Resource turnover time and consumer generation time as factors affecting the stability of coexistence: an experiment with Drosophila

Two multi-generation experiments were conducted, both identical except for the length of time the food resource was available. In the "fast-turnover' system, each bottle had a cage life of 3 weeks. In the "slower-turnover' system, each bottle remained in a cage for 6 weeks. In the fast-turnover system D. funebris became extinct or nearly so in 5 out of 6 mixed-species cages within 50 wk, despite surviving in all the monoculture cages. The population size of D. simulans was not affected by the presence of D. funebris, and so on the interaction was amensal. D. funebris was excluded because D. simulans lengthened the generation time of the former species such that only a few eclosed before the resource bottles were replaced. In the slow-turnover system, the 2 species coexisted stably. The extra time each resource bottle remained in the cages provided a temporal refuge for the larvae of D. funebris from the suppressive effects of D. simulans. -from Authors