We studied the relationship between the geographic distribution of the Pallas’ spadefoot (Pelobates vespertinus) and the soil temperature regime at the eastern boundary of this species’ range (south-western West Siberia and northwest Kazakhstan). This species overwinters underground, burrowing down to 1.5 m or deeper and has poor frost tolerance – it is unable to withstand temperatures below 0 °C, therefore, the temperature at its overwintering depth has to be above zero. A cartographic approach to identifying the distribution of zero isotherms was used. Winter soil temperatures at depths of 80 cm, 120 cm, 160 cm and 240 cm were plotted, based on deep soil thermometer data and the outline of the spadefoot’s range was compared with close-to-zero isotherms in deep soil. Within the range of this species, the depth of the position of zero isotherms increases eastwards: from 80 cm in European Russia, to more than 160 cm in the south-west of Western Siberia. The eastern boundary of the species’ range lies in the forest-steppe, steppe and semi-desert zones in the Tobol-Ishim interfluve and further south, on the left bank area of the Turgai River. This boundary clearly coincides with the zero isotherm, which lies here at a depth of 160 cm, forming an impermeable barrier to the spadefoot’s distribution.

中文翻译：

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越冬温度限制了Pallas的赤脚Pelobates vespertinus（Anura，Amphibia）地理范围的东部边界

我们研究了Pallas的赤脚（Pelobates vespertinus）的地理分布与该物种范围东部边界（西南西伯利亚和哈萨克斯坦西北部）的土壤温度状况之间的关系。该物种在地下越冬，挖洞至1.5 m或更深，抗冻性差–无法承受低于0°C的温度，因此，其越冬深度的温度必须高于零。使用了一种制图方法来识别零等温线的分布。根据深层土壤温度计数据绘制了80厘米，120厘米，160厘米和240厘米深度的冬季土壤温度，并将黑脚范围的轮廓与深层土壤中接近零的等温线进行了比较。在这个物种的范围内，零等温线位置的深度向东增加：从欧洲俄罗斯的80厘米到西西伯利亚的西南部的160厘米以上。该物种范围的东部边界位于图博伊河左岸地区Tobol-Ishim交汇处以及更南端的森林草原，草原和半沙漠地区。该边界与零等温线明显重合，零等温线位于此处160厘米深处，对黑脚的分布形成了不可渗透的屏障。