18
M. E. SOLOMON
however, many of them might serve well for the purpose, if the aftereffects were adequately observed and reported from this point of view.
Another field in which evidence of this sort could be collected is in the
exploitation of natural populations. Men concerned with the preservation of fisheries and of game stocks have a good deal of knowledge about
the speed of recovery of populations in the face of reduction by hunting.
I n a discussion about the light this sort of information might be
expected to throw upon regulation (Solomon, 1962b), I suggested that
the systematic exploitation of natural populations might be expected
to give measures of the degree of regulation in the following ways,
illustrated in Fig. 7.
(i) Assuming a population can recover from low density as illustrated
in Fig. 7a, after a measured reduction in density the speed of its
recovery to normal density can provide an index of the degree of regulation (Fig. 7b).
(ii) If a population is reduced by a set amount at intervals, and the
intervals are shortened until the population can barely reach its normal
density (Fig. 7c), this can provide an index of the degree of regulation.
Fig. 7d relates to the following sub-section.
2. B y the Way in which Mortality, Reproduction, or Net Increase are
Related to Density
Aspects of regulation, sometimes even the entire basis of the process,
may be represented by an increase in mortality, or by a decline in the
reproductive rate, as density rises. Examples of such relationships have
been referred to in Section 11, to illustrate density-dependence. Alternatively, we may study the relationship between density and net
increase or decrease.
Of these criteria, net increase or decrease come nearer to the basic
idea of regulation. Referring to Fig. 7d, if we observe the speed of
recovery from reductions to different density levels, we can assess to
what extent increase is greater a t the lower densities, and use this as an
index of the degree of regulation. In the context of exploitation, Fig. 7d
implies an increased productivity following reduction of density. Living
models of this sort of thing may be seen in certain laboratory experiments with insects. Those of Nicholson (1954b) with laboratory populations of the blow-fly Lucilia cuprina have already been referred to.
In some of these experiments (Nicholson, 1954a), the main limiting
factor was the supply of food for the larvae. When the experimenter
systematically removed 99% of all the emergent adults, the consequent
alleviation of adult crowding allowed a 6-fold increase in the numbers
reaching the adult stage. Watt (1955) used populations of the flow
beetle Tribolium confusum Duv. for a study of the optimum yield
M. E. SOLOMON
however, many of them might serve well for the purpose, if the aftereffects were adequately observed and reported from this point of view.
Another field in which evidence of this sort could be collected is in the
exploitation of natural populations. Men concerned with the preservation of fisheries and of game stocks have a good deal of knowledge about
the speed of recovery of populations in the face of reduction by hunting.
I n a discussion about the light this sort of information might be
expected to throw upon regulation (Solomon, 1962b), I suggested that
the systematic exploitation of natural populations might be expected
to give measures of the degree of regulation in the following ways,
illustrated in Fig. 7.
(i) Assuming a population can recover from low density as illustrated
in Fig. 7a, after a measured reduction in density the speed of its
recovery to normal density can provide an index of the degree of regulation (Fig. 7b).
(ii) If a population is reduced by a set amount at intervals, and the
intervals are shortened until the population can barely reach its normal
density (Fig. 7c), this can provide an index of the degree of regulation.
Fig. 7d relates to the following sub-section.
2. B y the Way in which Mortality, Reproduction, or Net Increase are
Related to Density
Aspects of regulation, sometimes even the entire basis of the process,
may be represented by an increase in mortality, or by a decline in the
reproductive rate, as density rises. Examples of such relationships have
been referred to in Section 11, to illustrate density-dependence. Alternatively, we may study the relationship between density and net
increase or decrease.
Of these criteria, net increase or decrease come nearer to the basic
idea of regulation. Referring to Fig. 7d, if we observe the speed of
recovery from reductions to different density levels, we can assess to
what extent increase is greater a t the lower densities, and use this as an
index of the degree of regulation. In the context of exploitation, Fig. 7d
implies an increased productivity following reduction of density. Living
models of this sort of thing may be seen in certain laboratory experiments with insects. Those of Nicholson (1954b) with laboratory populations of the blow-fly Lucilia cuprina have already been referred to.
In some of these experiments (Nicholson, 1954a), the main limiting
factor was the supply of food for the larvae. When the experimenter
systematically removed 99% of all the emergent adults, the consequent
alleviation of adult crowding allowed a 6-fold increase in the numbers
reaching the adult stage. Watt (1955) used populations of the flow
beetle Tribolium confusum Duv. for a study of the optimum yield