The influence of species frequency,temperature regime and previous development condition on relative competitive ability between Drosophila melanogaster and Drosophila simulans

Some fitness components of Drosophila melanogaster and D. simulans were measured in control and inter-specific competition tests. The effects derived from different relative frequencies of the competitors were examined under a factorial scheme with two temperatures, 21 °C or room temperature, and with adults developed in mixed- or pure-species cultures. D. melanogaster appeared as a strong competitor and outnumbered D. simulans in all the culture conditions. This was because intraspecific competition was stronger than inter-specific competition for D. melanogaster whereas the reverse occurred for D. simulans. In competition, the productivity of both species generally appeared as frequency-dependent, although density-dependent productivity seems to be a more accurate explanation. D. simulans was very sensitive to variations of laboratory conditions. Room temperature and previous development with D. melanogaster were more favorable for D. simulans than 21 °C and previous development in pure cultures. These factors did not substantially affect D. melanogaster, which showed a greater ability of adaptation to laboratory conditions than its sibling D. simulans.