Essay, Research Paper: Newts Of California

Biology

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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.

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