Small-mouthed salamander (Ambystoma texanum) COSEWIC assessment and status report: chapter 6

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Population Size and Trends

It is clear (Table 1) that the genomic hybrids outnumber both Ambystoma laterale and A. texanum on Pelee Island. Most of the specimens that were used to derive the data in Table 1 came from random samples of eggs and larvae. The large number of individuals that were sampled provides a fairly accurate estimate of both the presence, absence, and the frequency of Ambystoma texanum in the six breeding sites for Ambystoma. Because it is very difficult to distinguish A. texanum from some genomic hybrids without genetic confirmation, finding large numbers of eggs, larvae, or even adults only confirms breeding success and does not provide density estimates for A. texanum. It is known, however, that reproductive success of the genomic female hybrids depends on their association with males of either A. laterale or A. texanum (Bogart and Licht 1986). Thus, finding larvae and juveniles in populations that have been found to contain only A. texanum attests to the continued existence of that species at that site. Because of the problems identifying A. texanum, we do not know the population density of “pure” A. texanum and can not assess trends. All species of Ambystoma for which there are data on population sizes fluctuate extensively in abundance, as is typical of pond-breeding amphibians in general (Green, 2003). Two former breeding ponds have probably been extirpated (the North End Woods site and the Girl Guide Pond site). Both those sites are on private lands and the current vegetation is not typical of ephemeral pond habitat.