Over half of the world’s human population lives in cities. Are species adapting to life in these novel urban environments? A global team of researchers (including Tiffany Longo, Jesse Bragger, and Summer Shaheed, shown in in the photo) used white clover as a study system to find out. They measured the production of a compound called hydrogen cyanide (HCN) in rural and urban clover plants. Production of HCN deters herbivores and increases tolerance to drought but has a cost: Clover must expend energy to produce HCN.
The researchers measured the frequency of clover plants producing HCN along a transect from each city center out to its rural environment. The graph shows one example of results from Münster, Germany: Anna Bucharova and Christian Lampei sampled 765 plants in 40 populations along a 9.87 km transect. What does the data reveal? What was the prediction of the null hypothesis?