Temperature-Dependent Development and Competitive Ability of Three Species in the Drosophila affinis Subgroup

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Abstract
Eclosion rates were characterized for D. affinis, D. algonquin and D. athabasca at 18.degree. C and 25.degree. C in pure-species and mixed-species cultures. D. athabasca develops faster in monocultures and has a pronounced advantage over D. affinis at 18.degree. C, but not at 25.degree. C. The developmental rate of D. algonquin is much slower than either of the other 2 spp. at either temperature. In mixed-species cultures, D. athabasca is severely inhibited by the presence of either of the other 2 spp. Competition at 18.degree. C and 25.degree. C between D. affinis, D. algonquin and D. athabasca was analyzed by means of deWit''s Replacement Series. A species may facilitate or inhibit the other''s development, or do neither. Competitive fitness relationships derived from log input/log output regression analyses differed from relationships based on mean total number of progeny in monocultures. The fitness relationships in the mixed-species cultures were: D. affinis = D. algonquin > D. athabasca at 25.degree. C and D. algonquin > D. affinis > D. athabasca at 18.degree. C. Estimates of competitive abilities of the 3 spp. were affected by temperature in directions that were expected on the basis of field observations. The dependence of developmental rate and competitive ability on temperature is partly responsible for the differences between the species with respect to their geographic distributions and their spatial and temporal patterns in natural populations.

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