ALTERNATIVE ROUTES TO THE EVOLUTION OF COMPETITIVE ABILITY IN 2 COMPETING SPECIES OF DROSOPHILA

The evolution of components of interspecific competitive ability was e xamined in three different environments for three replicate pairs of D rosophila melanogaster and D. simulans populations. Populations evolve d enhanced competitive ability in three ways: (1) increased effectiven ess at reducing the numbers of the competitor species; (2) increased r esistance to the inhibitory effects of the competitor species; or (3) a combination of the two. Considerable variation was seen in the evolu tionary outcomes of competition among environments, and also among rep licate populations within environments. Significant replicate-by-envir onment interactions were also observed. The results suggest that the e volutionary routes to the evolution of enhanced competitive abilities can potentially differ among subdivided populations, creating a geogra phic mosaic of outcomes.