Urban ecology is the study of the so-called urban ecosystems and their relations with wider environment. Unlike simple ecological units that feature a community of organisms and its associated environment, the urban ecosystems are much more complex. This is in part due to the fact that in urban ecosystems biotic relationships and laws that govern behavior are accompanied by the more sophisticated system of culture.
Urban ecology derives from three other sciences - ecology, sociology and biology. Ecology also studies ecosystems, but it is focused on exploring life in pristine areas, generally lacking human presence or footprint. It has influenced the new field, giving it its methodology and laws.
Sociology has also influenced urban ecology. In fact, the term "human ecology", which is sometimes used with the same meaning as "urban ecology", was coined by a sociologist - Robert Ezra Park (1864-1944). Human ecology means that the human being was studied at its home, as the etymology of the word "ecology" suggests. Park was among the most distinguished figures of the Chicago school of sociology, as he developed new methods of studying urban life. It is to Park and the Chicago school that the urban ecology owes methods like participant observation and case-studying. Moreover, it was the Chicago school that pioneered quantitative methods like social surveys and community-based statistical research, mapping of social areas, and the local community fact-book.
Urban ecology has also benefited from biology and has been using its terminology and principles to describe phenomena of the city life.
The main factor that has spurred the emergence of urban ecology, along with other urban studies, is the rapid growth of the cities during the 20th century.
In fact, many of the first problems that urban ecologists sought to tackle were related to this rapid expansion. While seeking the models of city growth, urban ecologists have made use of the work of Ernest Burgess (1886 - 1966). His concentric zone model represents an ideal construction of the tendencies of any city to grow radially from its central business district.
A subsection of the city growth problem is the problem of urban sprawl, or urban fringe, the point where human activity and urban infrastructure meet and alter other ecological or natural settings.
To explain urban growth, urban ecologists have made use of concepts taken from ecology and biology, such as competition, succession and domination. Urban ecologists sometimes refer to a city as an urban forest and speak of its species diversity, population sizes, and energy flow. But with the regard to the human culture, new concepts like media and urban politics have come into use.
Urban ecology acknowledges that urban ecosystems are dependent systems, which means that they need other ecosystems and outside energy and resources in order to function. To measure the extent of dependency of a given urban ecosystem, William Rees (1943-), a researcher at the University of British Columbia, has created the "ecological footprint" tool. This analytical method is used to assess how much land is required to maintain the activities of a given city. Thus, Rees has found that Vancouver, British Columbia, had a footprint 180 times bigger than its own size in 1996. This means that much more land, in terms of resources, is needed to support Vancouver's inhabitants.
As almost half of the global population lives in urban areas and nearly 80 percent of people in the developed world live in cities, urban ecologists have quickly arrived at the conclusion that humanity's collective will is the dominant power in welfare and global environment.
This has been one of the factors for the interest of urban ecologists in the interaction between other ecological entities and the urban systems. From that perspective, urban ecology has looked at changes in the behavior of different animal species as they get into contact with humans more often. Such encounters may lead to alterations in areas like the predator-victim pattern.
Urban ecologists are also interested in the impact of gross urban ecosystems on other entities. Thus, urban ecology has expanded its scope to problems like pollution, deforestation, and global warming.
A recent trend in urban ecology is the increasing awareness that the health of cities is vital for the health of the overall environment. This awareness has led to the emergence of more activist areas, like ecological urbanism, new urbanism, and green living. Urban planning, meanwhile, has been affected by a drive for sustainable development, as activists aim for sustainable, pollution-free cities.