DYNAMICS O F FIELD POPULATION O F P I N E LOOPER
25 1
experiment and originally collected in the field. The differences between
these groups (“b large” minus “a small”) are as follows (cf. Table XVII).
males
4.53- 4.05 = 0.48
females
5.05 - 4.37 = 0.68
It is evident that the differences between the parental groups are
much more pronounced than those between the means of the b and a
categories in the experiment, in which the effects of environmental
variability were eliminated. This suggests that pupal variability in the
field is largely environmental. This raises the question of what factor is
responsible for the variation.
As remarked earlier (p. 247) field evidence riuggests that larval density
may be an important factor affecting larval growth and, hence, pupal
size. Now the larvae in the crowns of the trees are more or less randomly distributed, and consequently there will be some variation in
density from place to place. Thus, if larval density has a noticeable
effect, in principle this factor might contribute to pupal variation within
one year.
The influence of larval density can be studied by comparing the
groups “single” and “in couples” both in the a and in the b categories
of the experiment. The differences of pupal size between these groups
are as follows (see Table XIX):
a single - a in couplos
males
4-47 - 4.33 := 0.14
females
5.16 - 4.87 := 0.29
b single - b in couples
females
5.32 - 5-01 == 0.31
males
4.56 - 4.37 == 0.19
Again the comparisons are made between total numbers of pupae, i.e. fiveinstar and six-instar pupae taken together. This is the most logical comparison
because the total effect of density will be expressed in the overall numbers of
pupae. I n this case, however, it is worthwhile analysing the effect in more detail.
In Table XIX pupal size is also given for fivo- and six-instar individuals
separately. If we make the comparisons between the categories “single” and “in
couples” for the five-instar pupae only, then the results are the same aa for total
numbers of pupae, and the t-test shows that the differences are highly significant.
If we consider the six-instar individuals, which is only possible among females
in the a-category, then the difference is conformable and, again, significant.
Consequently, the effect of density is expressed in the size of the five-instar
pupae as well as in the diameter of the six-instar individuals. I n addition, however, there is some evidence that the fraction of six instar pupae in the category
“single” is greater than in t,he category ”in couples”. This is shown in Table XX,
in which the categories “a” and “b” and the sexes have been added. Although
25 1
experiment and originally collected in the field. The differences between
these groups (“b large” minus “a small”) are as follows (cf. Table XVII).
males
4.53- 4.05 = 0.48
females
5.05 - 4.37 = 0.68
It is evident that the differences between the parental groups are
much more pronounced than those between the means of the b and a
categories in the experiment, in which the effects of environmental
variability were eliminated. This suggests that pupal variability in the
field is largely environmental. This raises the question of what factor is
responsible for the variation.
As remarked earlier (p. 247) field evidence riuggests that larval density
may be an important factor affecting larval growth and, hence, pupal
size. Now the larvae in the crowns of the trees are more or less randomly distributed, and consequently there will be some variation in
density from place to place. Thus, if larval density has a noticeable
effect, in principle this factor might contribute to pupal variation within
one year.
The influence of larval density can be studied by comparing the
groups “single” and “in couples” both in the a and in the b categories
of the experiment. The differences of pupal size between these groups
are as follows (see Table XIX):
a single - a in couplos
males
4-47 - 4.33 := 0.14
females
5.16 - 4.87 := 0.29
b single - b in couples
females
5.32 - 5-01 == 0.31
males
4.56 - 4.37 == 0.19
Again the comparisons are made between total numbers of pupae, i.e. fiveinstar and six-instar pupae taken together. This is the most logical comparison
because the total effect of density will be expressed in the overall numbers of
pupae. I n this case, however, it is worthwhile analysing the effect in more detail.
In Table XIX pupal size is also given for fivo- and six-instar individuals
separately. If we make the comparisons between the categories “single” and “in
couples” for the five-instar pupae only, then the results are the same aa for total
numbers of pupae, and the t-test shows that the differences are highly significant.
If we consider the six-instar individuals, which is only possible among females
in the a-category, then the difference is conformable and, again, significant.
Consequently, the effect of density is expressed in the size of the five-instar
pupae as well as in the diameter of the six-instar individuals. I n addition, however, there is some evidence that the fraction of six instar pupae in the category
“single” is greater than in t,he category ”in couples”. This is shown in Table XX,
in which the categories “a” and “b” and the sexes have been added. Although