MAMMALS OF THE THINGVALLAVATN AREA

Mammals are poorly represented among the wild terrestrial fauna of Iceland. Only arctic foxes Alopex lagopus are indigenous to the country. However, wood mouse Apodemus sylvaticus and American mink Mustela vison, introduced by man, are also integral parts of the ecosystem of the Lake Thingvallavatn area now. Arctic foxes exhibit violent long-term fluctuations with the latest population trough occurring in the early 1970s and a continuous population increase since then. This increase is at least partly due to influx of foxes from the southwest. The size of the mink population is partly limited by the extent of ice-free areas on lakes and rivers during winter as evidenced by negative correlation between mink catches and ice cover of Lake Thingvallavatn. Wood mice exhibit irregular population explosions. Domestic mammals are chiefly represented by sheep, dairy cattle and Icelandic ponies. also termed Icelandic toelter horses. Sheep and ponies, grazing in pastures with active erosion, represent a certain threat to some areas around Lake Thingvallavatn. Cattle, however, are grazed only in cultivated fields and lowland meadows and can not be regarded as a threat to soil or vegetation. The number of sheep has been declining in the area while the number of ponies has increased in recent years.