Coevolution is when two species that share a relationship evolve together for mutual benefit of both species. An example of this can be seen in pollinators and plants. It can occur in predator and prey relationships or in host and parasite ones. One species is evolving so the other does so as well in order to keep up the symbiotic relationship.
PBS. (2013). Evolution. www.pbs.org/evolution/library/glossary
Brassica & BeesEditBrassica is a type of flower that serves as a food source for bees; they have evolved together. Brassica have bright yellow petals drawing the bee in. As the bee searches for nector, the anther & stigma brush against the bee favoring pollination. The bee is covered in tiny hairs & even has pollen baskets on its legs to collect pollen & distrubute to other plants.
Retrieved from http://www.fastplants.org/pdf/activities/bees_brassicas.pdf
Coevolution can be seen in the acacia plant and the ant. The plant has evolved certain traits that benefit both the plant and their symbiotic partners, the ants. The ants protect the plants from sunlight-stealing vines. They have evolved sharp cutting devices on their heads that make this possible. The ants also act as bodyguards and scare away any other insect that tried to eat the leaves. In exchange, the plant provides the ants with shelter, food and sap to survive. The plant has adapted certain hollow areas that allow a place for the ants to store/house their larvae. Both species have evolved together to provide a successful symbiotic relationship.