Over the last few decades, cities have grown rapidly in size and density. This trend will continue as urban areas are expected to absorb most of the global population growth in the upcoming decades (United Nations, 2012), thereby tripling in area (Seto et al., 2012). Although the conversion of natural habitat into built-up area has become one of the major reasons for habitat destruction worldwide, the effects of urbanization on biodiversity remain ambiguous, and underlying processes are poorly understood (reviewed in Faeth et al., 2011; McDonnell & Hahs, 2008; McKinney, 2008). However, most studies found that species diversity decreases due to urbanization, whereas species abundance increases, probably due to species specialized on urbanized areas, the so-called urban exploiters (Chace

& Walsh, 2006; McKinney, 2008; Møller, 2009; Faeth et al., 2011; Pickett et al., 2011; Aronson et al., 2014).