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RICHARD S. MILLER
geographic distances, as it does with pocket gophers which can only
be said to coexist within relatively large areas or at the point of disjunction between soil types. If, however, the competitors occupy small
territories and the habitat is suitably diverse, coexistence may be
possible within relatively small areas of habitat. Thus the area of
minimum coexistence is proportional to the area of interference and
varies inversely with habitat diversity -in the last analysis no two
individuals or species can occupy precisely the same point and a t this
extreme cannot coexist.
The possible parallels between mechanisms of population control and
of competitive interactions have received very little attention. Just as
it is impossible to account for natural control of all populations with
one general theory based on stress, food or climate, we cannot expect)
that the mechanisms of interference or exploitation will be the same in
every animal population. It would be interesting to know whether
species whose numbers tend to be controlled by climate also, as was
suggested earlier, tend to have weak interference elements and compete
mainly through exploitation; or, conversely, whether a strong interference component also suggests intraspecies control based on similar
mechanisms.
Another parallel may also exist between different kinds of isolating
mechanisms and forms of interference. We know, for example, that
birds have evolved strong ethological isolating mechanisms based on
auditory and visual stimuli (Sibley, 1961), which also seem to be important factors in territorial behavior and competitor interactions. It
would appear that the mechanisms which function in reproductive
isolation may be used also as interference mechanisms, and that in
each case there is a common evolutionary history. In certain fishes, on
the other hand, ethological mechanisms are poorly developed and
species isolation depends more on physical factors in the habitat. The
breakdown of isolation and subsequent hybridization occurs rather
frequently in these species - does this also mean that interspecies
interference is uncommon in such groups? Many insects (e.g. Drosophila)
have evolved pre-mating, ethological mechanisms of isolation but also
seem to depend on successive post-mating mechanisms for complete
reproductive isolation (Mayr, 1963). Species recognition in these animals
depends entirely on the adults, which suggests that this is the only
stage during which ethological interference mechanisms would be effective, but if species recognition is relatively weak, interspecies interference
might also be weak even among adults. There is, in other words, a
possible parallel between mechanisms of population control, interspecies
competition and species isolation, all of which influence the species
diversity of natural communities.
RICHARD S. MILLER
geographic distances, as it does with pocket gophers which can only
be said to coexist within relatively large areas or at the point of disjunction between soil types. If, however, the competitors occupy small
territories and the habitat is suitably diverse, coexistence may be
possible within relatively small areas of habitat. Thus the area of
minimum coexistence is proportional to the area of interference and
varies inversely with habitat diversity -in the last analysis no two
individuals or species can occupy precisely the same point and a t this
extreme cannot coexist.
The possible parallels between mechanisms of population control and
of competitive interactions have received very little attention. Just as
it is impossible to account for natural control of all populations with
one general theory based on stress, food or climate, we cannot expect)
that the mechanisms of interference or exploitation will be the same in
every animal population. It would be interesting to know whether
species whose numbers tend to be controlled by climate also, as was
suggested earlier, tend to have weak interference elements and compete
mainly through exploitation; or, conversely, whether a strong interference component also suggests intraspecies control based on similar
mechanisms.
Another parallel may also exist between different kinds of isolating
mechanisms and forms of interference. We know, for example, that
birds have evolved strong ethological isolating mechanisms based on
auditory and visual stimuli (Sibley, 1961), which also seem to be important factors in territorial behavior and competitor interactions. It
would appear that the mechanisms which function in reproductive
isolation may be used also as interference mechanisms, and that in
each case there is a common evolutionary history. In certain fishes, on
the other hand, ethological mechanisms are poorly developed and
species isolation depends more on physical factors in the habitat. The
breakdown of isolation and subsequent hybridization occurs rather
frequently in these species - does this also mean that interspecies
interference is uncommon in such groups? Many insects (e.g. Drosophila)
have evolved pre-mating, ethological mechanisms of isolation but also
seem to depend on successive post-mating mechanisms for complete
reproductive isolation (Mayr, 1963). Species recognition in these animals
depends entirely on the adults, which suggests that this is the only
stage during which ethological interference mechanisms would be effective, but if species recognition is relatively weak, interspecies interference
might also be weak even among adults. There is, in other words, a
possible parallel between mechanisms of population control, interspecies
competition and species isolation, all of which influence the species
diversity of natural communities.