individuals in early summer to nearly zero in late summer. During this
time many carcasses were collected, individuals showed symptoms of red-leg
disease, and blood from an affected individual contained the bacterial
pathogen characteristic of this disease, Aeromonas hydrophila. Also
during the summer of 1979, nearly all of the approximately 1100 tadpoles
began metamorphosis, but all metamorphosing individuals were consumed by
Brewer's blackbirds (Euphagus cyanocephalus). This population of
R. mucosa continued to exist until at least 1983, but was extinct
by 1989. Recolonization of the site will probably never occur because streams
connecting to extant populations of R. mucosa now contain introduced
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