NORSK ENTOMOLOGISK TIDSSKRIFT - Norsk entomologisk forening

I~zz~estigations regarding the Plecoptera fauna in Rogaland 115
August and dominates in September. The number of Plecoptera,
however, is small in September.
A. sulcicollis is found in large quantities in Storelva and have
here a stronger position than in SuldalslAgen. The main hatching
of A. borealis takes place between 14 days and one month earlier
in Storelva than p SuldalslAgen; L. fztsca, therefore, dominates
in July, alone.
A. borealis is the particular stone-fly which occurs in the greatest
number in both rivers and it comprises more than half of all
Plecoptera in this area. Of the 14 species, 13 are found in SuldalslAgen
and 12 in Storelva. The following species are found in
Suldalsligen but not in Storelva: Erachyfitera risi and Protonemzwa
meyeri. Conversely, Leztctrn nigra was found once in Storelva
but in Suldalsligen.
In Fl~gstadbekken (stream) 11 species were found. No Plecoptera
dominates here in the same manner as in the two rivers.
There is, however, during the early months of Spring, a slight
dominance of A. borealis. Three species are common besides
A. borealis, this applies to A. sulcicollis and L. fusca. D. nanseni
and Isofierla obscura have not been found in Fl~gstadbekken
where only one carnivorous species, I. grammatica, has been
found in a few specimens. Carnivorous nymphs have thus a far
larger percentage part of the Plecoptera fauna in the two rivers
where Diura nanseni is the chief predator in the bottom fauna.
Discussion
In a classification of Swedish rivers and streams according to
Plecoptera fauna, Brinck's terminology is used: eucoenic regarding
species which occur in one definite habitat only or, at all
events, are more common there than in other habitats, and
tychocoenic, regarding species which occur in both the named, and
similar. habitats. The suecies are fullv adiusted here to the habitat
mentioned but the ecol~gical adaptafionis wider than in the eucoespecies.
Brinck undertakes a division of rivers on the basis of temperature
and the species composition of the Plecoptera.
Two of the three species which dominate compositions in
Suldalsligen and Storelva, A. borealis and D. nanseni, are
eucoenic according to Brinck in what he calls northern streams.
In this investigation A. borealis forms more than half of the
Plecoptera in both streams and it should be possible to group these
near to what Brinck terms northern streams. Suldalsl$gen, in
particular, must be reckoned as belonging to this river type, even
if E. risi which is eucoenic in southern streams, has been found in
considerable number on a few occasions. B. risi, however,
belongs, mainly, to the tributaries where it is found in the largest