134 Ecology and Applied Environmental Science
dogs, which are abandoned domestic dogs that live in many cities all over
the world. Birds of prey also occur in many developed urban areas, characteristic examples being hawks and owls, which commonly overwinter in
cities, where they feed on the abundant sparrows, pigeons, mice and rats.
For some endangered species such as Peregrine falcons, this fact may be
decisive for their preservation.
6.8.3.1 The Urban Ecosystem
For the formation of an urban ecosystem, there must be the necessary biological species, suitable habitats, adequate sources of energy, and a rudimentarily stable environment. These preconditions are met in any city, and
therefore there is always an urban ecosystem that includes at least people,
the parasites that live off them and the microorganisms that decompose
dead organic matter. But apart from this minimum food chain, cities, as
a rule, also contain other organisms such as plants, animals that feed on
refuse, as well as predators of them. Thus a more complex urban ecosystem
is formed which includes food chains and primary trophic levels. The various species either arrive in the city from the countryside or are transported
from far away by humans. Habitats are formed either in the vestiges of the
natural landscape that always remain in a city (e.g. vacant lots, streams), in
various structures (roofs, cellars, holes, etc.) or in artificially created vegetation (gardens, parks, etc.). The main source of energy in urban eco systems,
unlike natural ecosystems, is not solar radiation but the introduced food
and waste of all kinds. The same sources furnish the various nutrients,
since in urban ecosystems recycling of chemical substances (Chapter 4) is
incomplete and probably negligible.
A range of important parameters affect the creation, complexity and
stability of an urban ecosystem:
• A stable environment, where changes (demolitions, reconstruction,
excavations, spatial layout, etc.) are small and rare, is a particularly
favourable factor.
• The existence of suitable biotopes in a substantial variety and size. The
most important habitat is vacant terrain covered with vegetation. The
ratio of vegetation to the area of the city is a decisive parameter. Also
of importance are the density of the vegetation, the presence of trees
and shrubs, the existence of natural corridors that permit communication between green areas and the short distances between them.
• The natural state of the landscape. The existence of suitable plants,
as a rule those that are native to the area, helps create robust, resilient and rich ecosystems. The needs for sustaining vegetation are
much smaller when it consists of native plants, and the development of a variety of the area’s animals that feed on them is favoured.
dogs, which are abandoned domestic dogs that live in many cities all over
the world. Birds of prey also occur in many developed urban areas, characteristic examples being hawks and owls, which commonly overwinter in
cities, where they feed on the abundant sparrows, pigeons, mice and rats.
For some endangered species such as Peregrine falcons, this fact may be
decisive for their preservation.
6.8.3.1 The Urban Ecosystem
For the formation of an urban ecosystem, there must be the necessary biological species, suitable habitats, adequate sources of energy, and a rudimentarily stable environment. These preconditions are met in any city, and
therefore there is always an urban ecosystem that includes at least people,
the parasites that live off them and the microorganisms that decompose
dead organic matter. But apart from this minimum food chain, cities, as
a rule, also contain other organisms such as plants, animals that feed on
refuse, as well as predators of them. Thus a more complex urban ecosystem
is formed which includes food chains and primary trophic levels. The various species either arrive in the city from the countryside or are transported
from far away by humans. Habitats are formed either in the vestiges of the
natural landscape that always remain in a city (e.g. vacant lots, streams), in
various structures (roofs, cellars, holes, etc.) or in artificially created vegetation (gardens, parks, etc.). The main source of energy in urban eco systems,
unlike natural ecosystems, is not solar radiation but the introduced food
and waste of all kinds. The same sources furnish the various nutrients,
since in urban ecosystems recycling of chemical substances (Chapter 4) is
incomplete and probably negligible.
A range of important parameters affect the creation, complexity and
stability of an urban ecosystem:
• A stable environment, where changes (demolitions, reconstruction,
excavations, spatial layout, etc.) are small and rare, is a particularly
favourable factor.
• The existence of suitable biotopes in a substantial variety and size. The
most important habitat is vacant terrain covered with vegetation. The
ratio of vegetation to the area of the city is a decisive parameter. Also
of importance are the density of the vegetation, the presence of trees
and shrubs, the existence of natural corridors that permit communication between green areas and the short distances between them.
• The natural state of the landscape. The existence of suitable plants,
as a rule those that are native to the area, helps create robust, resilient and rich ecosystems. The needs for sustaining vegetation are
much smaller when it consists of native plants, and the development of a variety of the area’s animals that feed on them is favoured.