POPULATION CYCLES IN SMALL MAMMALS
277
TABLE I1
Population trends among the volea (Microtus agrestis) at Lake Vyrnwy, Wales,
from 1932 to 1960.* P b e of the cycle waa judged from a mixture of map-trap
and live-trap samples. (After Chitty and Chitty, 1962)
Phase of population cycle
Increase
Peak
Decline or scarcity
1932
1933
1934
1935
91936
31936
1937
1938
1939
-
-
-
1946
1947
1947
1948
1949
1950
1951
1951
1952
1953
1954
1954
1955
1956
1957
1958
1959
1969
1960
* Data for 1932-39 from Marohnant area; 1946-54 from miscellaneous ereas; 1964-60
from Old Road area.
70
6 0
g 50
b 40
P
.- F 30
E
E
u,
3 20
1 0
0
46
4 8
50
52
54
56
58
60
62
64
66
*
* *
* * *
PEAK
YEARS *
YEAR
FIQ. 4. Population densities in summer of brown lemming, Lemmus trimucrmtus,
at Point Barrow, Alaska. (After Schultz, 1969.)
K