Temperature effects in relation to the patterns of distribution and abundance of three species in the Drosophila affinis subgroup

Abstract. 1. The effect of temperature on several aspects of the biology of Drosophila affinis, D.algonquin and D.athabasca were investigated in order to gain insight as to why these closely related species differ in their spatial and temporal patterns of occurrence.
2. No differences exist between the three species in the effect of temperature on egg hatchability.
3. Productivities of the three species were measured in a temperature gradient device. These measurements indicated that D.athabasca has an advantage in productivity over D.affinis at cooler temperatures (below 25°C). At warmer temperatures (above 25°C) the greater productivity of D.affinis makes it the better species. Drosophila algonquin , like D.athabasca , was characterized by its productivity curve as a species more adapted to cooler climates.
4. The competitive abilities of the three species were measured at 25°C, at 18°C, and in an environment which fluctuated between 18 and 25°C on a daily cycle. Competitive ability was estimated on the basis of the performance of the species in two- and three-species populations.
5. In general, D.affinis exhibited its highest competitive ability relative to the other two species at the highest experimental temperature. D.athabasca had its highest competitive ability at the lowest temperature. The competitive ability of Ddgonquin was intermediate; less than that of D.affinis but greater than D.athabasca .
6. The dependence of competitive ability and productivity on temperature is thought to be partly responsible for the differences between the species with respect to their geographic distributions and their spatial and temporal patterns in natural populations.