Feeding Ecology of Stream-Dwelling Pacific Giant Salamander Larvae (Dicamptodon tenebrosus)

Abstract

Pacific giant salamander larvae in a northern California stream were found to consume a wide variety and size range of prey in a one-year diet study. Aquatic insects made the greatest contribution to salamander diets, both numerically and by volume, with ephemeroptera nymphs being the most frequently consumed prey type. Although terrestrial invertebrates that fell into the stream constituted a small proportion of the diet numerically, they comprised a large proportion of diet volume throughout the year. Stomach contents mass and the proportion of intact prey in the stomach contents did not vary with time of day. In contrast, larval salamanders exhibited a strong diel activity pattern, being inactive and under cover during the day and active on the streambed surface at night. As larval salamanders grew, they included larger prey in their diet but continued to consume large numbers of very small prey. Small salamanders were able to consume a large proportion of the size range of most common prey, whereas only large salamanders were capable of consuming rare, large prey (e.g., large odonates, megalopterans, fish, and small salamanders). There was considerable dietary overlap among three co-occurring salamander size classes suggesting that food resources were not strongly partitioned among them. Relative abundances of prey in the diet were not correlated with their relative abundances in the environment, indicating that larval salamanders feed preferentially on certain prey taxa while avoiding, not encountering, or being unable to capture others. Electivity values were consistently positive for ephemeropterans and large, mobile invertebrate predators but were consistently negative for small, cryptic invertebrates and case-building caddisflies. In addition, mean sizes of three common mayflies were consistently larger in salamander stomach contents than in the benthos, indicating that predation on benthic invertebrates by larval Dicamptodon tenebrosus is size selective.