The mutual habitude of human beings, the growing industrialization and the density of the populations may deeply modify the natural ecological dynamics.
As a result of these modifications, the equilibrium of Ecology has long put under pressure, and by the assumption that populations and communities typically exist under equilibrium conditions in habitats saturated with both individuals and species. However, much evidence contradicts these assumptions and it is likely that nonequilibrium is much more widespread than might be expected.
The city represents an Artificial Ecosystem, made by man, and in continous transformation
To make the city safe and confortable to live in, it is necessary to know how to regulate the equilibrium mentioned above; through the relationships between the many differents species, the environmental conditions that help its growth and reproduction, and the negative mechanisms that work against it.
The study of ecosystems mainly consists of the study of certain processes that link the living, or biotic (biocenosi) , components to the non-living, or abiotic (biotopo), components.
Rather than worrying mainly about particular species, we try to focus on major functional aspects of the system. These functional aspects include such things as the amount of energy that is produced by photosynthesis, how energy or materials flow along the many steps in a food chain, or what controls the rate of decomposition of materials or the rate at which nutrients are recycled in the system.
