DAILY SCIENCE

Small Cities, Large Biodiversity Potential
In contrast to medium and large cities, small cities may retain a pretty healthy biodiversity of small mammals, similar to nearby rural areas.
August 15, 2017

Studies of urban wildlife that focus exclusively on large metropolises may overlook conservation opportunities in smaller cities, according to an analysis published in the journal Urban Ecosystems.

In the study, researchers surveyed small ground-dwelling mammals like mice, voles, and shrews in Chelm, a city of about 65,000 people in Poland. They found that outside of the oldest, densest portion of the city, Chelm’s green spaces retain a pretty healthy biodiversity of small mammals, similar to nearby rural areas.

That contrasts with most studies of biodiversity in medium and large cities, which typically find a relatively limited, uniform suite of urban-tolerant species even at sites on the city outskirts.

Very few studies of urban biodiversity have looked at small cities like Chelm – those with under 100,000 residents and covering fewer than 100 square kilometers. But there are more small cities than large cities in the world, and small cities cover more area than large cities.

“Moreover,” the researchers write, “in the near future, in many developing countries of the world most of the urban growth is expected to take place in small and medium-sized cities.” That means understanding the existing biodiversity of small cities is crucial so that it can be protected as these cities grow.

The researchers used live traps to collect small mammals at 21 sites within the Chelm city limits and 20 sites in a rural area outside the city. The city sites included 7 “downtown” green areas located in the oldest, densest part of Chelm and isolated from other habitat by buildings and roads; 7 “green corridor” sites located along the Uherka River or along the main railway line through town; and 7 green areas on the outskirts of the city.

Altogether they captured 2,333 small mammals representing 15 species. This included 1,213 individuals of 13 species at the city sites and 1,120 individuals of 14 species at the rural sites.

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Small mammals were less abundant at downtown compared to rural sites, the researchers found. Downtown sites also had fewer small mammal species, fewer urban-sensitive species, and a much higher proportion of urban-tolerant species than rural sites.

For example, 4 kinds of shrews and 5 kinds of voles – groups that are both known to be sensitive to urban development – appeared at the rural sites, but only 1 species of each at downtown sites. Meanwhile, mice in the urban-tolerant genus Apodemus made up the vast majority of animals found at downtown sites but were extremely scarce at the rural sites.

Those results are similar to what’s seen in studies of biodiversity in medium and large cities. But in Chelm only the downtown sites have a small mammal community that is significantly different from surrounding rural areas.

In contrast, the number and composition of species at green corridor and city outskirts sites were similar to rural sites. “These areas can be inhabited even by species sensitive to urbanization,” the researchers write.

They recommend that city planners consider how to maintain biodiversity as small cities grow, such as by leaving some blocks undeveloped, establishing a system of habitat corridors to connect green areas to each other, and securing long-term protections for the most valuable sites. “This phenomenon of relatively unchanged fauna outside the downtown area shows that small cities have the potential to maintain a high level of diversity of small ground-dwelling mammals if appropriate planning of further building expansion is implemented,” the researchers write.

Source: Lopucki L and I Kitowski. “How small cities affect the biodiversity of ground-dwelling mammals and the relevance of this knowledge in planning urban land expansion in terms of urban wildlife.” Urban Ecosystems. 2017.

Image: Banksy

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