Adaptive evolution refers to changes within species as a result of stimuli in the environment, and one example is Hypericum perforatum, also known as St. John's wort. This plant now has latitudinal clines in a number of characteristics pertaining to life history, as other plants have invaded its habitat.
Reed canary grass is another species that has benefited from adaptive evolution. As many different invasive plants have entered its habitat, the reed canary grass has responded by producing a greater amount of biomass and boosting its rate of clonal reproduction in order to continue thriving.
The purple loosestrife and white campion have shown adaptive evolution in their shifting of internal resources away from mechanisms for defense and toward growth and reproduction, as selection pressures in their habitats have increased significantly. The hybrid cattail has developed a wider spectrum of tolerances for such environmental factors as salinity and hydrology than either one of the two parent species has.
The kit fox and red fox are examples of varieties that have diverged from one another as they adapt to their environments. The red fox lives in forests and farmland, blending in with the trees with the same red color. The kit fox has developed larger ears, as its desert environment makes the ability to hear predators crucial. Structural similarities show that these different looking foxes have a common ancestor, but environmental conditions led to adaptive evolution.