Full-text - Norsk entomologisk forening

164 H. P. Leinaas
Table IV. The composition of adults and the different instars of P. lanceolatus from 7 sampling days
at Slerstad.
1972 1973
6 Dec. 9 Febr. 22 March 10 May 17 June 4 Aug. 4 Oct.
Adult 2 1 1 2 2
Subad. 1 1 3
3. instar 1 1 1 7 3
2. instar 2 17 1 3
1. instar 1 O 1 2 4 6
other soil-dwelling microarthropods, would
prefer the humus horizon as being most suitable.
It is very porous and is rich in fungal
mycelia and decaying organic matter, which
are considered to be the diet of both symphyl
genera from this investigation. It is difficult
to understand why a large soil animal like
S. sub~zuda (2.5 cm) prefers to live in the
dense mineral soil. The other animals found
here are much smaller (the collembols 0.2-0.5
mm and the mites 0.1-0.2 mm).
It might be possible that the symphyls
specialize in living on decaying roots, and the
hollows after these do serve as runways for
the animals. However, most of the roots are
found in the humus horizon.
The acidity possibly prevents the animals
from migrating up into the raw humus. This
horizon is far more acid than the mineral soil.
Edwards (1958) mentioned that he never
found dense symphyl populations in too acid
soils.
Most of the year the raw humus has a high
humidity. At Nordmoen the soil moisture
was measured each sampling day as long as
the soil was unfrozen. Except for one day, the
soil moisture was found to vary between 30
and 40 O10 of the water-holding capacity at
pF 0.5. Consequently this factor would not
explain the vertical distribution of the symphyls.
Edwards (1959 and 1961) found that there
are notable vertical migrations during the
season. He also found that egg-laying took
place in the deeper soil. During this survey
no specimens from the first two instars were
found. Reproduction probably takes place at
a deeper leve1 in the soil, which was not included
in my sample.
Concerning the pauropods in Scandinavia,
Brinck (1964 and Meidell (1971) state that
they are restricted to the soil in deciduous
forests which are relatively undisturbed by
human manipulation. The pauropods are
known to be quite common in coniferous
forests in the more southern areas of USA
and Europe (Starling 1944, Price 1973,
Scheller pers. comm.). For this reason one
could expect them to be found in this kind
of forest in Norway too. However, the conditions
for soil animals are often quite different
in these areas. In southern coniferous
forests it is not uncommon to find a distinct
ongüno-mineral layer (Al) (H. Hnydahl pers.
comm.). This laver shows favourable conditions
for many soil-dwelling animals. Starling
(1944) mentions an Al-layer of -6 cm thickness
where most of the myriapods were found.
Thirteen of the 14 paurapods found at
Nordmoen were A. verticillatus. The size of
these were about 0.5 mm. Scheller (1971)
mentions that this species was not found
above the 25 cm depth. In the present survey
it was found as high up as the 3-6 cm depth,
but it was never seen in samples from the
humus horizon. The finds of Scheller (1971)
were made in deciduous forests. It looks as
though the vertical distribution of this species
is somewhat different in these two soil types,
and that the humus content in the soil is the
maior factor.
Áll pauropods from Slorstad and one from
Nordmoen were P. lanceolatus. This species
is considerably larger than A. verticillatus,
about 1.5 mm, and its biology is quite different.
Table 111 shows that it is mainly
found in the humus horizon and even in
living moss. But some finds also show that
it might migrate down into the mineral soil.
This species was much more numerous than
A. verticillatus. However, the number of
animals per soil core from each sampling day
varied from O to 1.6, with an average for the
whole sampling period of 0.6. From the re-