Population structure, growth, and size of larval Dicamptodon ensatus (Eschscholtz)

The Pacific giant salamander, Dicamptodon ensatus (Eschscholtz), is a characteristicand dominant element of the salamander fauna of the western Coniferous ForestBiome. Although known to herpetologists since 1833, its life history is poorly under-stood. Rathke (in Eschscholtz, 1833) found a shrew in the stomach of the holotype;and since that time the remarkably voracious feeding habits of both the larvae andtransformed individuals have been repeatedly confirmed. Cope (1889) establishedthe fact that some individuals are neotenic. Little else of significance concerning thelife history of D. ensatus appeared in the literature until the studies of Henry and
Twiny (1940), Kessel and Kessel (1943a, 19436, 1944), and Dethlefsen (1948)
led to an hypothetical life history. Briefly, the proposed life cycle is as follows.The salamanders breed in the spring. Eggs are deposited underground in the headsof springs. Development is slow, and hatchlings do not appear until late fall or
winter. Kessel and Kessel (1943a), following Storer (1925), state that the younghatch at 17 mm total length. Earlier, however, Henry and Twitty (1940) showedthat Storer's data were based on hatchlings of the northwestern salamander, ilmbystomagracile (Baird) and not D. ,ensatus. Kessel and Kessel (1943a) estimated growth ratesof larvae to be 7.58 to 12.34 mm total length per month through their first summer,attaining a total length of about 100 mm one year after hatching. Larvae continueto grow into their second summer and transform from June to August at total lengthsof about 135 mm. Kessel and Kessel (1944) speculated that some individuals maynot transform during years of unusually high precipitation, and that these individualsmay become sexually mature larvae.
Recent field work with populations located throughout the range has shown thatthere is considerable, and to some extent predictable, variation in the life history ofD. ensatus. Information on variation in population structure, growth, and size oflarval D. ensatus is presented in this paper.