Small-mouthed salamander (Ambystoma texanum) COSEWIC assessment and status report: chapter 9

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Limiting Factors

Ambystoma texanum depends on ponds that maintain water through the larval stage that normally lasts from March through July. The low water level at Mosquito Point Woods could pose a problem if that area dried too soon and rainfall was not adequate to replenish the flooded woods. Although there are no longevity records for adult A. texanum in nature, captive specimens survive for at least 15 years (Bogart, unpublished) so unusually dry years with little or no recruitment would not be expected to be a major factor in the possible extirpation of A. texanum. Competition with nuclear hybrids may also be a factor that reduces the density of A. texanum but these hybrids require male A. texanum or male A. laterale for their continued survival. Perhaps, A. laterale could replace A. texanum but that species is mostly restricted to the Sheridan Point area where the habitat is quite different. It is also more likely that A. texanum would displace A. laterale because A. texanum are larger, can produce more eggs than A. laterale, and have been found in more diverse habitats over a larger area of the Island. We have no new information with respect to possible predators or unusual weather conditions that might have had a detrimental effect on A. texanum.

Climatic conditions are considered to be the most important factor limiting the northern spread of this species. Ambystoma texanum reaches the northern limit of their extensive range in Michigan where they are considered endangered (Harding 1997) with a heritage rank status of S1 (critically imperiled). Ambystoma texanum is fairly tolerant of human environmental disturbances throughout its range but does require shallow fish-free ponds that hold water into mid-summer. Because Pelee Island is also close to the northern limit of its range the species is probably limited by climatic conditions on the Island but we have no information on this aspect of its biology.