52
M. E. SOLOMON
in nature if there are also mechanisms at work that damp the oscillations, and to suggest or investigate what these mechanisms may be.
There has been no lack of suggestions. Nicholson (1933) himself argued
that host populations become fragmented into sub-populations some of
which, at any given time, have not yet been discovered by the parasite,
while others are in different phases of interaction with it. Although
increasing oscillations lead to the extinction of some of the subpopulations, others will survive for a time, and new ones will be formed.
Some ecologists have protested that they do not see this pattern in
nature (e.g. Tinbergen and Klomp, 1960). Evidence that it could have
the kind of effect Nicholson sought is provided by the experiments of
Huffaker (1958), who set up an experimental equivalent of Nicholson’s
idea, using a phytophagous and a predatory mite on groups of oranges
in trays. Nicholson (1933) also argued that oscillations could be damped
if the parasite had one or more other hosts which were not regulated
by it. This possibility seems to have been generally neglected. Tinbergen and Klomp (1960) argue against it on general grounds.
Varley (1947) claimed that “it can be shown with Nicholson and
Bailey’s theory that if a proportion of hosts is not available to parasitism, oscillations will be damped instead of increasing in amplitude”.
Nicholson (1954b) replied that this was so only with low powers of host
increase combined with the protection of the greater part of the hosts
that must survive to ensure population maintenance. Retreating
slightly, Varley and Gradwell (1958) listed host-protection as having an
effect “in the direction which leads to quenching”. Recently, Bailey et al.
(1962) returned to the theoretical model to examine the effects “when
some host individuals are more difficult to find than others”. They
deduced that “systems of damped or growing oscillations are produced
according to the circumstances, which are defined”. The set of circumstances required to produce damped oscillations and a stable
system was very restricted.
DeBach and Smith (1941a) pointed out that oscillations could be
damped if the reproductive rate of the host were strongly densitydependent, but considered such a thing likely only at very high densities,
a view endorsed by Tinbergen and Klomp (1960). Possibly the amplitude
of fluctuation in Utida’s experiments with pulse beetles and their
parasites was prevented from increasing by the effect of crowding in
restricting the increase of the host.
Varley and Gradwell (loc. cit.), continuing their list of processes
tending t o damp oscillations, mentioned the protection of some hosts
by the odour of parasites that had previously examined and rejected
them ; imperfect synchronization of the susceptible host stage with the
peak of parasite activity; hindering of the parasites by unfavourable
M. E. SOLOMON
in nature if there are also mechanisms at work that damp the oscillations, and to suggest or investigate what these mechanisms may be.
There has been no lack of suggestions. Nicholson (1933) himself argued
that host populations become fragmented into sub-populations some of
which, at any given time, have not yet been discovered by the parasite,
while others are in different phases of interaction with it. Although
increasing oscillations lead to the extinction of some of the subpopulations, others will survive for a time, and new ones will be formed.
Some ecologists have protested that they do not see this pattern in
nature (e.g. Tinbergen and Klomp, 1960). Evidence that it could have
the kind of effect Nicholson sought is provided by the experiments of
Huffaker (1958), who set up an experimental equivalent of Nicholson’s
idea, using a phytophagous and a predatory mite on groups of oranges
in trays. Nicholson (1933) also argued that oscillations could be damped
if the parasite had one or more other hosts which were not regulated
by it. This possibility seems to have been generally neglected. Tinbergen and Klomp (1960) argue against it on general grounds.
Varley (1947) claimed that “it can be shown with Nicholson and
Bailey’s theory that if a proportion of hosts is not available to parasitism, oscillations will be damped instead of increasing in amplitude”.
Nicholson (1954b) replied that this was so only with low powers of host
increase combined with the protection of the greater part of the hosts
that must survive to ensure population maintenance. Retreating
slightly, Varley and Gradwell (1958) listed host-protection as having an
effect “in the direction which leads to quenching”. Recently, Bailey et al.
(1962) returned to the theoretical model to examine the effects “when
some host individuals are more difficult to find than others”. They
deduced that “systems of damped or growing oscillations are produced
according to the circumstances, which are defined”. The set of circumstances required to produce damped oscillations and a stable
system was very restricted.
DeBach and Smith (1941a) pointed out that oscillations could be
damped if the reproductive rate of the host were strongly densitydependent, but considered such a thing likely only at very high densities,
a view endorsed by Tinbergen and Klomp (1960). Possibly the amplitude
of fluctuation in Utida’s experiments with pulse beetles and their
parasites was prevented from increasing by the effect of crowding in
restricting the increase of the host.
Varley and Gradwell (loc. cit.), continuing their list of processes
tending t o damp oscillations, mentioned the protection of some hosts
by the odour of parasites that had previously examined and rejected
them ; imperfect synchronization of the susceptible host stage with the
peak of parasite activity; hindering of the parasites by unfavourable