Size does matter: Passive sampling in urban parks of a regional bat assemblage Elena Tena 1 & Guillermo Fandos 1 & Óscar de Paz 1,2 & Roberto de la Peña 1 & José Luis Tellería 1 # Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract We studied the occurrence of bats in urban parks in the city of Madrid (Spain), and the resulting patterns were compared with bat occurrence in the surrounding region. In this way, we addressed if the presence of individual species in the study parks was positively related to their regional occurrence and the way some geographical and environmental traits affected bat richness and composition in urban parks. We analysed urban parks varying in area, structure and distance to the edge of the town. During two years, bats occurring in parks were sampled using ultrasound detectors. A similar sampling method was carried out for four years in the countryside around the city to detect the regional pool of species. The results show that the occurrence of individual species in urban parks was a reduced sample of the regional pool of species and that there was a positive relationship between the occurrence of species in urban parks and the surrounding countryside. This pattern suggests that the more distributed bats at a regional scale were the most frequent ones in parks within the urban matrix. Park area was the main determinant of bat richness. In addition, bat richness distribution reported a nested pattern of species loss as park area decreased. This suggests that bat occurrence in the study parks can be interpreted as the results of a passive sampling of individual species occurring at the regional scale, and that park size was the main determinant of the species occurrence. We conclude that more proactive approaches to bat conserva- tion could be carried out in order to improve the presence of some rare species in urban parks. Keywords Area effect . Chiroptera . Habitat fragmentation . Habitat selection . Nested species distribution . Species richness Introduction Urbanization is spreading rapidly at a global scale, a trend that affects biodiversity conservation in many areas. Thus, under- standing the effect of urbanization on biodiversity and the way it can be managed is a basic challenge in conservation biology (McKinney 2002). In this context, urban parks are key areas to conserve biodiversity since they are patches of semi-natural habitats where many species thrive within the urban matrix (Baker and Harris 2007). In this respect, and despite bats (Order Chiroptera) being one of the most diverse and distrib- uted mammal orders (Altringham 2011), little attention has been dedicated to explore the way these animals are distribut- ed in urban parks (Gilbert 1989; Jung and Threlfall 2018). The most studied issues have been related to the comparison be- tween rural and urban bat assemblages (Kurta and Teramino 1992; Johnson et al. 2008), the factors influencing bat distri- bution (Krauel and LeBuhn 2016; Moretto and Francis 2017) or the potential benefits of urbanization for these species (Ancillotto et al. 2015). However, little work has been devoted Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11252-019-00913-2) contains supplementary material, which is available to authorized users. * Elena Tena e.tena@ucm.es Guillermo Fandos gfandos@ucm.es Óscar de Paz odepaz6@gmail.com Roberto de la Peña delapenaroberto@gmail.com José Luis Tellería telleria@bio.ucm.es 1 Departamento de Biodiversidad, Ecología y Evolución, Universidad Complutense de Madrid, E-28040 Madrid, Spain 2 Departamento de Ciencias de la Vida, Facultad de Biología, Ciencias Ambientales y Química, Universidad de Alcalá, E-28801, Alcalá de Henares, Madrid, Spain Urban Ecosystems https://doi.org/10.1007/s11252-019-00913-2