1925 1 Storer: A Synopsis of the Amphibia of California 
7 
GENERAL DISCUSSION 
Amphibians are controlled in their distribution chiefly by con- 
ditions of temperature and moisture. The interplay of these two, in 
varying combination, sets the limits within which certain species may 
and others may not exist. Other factors are effective, at least in some 
cases, but a majority of species are limited by the two controls men- 
tioned. Freezing temperatures can be withstood by amphibians for 
only brief periods of time; prolonged exposure results in death. The 
upper thermal death point for our amphibians is not known with any 
degree of accuracy. It varies greatly with different species. Ascaphus 
truei seems unable to withstand a temperature greater than 40° F. 
Some of our species seem to be able to withstand short exposure to 
temperatures up to 100° F. Ellis and Henderson (1915, pp. 254-255) 
report Bufo boreas in numbers in water at a temperature of 34° C. 
(93.2° F.). The limiting requirements with respect to moisture have 
already been indicated. 
In the general geographic distribution of amphibians three factors 
have been postulated (see Gadow, 1901) as of prime importance in 
delimiting the ranges of these animals: salt water, permanently frozen 
ground, and complete deserts. The presence of large amounts of lime 
salts in the soil is also believed to be a barrier. 
No marine species of amphibian is known. Salt water is in 
general an effective barrier to the entire group, though in diluted 
form it is at times inhabited by amphibians. Pearse (1911) has 
reported the successful development of ranid larvae in a branch of 
Manila Bay where the salinity was as great as 20.96 parts per 
thousand. The California Toad ( Bufo boreas halophilus) has been 
observed on at least two occasions in the strongly brackish water at 
the head of San Pablo Bay; one individual was seen alive and swim- 
ming a quarter-mile from shore. Salt water, in combination with 
other factors, is at present operating to limit the range of certain 
species of amphibians in California. Dicamptodon ensatus and 
Aneides flavipunctatus occur in the coastal territory between the 
Golden Gate and Monterey Bay, but the individuals which live there 
are cut off from contact with the remainder of their respective species- 
