Urban size effect on biodiversity: The need for a conceptual framework for the implementation of urban policy for small cities
Introduction
Studies of wild animals in urbanized areas are usually focused on ecological or evolutionary issues (Magle, Hunt, Vernon, et al., 2012). Thousands of cities around the world provide many research polygons in which one can observe how wild species react and adapt to urban conditions, how urbanization affects their behavior or physiology, and the evolutionary consequences of living in such a specific environment. These issues have been widely studied for birds, but for other groups of animals an increasing amount of research and information is also available (Bonier, 2012; Chace & Walsh, 2006; Fischer, Cleeton, Lyons, et al., 2012; Hall, Camilo, Tonietto, et al., 2017; Hamer & McDonnell, 2008; Hamer & McDonnell, 2010; Łopucki, Klich, Ścibior, & Gołębiowska, 2019; Peressin & Cetra, 2014; Slabbekoorn, 2013; Tryjanowski, Møller, Morelli, et al., 2016; Vignoli, Mocaer, Luiselli, & Bologna, 2009).
Studies on urban fauna may also have a conservation aspect. While fundamental research tries to investigate and describe the specific nature of urban populations living in this “new evolutionary situation”, conservation research asks how to plan and manage cities to avoid or mitigate the negative effects of urbanization on wildlife (Birnie-Gauvin, Peiman, Gallagher, et al., 2016; Garden, McAlpine, & Possingham, 2010; Magle et al., 2012; Marzluff & Ewing, 2001). These negative effects are related not only to the loss of species sensitive to urbanization (Łopucki, Klich, & Kitowski, 2019; McKinney, 2008; Waldstein Parsons, Forrester, Baker-Whatton, McShea, et al., 2018), but also to the condition of populations of species that successfully inhabit cities (Birnie-Gauvin et al., 2016). There is already a lot of evidence indicating that even urban adapters are often the object of non-adaptive evolution, i.e. reduced gene flow and stronger genetic drift leads to decreased genetic diversity within populations (Santangelo, Rivkin, & Johnson, 2018). These findings suggest the need to intensify conservation actions for urban wildlife, mainly by ensuring the appropriate quantity and quality of urban green areas and functional connections between them (Ikin, Knight, Lindenmayer, Fischer, & Manning, 2012; Kong, Yin, Nakagoshi, & Zong, 2010; LaPoint, Balkenhol, Hale, et al., 2015; Matthies, Rueter, Schaarschmidt, et al., 2017). Humans can also indirectly benefit from such activities because the quality of life is better in cities with rich and varied urban greenery (Amano, Butt, & Peh, 2018; Dean, van Dooren, & Weinstein, 2011; Fuller, Irvine, Devine-Wright, et al., 2007; Shwartz, Turbe, Simon, et al., 2014).
The effects of urbanization on wildlife have commonly been studied across urban–rural gradients, thus providing a useful framework for comparative studies on a global scale (McDonnell & Hahs, 2008; McKinney, 2008; Niemelä & Kotze, 2009; Waldstein Parsons et al., 2018). The results obtained in this way clearly show that the most intense effects of urban conditions on wildlife occur in older, more man-modified centers of cities, and these effects decrease farther away from city centers (McDonnell & Hahs, 2008). It can therefore be said that areas with impoverished wildlife or a lack of ground-dwelling wildlife are formed in the central parts of cities.
In this paper, we focus on the central part of cities and try to determine the minimum size of city from which the central part loses most of its potential biodiversity that is typical of city surroundings. On the one hand, we want to determine the rate of decline in species richness and biodiversity in cities of various sizes; on the other hand, we want to determine the size of city whose central zone is still relatively biodiverse and when depletion of wildlife species richness and biodiversity begins in this zone. This knowledge may facilitate the design of more sustainable cities and could be particularly useful for smaller cities because in the early stages of city development the opportunities for introducing measures that could reduce the negative effects of urbanization are greater. Even though small cities are much more common than large cities (in number and in total occupied area), the theory of sustainable design of small cities is still insufficient; in the near future, in many developing countries of the world, most urban growth is expected to take place in small and medium-sized cities (Łopucki & Kitowski, 2017; Secretariat of the CBD, 2012; Sun, Xiu, Wang, & Ding, 2012).
Section snippets
Object of the study
In this paper, we studied the effect of city size on wild ground-dwelling small mammals, specifically non-synanthropic rodents (order Rodentia, family Arvicolinae and Muridae) and shrews (order Soricomorpha, family Soricidae) that commonly live in various habitats of central Europe. Small mammals belonging to these systematic groups have several advantages that make them suitable for this purpose. First, they live in multi-species assemblages, so urbanization effects can be observed not only at
Differences in species richness and species diversity between the built-up and control areas
The Kruskal-Wallis test showed that the studied areas differed significantly both in terms of species richness (H(5) = 46.1; p < 0.001; N= 78) and the species diversity index (H(5) = 48.0; p < 0.001; N = 78). Post hoc tests showed that these differences mainly result from differences between the studied built-up and control areas. In the case of species richness (Fig. 1), all the studied built-up areas had significantly fewer species than the control areas. In the case of the species diversity
Discussion
As predicted, in our work we observed very strong negative effects of city size on the fauna of small ground-dwelling mammals. This effect was revealed by a decline in species richness and the species diversity index. The strongest negative reaction occurred in species known to be the most sensitive to urbanization, such as shrews and voles (Łopucki & Kitowski, 2017). On the other hand, there was one species, the striped field mouse, that showed a positive reaction, and which can be considered
Conclusions
When comparing fauna of small ground-dwelling mammals in urban areas, strong negative effects of city size (revealed by a decline in species richness and species diversity) may be observed. Our results indicate that this negative effect begins in very small cities. This means that in order to preserve the relatively high biodiversity of native wildlife in cities (even in central areas), appropriate actions should be taken in the early stages of city development. Proposals for such activities
CRediT authorship contribution statement
Rafał Łopucki: Conceptualization, Methodology, Investigation, Formal analysis, Writing - original draft, Writing - review & editing, Supervision, Project administration.Daniel Klich: Formal analysis, Writing - original draft, Writing - review & editing.Ignacy Kitowski: Investigation, Writing - review & editing.Adam Kiersztyn: Formal analysis, Writing - review & editing.
Acknowledgments
We would like to thank the anonymous reviewers for their suggestions that improved the quality of the paper and Iwona Mróz for support during the field study and agreeing to use her unpublished data.
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