12
RICHARD 9. MILLER
“Exploitation” is the utilization of a resource once access to it has
been achieved. Two individuals or species with unlimited access to a
common source of food or nutrients will frequently have different
abilities to exploit the available supply. This form of competition is
referred to by Nicholson (1955) as a “scramble”, in that the most
efficient competitor is the one that can obtain and utilize the greatest
amount. Elements of both interference and exploitation are undoubtedly
present in almost any competitive interaction, but we may inquire
whether their relative values in any particular interaction are such that
there are distinct theoretical consequences. Interference seems, for
example, to be especially well developed among certain of the higher
vertebrates, especially birds, and is often so effective that direct exploitation is a relatively unimportant element of competition. Conversely, exploitation seems to be characteristic of simple metazoans in
which the populations are more directly controlled by factors in the
physical environment apd social interactions are simple. In other words,
exploitation seems to be the dominant form of competition whenever
interference mechanisms are poorly developed. If this is indeed the
case, it implies that competition by direct exploitation is a primitive
and unstable form of interaction, and that interference mechanisms
such as territoriality represent evolutionary advances toward more
effective biotic control of population interactions and numerical stability,
as partly suggested by Wynne-Edwards (1962).
Wynne-Edwards (1962) states “The substitution of a parcel of ground
as the object of competition in place of the actual food it contains . . .
is the simplest and most direct kind of convention it is possible to have.”
Such an arrangement implies interference with access to a resource,
which Wynne-Edwards assumes is a property of all species; buti for
many species such conventions have not evolved and direct exploitation
of food resources is a characteristic form of competition. Examples of
competition through exploitation are found in laboratory studies of
insects which spend all or part of their life cycle within their food
medium, and there is evidence that similar interactions occur under
certain circumstances in natural environments. Such species seem,
generally, to be limited by absolute amounts of food or nutrients and
there is little evidence of spatial organization in their populations. As
the level of population increases relative to the volume of food and
space available, there tends to be a non-linear increase in mortality
which may ultimately result in the complete extinction of all members
of a population.
During artificially induced crowding in larval populations of Drosophila (Sokoloff, 1955; Robertson, 1960; Mishima, 1964; Miller, 1964b),
moderate increases in density relative to available food and space cause
RICHARD 9. MILLER
“Exploitation” is the utilization of a resource once access to it has
been achieved. Two individuals or species with unlimited access to a
common source of food or nutrients will frequently have different
abilities to exploit the available supply. This form of competition is
referred to by Nicholson (1955) as a “scramble”, in that the most
efficient competitor is the one that can obtain and utilize the greatest
amount. Elements of both interference and exploitation are undoubtedly
present in almost any competitive interaction, but we may inquire
whether their relative values in any particular interaction are such that
there are distinct theoretical consequences. Interference seems, for
example, to be especially well developed among certain of the higher
vertebrates, especially birds, and is often so effective that direct exploitation is a relatively unimportant element of competition. Conversely, exploitation seems to be characteristic of simple metazoans in
which the populations are more directly controlled by factors in the
physical environment apd social interactions are simple. In other words,
exploitation seems to be the dominant form of competition whenever
interference mechanisms are poorly developed. If this is indeed the
case, it implies that competition by direct exploitation is a primitive
and unstable form of interaction, and that interference mechanisms
such as territoriality represent evolutionary advances toward more
effective biotic control of population interactions and numerical stability,
as partly suggested by Wynne-Edwards (1962).
Wynne-Edwards (1962) states “The substitution of a parcel of ground
as the object of competition in place of the actual food it contains . . .
is the simplest and most direct kind of convention it is possible to have.”
Such an arrangement implies interference with access to a resource,
which Wynne-Edwards assumes is a property of all species; buti for
many species such conventions have not evolved and direct exploitation
of food resources is a characteristic form of competition. Examples of
competition through exploitation are found in laboratory studies of
insects which spend all or part of their life cycle within their food
medium, and there is evidence that similar interactions occur under
certain circumstances in natural environments. Such species seem,
generally, to be limited by absolute amounts of food or nutrients and
there is little evidence of spatial organization in their populations. As
the level of population increases relative to the volume of food and
space available, there tends to be a non-linear increase in mortality
which may ultimately result in the complete extinction of all members
of a population.
During artificially induced crowding in larval populations of Drosophila (Sokoloff, 1955; Robertson, 1960; Mishima, 1964; Miller, 1964b),
moderate increases in density relative to available food and space cause