POPULATION CYCLES IN SMALL MAMMALS
327
TABLE XI11 (contd.)
yo Available
Principal
food consumed
-
Ecosystem
small ma&als
(kcal)
Oak-hornbeam
Cracow, Poland
Beechwood
Ojc6w, Poland
Spruce plantation
Bjornstorp,
South Sweden
Forest plantation
on peat bog August6w
Forest, Poland
Bieszczady Mountains,
Poland
South-eastern Poland
Ingels, South Finland
and refuge habitats,
Poland
Alpine meadow
Cultivated plants
Old field
Cultivated fields
Old field
Alaskan Taiga
Forest
C . glareolus
A . jeavicollis
C . glareolua
A . Jlavicollb
Microtus agreati8
M . oeconomus
Pitymy8 subterranew,
M . agreatis
M . arvalb
M . agreatb
M . arvalb
M . penmylvanicw,
C . rmtilw, M . omnomua
Tamkzaciecrme
hudaonicua, ~ h w o m y s
aabrinw,, Sorex
cinereua
4.6
3.9
16-24
3.1
1.03
1-20
3-14
0-6-1-3
04-1.6
3-47
Reference
Grodzinski (1971)
Grodzinski et al. (1969)
Hansson (1971)
Gebczynska (1970)
Grodzinski et al. (1966)
Migula et al. (1970)
Myllymiiki (1969)
Trojan (1969)
Golley (1960)
Grodzinski (1971)
sumed by the microtines has been estimated to be less than 5% of the
available net primary production. The opposite side of the coin is to
determine the influence of microtines on the production of the habitat.
Schultz (1965) measured grass production in a tundra area from which
lemmings were excluded and found that over seven years of observation,
the production by vegetation in the exclosures declined (Fig. 33).
Outside in grazed areas the production waa almost always greater than
in the exclosure although there was some vaziation from year to year.
However, this relationship waa not simple since the exclosures were
actually built in 1949 and during the fist four years (1960-1963) the
measured production of the vegetation averaged 600 pounds per acre.
The standing crop of the tundra vegetation was measured by
Schultz (1965) and these measurements showed the same variation as
did the production data. While years of high lemming density seemed