STUDIES ON THE CEREAL ECOSYSTEM
187
field, their study could resolve many resource management problems
today.
Prior to the recent series of changes in agricultural practices, the
larger game preserves in East Anglia and certain other areas realized a
sustained mean yield of 45 grey partridges per km2 per annum. As a
rule this would be 1-5 birds per nesting pair; a high rate of cropping.
Most people concerned in the management of this natural resource
believed that rigorous predator control was essential. The exploitation
regime developed as an empirical art but our data tend to support the
general validity of their belief, even though this kind of management
would not often be justified on contemporary farmland. Increased
predator control could not have reversed the decline of the partridge,
but the effect of the temporary disappearances of the rabbit probably
increased the losses to predation.
It is important to realize that predator control must be accompanied
by intelligent cropping, otherwise some other limiting factor may assert
itself and eventually reduce the stock below the lower equilibrium
level. We have seen how grey partridges can be limited by disease in
certain predator-free situations.
There is scattered evidence that pest outbreaks often occur when the
predator pressure is reduced (Ripper, 1956; Smith and Hagen, 1959;
Pimentel, 1961), and that prey species survive better when predators
are experimentally removed (Huffaker and Kennett, 1956; Wright et al.,
1960; Pollard, 1969). Morevoer, it is also becoming clear that predators
are a satisfactory means of biological control (De Bach, 1964; Gould,
1971).
Our studies suggest that the abundance of cereal aphids may often
be affected by predation. The predators in this case are generalized
versatile polyphagous species rather than aphid specialists. Although
we know the identity of some of these predators, further detailed
studies are required and are in progress. Although we have no extensive
quantitative information on the composition of the nocturnal fauna
of cereal crops, we know that large numbers of Staphylinidae and
Araneae are active on the vegetation at night. We have not yet calculated the density of these or studied their vertical distribution in the
crop, but work now in progress will shortly provide these data.
These and current studies on cereal aphids (Potts and Vickerman,
1974) have shown that it appears to be the predator-prey ratio, rather
than the absolute number of predators, that is important in determining
the extent of predation. Much the same conclusion has resulted from
our partridge studies, and is inherent in the concept of “buffer prey” as
used by Bump et aZ. (1947). Further support comes from the work of
King (1971 and in Zitt), which has shown that weasel predation on
187
field, their study could resolve many resource management problems
today.
Prior to the recent series of changes in agricultural practices, the
larger game preserves in East Anglia and certain other areas realized a
sustained mean yield of 45 grey partridges per km2 per annum. As a
rule this would be 1-5 birds per nesting pair; a high rate of cropping.
Most people concerned in the management of this natural resource
believed that rigorous predator control was essential. The exploitation
regime developed as an empirical art but our data tend to support the
general validity of their belief, even though this kind of management
would not often be justified on contemporary farmland. Increased
predator control could not have reversed the decline of the partridge,
but the effect of the temporary disappearances of the rabbit probably
increased the losses to predation.
It is important to realize that predator control must be accompanied
by intelligent cropping, otherwise some other limiting factor may assert
itself and eventually reduce the stock below the lower equilibrium
level. We have seen how grey partridges can be limited by disease in
certain predator-free situations.
There is scattered evidence that pest outbreaks often occur when the
predator pressure is reduced (Ripper, 1956; Smith and Hagen, 1959;
Pimentel, 1961), and that prey species survive better when predators
are experimentally removed (Huffaker and Kennett, 1956; Wright et al.,
1960; Pollard, 1969). Morevoer, it is also becoming clear that predators
are a satisfactory means of biological control (De Bach, 1964; Gould,
1971).
Our studies suggest that the abundance of cereal aphids may often
be affected by predation. The predators in this case are generalized
versatile polyphagous species rather than aphid specialists. Although
we know the identity of some of these predators, further detailed
studies are required and are in progress. Although we have no extensive
quantitative information on the composition of the nocturnal fauna
of cereal crops, we know that large numbers of Staphylinidae and
Araneae are active on the vegetation at night. We have not yet calculated the density of these or studied their vertical distribution in the
crop, but work now in progress will shortly provide these data.
These and current studies on cereal aphids (Potts and Vickerman,
1974) have shown that it appears to be the predator-prey ratio, rather
than the absolute number of predators, that is important in determining
the extent of predation. Much the same conclusion has resulted from
our partridge studies, and is inherent in the concept of “buffer prey” as
used by Bump et aZ. (1947). Further support comes from the work of
King (1971 and in Zitt), which has shown that weasel predation on