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1 A global review of urban pollinators and implications for maintaining 2 pollination services in tropical cities 3 4 Authors: 5 Pietro K. Maruyama1,*, Jéssica Luiza S. Silva2, Ingrid N. Gomes3, Camila Bosenbecker4, 6 Oswaldo Cruz-Neto2, Willams Oliveira5, João Custódio Fernandes Cardoso4, Alyssa B. 7 Stewart6, Ariadna Valentina Lopes2 8 9 1. Departamento de Genética, Ecologia e Evolução - ICB, Universidade Federal de Minas 10 Gerais, Belo Horizonte-MG, Brazil 11 2. Departamento de Botânica, Universidade Federal de Pernambuco, Recife-PE, Brazil 12 3. Programa de Pós-Graduação em Ecologia, Conservação e Manejo da Vida Silvestre, 13 Universidade Federal de Minas Gerais, Belo Horizonte-MG, Brazil 14 4. Programa de Pós-Graduação em Ecologia e Conservação dos Recursos Naturais, 15 Universidade Federal de Uberlândia, Uberlândia-MG, Brazil 16 5. Programa de Pós-Graduação em Biologia Vegetal, Universidade Federal de Pernambuco, 17 Recife-PE, Brazil 18 6. Department of Plant Science, Faculty of Science, Mahidol University, Bangkok 10400, 19 Thailand 20 *Correspondence: [email protected] 21 22 23 Manuscript submitted as a book chapter for: 24 Ecology of Tropical Cities: Natural and Social Sciences Applied to the 25 Conservation of Urban Biodiversity 26 Editors: Fabio Angeoletto, Piotr Tryjanowski & Mark Fellowes 27 Publisher: Springer Nature, 2022 28 29 Abstract: 30 Pollinators provide essential ecosystem services worldwide, but dependence on biotic 31 pollination is higher in the tropics, where urbanization is expected to impact biodiversity more 32 severely. Here, we present a global review on urban pollinator studies with emphasis on the 33 tropics. From the 308 published studies that included information on pollinator groups, only 34 ~25 % were conducted in tropical regions, while ~65 % were carried out in the non-tropical 35 northern hemisphere. This overall trend was similar for all the major insect pollinator groups, 36 but not for vertebrates, which were overall less studied in both tropical and non-tropical 37 regions. The effects of urbanization on tropical pollinators are diverse and complex and likely 38 depend on the extent and type of urbanization, as well as the pollinator taxa studied. For both 39 insect and vertebrate pollinators, the existing studies suggest that tropical cities can support 40 generalist species tolerant of human activity, but the lack of studies hampers other general 41 conclusions. The underrepresentation of pollinator studies in tropical cities undermines the 42 value of urban biodiversity conservation in the most biodiverse regions of the world and 43 highlights a missing opportunity. Since promoting urban biodiversity benefits both nature and 44 people, it could be especially relevant in the Global South, where economic and social 45 inequalities are severe and pollinator conservation may contribute to sustainability goals. In 46 this context, initiatives that foster more international collaborations and research in the tropics 47 are essential for a better understanding of the effects of urbanization and the value of pollinators 48 in urban areas. Such knowledge can provide the basis for better urban planning strategies that 49 contribute to the conservation of biodiversity and maintenance of pollination services in 50 tropical cities. 51 1. Introduction 52 Human population growth has been accompanied by increasing conversion of natural 53 areas to urban ones, i.e., urbanization, often in regions considered as biodiversity hotspots (Seto 54 et al. 2012). Although sometimes erroneously considered as “biological deserts” because of the 55 loss of natural habitats, cities also hold the potential to harbor considerable diversity when 56 biodiversity-friendly urban “green spaces” are available and promoted (Sandström et al. 2006; 57 Aronson et al. 2017). In addition, urban biodiversity brings additional benefits through its 58 social and educational value, as an appreciation and broader understanding of the natural world 59 may lead to public involvement in conservation (Miller and Hobbs 2002). At the same time, 60 cities have unique conditions and act as strong biological filters, influencing the species able 61 to thrive in such environment (Spotswood et al. 2021 and references therein). 62 Among the many animals that are found across the urban landscape, pollinators are 63 known to provide important ecosystem services through their interactions with flowering 64 plants, and the role of urban green areas in promoting the conservation of pollinators has 65 received much attention recently (Hall et al. 2017; Wenzel et al. 2020; Silva et al. 2021a). 66 Plant-pollinator interactions are one of the most important ecological interactions and 67 ecosystem services in the world, as an estimated 87.5 % of angiosperms rely on biotic 68 pollination (Ollerton et al. 2011). Thus, these interactions are directly related to the persistence 69 and maintenance of biodiversity for both plants and their associated animals, and food supply 70 worldwide (Potts et al. 2010; IPBES 2016; Ollerton et al. 2017; Silva et al. 2021b). 71 Nevertheless, it is still unknown in many regions of the world how urbanization threatens 72 pollination, and therefore ecological function and ecosystem services in urban areas. 73 Globally, estimates indicate that dependence on biotic pollination in natural areas is 74 higher in the tropics than in non-tropical regions (Ollerton et al. 2011; Rech et al. 2016). 75 Interactions between plants and pollinators in the tropics are also potentially more specialized, 76 considering the set of floral traits involved, than in non-tropical areas (Rosas-Guerrero et al. 77 2014). Moreover, some pollinator groups, such as vertebrates, are more diverse and relatively 78 more important for plant reproduction in the tropics (Fleming and Muchhala 2008; Ratto et al. 79 2018). Despite these differences, recent reviews of plant-pollinator interactions in urban areas 80 suggest that tropical studies are underrepresented in the international literature (Wenzel et al. 81 2020; Silva et al. 2021a). This reflects a general trend that, while the importance of urban 82 biodiversity is widely recognized (e.g., Aronson et al. 2017, Spostwood et al. 2021), the world’s 83 most biodiverse regions from the Global South are often understudied regarding urban 84 biodiversity (McDonald et al. 2020). Considering the paradox between the higher importance 85 of biotic pollination and the underrepresentation of urban pollinator studies in the tropics, in 86 this chapter we discuss known patterns about the global distribution of pollinators, with an 87 emphasis on urban areas, and compare tropical and non-tropical regions. Then, we review some 88 relevant studies conducted on tropical urban pollinators, highlighting their findings to foster 89 future studies. 90 91 2. Global distribution of urban pollinator groups 92 Biodiversity is unevenly distributed throughout the world, with tropical regions 93 harboring higher overall biodiversity (Gaston 2000). This pattern includes plants (Kreft and 94 Jetz 2007) and many of the animal taxa that act as pollinators (Ollerton 2017; Eggleton 2020). 95 However, when considering distinct taxa separately, global distribution patterns may differ 96 among groups. For instance, bees, the dominant group of pollinators worldwide (Ollerton 97 2017), have the highest diversity not close to the equator, but at more arid mid-latitude regions, 98 resulting in a bimodal pattern of species richness (Orr et al. 2021). Detailed assessments of 99 diversity patterns for other specific groups of pollinators are not readily available, with many 100 scattered sources for distinct groups (Ollerton 2017). Bird- and bat-pollinated plants typically 101 evolved from bee-pollinated ancestors (e.g., Tripp and Manos 2008), and may comprise a 102 substantial proportion of pollination modes in distinct tropical regions of the world (e.g., 103 Machado and Lopes 2004; Girão et al. 2007; Ballesteros-Mejia et al. 2016). Hence, when 104 comparing tropical and non-tropical urban pollinators, we may expect to find a higher 105 representation of non-insect groups in the tropics because the species richness of both 106 vertebrate-pollinated plants and vertebrate pollinators are higher there (Nascimento et al. 107 2020). 108 109 2.1. Overview of urban studies 110 To assess the global distribution of pollinator groups found in urban areas, we carried 111 out a literature search using the ISI Web of Science – Science Citation Index Expanded 112 platform (www.webofknowledge.com) (last accessed on June 29, 2020) with the following 113 search strings: ‘‘urban* and pollinat*’’ in the title, keywords and/or abstract (see also Silva et 114 al. 2021a). After searching and sorting the references, we kept papers with information on 115 pollinator distribution in urban areas. These references included studies on plant-pollinator 116 interactions as well as those dealing exclusively with pollinator/floral visitor lists and natural 117 history information of animals in urban areas if these were referred by authors or identified by 118 us as potential pollinators. Studies that did not include information on pollinator groups were 119 excluded. Then, for each study, we extracted: (1) the geographical coordinates of the cities 120 studied (using information provided or accessing the centroid of the city reported) and (2) the 121 group of pollinators investigated. We considered the functional group or groups of pollinators 122 investigated