ANALYSIS OF PROCESSES I N CONTROL O F INSECTS
13
Taking 10-year periods, the ranges of fluctuation for Panolis are
approximately x 86, x 81, x 7.4, x 209, x 14.5 and x 77. The corresponding value from Klomp’s data (above) was x 16. The diEerence
between this relatively low value and the three higher ones from
Schwerdtfeger’s data is an expression of the fact remarked upon by
Klomp (loc. cit., p. 97) that in the pine forests of the Netherlands real
outbreaks of pine caterpillars do not occur (except, rarely and locally,
for Panolis). Klomp interprets this as evidence of regulation in the
Netherlands forests. Returning to Schwerdtfeger’s data, the ranges of
fluctuation of Panolis over three 20-year periods are approximately
x 188, x 205 and x 124; for the whole 60 years it is x 438.
The corresponding values for Bapalus are: 10-year periods, x 753,
x 393, x 3 236, > x 3 236, x 14 190, x 102; 20-year periods, x 1021,
x 3 236, x 14 190; 60 years, x 27 160. Klomp’s data give the value
x 30 over 10 years.
The values for Hyloicus are: 10-year periods, x 53, x 6.6, x 6.0,
> x 86, x 72; 20-year periods, x 53, > x 86; 50 years, x 330. In the
Netherlands, this species remains at a low level (Klomp, loc. cit.).
The values for Dendrolimus are: 10-year periods, x 841, x 7-9, x 16-9,
x 19.6, x 124, x 1 611; 20-year periods, x 2 489, x 19.6, > x 3 381;
60 years, > x 17 580.
Equally striking fluctuations in abundance were demonstrated by
Nicholson (1954b) in laboratory experiments with the blowfly Lucilia
cuprinu Wed. In this case, the external conditions were constant, and
the fluctuations were due to delayed responses to a limiting food
For strictly valid comparisons of the ranges of fluctuation one should
take account of which stages in the life cycle are the more subject to
disturbing influences, and which are the more closely regulated. When
this is not done, we may inadvertently compare one population in its
most variable phase with another at its least variable. To avoid this sort
of error, we need censuses of the different stages, or life tables for the
successive generations of the populations concerned, to be examined
as on pages 31-35. We should certainly not be justified in assuming,
without some such observations, that the adults will fluctuate less, in
proportion to their numbers, than the larvae do, or vice versa.
The range of fluctuation is no doubt influenced by many different
factors, including the variability of the climate, the reproductive
capacity of the species concerned, the degree of regulation, and the
number of different regulatory factors. In connection with the last of
these, it has been argued that the ffuctuations are likely to be less violent
in a population that is part of a complex community, which provides a
variety of inter-compensatory influences buffering the effect of any
supply.
13
Taking 10-year periods, the ranges of fluctuation for Panolis are
approximately x 86, x 81, x 7.4, x 209, x 14.5 and x 77. The corresponding value from Klomp’s data (above) was x 16. The diEerence
between this relatively low value and the three higher ones from
Schwerdtfeger’s data is an expression of the fact remarked upon by
Klomp (loc. cit., p. 97) that in the pine forests of the Netherlands real
outbreaks of pine caterpillars do not occur (except, rarely and locally,
for Panolis). Klomp interprets this as evidence of regulation in the
Netherlands forests. Returning to Schwerdtfeger’s data, the ranges of
fluctuation of Panolis over three 20-year periods are approximately
x 188, x 205 and x 124; for the whole 60 years it is x 438.
The corresponding values for Bapalus are: 10-year periods, x 753,
x 393, x 3 236, > x 3 236, x 14 190, x 102; 20-year periods, x 1021,
x 3 236, x 14 190; 60 years, x 27 160. Klomp’s data give the value
x 30 over 10 years.
The values for Hyloicus are: 10-year periods, x 53, x 6.6, x 6.0,
> x 86, x 72; 20-year periods, x 53, > x 86; 50 years, x 330. In the
Netherlands, this species remains at a low level (Klomp, loc. cit.).
The values for Dendrolimus are: 10-year periods, x 841, x 7-9, x 16-9,
x 19.6, x 124, x 1 611; 20-year periods, x 2 489, x 19.6, > x 3 381;
60 years, > x 17 580.
Equally striking fluctuations in abundance were demonstrated by
Nicholson (1954b) in laboratory experiments with the blowfly Lucilia
cuprinu Wed. In this case, the external conditions were constant, and
the fluctuations were due to delayed responses to a limiting food
For strictly valid comparisons of the ranges of fluctuation one should
take account of which stages in the life cycle are the more subject to
disturbing influences, and which are the more closely regulated. When
this is not done, we may inadvertently compare one population in its
most variable phase with another at its least variable. To avoid this sort
of error, we need censuses of the different stages, or life tables for the
successive generations of the populations concerned, to be examined
as on pages 31-35. We should certainly not be justified in assuming,
without some such observations, that the adults will fluctuate less, in
proportion to their numbers, than the larvae do, or vice versa.
The range of fluctuation is no doubt influenced by many different
factors, including the variability of the climate, the reproductive
capacity of the species concerned, the degree of regulation, and the
number of different regulatory factors. In connection with the last of
these, it has been argued that the ffuctuations are likely to be less violent
in a population that is part of a complex community, which provides a
variety of inter-compensatory influences buffering the effect of any
supply.