Full-text - Norsk entomologisk forening

Norwegian stoneflies II 247
2). There are differences between Rogaland
and the Oslofjord in the inner lowland areas
as there are two distinctly north-eastern
species in Rogaland while there is only one
in the Oslo area.
Finally, the areas in northern Norway
which are near the immigration routes of
the north-eastern species support the highest
number of species. In southern Norway, the
areas with the most continental climate have
the highest number of such species, while the
areas with the most pronounced atlantic
climate have very few north-eastern species.
CONCLUSION
In general the distribution of Norwegian
stoneflies seems to be connected with major
factors such as differences in climate, vegetation
region and historical immigration.
However, the more local distribution seems
to be associated with several other factors,
of which the amount of deciduous vegetation
in the vicinity of the watercourse, the amount
of allochthonous organic matter, substratum
and temperature are among those shown to
be of importance in the present study. Such
factors clearly interact differently to produce
different faunal associations in the various
areas. In part Ill: Field studies on ecological
factors influencing distribution, and in part
IV: Laboratory tests on ecological factors influencing
distribution, these factors will be
documented and discussed individually in
more detail.
SUMMARY
In the present work about 500 streams and
lakes from all parts of Norway were investigated.
The material consists of about 45,000
specimens.
The distribution of the Norwegian species
is plotted in Figs. 25-58.
Thirty-four of the 35 Norwegian species
have been collected by the author, twentynine
of these 35 species in southern Norway
and 32 in northern Norway. Seven of the species
present in southern Norway have not been
recorded west of the central mountain chain
(Langfjellene).
The most continental areas in southern
Norway, North 0sterdalen and its surroundings,
support the highest number of species.
In the south there is a decrease in number
of species towards west, south-west and south.
There is also a reduction in species towards
the coastal areas. This trend was examined
in southern Norway and in the north there
also seems to be a similar trend.
There are differences between southern
and northern Norway in the presence of different
species in various vegetation belts.
While Capnia pygmaea, Amphinemura borealis
and Isoperla difformis only occur in
the Boreal coniferous areas in southern Norway,
they all occur in the Sub-Alpine belt
in northern Norway.
A reduction in species paralleled by the
reduction in deciduous vegetation and the
amount of organic allochthonous matter in
the streams was observed in all parts of
Norway. This trend was investigated in different
vegetation belts in three study areas.
The trend is mainly connected with the reduction
in Salix vegetation along the streams.
Above the Salix belt only a few species are
common, Diura bicaudata, Arcynopteryx compacta,
Capnia atra, Amphinemura standfussi,
N emoura cinerea, N emurella picteti and in
northern Norway Nemoura arctica. Only two
or three of them are usually taken together
in each area.
The Capniids are mainly distributed in the
eastern parts of southern Norway and they
are most common where there is a rich soil
and deciduous trees along the streams.
Seventeen of the Norwegian species were
taken in lakes at least once. The highest number
of species was taken in the high altitude
lake, 0vre Heimdalsvann, and in the lakes
in northern Norway.
Some species seemed to be restricted to
certain substrata and streams of certain size
in some areas of Norway, but had a wider
distribution in other areas. There were great
differences in this respect between southern
and northern Norway and between low and
high altitudes.
The investigations have shown that there
are such great faunistic differences between
the different areas of Norway that previous
generalizations about the classification of