62
RICHARD S. MILLER
The following table categorizes forms of interference and the factors
which seem to be related to their effectiveness:
Forms of Interference
Related Factors
11. Direct
I. Indirect
1. Chemical communication
A. Physical Contact
B. Threat
2. Aggression
C. Epidiectic Display
3. Territory
4. Body size
5. Coloration
6. Voice
1. Population growth
A requirement of indirect ipterference is that a signal be produced
which will be effective in the owner's absence, and this will almost
invariably involve some form of chemical communication. 'Wilson and
Bossert (1964), as mentioned earlier, have surveyed this topic, mostly
with respect to intraspecies relationships, but there is a need for research
on how chemical signals are transmitted between species and how effective they are. Regardless of whether a chemical is produced to act
specifically as a signal, or whether such chemicals as metabolic wastes
inadvertently condition the environment, the effect in either case may
be indirect interference with access to parts of the environment or the
resources it contains.
The simplest form of direct interference in the preceding examples
was the physical destruction of Chthumalus stellatus by populations of
Balanus balanoides. This was due to the greater rate of growth of the
Balanus populations, greater tolerance of crowding and, eventually, the
reduced size and efficiency of the crowded Chthumalus. Competitive
superiority of the ant Messor aegyptiacus was also due to direct physical
aggression and a relatively primitive form of territoriality. The chipmunks Eutamias amoenus and E . minimus showed a kind of interference
intermediate between physical combat and threat. Chases resulted in
the establishment of dominance of E . amoenus, but with no apparent
physical harm to either animal. The larger titmouse Parus inornatus
is the more successful aggressor in competition with the chickadee, P.
rufescens (Dixon, 1954), and the red-headed woodpecker (Melanerpes
erythrocephalus) excludes the smaller downy woodpecker (Dendrocopus
pubescens) from desired nest holes (Schwab and Monnie, 1959). In competition between the hummingbirds Calypte anna and Selasphorus sasin
(Legg and Pitelka, 1956), the former exercises dominance by earlier
breeding and territory occupation, more effective flight displays and
larger body size (see also Hartley, 1950; Marler, 1956). If the process of
interference consists of direct or overt aggression, body size would seem
logically to be advantageofis, and this hypothesis is supported by
RICHARD S. MILLER
The following table categorizes forms of interference and the factors
which seem to be related to their effectiveness:
Forms of Interference
Related Factors
11. Direct
I. Indirect
1. Chemical communication
A. Physical Contact
B. Threat
2. Aggression
C. Epidiectic Display
3. Territory
4. Body size
5. Coloration
6. Voice
1. Population growth
A requirement of indirect ipterference is that a signal be produced
which will be effective in the owner's absence, and this will almost
invariably involve some form of chemical communication. 'Wilson and
Bossert (1964), as mentioned earlier, have surveyed this topic, mostly
with respect to intraspecies relationships, but there is a need for research
on how chemical signals are transmitted between species and how effective they are. Regardless of whether a chemical is produced to act
specifically as a signal, or whether such chemicals as metabolic wastes
inadvertently condition the environment, the effect in either case may
be indirect interference with access to parts of the environment or the
resources it contains.
The simplest form of direct interference in the preceding examples
was the physical destruction of Chthumalus stellatus by populations of
Balanus balanoides. This was due to the greater rate of growth of the
Balanus populations, greater tolerance of crowding and, eventually, the
reduced size and efficiency of the crowded Chthumalus. Competitive
superiority of the ant Messor aegyptiacus was also due to direct physical
aggression and a relatively primitive form of territoriality. The chipmunks Eutamias amoenus and E . minimus showed a kind of interference
intermediate between physical combat and threat. Chases resulted in
the establishment of dominance of E . amoenus, but with no apparent
physical harm to either animal. The larger titmouse Parus inornatus
is the more successful aggressor in competition with the chickadee, P.
rufescens (Dixon, 1954), and the red-headed woodpecker (Melanerpes
erythrocephalus) excludes the smaller downy woodpecker (Dendrocopus
pubescens) from desired nest holes (Schwab and Monnie, 1959). In competition between the hummingbirds Calypte anna and Selasphorus sasin
(Legg and Pitelka, 1956), the former exercises dominance by earlier
breeding and territory occupation, more effective flight displays and
larger body size (see also Hartley, 1950; Marler, 1956). If the process of
interference consists of direct or overt aggression, body size would seem
logically to be advantageofis, and this hypothesis is supported by