Studies show that the relationships between species diversity and community function (measured as productivity and stability) are often positive. Species diversity enhances productivity because species use resources in slightly different ways; mixtures of species tend to result in a more complete use of limiting resources. Species diversity is hypothesized to enhance stability (a measure of resistance to, or recovery from, disturbance) because the more species a community contains, the more likely some species can persist under variability. These species diversity–
learning outcome
You should be able to:
Describe how and why growing polycultures can increase agricultural productivity.
Why do Costa Rican farmers often grow multiple crops on the same plot, and why might this be a good strategy under drought conditions?
Costa Rican farmers often grow multiple crops together (such as corn and sweet potatoes) to reduce the number of insect pests that attack the plants. For example, parasitoid wasps are attracted to corn pollen and attack sweet potato pests, thus benefitting the sweet potato crop. Likewise, the corn plants receive pollination services from the wasps.
Growing polycultures could be a good strategy under drought conditions if each species performs differently under low water conditions. For example, if one species performs better than another, overall productivity could still be high compared with a condition in which only one species, or monoculture, that did not respond favorably to drought.