Newts Of California
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.
Bibliography
Kerby, L.J. and L.B. Kats. 1998. Modified
interactions between salamander
life stages caused by wildfire-induced
sedimentation. Ecology,
79:740-745