Temperature-dependent competitive outcomes between the fruit flies Drosophila santomea and D. yakuba

Changes in temperature associated with climate change can alter species distributions, drive adaptive evolution, and, in some cases, cause extinction. Research has tended to focus on the direct effects of temperature, but changes in temperature can also have indirect effects on populations and species. Here we test whether temperature can indirectly affect the fitness of Drosophila santomea and D. yakuba by altering interspecific competitive outcomes. We show that, when raised in isolation, both D. santomea and D. yakuba show maximal performance at temperatures near 22{degrees}C. However, when raised together, D. santomea outcompetes D. yakuba at a lower temperature (18{degrees}C), while D. yakuba outcompetes D. santomea at a higher temperature (25{degrees}C). We then use a coexistence experiment to show that D. santomea is rapidly (within 8 generations) extirpated when maintained with D. yakuba at 25{degrees}C. By contrast, D. santomea remains as (or more) abundant than D. yakuba over the course of ~10 generations when maintained at 18{degrees}C. Our results provide an example of how the thermal environment can indirectly affect interspecific competitive outcomes and suggest that changes in the competitive advantage of species can lead to some species becoming more prone to extinction by competitive exclusion.