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In southern California, adult California newts (Taricha torosa)have been
found to frequently cannibalize both larvae and egg masses. In turn, for those
adult newts that remain in the stream pools after breeding, conspecifics have
become one of their main sources of prey in the chaparral stream pools of the
Santa Monica Mountains. This study was undertaken to examine whether
wildfire-induced sedimentation would provide an alternative prey, such as
earthworms, and modify interactions between life stages of T. torosa. A diet
analysis, field surveys, and a laboratory experiment provided observations and
data for this study. For the diet analysis and field surveys, three sites were
studied: Cold Creek Canyon, which was burned in 1993, and Newton Creek Canyon
and Trancas Creek Canyon, which were unburned sites and served as controls.
Adult newts were collected during the spring and summer of 1992-1996 from Cold
Creek and during 1995 from Trancas Creek for diet analysis. A water lavage was
used to collect the stomach contents, which were then examined by microscope. In
addition, both burned and unburned sites were surveyed and monitored for the
availability of both earthworms and conspecifics. In the laboratory experiment,
a gravitational flow-through system was used to examine the behavioral responses
of larval newts to chemical cues of both adult newts and earthworms. Previous
studies had determined that larval newts hid from chemical cues of the adult
newts.
Through diet analysis, it was found that most of the stomach samples of
the adult newts contained conspecifics, earthworms, beetles, and mayflies.
Stomach samples from Cold Creek indicated that conspecifics were consumed
significantly more often than earthworms were consumed during the two years
before the fire(1992, 1993). However, during the two years after the fire (1994,
1995), more earthworms were consumed and conspecifics were eliminated as a food
source. In 1996, diet analysis showed a reappearance of conspecifics, but the
frequency of earthworms in adult newt stomachs was still greater. Frequency of
beetles and mayflies appeared to be similar before and after the fire. In
1995,stomach contents from Cold Creek and Trancas Creek indicated that more
earthworms were available at burned sites than at unburned sites.
In the
laboratory study, it was determined that the larvae tended to hide more when the
adult newt was present, but larval hiding appeared to depend on the earthworm
cues. If the earthworms were present, the larvae did not attempt to hide; if the
earthworms were absent, the larvae would attempt to hide. In addition, they
tended to hide more with adult newts present minus the earthworms than in the
company of both. Before the fire, adult newts frequently fed on their own larvae
and egg masses. Due to wildfires, stream banks were disrupted causing
sedimentation and the input of earthworms in the streams.
As a result,
earthworms became an alternative prey eliminating cannibalism for two years
after the fire. With the availability of the earthworms, larvae and eggs were
allowed to focus on development rather than survivorship. This is evident in the
two years after the fire for the density of the larvae and egg masses appeared
to have increased slightly. However, cannibalism reappeared three years after
the fire. By this time, vegetation growth had recovered and the stream banks
were more stable resulting in less sedimentation and fewer available earthworms.
Perhaps, after a few more years, conspecifics will become a main source of food
once again.
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