PATTERN AND PROCICSS IN COMPETI‘CION
35
axiom of inequality. Kostitzin (1939), who also dismisses the case of
coexistence, reaches the further conclusion that intraspecies competition
should be less violent than competition between two allied species. This
statement introduces a curious mystique whereby speciation involves not
only the evolution of normal isolating mechanisms, but also the sudden
emergence of a competitive antagonism. Interspecies competition is
assigned an arbitrary force which is presumed not t o exist within
species. Cole (1960) finds no basis for these pronouncements and notes
that Darwin not only referred to the fact that competition between
closely related species will be more severe than between more distant
relations, but that “the struggle will almost invariably be most severe
between the individuals of the same species.” Cole (1960) states, “If
Darwin was right the Volterra-Lotka analyses predict not competitive
exclusion but coexistence.”
Let us accept the proposition that some degree of ecological differentiation is one condition that will permit coexistence, provided the
differentiation is great enough. The species diversity of any self-sustaining ecosystem, no matter how small, is sufficient t o substantiate this
conclusion. We generally assume that the different species in such an
ecosystem have distinct adaptations and requirements and are therefore
compatible to this extent. It is also evident, at the other end of the
scale of species difference, that members of the same species are able
to coexist, even tbough their individual requirements are nearly identical. As they will also exhibit approximately identical responses to
factors affecting their distribution and abundance, competitive advantage should be least pronounced among members of the same
species. Or, stated in another way, the individual interaction values
that comprise u or /3 should be nearly equal. Following this line of
reasoning further, the degree of similarity between two species should
also be reflected in the species interaction values u and /3. It is quite
conceivable, in fact, that less competitive advantage ( u - /3) might
exist between two sibling species than between the individuals of a
highly polytypic species. Competitive exclusion, in such a case, would
depend on the extent to which critical resources were limiting (e.g. the
size of the total two-species population that the environment could
support) and the constancy of the environment.
Miller (1964b) examined the case of competition between larvae of
the sibling species Drosophila melanogaster and D . sirnulam. These
species are sympatric and apparently coexist in similar habitats
throughout most of the temperate and tropic regions of the world.
An initial assumption in the experiments was that these sibling species,
because of the genetic similarity that underlies “their unusual morphological similarity (Moore, 1952; Miller, 1964b), are not only likely to
35
axiom of inequality. Kostitzin (1939), who also dismisses the case of
coexistence, reaches the further conclusion that intraspecies competition
should be less violent than competition between two allied species. This
statement introduces a curious mystique whereby speciation involves not
only the evolution of normal isolating mechanisms, but also the sudden
emergence of a competitive antagonism. Interspecies competition is
assigned an arbitrary force which is presumed not t o exist within
species. Cole (1960) finds no basis for these pronouncements and notes
that Darwin not only referred to the fact that competition between
closely related species will be more severe than between more distant
relations, but that “the struggle will almost invariably be most severe
between the individuals of the same species.” Cole (1960) states, “If
Darwin was right the Volterra-Lotka analyses predict not competitive
exclusion but coexistence.”
Let us accept the proposition that some degree of ecological differentiation is one condition that will permit coexistence, provided the
differentiation is great enough. The species diversity of any self-sustaining ecosystem, no matter how small, is sufficient t o substantiate this
conclusion. We generally assume that the different species in such an
ecosystem have distinct adaptations and requirements and are therefore
compatible to this extent. It is also evident, at the other end of the
scale of species difference, that members of the same species are able
to coexist, even tbough their individual requirements are nearly identical. As they will also exhibit approximately identical responses to
factors affecting their distribution and abundance, competitive advantage should be least pronounced among members of the same
species. Or, stated in another way, the individual interaction values
that comprise u or /3 should be nearly equal. Following this line of
reasoning further, the degree of similarity between two species should
also be reflected in the species interaction values u and /3. It is quite
conceivable, in fact, that less competitive advantage ( u - /3) might
exist between two sibling species than between the individuals of a
highly polytypic species. Competitive exclusion, in such a case, would
depend on the extent to which critical resources were limiting (e.g. the
size of the total two-species population that the environment could
support) and the constancy of the environment.
Miller (1964b) examined the case of competition between larvae of
the sibling species Drosophila melanogaster and D . sirnulam. These
species are sympatric and apparently coexist in similar habitats
throughout most of the temperate and tropic regions of the world.
An initial assumption in the experiments was that these sibling species,
because of the genetic similarity that underlies “their unusual morphological similarity (Moore, 1952; Miller, 1964b), are not only likely to