Fluctuation in the Abundance of the Narrow-Headed Ant (Formica exsecta, Hymenoptera, Formicidae) and Climatic Changes in the Northeastern Part of Its Range

摘要

In some localities of the upper reaches of the Kolyma River, the narrow-headed ant (Formica exsecta Nylander, 1846) has become the dominant species instead of a rare one during the last decade. To study this phenomenon, soil temperatures at a depth of20 cm were measured in the winter of 2008-2009, near 11 nests of this species and in 11 more biotopes without nests, in the same localities where similar measurements had been carried out in the 1980s. The growth of minimum air temperatures by 2-2.5°Ccombined with increased snow cover since the end of the past century by the present time, has resulted in the minimal soil temperatures at a depth of 20 cm rising by 3-7°C. Being one of the least cold-resisting species of the genus (with limit of tolerance -12...-15°C), the narrow-headed ant has responded to winter warming of soils by increasing the variety of inhabited biotopes by 3-4 times, from 5-6 to 20-23 out of more than 43 examined; its abundance has grown sharply, to 130 nests per survey route1300 m long and 20 m wide. Within the frame of the existing climate such deviations of soil temperature may occur once every 15-20 years. Therefore the changes observed may represent regular fluctuations. The prediction of population dynamics of F. exsecta in other parts of the subarctic belt within the permafrost zone should take into account the climatic specificity of the region which may considerably differ from that in adjoining territories.