Fróðskaparrit - 01.07.2004, Síða 71

EITURKOPPAR (ARANEAE) í FØROYUM: EITT ENDURSKOÐAÐ YVIRLIT
OG EIN DAGFØRING AV ÚTBREIÐSLU INNANOYGGJA
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identifíed them as belonging to M. morulus.
Also Holm’s paper needs, however, to be
revised as he listed 66 species but did not
include C. bicolor, although he did himself
collect and identify it from the the Faroes
(see the annotated species list). Thus, the
two papers converge on 67 species and with
the additional 16 the total number now
amounts to 83; 59 of which (i.e. 71 %) be-
long to the family Linyphiidae. At least 7
species on the list are synanthropic (viz. P.
phalangioides, U. plumipes, L. leprosus, M.
merianae, N. umbratica, T. domestica, and
T. atrica) and quite possibly some more,
e.g. B. index and T. affinis , both considered
accidental (Brændegaard 1928), and the
two Araneus species, which leaves at the
most 76 non-synanthropous species native
to the Faroes, about 78% of which are
linyphiids. For comparison, Agnarsson
(1996) gives 84 species native to Iceland of
which 61 (73 %) are linyphiids, which is
representative for northern latitudes (Kopo-
nen, 1993).
The preceding historical sketch indi-
cates some factors that obviously con-
tribute to the present, considerable exten-
sion of the previous species lists. For in-
stance, increased sample sizes will, for
purely statistical reasons, yield more
species, as will the use of different collect-
ing methods and an increased geographical
coverage and inclusion of different habitats
(e.g. mountain tops), and perhaps more im-
portantly collecting also outside the sum-
mer season. The commonness of C. concin-
na is a striking example of the latter, as only
1 % (of 1639) individuals from Havnar-
dalur and Eiðisvatn were caught during
June - August. Holm (1980) considered the
species common and suspected that earlier
investigators had misidentified it for C. bi-
color. This does not, however, explain the
complete absence of C. concinna in the
summer collections of 1978 (Bengtson and
Hauge, 1979). Ashmole (1979: 89) notes
that in Shetland in spring the pitfall traps
contained C. bicolor but no C. concinna.
Other Faroese species for which collecting
outside the summer season is, or may be,
particularly important in order to establish
their status are e.g. A. pulverulenta, B. lute-
olus, C. prudens, C. brevipes, D. bidentata,
G. vivum, S.faustus, L. mengei, and W. an-
lica. Another factor that in recent years has
contributed to the extension of the species
list is the increased public awareness of spi-
ders indoors and on buildings.
There are, of course, biological reasons
for anticipating amendments to the species
list; e.g. an ongoing immigration. Spiders
in general have a good ability to disperse
and many linyphiids are well-known aero-
nauts (e.g. Bristowe, 1929; Duffey, 1956).
In this context it can be noted that the vast
majority of spiders on the Faroese list are to
be found both in the British Isles and in SW
Norway and may thus have emigrated from
either of these two regions, and there are
relatively few species that occur in only one
of them (see Ashmole, 1979; Holm, 1980).
The Faroes undoubtedly receive immi-
grants from time to time and some of them
may get established, whereas others go ex-
tinct after a while. It is however, extremely
hard to distinguish between a new immi-
grant and a rare species that has previously
been overlooked (McArdle, 1990) and even