Maps to Play, or Why Doesn’t Pallas’ Spadefoot Toad Go East

We revealed the reasons that prevent the Eastern European amphibian, Pallas’s spadefoot toad (Pelobates vespertinus), to move into Asia beyond the Tobol River valley. It dig itself into a burrow in the fall and thus avoids the negative wintering temperatures. There are no known meridional geographical boundaries on the eastern border of its range. The average soil temperatures for January at depths of 80, 120, 160, and 240 cm from 390 meteorological stations have been plotted on the map, as well as isotherms, to compare the outline of the P.vespertinus range borders. The depth of the soil 0°C isotherm increases from 80 cm in Europe to more than 160 cm in the southwest of Western Siberia and Kazakhstan, and the eastern border of the Pallas’s spadefoot toad range clearly coincides with it. The subsequent depth-determined increase of temperatures is small and by 240 cm approaches only 2°C, while for the Pallas’s spadefoot toad activity it is believed to be 3–4°C. The cumulative effect is expressed in the form of a “buried frontier” of this amphibian distribution. The described phenomenon can be useful as an example of the formation of habitat boundaries when conditions change not on the surface, but deep in the ground.

Pelobates vespertinus, Pallas’ spadefoot toad, Pelobates vespertinus, range, wintering temperatures, soil freezing, limiting fac