Fróðskaparrit - 01.07.2004, Síða 53

FØROYSKAR VATNKLUKKUR
51
Discussion
The current work has not generated any ad-
ditions to the Faroese checklist, but it has at
least consolidated the position. The fauna is
highly impoverished, without whirligig
beetles (Gyrinidae), larger diving beetles,
reed beetles (Donaciinae), or Dryopoidea.
The paucity of the beetle fauna is matched
by impoverishment in other parts of the
fauna. In particular the absence of mosqui-
toes and amphibians must surely explain
the absence of Colymbetinae and Dytisci-
nae. Arguments concerning the potential
for dispersal to the Faroes are irrelevant if
there is no food available upon arrival.
Of the fourteen aquatic species known
with some certainty from the Faroes, three
are also Nearctic as well as being Palaearc-
tic, with a further two introduced to the
New World. Six of the species extend to
North Africa, a further five occur as far
south as the Iberian Peninsula, two get to
France, and only one, S. multilineatus, is
particularly restricted, being known south
to Ireland and east to West Siberia.
However, the precise distribution of S.
tnultilineatus and S. griseostriatus (De-
Geer) remains to be clarified, the latter be-
ing known south to Morocco, and also in
North America and Asia. But whatever the
precise status of S. multilineatus it is the
only boreomontane water beetle in the
Faroes, the rest being widely distributed
species in western Europe frequently found
in lowlands. Thus the affinities of the fauna
are primarily western and Atlantic, entirely
as would be expected on islands influenced
by the Gulf Stream.
With one exception, all of the species
found are known to fly, Agabus bipustula-
tus, Hydroporus pubescens, the Cercyon
and the Helophorus taking readily to flight
throughout adult life. The exception is
Anacaena globulus, well known for its lack
of flight ability (Jackson, 1956) and also, of
course, for its occurrence in most wetland
habitats on remote islands within its range.
Phenomena typical of island faunas are ev-
ident. Those species that have become es-
tablished are very common and occupy a
wider range of habitats than on the main-
land. Hydroporus memnonius and H. nigri-
ta might have been thought rare on the ba-
sis of West (1930) having only found one of
each, neither having been otherwise previ-
ously recorded, but we found them com-
mon once an appropriate sampling method
was used. Species that we could not fínd,
Helophorus brevipalpis and Cercyon mari-
nus, might well have occurred as a result of
temporary colonisation. Colour forms oc-
cur more frequently than on the mainland.
The pale form of Hydroporus palustris in
the Nykutjørn is particularly striking.
Mjoberg (1917) referred to a spotted form
of Cercyon littoralis, and West (1930) con-
firmed that Mjoberg’s series from Trongis-
vágur includes both dark and spotted
forms. Finally the “rules of substitution” on
islands, i.e. where species normally not oc-
cupying certain habitats do so in the ab-
sence of the species normally occupying
this habitat, are always of interest. The oc-
currence of Anacaena globulus in the
“wrong” habitat has been noted. The domi-
nance of Hydroporus palustris in larger wa-
ter bodies and that of H. erythrocephalus in
smaller pools will be established by refer-