My answer is very different to that given by most people. It is women and small farmers working with biodiversity who are the primary food providers in the Third World, and contrary to the dominant assumption, their biodiversity based small farms are more productive than industrial monocultures. The rich diversity and sustainable systems of food production are being destroyed in the name of increasing food production. However, with the destruction of diversity, rich sources of nutrition disappear. Yields usually refers to production per unit area of a single crop.
Output refers to the total production of diverse crops and products.
Planting only one crop in the entire field as a monoculture will of course increase its individual yield. Planting multiple crops in a mixture will have low yields of individual crops, but will have high total output of food. Yields have been defined in such a way as to make the food production on small farms by small farmers disappear. From the biodiversity perspective, biodiversity based productivity is higher than monoculture productivity. The Mayan peasants in the Chiapas are characterised as unproductive because they produce only 2 tons of corn per acre.