DYNAMICS O F FIELD POPULATION OF rnm LOOPER
'707
Fig. 26. Mean fecundity decreases with an increase of larval density
and, consequently, the reproductive rate is density dependent in the
sense of Varley (1953). From the viewpoint of density regulation this
result is of paramount importance, and its significance will be discussed
later (pp. 288 and 297).
Summarizing this chapter on annual variations of the reproductive
rate very briefly, we can state that differences of population density of
larvae between years cause differences in the intensity of mutual contact among the individuals. A t high densities the relatively high frequency of contact causes an inhibition of larval growth, resulting in a
low fecundity of the moths in the following spring.
v. THE COMPOSITION O F L I F E TA13LES
To have a general survey on density, fecundity and mortality the
data concerned have been arranged in life tables (Table XXIII). The
columns in these tables are indicated by the usual s*ymbols E, 100 q, and
d, respectively representing the density in nurnbers/m2, the mortality
in yo, and the mortality in numbers/m2. The bold type numerals in
column E are direct density estimates from Tables 111, IV, V, V I I I and
X; those in column 100 q are the mortality rates obtained by the rearing
of the insects detailed in Tables XIII, XIV and XV. The sex ratio
figures in 100 p-column are an exception to this rule. They represent
the percentages males in the April collections of pupae (p. 240).
All other numerals in columns 1 and 100 q are concerned with indirect
measurements, such as differences between successivc: density estimates,
or previous density estimates multiplied by survival rates. This is more
clearly elucidated below. There is again one exception, namely the mortality or emigration index of the moths. This index if3 computed according to the method explained in the bottom part of the life tables. As
shown it is based on the difference between the expected and the actual
densities of eggs, being an index for the fraction of females which did
not deposit their total potential quantity of eggs. .Q number of these
females certainly died prior to the deposition of the Grst batch, others
after having laid a smaller or larger proportion of their potential production.
The difference between expected and actual egg densities may also be
caused by an emigration surplus but the females show little flight
activity, and I am inclined to attach little or no value to migration in
general. True, the males leave the study area regularly during their
courtship flight, but measurements showed that the,y entered the area
in the same numbers. I am not informed about movements during the
night (see also p. 293).
'707
Fig. 26. Mean fecundity decreases with an increase of larval density
and, consequently, the reproductive rate is density dependent in the
sense of Varley (1953). From the viewpoint of density regulation this
result is of paramount importance, and its significance will be discussed
later (pp. 288 and 297).
Summarizing this chapter on annual variations of the reproductive
rate very briefly, we can state that differences of population density of
larvae between years cause differences in the intensity of mutual contact among the individuals. A t high densities the relatively high frequency of contact causes an inhibition of larval growth, resulting in a
low fecundity of the moths in the following spring.
v. THE COMPOSITION O F L I F E TA13LES
To have a general survey on density, fecundity and mortality the
data concerned have been arranged in life tables (Table XXIII). The
columns in these tables are indicated by the usual s*ymbols E, 100 q, and
d, respectively representing the density in nurnbers/m2, the mortality
in yo, and the mortality in numbers/m2. The bold type numerals in
column E are direct density estimates from Tables 111, IV, V, V I I I and
X; those in column 100 q are the mortality rates obtained by the rearing
of the insects detailed in Tables XIII, XIV and XV. The sex ratio
figures in 100 p-column are an exception to this rule. They represent
the percentages males in the April collections of pupae (p. 240).
All other numerals in columns 1 and 100 q are concerned with indirect
measurements, such as differences between successivc: density estimates,
or previous density estimates multiplied by survival rates. This is more
clearly elucidated below. There is again one exception, namely the mortality or emigration index of the moths. This index if3 computed according to the method explained in the bottom part of the life tables. As
shown it is based on the difference between the expected and the actual
densities of eggs, being an index for the fraction of females which did
not deposit their total potential quantity of eggs. .Q number of these
females certainly died prior to the deposition of the Grst batch, others
after having laid a smaller or larger proportion of their potential production.
The difference between expected and actual egg densities may also be
caused by an emigration surplus but the females show little flight
activity, and I am inclined to attach little or no value to migration in
general. True, the males leave the study area regularly during their
courtship flight, but measurements showed that the,y entered the area
in the same numbers. I am not informed about movements during the
night (see also p. 293).