Effects of urbanisation and landscape heterogeneity mediated by feeding guild and body size in a community of coprophilous beetles

Urban Ecosystems https://doi.org/10.1007/s11252-020-00997-1 Effects of urbanisation and landscape heterogeneity mediated by feeding guild and body size in a community of coprophilous beetles Christopher W. Foster 1 1 1 & Christopher Kelly & Jordan J. Rainey & Graham J. Holloway 1 # The Author(s) 2020 Abstract Although the impacts of urbanisation on biodiversity are well studied, the precise response of some invertebrate groups remains poorly known. Dung-associated beetles are little studied in an urban context, especially in temperate regions. We considered how landscape heterogeneity, assessed at three spatial scales (250, 500 and 1000 m radius), mediates the community composition of coprophilous beetles on a broad urban gradient. Beetles were sampled using simple dung-baited traps, placed at 48 sites stratified across three distance bands around a large urban centre in England. The most urban sites hosted the lowest abundance of saprophagous beetles, with a lower mean body length relative to the least urban sites. Predicted overall species richness and the richness of saprophagous species were also lowest at the most urban sites. Ordination analyses followed by variation partitioning revealed that landscape heterogeneity across the urban gradient explained a small but significant proportion of community composition. Heterogeneity data for a 500-m radius around each site provided the best fit with beetle community data. Larger saprophagous species were associated with lower amounts of manmade surface and improved grassland. Some individual species, particularly predators, appeared to be positively associated with urban or urban fringe sites. This study is probably the first to examine the response of the whole coprophilous beetle community to urbanisation. Our results suggest that the response of this community to urbanisation matches expectations based on other taxonomic groups, whilst emphasising the complex nature of this response, with some smaller-bodied species potentially benefitting from urbanisation. Keywords Urban gradient . Landscape heterogeneity . Dung beetles . Community analysis Introduction Urbanisation is among the foremost threats to biodiversity, with an increasing proportion of the global human population living in cities (United Nations 2014). Yet it is this high population density that makes urban green spaces a key point of interaction between humans and wildlife, driving the need for researching biodiversity in urban areas (Niemelä 1999). Key to this is understanding how functional traits drive community assembly. Urban species communities may be filtered by traits, at a regional scale (Croci et al. 2008a; Vallet et al. 2010), with a consequential reduction in phylogenetic diversity (Knapp et al. 2008). At a local level (i.e. along a single * Christopher W. Foster 1 Centre for Wildlife Assessment and Conservation, School of Biological Sciences, University of Reading, Reading, UK urban gradient) the community composition may be more randomly structured (Magura et al. 2018) and not necessarily filtered by the same traits as at a regional scale – potentially threatening ecosystem function (Croci et al. 2008a; Magura et al. 2018). Historically, much urban biodiversity research concerned birds, which undergo significant community homogenisation and restructuring along gradients of urbanisation (Baker et al. 2010; Gagné and Fahrig 2011). An increasing number of studies address invertebrates in urban areas (Jones and Leather 2012) and show that the response to urbanisation is far from uniform, varying both within and between taxonomic groups (McIntyre et al. 2001; Gibb and Hochuli 2002; Angold et al. 2006; Egerer et al. 2017) and mediated by factors such as body size (Magura et al. 2006), feeding guild (Hochuli et al. 2004; Magura et al. 2013), degree of specialism (Gaublomme et al. 2008) and mobility (Angold et al. 2006; Snep et al. 2006; Delgado de la Flor et al. 2017). These non-uniformly negative impacts mean that urban greenspaces can host a diverse range of species (Angold Urban Ecosyst et al. 2006), and ecosystem function is not necessarily impaired by urbanisation beyond its fragmentation of habitats (Wolf and Gibbs 2004). Bee diversity can be particularly high in urban green spaces (Lowenstein et al. 2014; Baldock et al. 2015; Banaszak-Cibicka et al. 2018), suggesting that urban areas may contribute to maintaining pollination services across the wider landscape (Theodorou et al. 2017). Pest regulation may also be supported by the relatively high diversity of open-habitat spiders (Lövei et al. 2019). This highlights that urban areas are an important part of the contemporary landscape mosaic and their ‘spillover’ effect into agricultural landscape or neighbouring semi-natural habitats, whether positive or negative, needs to be addressed. Some argue that by hosting novel ecosystems (Hobbs et al. 2009; Kowarik 2011) urban areas actually boost overall biodiversity at a broad landscape scale, e.g., regional or national (Sattler et al. 2011). Species communities in a habitat patch may even be modified by the presence of urban areas in the surrounding landscape (Neumann et al. 2016a). To assess the full effect of landscape heterogeneity on biodiversity, including how urban areas interact with other land cover types, ideally a measure of gamma diversity would be obtained, i.e., the species diversity of the whole landscape. However, studies that address this are not particularly common (Duflot et al. 2014, 2017). Though not a complete substitute, sampling insects on ecotones using a common attractant, such as baited traps or flowers (e.g. Foster et al. 2019), may provide a snapshot of landscape biodiversity that can be assessed at a large number of sites relatively easily. Such a method can be carried out in urban sites as well as rural, where a habitat-focussed experimental design is not always feasible. It may also facilitate focussing on a particular functional group, which may be a more meaningful measure for assessing the value of urban greenspaces than the more random assemblages of species collected by passive trapping methods (Gagic et al. 2015; Pinho et al. 2016). Scarabaeoidea are a well-studied group, especially the true dung beetles in the families Geotrupidae and Scarabaeidae subfamilies Aphodiinae and Scarabainae (henceforth ‘dung beetles’). Dung beetles are important ecosystem-service providers in pastoral agricultural systems (Nichols et al. 2008; Manning et al. 2016) and often used as indicators in tropical ecosystems (Nichols et al. 2007), where they are threatened by habitat fragmentation including urbanisation (Korasaki et al. 2013). They are usually sampled using a variety of dungbaited trapping techniques or by direct searching of dung. Very few studies consider dung beetles in an urban context (Ramírez-Restrepo and Halffter 2016). Not all dung-feeding Scarabaeoidea are obligate dung feeders (Gittings and Giller 19 (...truncated)