It seems obvious that how different living things in a community or ecological system bump up against one another would affect how they evolve. That would include everything from the mix of fish in a lake to the bacteria, fungi and insects that coexist in rainwater that pools in the roots at the base of a beech tree.

But, says Diane Lawrence, a graduate student in biology at Imperial College London, what actually happens when a number of species grow together over generations has rarely been examined in the laboratory, since most studies of adaptation involve one species alone, or perhaps two species. “We found that species interactions are really important in shaping the way that species evolve,” Ms. Lawrence said of her research, which was published in the journal PLoS Biology.