PATTERN AND PROCESS IN COMPETITION
39
within species and a = j l = 1. This means that K , = K,/a and K , =
Rs/B and the isoclines in Fig. 6 (Case 1) coincide. We may now state
the general case for this relationship as follows:
N , and N , will coexist at equilibrium densities which depend on
initial concentration when :
(7)
a = K,/K, and / 3 = K , / K ,
These experiments were designed so that the initial concentrations
of the larvae were always equal. The predictability of this model for
different concentrations of the two species was not tested. However,
equilibria occurred at points along the line 0s which corresponded to
the density levels in the design of the experiments, and to this extent
the data for N , = N , confirm the prediction of the general case for a
two-species equilibrium.
As this study only considered the case of competition during the
larval stages of the Drosophila life cycle, there remained the possibility
that factors affecting fecundity and fertility and the selection of oviposition sites will alter the course of competition by varying the initial
concentrations of the two species in this system. A series of experiments
waa therefore designed to test competition between these two species
for one complete life cycle (Miller, 1964~). Controls consisted of two
pairs of adults of one species in each vial containing the same food
medium used in the larval experiments; the experimental vials contained one pair of each species. The adult flies were allowed to lay eggs
for 6 days and were then removed and the subsequent production of
F, adults recorded.
A total of 3 705 flies was produced from 111 competition replicates.
The ratio of D. melanogaster to D. simulans F, adults was 51.1 to 48.9,
which was not a significant difference. However, each replicate was a
self-contained population in which the course of events had no direct
relation to events in other replicates, and it was noted that there was
marked dominance of one species or the other in individual populations.
As competition was confined to a single generation and the total
elimination of one species or the other was not a criterion of the experiments, there were two measurable categories of species dominance or
competitive superiority: (1) the number of replicates in which a species
waa the more successful (between-replicate dominance) and (2) the
numerical dominance of one species over the other in individual replicates (within-replicate dominance). The lack of competitive advantage
shown in the total numbers of each species produced was also reflected
in the relative numbers of replicates in which each species was the more
successful. D. melanogaster produced greater numbers in 51 -4% of the
111 Competition replicates and D . simulans was dominant in 46.8%
39
within species and a = j l = 1. This means that K , = K,/a and K , =
Rs/B and the isoclines in Fig. 6 (Case 1) coincide. We may now state
the general case for this relationship as follows:
N , and N , will coexist at equilibrium densities which depend on
initial concentration when :
(7)
a = K,/K, and / 3 = K , / K ,
These experiments were designed so that the initial concentrations
of the larvae were always equal. The predictability of this model for
different concentrations of the two species was not tested. However,
equilibria occurred at points along the line 0s which corresponded to
the density levels in the design of the experiments, and to this extent
the data for N , = N , confirm the prediction of the general case for a
two-species equilibrium.
As this study only considered the case of competition during the
larval stages of the Drosophila life cycle, there remained the possibility
that factors affecting fecundity and fertility and the selection of oviposition sites will alter the course of competition by varying the initial
concentrations of the two species in this system. A series of experiments
waa therefore designed to test competition between these two species
for one complete life cycle (Miller, 1964~). Controls consisted of two
pairs of adults of one species in each vial containing the same food
medium used in the larval experiments; the experimental vials contained one pair of each species. The adult flies were allowed to lay eggs
for 6 days and were then removed and the subsequent production of
F, adults recorded.
A total of 3 705 flies was produced from 111 competition replicates.
The ratio of D. melanogaster to D. simulans F, adults was 51.1 to 48.9,
which was not a significant difference. However, each replicate was a
self-contained population in which the course of events had no direct
relation to events in other replicates, and it was noted that there was
marked dominance of one species or the other in individual populations.
As competition was confined to a single generation and the total
elimination of one species or the other was not a criterion of the experiments, there were two measurable categories of species dominance or
competitive superiority: (1) the number of replicates in which a species
waa the more successful (between-replicate dominance) and (2) the
numerical dominance of one species over the other in individual replicates (within-replicate dominance). The lack of competitive advantage
shown in the total numbers of each species produced was also reflected
in the relative numbers of replicates in which each species was the more
successful. D. melanogaster produced greater numbers in 51 -4% of the
111 Competition replicates and D . simulans was dominant in 46.8%