Adult Newts Present Minus The Earthworms example essay topic

In southern California, adult California newts (Tari cha 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.

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