The expansion of urbanization has led to major declines in the populations of many unique species and the successive introduction of nonnative species. Several studies confirm that population numbers and genetic diversity of native species of plants, animals, and insects drop with greater urbanization [1,2,3].
One of the major causes of biodiversity decline in cities is the land-use change and, what is very closely connected, loss of habitat. As traditional ecosystems are altered to support complex urban infrastructure, the original wildlife is often not able to keep up with those sudden changes in available resources and begins to strive.
Urban impacts on biodiversity reach their most devastating effects in developing countries. For example, less than 2% of the Atlantic forests of coastal Brazil within the urban reach of Sao Paulo remain, and it has been estimated that thousands of species from this region of high endemism have been driven to extinction, most never having been described by taxonomists.— Dennis D. Murphy
The enemies of urban biodiversity
The loss of habitat is not the only adverse effect of urbanization. The impacts of human activity when altering land cover also introduce the phenomenon of habitat fragmentation. Original ecosystems are split into small fragments when buildings and related infrastructure are built progressively over them.
For example, think of a moss on the forest floor when a road is built directly in the middle of its natural habitat. What impact does that have on its living conditions? Temperature increases due to the direct exposure to sunlight, the soil gets drier and different species take over, stealing necessary nutrition from its poor existence.
Consequently, fragmentation comes with another toll for native species, the edge effect. The edge effect means that there are different conditions on the edges of a habitat than in the middle, which further decreases the inhabitable range for some species. The genetic diversity of populations declines as well, since small islands of habitats cannot possibly provide enough nutrients or space for large families to flourish.
Along with the negative impacts of fragmentation, city centers and suburbs usually struggle with the spread of nonnative species. Overall, the percentage of nonnative species rises up to more than 50% in urban areas . The cause of this trend is simple – human intervention. It is our intervention, such as planting exotic trees in city parks for aesthetic purposes, that dramatically affects delicate balance of native populations. Often, the urban ecosystem consists of significantly different species than surrounding natural areas.
Higher occurrence of nonnative species in the urban ecosystem is especially risky for native populations. Nonnative species easily get out of control in conditions where their natural enemy is missing, and can therefore outcompete native species.
Furthermore, nonnative species also increase the threat of disease outbreak with destructive consequences for native populations with low or no resistance to such diseases. To protect the health of original ecosystems, it is important to promote the diversity of native species over the introduction of nonnative species in urban areas.
Can be urban biodiversity protected?
With the growth of urbanization globally, cities are becoming the main force driving trends in environmental protection. Future development planners should prioritize biodiversity protection within a city as one of the most important aspects of landscape planning. This includes techniques that cherish the natural elements of an area, and allow sustainable co-existence of people with native species .
In areas where original ecosystems have been nearly wiped out, biodiversity can be restored by cultivating diverse native species. Their re-introduction in an area offers multiple benefits, such as reduction of the spread of invasive species, improved resistance to diseases of an ecosystem, and increase of local biodiversity naturally and over the time.
Our endeavors to include biodiversity preservation on the list of future urban planning is the first step in tackling the problem of globally disappearing ecosystems. It is time to set our focus on our closest neighborhoods and begin their transformation into biodiversity guardians because our survival is ultimately dependent on it.