Conservation
Biology
Early
View (Online Version of Record published before inclusion in an issue)
MAUREEN
E. RYAN1,*,
JARRETT
R. JOHNSON2,
BENJAMIN
M. FITZPATRICK3,
LINDA
J. LOWENSTINE4,
ANGELA
M. PICCO5,
H.
BRADLEY SHAFFER6
1Department
of Evolution and Ecology, and Center for Population
Biology, University of California, Davis, CA, U.S.A
2Department
of Biology, Western Kentucky University, Bowling Green, KY, U.S.A
3Department
of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN,
U.S.A
4Department
of Pathology, Microbiology, and Immunology, School of Veterinary Medicine,
University of California, Davis, CA, U.S.A
5United
States Fish and Wildlife Service, Pacific Southwest Regional Office,
Sacramento, CA, U.S.A
6Department
of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Room
LS5120, Box 951606, Los Angeles, CA 90095 & La Kretz Center for California
Conservation Science, Institute of the Environment and Sustainability, La Kretz
Hall, Suite 300, Box 951496, 619 Charles E. Young Drive East, University of
California, Los Angeles, CA, U.S.A
*Current
address: Department of Civil & Environmental Engineering, University of
Washington, 201 More Hall, Box 352700, Seattle, WA 98195, U.S.A.
emails moryan@u.washington.edu, ambystomo@gmail.com
Article
first published online: 9 NOV 2012
DOI: 10.1111/j.1523-1739.2012.01955.x
Abstract
Biological
invasions and habitat alteration are often detrimental to native species, but
their interactions are difficult to predict. Interbreeding between native and
introduced species generates novel genotypes and phenotypes, and human land use
alters habitat structure and chemistry. Both invasions and habitat alteration
create new biological challenges and opportunities. In the intensively farmed
Salinas Valley, California (U.S.A.), threatened California tiger salamanders
(Ambystoma californiense) have been replaced by hybrids between California
tiger salamander and introduced barred tiger salamanders (Ambystoma tigrinum
mavortium). We conducted an enclosure experiment to examine the effects habitat
modification and relative frequency of hybrid and native California
tiger salamanders have on recruitment of salamanders and their prey, Pacific
chorus frogs (Pseudacris regilla). We tested whether recruitment differed among
genetic classes of tiger salamanders (hybrid or native) and pond
hydroperiod (seasonal or perennial). Roughly 6 weeks into the experiment, 70%
(of 378 total) of salamander larvae died in 4 out of 6 ponds. Native
salamanders survived (n = 12) in these ponds only if they had metamorphosed
prior to the die-offs. During die-offs, all larvae of native salamanders died,
whereas 56% of hybrid larvae died. We necropsied native and hybrid salamanders,
tested water quality, and queried the California Department of Pesticide Regulation
database to investigate possible causes of the die-offs. Salamander die-offs,
changes in the abundance of other community members (invertebrates, algae, and
cyanobacteria), shifts in salamander sex ratio, and patterns of pesticide
application in adjacent fields suggest that pesticide use may have contributed
to die-offs. That all survivors were hybrids suggests that environmental stress
may promote rapid displacement of native genotypes.
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