Since I studied landscape architecture, I will first try to give the definition of ecology and landscape ecology. Ecology is generally defined as the study of the interaction among organism and their environment, and a landscape is a kilometers-wide mosaic over which particular local ecosystems and land-use recur. Thus landscape ecology is simply the ecology of landscape, and regional ecology, in which biological communities interacted with the physical environment. So we can just take the urban system as another kind of landscape ecosystem and apply this definition to define urban ecology. Urban ecology is the study of the interaction between living organisms and urban environment which is composed by man-made constructions, transportation, non-nature landscape and so on. This definition involves the sum of society, human beings and nature. And urban ecology is the process of the coordination and relationships between the structure and the function of the city.
 WE Dramstad, JD Olson, RTT Forman. Landscape Ecology Principles in Landscape Architecture and Land-use Planning. Island Press, 1996.