Zoogeographical Studies on Fennoscandian Stoneflies (Plecoptera)

Abstract

Forty species of stoneflies, belonging to seven different families, occur in Fennoscandia. In Norway all these families are represented in the inner fjord areas and in the continental lowland. The highest number of species are found in continental areas subject to a wide annual amplitude in temperature and the lowest number in coastal areas with a small temperature amplitude. In Fennoscandia the highest number of different stonefly species have been recorded from areas north of the polar circle and in the continental parts of the boreal and subalpine vegetation belts. The lowest number have been recorded from the coastal areas and on the islands. The former is due to the strong represen- tation of north-eastern species, as exemplified by the genus Nemoura, and the latter phenomenon is also due to special ecological factors. Predatory species are sparsely distributed in the coastal areas in southern Fennoscandia and are absent from islands such as Gotland, Oland and Bornholm. They are commonest at high altitudes and latitudes, being especially abundant in the northernmost parts of Norway, such as the areas close to the North Cape. The herbivorous species of the genus Amphinemura are especially abundant in south-western Norway, also to some extent in the east. Capnia species are most abundant at high altitudes and latitudes and is sparsely distributed in southern Fennoscandia. In northern Norway, Nemoura species are often the most abun- dant herbivores, while N. cinerea is the most successful species in the coastal areas and on islands such as Oland and Gotland. One or two Leuctra species seem to be abundant in most parts of Fennoscandia. The individual stonefly species show local differences in distribution, largely due to differences in dura- tion of their egg incubation periods and in the growth rates of the nymphs.