Fróðskaparrit - 01.01.1987, Side 46

When, How, and Whence?
A Tentative Background for the Post-Glacial Immigration
of Terrestrial Invertebrates of the Faroes
Pehr H. Enckell
Abstract
An attempt is made to distinguish between
different phases in the immigration history
of terrestrial invertebrates to the Faroe Is-
lands and to estimate their relative import-
ance. It is shown that a phase of large-scale
immigration over the sea occurred some
time between 10000 BP and 9000 BP, and
that immigration by this means later be-
came less important. Immigration by drift-
wood has probably occurred now and then;
it probably started earlier from the Ameri-
can continent than from the northern parts
of Eurasia. Aerial immigration has been
important continuously since the islands
became available for invasion; this process
has increased in importance over time bec-
ause of increased species richness in the
main source areas in NW Europe. Immi-
gration by agency of Man has taken place
only during the last 1100 or so years; source
areas have been western Norway, Den-
mark, and the northern part of the British
Isles. Chance immigration of species with
special habitat requirements has occurred
during the human occupancy of the islands;
examples are e.g. species that require deep
soil layers, and forest-dwelling species in
the recently established forest plantations.
The place of the Faroes in the North At-
lantic biogeographic context is shown by a
comparison between the occurrence of
four groups (Coleoptera, Araneae, Lum-
bricidae, and Gastropoda) in the Faroes
and the surrounding areas. Differences in
species numbers between the areas are
small for anthropochorous groups (Lum-
bricidae, Gastropoda); they are consider-
ably greater for groups where the main
immigration has been by other means than
by Man (Coleoptera, Araneae). For these
groups isolation, island area, and plant
cover are important, in addition to the
respective species’ dispersal ability.
Introduction
The Faroe Islands is the most isolated is-
land group in the temperate Atlantic. It is
situated 320 km from Scotland (the nearest
mainland), while, e.g. Shetland is only
Fróðskaparrit 34. bók (1988): 50-67