40
RICHARD S. MILLER
with the numbers of each species equal in only 1 4 % . Table I11 shows
the within-replicate dominance that existed in the competition cultures
and Table I V shows the numbers of each species produced in control
cultures. Three important facts emerge from these data: (1) the total
numbers of adults produced in both the experimental and control replicates was well below the numbers that would be expected if the
initial numbers of eggs and larvae were at the saturation densities
established previously (Miller, 1964b); (2) total numbers of F, adults
were not significantly different in the control and experimental populations; and (3) there was a distinct tendency for one species or the
other to establish strong numerical dominance in each mixed-species
population.
A quantitative estimate of the species interactions within replicate
populations was obtained by calculating the numbers produced by one
species at each density level of the other. This relationship showed a
general decrease of X2 ( D . simulans) with each increase in N , ( D .
melanogaster) and vice versa. The rate of change of N , with each change
in N , and the rate of change of N , with each change in N , was as
follows :
With these and other data (see Miller, 1964c for details) it is now
possible to construct a revised model of competition for one generation
between D. melanogaster and D. simulans. This model (Fig. 8) shows
that the numbers of F, adults that would be expected from the saturation densities established for larval populations of these species (Miller,
1964b) are not obtained when production depends on eggs oviposited
by adult females. Secondly, when within-replicate dominance strongly
favors one species over the other, the total numbers produced are higher
than would be expected by chance; when the numbers of each species
are nearly equal, the total numbers in each replicate are less than
expected.
I n what way can these data be used to explain the possible consequences of interactions in natural populations? There are two stages
in the Drosophila life cycle that might be affected by competition: (1)
the larval period when food quantity and quality might be critical and
(2) the adult stage which is responsible for dispersal, habitat selection
and reproduction. Larval competition, when it occurs, seems to consist
of direct exploitation of the available food resources and will only be a
RICHARD S. MILLER
with the numbers of each species equal in only 1 4 % . Table I11 shows
the within-replicate dominance that existed in the competition cultures
and Table I V shows the numbers of each species produced in control
cultures. Three important facts emerge from these data: (1) the total
numbers of adults produced in both the experimental and control replicates was well below the numbers that would be expected if the
initial numbers of eggs and larvae were at the saturation densities
established previously (Miller, 1964b); (2) total numbers of F, adults
were not significantly different in the control and experimental populations; and (3) there was a distinct tendency for one species or the
other to establish strong numerical dominance in each mixed-species
population.
A quantitative estimate of the species interactions within replicate
populations was obtained by calculating the numbers produced by one
species at each density level of the other. This relationship showed a
general decrease of X2 ( D . simulans) with each increase in N , ( D .
melanogaster) and vice versa. The rate of change of N , with each change
in N , and the rate of change of N , with each change in N , was as
follows :
With these and other data (see Miller, 1964c for details) it is now
possible to construct a revised model of competition for one generation
between D. melanogaster and D. simulans. This model (Fig. 8) shows
that the numbers of F, adults that would be expected from the saturation densities established for larval populations of these species (Miller,
1964b) are not obtained when production depends on eggs oviposited
by adult females. Secondly, when within-replicate dominance strongly
favors one species over the other, the total numbers produced are higher
than would be expected by chance; when the numbers of each species
are nearly equal, the total numbers in each replicate are less than
expected.
I n what way can these data be used to explain the possible consequences of interactions in natural populations? There are two stages
in the Drosophila life cycle that might be affected by competition: (1)
the larval period when food quantity and quality might be critical and
(2) the adult stage which is responsible for dispersal, habitat selection
and reproduction. Larval competition, when it occurs, seems to consist
of direct exploitation of the available food resources and will only be a