42
M. 1. SOLOMON
function of the sub-section on successive mortalities is the same as
that of mathematical studies. It points out consequences of the different
ways in which mortality may be related to population density.
While a number of actual examples have been studied, some of the
methods have been illustrated with hypothetical examples. This is
partly but not primarily a matter of convenience. I n spite of the increase
in the data available from studies in population dynamics, there are
still too few realistic demonstrations and convincing tests of many of
the methods discussed. More detailed information is needed, and more
extended studies through long series of generations.
It is also desirable that field investigators should bear in mind the
various ways in which the phenomena of population dynamics can be
assessed, so that these methods and the investigations can be developed
together. Although simple ideas make good starting points, they often
have to be modified and elaborated before they can be successfully
applied to real examples.
V. DENSITY RELATIONSHIPS IN THE ACTION OF
PREDATORS A N D PARASITES
A. F U N C T I O N A L A N D N U M E R I C A L RESPONSES O F NATURAL ENEMIES
Predators and insect parasites (parasitoids) are so often involved in
natural control that it is appropriate to pay some attention to recent
advances in our understanding of their mode of action. Since my prime
concern is with the role that natural enemies may play in regulating
the populations of their prey, I shall concentrate attention on the ways
in which their action is related to the prey population density.
Some time ago, in a discussion of the theory of natural control
(Solomon, 1949), I pointed out that natural enemies could respond to a
change in the density of their prey (e.g., an increase) in two distinguishable ways: (i) by a functional response, in which each predator takes
more of the prey, ‘or takes them sooner, and commonly also (ii) by
increasing in numbers (numerical response) through increased survival
or. reproduction or through immigration. Recently, C. S. Holling has
greatly developed this theme, both with reference t o his own field
studies of predation by shrews and deer-mice on pupae of the pine
sawfly Neodiprion sertijer (Geoff.) (Holling, 1959a), and also in the course
of a more general study of the relationships involved in predation
(Holling, 195910, 1961).
B. A LABORATORY M O D E L O F F U N C T I O N A L RESPONSE
Unless a predator can reproduce fairly promptly when the prey
increases (or unless there is a reduced mortality of the predator or
M. 1. SOLOMON
function of the sub-section on successive mortalities is the same as
that of mathematical studies. It points out consequences of the different
ways in which mortality may be related to population density.
While a number of actual examples have been studied, some of the
methods have been illustrated with hypothetical examples. This is
partly but not primarily a matter of convenience. I n spite of the increase
in the data available from studies in population dynamics, there are
still too few realistic demonstrations and convincing tests of many of
the methods discussed. More detailed information is needed, and more
extended studies through long series of generations.
It is also desirable that field investigators should bear in mind the
various ways in which the phenomena of population dynamics can be
assessed, so that these methods and the investigations can be developed
together. Although simple ideas make good starting points, they often
have to be modified and elaborated before they can be successfully
applied to real examples.
V. DENSITY RELATIONSHIPS IN THE ACTION OF
PREDATORS A N D PARASITES
A. F U N C T I O N A L A N D N U M E R I C A L RESPONSES O F NATURAL ENEMIES
Predators and insect parasites (parasitoids) are so often involved in
natural control that it is appropriate to pay some attention to recent
advances in our understanding of their mode of action. Since my prime
concern is with the role that natural enemies may play in regulating
the populations of their prey, I shall concentrate attention on the ways
in which their action is related to the prey population density.
Some time ago, in a discussion of the theory of natural control
(Solomon, 1949), I pointed out that natural enemies could respond to a
change in the density of their prey (e.g., an increase) in two distinguishable ways: (i) by a functional response, in which each predator takes
more of the prey, ‘or takes them sooner, and commonly also (ii) by
increasing in numbers (numerical response) through increased survival
or. reproduction or through immigration. Recently, C. S. Holling has
greatly developed this theme, both with reference t o his own field
studies of predation by shrews and deer-mice on pupae of the pine
sawfly Neodiprion sertijer (Geoff.) (Holling, 1959a), and also in the course
of a more general study of the relationships involved in predation
(Holling, 195910, 1961).
B. A LABORATORY M O D E L O F F U N C T I O N A L RESPONSE
Unless a predator can reproduce fairly promptly when the prey
increases (or unless there is a reduced mortality of the predator or