Fróðskaparrit - 01.07.2004, Síða 72

70
SPIDERS (ARANEAE) IN THE FAROE ISLANDS: A REVISED CHECKLIST
AND AN UPDATE ON INTER-ISLAND DISTRIBUTIONS
harder to establish the extinction of a small
spider population. Indeed, it is difficult to
document changes in distribution and/or
abundance of spiders. However, the present
data considerably increased the knowledge
about Faroese spiders and in addition to
new species on the list there are some 80
new island records; not unexpectedly many
of them refer to the islands most intensive-
ly studied viz. Kunoy and Koltur. Several of
the 18 islands obviously need to be more
thoroughly surveyed and so far only 18
species have been recorded on 9-16 islands,
while 24 species occur on 4-8 islands, and
25 species seem to have restricted distribu-
tions and are each found on one island and
often only once. In the case of the Iatter cat-
egory (the seemingly rare species) a com-
parison with, and reference to, other animal
taxa (flying ones, and species liable to be
transported by winds or by Man) seem jus-
tified. Following the passage of low-pres-
sure areas the Faroes receive immigrants of
insects, e.g. invasions of Lepidoptera and
Syrphidae (e.g. Kaaber, 1997a; 1997b;
Kaaber and Andreassen, 1999; Jensen,
2000; 2001), that may or may not get es-
tablished, but result in amendments to the
list of species recorded in the islands.
Among the spiders that have recently been
discovered in the Faroes, some are presum-
ably already established, e.g. the intro-
duced P. phalangioides and U. plumipes',
the former is a cosmopilitan species that is
widespread in Europe and at least used to
be absent from the extreme north (see
Roberts, 1995) and the latter species is cur-
rently extending its range in NW Europe
(Jonsson, 1998). O. melanopygius is inter-
esting because it is a cosmopolitan species
that is usually closely linked to human ac-
tivities (Aakra and Olsen, 2003). In the
Faroes it was not found until 1988, and is
now known from 4 islands but nowhere in
association with inhabited settlements
(though the abandoned ones at Skarð and
Skálatoftir); a spontaneous successful colo-
nization or a remnant of past introductions?
For some species there are at least some
indications of changes in status, long-term
or short-term, worthy of comment. The fact
that Holm (1980) in 1966 found C. concin-
na to be common and that we now found it
in summer samples from 13 localities but in
none from 1978 (Bengtson and Hauge,
1979) is not fully explained by the species’
seasonal activity pattern. Could it be that
the species had a poor year in 1978; a short-
term flucuation indicating the risk of sto-
chastic extinctions? Similarly, T. zimmer-
manni and L. robustum have both been re-
garded as common in the islands (Brænde-
gaard, 1928; Bengtson and Hauge, 1979;
Holm, 1980) but in the present study re-
markably fewer individuals were caught.
Another two species, B. luteolus and P. var-
iegata, were both considered common by
Brændegaard (1928), which is not support-
ed by later studies (Bengtson and Hauge,
1979 and Holm, 1980). In the case of the
former the explanation for this discrepancy
may be that the species is rnainly winter ac-
tive and mainly to be found on high
grounds. For P variegata it may be a ques-
lion of a long-term decline, which has been
indicated for Shetland (Ashinole, 1979:
91). Finally, and to further illustrate the dif-
ficulties in distinguishing between single