Ecological economics is the study of the interactions and co-evolution in time and space of human economies and the ecosystems in which human economies are embedded. It uncovers the links and feedbacks between human economies and ecosystems, and so provides a unified picture of ecology and economy. The link between ecology and human economies has been manifested in the development of resource management or bio-economic models, in which the main focus has been on fishery or forestry management where the impact of humans on ecosystems is realized through harvesting. More closed links have been developed, however, as both disciplines evolve.