Impacts of urbanisation on biodiversity: the role of species mobility, degree of specialisation and spatial scale

Abstract

Urbanisation has an important impact on biodiversity, mostly driving changes in species assemblages, through the replacement of specialist with generalist species, thus leading to biotic homogenisation. Mobility is also assumed to greatly affect species' ability to cope in urban environments. Moreover, specialisation, mobility and their interaction are expected to greatly influence ecological processes such as metacommunity dynamics and assembly processes, and consequently the way and the spatial scale at which organisms respond to urbanisation. Here we investigate urbanisation impacts on distinct characteristics of species assemblages -namely specialisation degree in resource use, mobility and number of species, classified according to both characteristics and their combination -for vascular plants, butterflies and birds, across a range of spatial scales (from 1 × 1 km plots to 5 km-radius buffers around them). We found that the degree of specialisation, mobility and their interaction, greatly influenced species' responses to urbanisation, with highly mobile specialist species of all taxonomic groups being affected most. Two different patterns were found: for plants, urbanisation induced trait divergence by favouring highly mobile species with narrow habitat ranges. For birds and butterflies, however, it reduced the number of highly mobile specialist species, thus driving trait convergence. Mobile organisms, across and within taxonomic groups, tended to respond at larger spatial scales than those that are poorly mobile. These findings emphasize the need to take into consideration species' ecological aspects, as well as a wide range of spatial scales when evaluating the impact of urbanisation on biodiversity. Our results also highlight the harmful impact of widespread urban expansion on organisms such as butterflies, especially highly mobile specialists, which were negatively affected by urban areas even at great distances.

Is there a relationship between socio-economic factors and biodiversity in urban ponds? A study in the city of Stockholm

“…Interesting, Goertzen and Suhling (2013) found no strong effect on land use variables around city ponds in their study on biodiversity of Odonata when using a radius of 500 m. Nevertheless, the insect order and scale differences, could be related to dispersal and or niche specialisation. In general, we would expect species with high dispersal and a general niche to be affected at larger scales, compared to those with limited dispersal and a more specialised niche (Concepción et al 2015). Information on dispersal abilities in our insect taxa is limited, and therefore an analyses including some kind of dispersal variable would be very weak.…”

Urban stress is associated with variation in microbial species composition—but not richness—in Manhattan

“…Boxplots of the relative abundances of the most dominant bacterial phyla (a) and fungal classes (b) show no significant differences in relative abundance between parks (black) and medians (gray). Saito and Koike, 2013;Concepción et al, 2015), we re-acknowledge that many macroorganisms decline in diversity in cities relative to rural areas and that some species are absent in cities, resulting in changes in composition. Recent work (Beninde et al, 2015) has surveyed the causes of intra-urban biodiversity variation for a range of macroorganisms and found that, to a great extent, shifts in composition and declines in diversity in cities are due to the effects of habitat area and connectivity, with the most affected green spaces in cities being both small and disconnected.…”

“…Plant and animal communities often show these expected patterns of intermediate optima, while minimal diversity is seen in the most urbanized sites (for example, Blair, 1996;Blair and Launer, 1997;Cam et al, 2000;Marzluff, 2005;McKinney, 2008;Minor and Urban, 2010;Saito and Koike, 2013). Response to urbanization varies within a city depending on site characteristics (Sushinsky et al, 2013) as well as on the species assemblage and the spatial scale investigated (Concepción et al, 2015). It also varies between cities, with the amount of species loss best explained best by land cover and city's age (Aronson et al, 2014).…”

“…Based on studies of animals and plants in urban ecosystems, we expected that species richness would be lower in street medians than in city parks. Additionally, we expected the composition of microbial communities to be distinct in the two habitat types because previous studies have shown that persisting in high-stress habitats and/or maintaining viable populations in small habitat patches can be strongly influenced by speciesspecific traits (Schleicher et al, 2011;Slade et al, 2013;Concepción et al, 2015).…”

How to preserve a butterfly species within an urbanising settlement and its surroundings: a study of the scarce copper (Lycaena virgaureae L.) in southern Sweden

“…Seto et al 2012), habitat alternation/degradation (Schochet et al 2016) and fragmentation (Gibb and Hochuli 2002), which lead to species loss (Buczkowski and Richmond 2012), a decline in species density (Aronson et al 2014) or a change in species composition (Gibb and Hochuli 2002). Homogenisation of species composition has often been observed in the context of urbanisation (McKinney 2006;Knapp and Wittig 2012) whereby specialists (for butterflies here defined as species with comparatively lower mobility, fewer larval and adult food plants) are often replaced by generalists (Concepción et al 2015). Peri-urban fringes often experience the most profound changes (New 2015), resulting in negative impacts on biodiversity.…”