key: cord-0270629-78nhm5wz authors: Vereecken, Nicolas J.; Weekers, Timothy; Marshall, Leon; D’Haeseleer, Jens; Cuypers, Maarten; Vanormelingen, Pieter; Pauly, Alain; Pasau, Bernard; Leclercq, Nicolas; Tshibungu, Alain; Molenberg, Jean-Marc; De Greef, Stéphane title: Five years of citizen science and standardized field surveys reveal a threatened urban Eden for wild bees in Brussels, Belgium date: 2021-03-10 journal: bioRxiv DOI: 10.1101/2021.03.10.434823 sha: dee957e90a6da3b7d26fa01410fc7313c8ce5bca doc_id: 270629 cord_uid: 78nhm5wz Urbanisation is often put forward as an important driver of biodiversity loss, including for pollinators such as wild bees. However, recent evidence shows that the mosaics of urban green spaces, and in particular certain categories of informal urban green spaces (IGS), can play an important role to help native wild bees thrive in cities. Here, we describe the results of five years of citizen science and standardised field surveys of wild bees conducted at the Friche Josaphat, a 24-ha urban wasteland in the Brussels-Capital Region (Belgium). These field surveys were initiated following the planned restructuring and partial destruction of this site by the regional authorities. We recorded a total of 2,507 specimens belonging to 127 species of wild bees, i.e. 60.5% of the 210 species recorded regionally, including nine that are threatened with extinction at national or European scales. The Friche Josaphat encompasses a significant share of the functional and phylogenetic diversity of wild bees known from the Brussels-Capital Region and is one of the most species-rich localities known to date for wild bees in Belgium. Collectively, our results highlight the strong complementarity of citizen science and academic approaches in biodiversity surveys, and they reaffirm that wastelands are essential components of urban biodiversity. Our study stresses the need to provide biodiverse IGS with a formal status within the mosaic of urban green spaces, but also to acknowledge and safeguard their natural capital and the multiple ecosystem services they provide. Urbanisation as a spatial process is a priori expected to have deleterious impacts on 54 biodiversity, through its contribution to habitat fragmentation and the irreversible conversion 55 of green spaces into impervious surfaces (e.g., McDonald et al., 2008; Vimal et al., 2012) . 56 Yet, parallel evidence suggests that some groups of organisms might actually thrive in cities 57 (Miller & Hobbs, 2002; Araujo, 2003; Kühn & Klotz, 2006) . By and large, our cities and The added value of cities for biodiversity conservation lies in their mosaics of typologically 74 diverse urban green spaces (UGS), from playing fields to highly manicured environments 75 such as managed forests, parks or cemeteries, to semi-natural landscapes, including urban 76 4 nature reserves (Lepczyk et al., 2017) . However, besides these formally acknowledged and 77 managed UGS, a multitude of so-called informal urban green spaces (IGS) such as "vacant" 78 lots, street or railway sidings, utility easements, corridors between buildings and riverbanks 79 are typically deprioritized and often represent an underrated piece of the urban nature and 80 urban planning puzzle (Rupprecht & Byrne, 2014) . Among these neglected IGS, urban 81 wastelands (or "brownfield" lands) come in all sizes and shapes, and unlike the coherently 82 managed urban parks, they often meet the diverse "nature needs" of their users who, contrary 83 to urban planners, do not view IGS as being "vacant" or as an "empty space" that should be In this study, we assess the contribution of the Friche Josaphat, the largest urban wasteland in 94 Brussels, to the diversity of wild bees at the scale of the Brussels-Capital Region. We 95 compiled five years of field surveys to characterize the fauna of this site, and we compare it 96 to the regional checklist of wild bees. Specifically, we use taxonomic, traits-based functional 97 and phylogenetic diversity metrics, as well as null models of community assembly to test if 98 the wild bee species assemblage recorded at our study site is functionally and 99 phylogenetically clustered or over-dispersed (i.e., with significantly less or more similarities 100 among co-occurring species than in a random community, respectively). The importance of Our dataset for the Friche Josaphat comprises 2,507 individual records, representing 7,188 205 specimens and 127 species of wild bees, as well as the honey bee (Apis mellifera) (Table S1 ). The highest estimation of species richness for the Friche Josaphat was associated with the The 12 most common species are illustrated and listed in Figure S1 along with their 218 abundance in the dataset; they represented 74.9% of all samples recorded. Our records 219 encompass seven wild bee species of conservation concern at the scale of Belgium: these 220 include the nationally "Vulnerable" species Eucera longicornis (Apidae) and the "Near process. As such, the Friche Josaphat is therefore currently the richest semi-natural site at the 267 regional level, and the fact that its functional and phylogenetic structure is not significantly 268 different from random communities makes it an ideal site to "showcase" the diversity of 269 urban bees in Brussels. 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