64
RICHARD 8. MlLLICIt
interspersed in apparently less favorable nesting sites than those
occupied by the territorial red-winged blackbird (A. phoeniceus). Moore
(1964) measured the steady densities of the territorial males of 15
species of dragonfly in comparable habitats and found that territory
size, as reflected in density, was correlated with the size of the species.
On the other hand, Pickles (1944) found an opposite relationship between territory and foraging distance and competitive ability in the
ants Messor barbarus and M . aegyptiacus. Gibb (1956) states, “Specific
differences in size of territory have never yet been satisfactorily explained in terms of any particular biological requirement”, and we
must conclude at this stage that if territory size is significant in competitive interactions between species it does not have a value which is
consistent for different taxonomic groups.
In the absence of interspecies competition the fundamental niche of
each species will eventually be fully occupied as a result of the pressures
of intraspecies population growth, with the more desirable parts of the
niche space occupied by the stronger individuals of the population. In
the case of an included niche, for example, intraspecies and interspecies
population pressures will tend to oppose each other in the manner
shown in Fig. 12. The most preferred space of the two fundamental
C a s e 1
FIQ. 12. Forces of population pressure within and between species in their realized niches
N, and N,.
RICHARD 8. MlLLICIt
interspersed in apparently less favorable nesting sites than those
occupied by the territorial red-winged blackbird (A. phoeniceus). Moore
(1964) measured the steady densities of the territorial males of 15
species of dragonfly in comparable habitats and found that territory
size, as reflected in density, was correlated with the size of the species.
On the other hand, Pickles (1944) found an opposite relationship between territory and foraging distance and competitive ability in the
ants Messor barbarus and M . aegyptiacus. Gibb (1956) states, “Specific
differences in size of territory have never yet been satisfactorily explained in terms of any particular biological requirement”, and we
must conclude at this stage that if territory size is significant in competitive interactions between species it does not have a value which is
consistent for different taxonomic groups.
In the absence of interspecies competition the fundamental niche of
each species will eventually be fully occupied as a result of the pressures
of intraspecies population growth, with the more desirable parts of the
niche space occupied by the stronger individuals of the population. In
the case of an included niche, for example, intraspecies and interspecies
population pressures will tend to oppose each other in the manner
shown in Fig. 12. The most preferred space of the two fundamental
C a s e 1
FIQ. 12. Forces of population pressure within and between species in their realized niches
N, and N,.