Environmental problems – An overview - Environmental Deterioration and Contamination: Problems and their Management - page 34

Invasive species are often transported by biological vectors, which cause a more or
less natural scale of expansion of certain species, but human activities largely increased
the rate of these natural changes. Amongst human activities, the transportation of
plants and animals (which may carry seeds, insects, etc.), navigation (the balance
water of ships full of living organisms is let out in remote locations), and ground
transport (with uninvited passengers) increase the risk of introducing alien species.
Species have also been introduced intentionally for the inhabitation of surface waters,
bird habitats, or to help certain species survive. The escape of pets is also a common
cause of invasion.
Biotic invasion is considered as one of the top drivers for global biodiversity loss.
It is growing gradually due to globalization, transport, and tourism. Trade growth
largely contributes to global changes because of the species' dispersal through trade
and the alteration of ecosystem structure as a result. Brock et al. (2007) have developed
mathematical models for the quantitative description of the impact of trade, the effect
of harvest and the lack of well-defined property rights in environmental resources on
species richness and abundance. They evaluated the effect of inspections and tariffs, and
concluded that the introduction of new species can be reduced by reducing trade, but
the other factors impacting biodiversity (harvest and property rights) can be influenced
by enforcing optimal harvest and identified property rights.
Even pathogens can be considered as invasive species. Ecologists, epidemiolo-
gists, mathematicians, and economists are working together to develop mathematical
models of disease risks. SPIDER (2011) models differ from standard epidemiological
models of disease risks: it focuses on emerging infectious diseases that are caused by
novel pathogens and focuses on the so-called endogenous risk, meaning that the prob-
ability and consequences of an event such as disease emergence depends on people's
reactions to that event.
6.6 Urban ecosystems
Cities are urban ecosystems which include both nature and humans in a largely man-
built environment. Urban ecosystems have special properties that cannot be described
as the sum of the parts. By applying the ecosystem approach to dynamic ecosystems of
urban areas, one can realize that urban ecosystems are characterized by similar interac-
tions and behaviors as natural ecosystems. However, unlike natural ecosystems, urban
ecosystems are a hybrid of natural and man-made elements whose interactions are
affected not only by the natural environment, but also by culture, personal behavior,
politics, economics, and social organization. The definition of an ecosystem as a com-
munity of living organisms interacting with its nonliving environment can be applied
for urban ecosystems and helps to understand that cities are not separate from nature.
There are research projects on this topic from the future vision of eco-cities with
regenerative buildings (WBDG, 2013) through the Global Ecovillage Network (GEN,
2013) of sustainable communities or the United Nations University's course on Sus-
tainable Urban Futures (UN-SUF, 2013) to the scientific description of the differences
in the biodiversity of soil and urban soil (Vilisics & Hornung, 2009).
The City Biodiversity Summit (2010) endorsed a Plan of Action on Sub-national
Governments, Cities and Other Local Authorities for Biodiversity (2011-2020). The
summit concluded that “the process of interaction between cities and biodiversity is