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Cities can host significant biological diversity. Yet, urbanisation leads to the loss of habitats and, potentially, to local extinctions. Understanding how multiple taxa respond to urbanisation globally is essential to promote and conserve biodiversity in cities and surrounding landscapes. Using a dataset with site-level occurrence and trait data of 5302 species from six terrestrial fauna taxonomic groups across 379 cities on 6 continents, we show that urbanisation produces taxon-specific changes in trait composition, with traits related to reproductive strategy consistently showing the strongest response. The effect of urbanisation on community trait composition is strongest at the largest spatial scale considered, and more closely linked to landscape composition (% urban) than arrangement (aggregation), although latitude and climatic variables remain a stronger influence. This study did not find evidence in support of a global urban taxa syndrome, but instead we suggest that there are four general urban trait syndromes, with resources associated with reproduction and diet likely to be driving patterns in traits associated with mobility and body size. Functional diversity measures showed a wide range of responses, leading to a shift in trait space that is most likely driven by the distribution and abundance of critical resources, and the urban trait syndrome displayed by individual species within a community. Further research is required to understand the interactions between the four general urban trait syndromes, resource distribution and abundance and changes in functional diversity of taxa at different spatial and temporal scales. Maximising opportunities to support species within taxa groups with different urban trait syndromes should be pivotal in conservation and management programmes within and among cities. This will reduce the likelihood of biotic homogenisation at the taxa level, and helps ensure that urban environments have the ecological capacity to respond to challenges such as climate change, further habitat fragmentation and loss, and other disruptions. These actions are critical if we are to reframe the role of cities in global biodiversity loss.

Wild bees are declining worldwide, and many species are now threatened with extinction. Decline is caused by a combination of threats, including disease spillover from managed bees that reduces health of wild bees. An increasing number of studies thus aim to characterize bee health. The common approaches, however, require sacrificing tens to hundreds of individual bees per site or species, with reports of several thousand individuals collected per study. Considering the widespread need to assess bee health, this sampling approach is not sustainable, especially for endangered populations or species. Here, we propose a non-destructive method to assess parasite loads of wild-caught bumble bees. The standard protocol consists of net-capturing individual bumble bees and placing them in a 10 cm (diameter) petri dish to collect faeces. Although this approach is frequently used in laboratory settings, it is not in the field, because of the low success in collecting faeces. Placing bumble bees in a previously refrigerated cooler, we significantly improved faecal collection in the field from 76% with the standard protocol to 86% with the cooler protocol. We also successfully identified spores and cells of two common gut parasites Crithidia spp. and Vairimorpha spp. in faecal samples. The efficacy of the cooler protocol, combined to the low-cost and widespread availability of the equipment should promote its use in field studies. Implication for insect conservation: As there are calls to reduce destructive sampling methods in bee research, using the updated cooler protocol will contribute to achieving this goal. This opens future avenues of combining this non-destructive approach to assess bee health with molecular tools.

Invertebrates comprise the most diversified animal group on Earth. Due to their long evolutionary history and small size, invertebrates occupy a remarkable range of ecological niches, and play an important role as “ecosystem engineers” by structuring networks of mutualistic and antagonistic ecological interactions in almost all terrestrial ecosystems. Urban forests provide critical ecosystem services to humans, and, as in other systems, invertebrates are central to structuring and maintaining the functioning of urban forests. Identifying the role of invertebrates in urban forests can help elucidate their importance to practitioners and the public, not only to preserve biodiversity in urban environments, but also to make the public aware of their functional importance in maintaining healthy greenspaces. In this review, we examine the multiple functional roles that invertebrates play in urban forests that contribute to ecosystem service provisioning, including pollination, predation, herbivory, seed and microorganism dispersal and organic matter decomposition, but also those that lead to disservices, primarily from a public health perspective, e.g., transmission of invertebrate-borne diseases. We then identify a number of ecological filters that structure urban forest invertebrate communities, such as changes in habitat structure, increased landscape imperviousness, microclimatic changes and pollution. We also discuss the complexity of ways that forest invertebrates respond to urbanisation, including acclimation, local extinction and evolution. Finally, we present management recommendations to support and conserve viable and diverse urban forest invertebrate populations into the future.

Since the 1990s, recognition of urban biodiversity research has increased steadily. Knowledge of how ecological communities respond to urban pressures can assist in addressing global questions related to biodiversity. To assess the state of this research field in meeting this aim, we conducted a systematic review of the urban biodiversity literature published since 1990. We obtained data from 1209 studies that sampled ecological communities representing 12 taxonomic groups. While advances have been made in the field over the last 30 years, we found that urban biodiversity research has primarily been conducted in single cities within the Palearctic and Nearctic realms, within forest remnants and residential locations, and predominantly surveys plants and birds, with significant gaps in research within the Global South and little integration of multi-species and multi-trophic interactions. Sample sizes remain limited in spatial and temporal scope, but citizen science and remote sensing resources have broadened these efforts. Analytical approaches still rely on taxonomic diversity to describe urban plant and animal communities, with increasing numbers of integrated phylogenetic and trait-based analyses. Despite the implementation of nature-based solutions across the world's cities, only 5% of studies link biodiversity to ecosystem function and services, pointing to substantial gaps in our understanding of such solutions. We advocate for future research that encompasses a greater diversity of taxonomic groups and urban systems, focusing on biodiversity hotspots. Implementing such research would enable researchers to move forward in an equitable and multidisciplinary way to tackle the complex issues facing global urban biodiversity.

Rapid urbanization and the global loss of biodiversity necessitate the development of a research agenda that addresses knowledge gaps in urban ecology that will inform policy, management, and conservation. To advance this goal, we present six topics to pursue in urban biodiversity research: the socioeconomic and social–ecological drivers of biodiversity loss versus gain of biodiversity; the response of biodiversity to technological change; biodiversity–ecosystem service relationships; urban areas as refugia for biodiversity; spatiotemporal dynamics of species, community changes, and underlying processes; and ecological networks. We discuss overarching considerations and offer a set of questions to inspire and support urban biodiversity research. In parallel, we advocate for communication and collaboration across many fields and disciplines in order to build capacity for urban biodiversity research, education, and practice. Taken together we note that urban areas will play an important role in addressing the global extinction crisis.

Multitrophic interactions are ubiquitous in nature and form the basis of biodiversity. For example, bumble bees visit flowers to collect pollen, on which a variety of bacteria exist. Such bacteria consist of pathogens and mutualists and therefore have consequences for bumble bee colony fitness. However, we still know little about how plant diversity and floral selection by bees translate into the bacterial diversity and composition on the pollen consumed by important pollinators. The aim of this study was to characterize the bacterial and floral alpha and beta diversity from bumble bee corbicula (pollen baskets), identify core communities, and characterize their functional role. We found that bacterial alpha diversity (i.e., the diversity of bacteria determined from the pollen basket of a single bumble bee) was positively correlated with floral pollen alpha diversity (i.e., the diversity of plants from that same pollen basket). Bacterial beta diversity (i.e., bacterial composition) was generally weakly correlated with pollen beta diversity (i.e., floral composition). The abundance of some bacterial genera and pollen families was correlated, specifically Lactobacillus and Acinetobacter were positively correlated with Asteraceae pollen and negatively correlated with Lamiaceae pollen. The most widespread bacteria (the “core OTU”) in bumble bee pollen baskets included both possibly beneficial (Lactobacillus) and potentially pathogenic (Pseudomonas) taxa, but more core OTU functions were unknown vs. known for bumble bees, illustrating the importance of understanding bee–flower–microbe relationships in natural settings.

Anthropogenic activity underpins the creation of urban ecosystems, often with introduced or invasive species playing a large role in structuring ecological communities. While the effects of urbanization on charismatic taxa such as birds, bees or butterflies have received much attention, the impacts on small and inconspicuous organisms remain poorly understood. Here, we assess how the community structure of leaf litter-inhabiting microarthropods in city parks varies along an urbanization gradient in Toronto, Canada. At each park, we established paired forest understory plots which were either dominated by native vegetation or dog-strangling vine (Vincetoxicum rossicum), an invasive species that is spreading throughout northeastern North America and abundant in urban areas. We compared microarthropod richness, abundance, and diversity in ecological traits between invaded and non-invaded plots as well as compositional dissimilarities among plots across the urbanization gradient. We recorded 123 genera and found: i) there was a negative effect of urbanization on microarthropod richness and abundance but only in invaded plots; ii) richness and abundance increased continuously with urbanization in non-invaded plots, but peaked at intermediate urbanization levels in invaded plots; and iii) there was significant turnover with increasing urbanization, with distinct communities represented in highly urbanized areas compared to less urbanized areas, regardless of whether invaded. We also found litter microarthropod richness and abundance increased with soil ammonium and decreased with nitrate. These trends were especially strong for fungivorous microarthropods, however there was no relationship between soil nutrients and urbanization or invasion. Urbanization and biological invasion drive biodiversity change, and there is a need to disentangle these effects on ecological communities and related ecosystem processes. We show microarthropod communities change with urbanization, with the effects of invasion most prominent in non-urban areas. Here, there is high richness and abundance but low ecological trait diversity, possibly because certain feeding traits are excluded and others overrepresented. Understanding of urban ecological systems must include knowledge of the microarthropods that interact widely across food webs, form distinct communities in highly urban areas, and drive many of the important ecological functions upon which people in cities depend.

The development of buildings and other infrastructure in cities is viewed as a threat to local biodiversity and ecosystem functioning because natural habitat is replaced. However, there is momentum for implementing green infrastructure (GI), such as green roofs, wetland detention basins and community gardens, that partially offset these impacts and that benefit human health. GI is often designed to explicitly support ecosystem services, including implied benefits to biodiversity. The effects of GI on biodiversity have been rarely quantified, but research on this topic has increased exponentially in the last decade and a synthesis of the literature is needed. Here, we examined 1,883 published manuscripts and conducted a meta‐analysis on 33 studies that were relevant. We determined whether GI provides additional benefits to biodiversity over conventional infrastructure or natural counterparts. We also highlighted research gaps and identified opportunities to improve future applications. We determined that GI significantly improves biodiversity over conventional infrastructure equivalents, and that in some cases GI had comparable measures of biodiversity to natural counterparts. Many studies were omitted from these analyses because we found GI research has generally neglected conventional experimental design frameworks, including controls, replication or adequate sampling effort. Synthesis and applications. Our synthesis identified that taxa specificity is an important consideration for green infrastructure (GI) design relative to the more common measurements at the community level. We also identified that ignoring multi‐trophic interactions and landscape‐level patterns can limit our understanding of GI effects on biodiversity. We recommend further examination of species‐specific differences among infrastructures (i.e. green, conventional or natural equivalents) or using functional traits to improve the efficacy of GI implementation on urban biodiversity. Furthermore, we encourage policy makers and practitioners to improve the design of GI to benefit urban ecosystems because of the potential benefits for both humans and global biodiversity.

The contrasting and idiosyncratic changes in biodiversity that have been documented across urbanization gradients call for a more mechanistic understanding of urban community assembly. The reproductive success of organisms in cities should underpin their population persistence and the maintenance of biodiversity in urban landscapes. We propose that exploring individual‐level reproductive traits and environmental drivers of reproductive success could provide the necessary links between environmental conditions, offspring production, and biodiversity in urban areas. For 3 years, we studied cavity‐nesting solitary bees and wasps in four urban green space types across Toronto, Canada. We measured three reproductive traits of each nest: the total number of brood cells, the proportion of parasite‐free cells, and the proportion of non‐emerged brood cells that were parasite‐free. We determined (a) how reproductive traits, trait diversity and offspring production respond to multiple environmental variables and (b) how well reproductive trait variation explains the offspring production of single nests, by reflecting the different ways organisms navigate trade‐offs between gathering of resources and exposure to parasites. Our results showed that environmental variables were poor predictors of mean reproductive trait values, trait diversity, and offspring production. However, offspring production was highly positively correlated with reproductive trait evenness and negatively correlated with trait richness and divergence. This suggests that a narrow range of reproductive traits are optimal for reproduction, and the even distribution of individual reproductive traits across those optimal phenotypes is consistent with the idea that selection could favor diverse reproductive strategies to reduce competition. This study is novel in its exploration of individual‐level reproductive traits and its consideration of multiple axes of urbanization. Reproductive trait variation did not follow previously reported biodiversity‐urbanization patterns; the insensitivity to urbanization gradients raise questions about the role of the spatial mosaic of habitats in cities and the disconnections between different metrics of biodiversity., We studied intraspecific reproductive traits and offspring production of cavity‐nesting bees and wasps across in the city of Toronto, Canada. We found that offspring production was highly positively correlated with reproductive trait evenness and negatively correlated with trait richness and divergence. This suggests that a narrow range of reproductive traits are optimal for reproduction, and the even distribution of individual reproductive traits across those optimal phenotypes could indicate selection for diverse reproductive strategies to reduce competition. We found little changes in reproductive trait variation or offspring production along urbanization gradients.

In an urbanizing world there is an increasing priority for making cities nature-inclusive environments. Cities offer places for human-wildlife experiences, and thus for broad societal support of biodiversity conservation. Cities also depend on ecosystem services provided by biodiversity to remain healthy, liveable places. Although biodiversity is frequently addressed in urban green infrastructure plans, it often is not an integral topic in city planning, urban design and housing development. As a result, wildlife-rich urban green is often lacking in those parts of the cities where people live and work. Here, we introduce the concept of ‘wildlife-inclusive urban design’ for the built-up area of cities that integrates animal needs into the urban planning and design process. To identify key features that determine the success of wildlife-inclusive urban design, we evaluated lessons learnt from existing best practices. These were collected during an international workshop with architects, landscape practitioners, ecological consultants, conservationists and urban ecologists. We propose that features of successful wildlife-inclusive urban design projects are: 1) interdisciplinary design teams that involve ecologists early on, 2) consideration of the entire life-cycle of target species, 3) post-occupancy monitoring and evaluation with feedback to communicate best practices, and 4) stakeholder involvement and participatory approaches. We propose how wildlife-inclusive urban design could be included into the different steps of the urban planning cycle. We conclude that following these principles will facilitate incorporation of wildlife-inclusive urban design into urban planning and design and enable urban environments where humans and animals can thrive in the built-up areas.

The thermoregulation of buildings and cities by green roofs is a primary driver of their integration into urban environments. In warm seasons, green roofs cool buildings (thereby reduce interior air conditioning costs), and cities (impervious surfaces contribute to urban heat islands and vegetation mitigates contributions by conventional roof surfaces). In cool seasons, green roofs insulate buildings by reducing heat flux through the roof surface. Here we investigate thermoregulation services provided by extensive green roofs in warm and cool seasons from temperature data points recorded at 5-minute intervals over a four-year period, and from modules containing either Sedum or perennial grasses and herbaceous flowers, mineral- or organic-based substrate, 10 cm or 15 cm substrate depth, and supplemental irrigation or none. We demonstrate that Sedum outperformed a mixture of perennial grasses and herbaceous flowers over the total inter-annual survey period. The meadow mixture was more dependent on supplemental irrigation than Sedum, but more susceptible to inter-annual climate variability. Our findings point to the durability of Sedum as a plant for extensive green roof cooling, as well as the importance of plant selection and identifying traits that match not just microclimatic conditions in summer, but also in winter.

Trophic interactions are a fundamental part of ecosystems; yet, most ecological studies focus on single trophic levels and this hampers our ability to detect the underlying mechanisms structuring communities as well as the effects of environmental change. Here, we argue that the historical dominance of studying competition within trophic levels, and the focus on taxonomic groups without differentiating the trophic level, has led to the under-representation of multitrophic research in community ecology. There are many hurdles that challenge multitrophic approaches and we discuss solutions to overcome these. To advance our understanding of the fundamental drivers of community assembly and to provide the necessary guidance for managing and mitigating the effects of environmental change, we argue that ecologists should better align research with a trophically inclusive definition of a community.

Plant selection and diversity can influence the provision of key ecosystem services in extensive green roofs. While species richness does predict ecosystem services, functional and phylogenetic community structure may provide a stronger mechanistic link to such services than species richness alone. In this study, we assessed the relationship between community-weighted trait values from four key leaf and canopy functional traits (plant height, leaf area, specific leaf area, dry leaf matter content), functional diversity, and phylogenetic diversity to ten different green roof functions, including ecosystem multifunctionality, in experimental polycultures. Functional traits of dominant plant species were a major driver for indicators of multiple green roof functions, such as substrate nitrate-N, substrate phosphorus, aboveground biomass and ecosystem multifunctionality. In contrast, functional diversity alone increased substrate organic matter. Moreover, both functional/phylogenetic diversity and identity predicted canopy density, substrate cooling. This study highlights the first line of evidence that distinct aspects of phylogenetic and functional diversity play a major role in predicting multiple green roof services. Therefore, we provide further evidence that to maximize green roof functioning, a very careful selection of plant traits and polycultures are needed.

Although urban ecosystems are hotspots for biological invasions, the field of invasion science has given scant attention to invasion dynamics and the challenges facing managers in towns and cities. This paper provides an introduction to the growing challenges of understanding and managing invasive species in urban systems, and the context for a special issue of Biological Invasions, comprising 17 papers, that arose from a workshop on “Non-native species in urban environments: patterns, processes, impacts and challenges” held in Stellenbosch, South Africa, in November 2016. Contributions explore the following key questions: Are patterns and processes of urban invasions different from invasions in other contexts? Why is it important to manage non-native species in urban ecosystems? What are the special management needs in an urban context? How can we bridge the gaps between science, management, and policy with regards to biological invasions in urban ecosystems? The papers in this special issue show that patterns and processes of urban invasions differ in many ways from invasions in other contexts, and that managing invasive species in cities poses unique and increasingly complex challenges. Progress in urban invasion science requires further work to: (1) address key limitations that hinder our understanding of invasion dynamics in cities; (2) clarify whether fundamental concepts in the field of invasion science are appropriate for urban ecosystems; (3) integrate insights from invasion science with those from the burgeoning literature on the “Anthropocene biosphere”, novel ecosystems, social–ecological systems, human–wildlife conflicts, urban green infrastructure, urban planning and design, and ecosystem services/disservices.

Urban environments are often seen as unique or degraded habitats that both present hardships for some sensitive species and provide opportunities to others. Non-indigenous species (NIS) are commonly referenced in the latter group, and are comprised of species that can tolerate the unique conditions or capitalize on the opportunities found in urban environments. Moreover, these urban beneficiaries may be those that normally cannot overcome competitive interactions in intact native communities, but find opportunity to flourish in urban habitats. We ask the question: do NIS benefit from urbanization? We answer this question using three strategies. First, we explore the problem conceptually, using community assembly theory. Second, we perform a broad literature review. Finally, we analyze studies with sufficient information using a meta-analysis. We show that the available evidence supports the proposition that NIS benefit from urbanization, with NIS obtaining higher abundances and greater diversity in more urbanized habitats. There were only 43 studies that measured NIS abundance and diversity while adequately quantifying the degree of urbanization surrounding plots, and effect sizes (measured by Hedge’s D) reveal that NIS obtain higher abundances in more urbanized habitats, and especially for invertebrates. Despite the intense interest in NIS dynamics and impacts, we note a general dearth of robust studies that adequately quantify ‘urbanization’, and we end with a general call for more detailed research.

As urban areas expand, understanding how ecological processes function in cities has become increasingly important for conserving biodiversity. Urban green spaces are critical habitats to support biodiversity, but we still have a limited understanding of their ecology and how they function to conserve biodiversity at local and landscape scales across multiple taxa. Given this limited view, we discuss five key questions that need to be addressed to advance the ecology of urban green spaces for biodiversity conservation and restoration. Specifically, we discuss the need for research to understand how green space size, connectedness, and type influence the community, population, and life-history dynamics of multiple taxa in cities. A research framework based in landscape and metapopulation ecology will allow for a greater understanding of the ecological function of green spaces and thus allow for planning and management of green spaces to conserve biodiversity and aid in restoration activities.

Cities play important roles in the conservation of global biodiversity, particularly through the planning and management of urban green spaces (UGS). However, UGS management is subject to a complex assortment of interacting social, cultural, and economic factors, including governance, economics, social networks, multiple stakeholders, individual preferences, and social constraints. To help deliver more effective conservation outcomes in cities, we identify major challenges to managing biodiversity in UGS and important topics warranting further investigation. Biodiversity within UGS must be managed at multiple scales while accounting for various socioeconomic and cultural influences. Although the environmental consequences of management activities to enhance urban biodiversity are now beginning to be addressed, additional research and practical management strategies must be developed to balance human needs and perceptions while maintaining ecological processes.

Extreme climate events are predicted to increase in the future, which will have significant effects on insect biodiversity. Research into this area has been rapidly expanding, but knowledge gaps still exist. We conducted a review of the literature to provide a synthesis of extreme climate events on insects and identify future areas of research. In our review, we asked the following questions: 1) What are the direct and indirect mechanisms that extreme climate events affect individual insects? 2) What are the effects of extreme climate events on insect populations and demography? 3) What are the implications of the extreme climate events effects on insect communities? Drought was among the most frequently described type of extreme climate event affecting insects, as well as the effects of temperature extremes and extreme temperature variation. Our review explores the factors that determine the sensitivity or resilience to climate extremes for individuals, populations, and communities. We also identify areas of future research to better understand the role of extreme climate events on insects including effects on non-trophic interactions, alteration of population dynamics, and mediation of the functional the trait set of communities. Many insect species are under threat from global change and extreme climate events are a contributing factor. Biologists and policy makers should consider the role of extreme events in their work to mitigate the loss of biodiversity and delivery of ecosystem services by insects.

International audience; AbstractA variety of solitary bee species that naturally nest in wood and plant stems aboveground also readily accept nest boxes, which are human-made devices that aggregate these nesting conditions. Nest boxes are sheltered bundles of hollow plant stems, bamboo or reeds, and holes drilled into wood or cavities made of other materials such as glass or polystyrene. In this paper, I examine the best practises in nest box material selection and construction, and the use of nest boxes to address four basic objectives related to our understanding of bee biology and enhancement of pollination services. A variety of materials and cavity dimensions are included in nest boxes that are used to monitor local bee diversity or to address fundamental questions in community ecology and environmental change. Others examine bee biology, physiology and behaviour that use nest boxes to obtain bees for further experimentation. The majority of studies use nest boxes in agricultural landscapes and in alternative pollinator management; these studies improve nest box design for target bee species to augment their numbers. Continued design and data sharing, as well as the refinement of nest box construction and deployment for specific objectives, will ensure they remain useful tools for bee science, conservation and alternative pollinator management.

Vegetated roofs are a widely accepted form of green infrastructure deployed around the world to contribute to building efficiency and climate change mitigation and adaptation through improved thermoregulation and water capture. No two roofs are the same, and the evaporative cooling functions of green roofs have been linked to a number of attributes including plant species combinations and cover, substrate type, and the use of supplemental irrigation. Using a replicated extensive green roof modular array, temperature change at five thermal sensor stations along a vertical gradient was determined to examine the effects of irrigation and attributes of the vegetation and substrate. Over two seasons, a significant 2 °C difference at the surface of the substrate and 1.5 °C difference 15 cm above the substrate layer was found between the treatment combination with the highest temperature (grasses and wildflower ‘meadow’ mix, inorganic substrate, no irrigation) and the lowest temperature ( Sedum plant community, organic substrate, supplemental irrigation). Vegetation type and cover were important for roof cooling, and overall, Sedum cooled the roof significantly more than meadow vegetation. Irrigated meadow vegetation in organic substrate performed as well as unirrigated Sedum . Supplemental irrigation and organic substrate were important variables for roof cooling, although these lead to additional inputs that could reduce sustainability in the overall design. Sedum should be promoted to improve green roof cooling due to constant, near 100% vegetative cover. However, additional study is needed to interpret additional benefits that might come from combining Sedum and other suitable wildflowers and grasses, as well as the role of plant and substrate diversity in improving multiple green roof functions.

Vegetated, “green” infrastructure, including terraces, balconies, and vegetated roofs and walls are increasingly common in urban landscapes, elevating habitat into novel contexts above ground. Highly mobile species, like bees and wasps, are often seen foraging on green infrastructure, but whether nesting opportunities are facilitated is not known. Cavity-nesting bees and wasps that provision brood in human-made trap nests were monitored over three years on 29 vegetated and non-vegetated roofs in Toronto, Canada. The study identified 27 species nesting on rooftops but found that building height was negatively correlated with the abundance of brood cells provisioned in trap nests, and positively correlated with the number of unfinished nests. A decline in green space area within a 600 m radius around each rooftop resulted in decreasing species richness and abundance. Although the introduced bee, Megachile rotundata (Fabricius) occupied more sites than any other bee or wasp (27.6%) and was the most abundant species, amounting to half (48.9%) of all brood reared, native bees were 73% of all bee species reared. The most abundant wasp was the native spider-collecting Trypoxylon collinum Smith (11.4%), but the introduced aphid-collecting Psenulus pallipes (Panzer) occurred at more sites (24.1%). For the pollination and pest controlling services they provide, bees and wasps should be considered in the design of vegetated roofs. Evidence here suggests that building height and surrounding green space at ground level impact bee and wasp diversity on vegetated roofs. Efforts supporting their populations using trap nests should target low- and mid-rise buildings (

Global pollinator declines have resulted in an increasing number of policies and actions to help bee populations. In North America, there is strong public engagement, but also growing controversies over how to address declines. This is fueled by complex scientific evidence across species, habitat types, geographic regions, as well as intense lobbying by NGOs, beekeeping, agro-chemical and farming industries. Policy and conservation initiatives often focus on the Western Honeybee, Apis mellifera Linnaeus, a domesticated species not native to North America. Although losses of managed honeybee colonies are recorded annually, we argue that honeybee losses are not a conservation problem, but instead a domesticated animal management issue. By focusing attention on honeybees, policies and subsequent resources may undermine native bee conservation and have negative impacts ecologically and socially. This article is protected by copyright. All rights reserved

Plant species and functional trait diversity have each been shown to improve green roof services. Species and trait differences that contribute to ecosystem services are the product of past evolutionary change and phylogenetic diversity (PD), which quantifies the relatedness among species within a community. In this study, we present an experimental framework to assess the contribution of plant community PD for green roof ecosystem service delivery, and data from one season that support our hypotheses that PD would be positively correlated with two services: building cooling and rainwater management. Using 28 plant species in 12 families, we created six community combinations with different levels of PD. Each of these communities was replicated at eight green roofs along an elevation gradient, as well as a ground level control. We found that the minimum and mean roof temperature decreased with increasing PD in the plant community. Increasing PD also led to an increase in the volume of rainwater captured, but not the proportion of water lost via evapotranspiration 48 hr following the rain event. Our findings suggest that considering these evolutionary relationships could improve functioning of green infrastructure and we recommend that understanding how to make PD (and other measures of diversity) serviceable for plant selection by practitioners will improve the effectiveness of design and ecosystem service delivery. Lastly, since no two green roof sites are the same and can vary tremendously in microclimate conditions, our study illustrates the importance of including multiple independent sites in studies of green roof performance.

Green roofs reduce building energy consumption in hot seasons, but cold season thermal performance has received little attention. The goals of this study were to quantify heat flux in an extensive green roof system, relate heat flux to solar radiation, substrate temperature and snow depth, and to determine the relationships between vegetation type, snow accumulation, and substrate temperature. Over the building heating season, we found lower net heat loss from green compared to conventional roofs. Doubling green roof substrate depth had no additional impact in lowering net heat loss. We also quantified substrate temperatures and snow depths from green roofs in different microclimates and vegetation types. Different roof microclimates (sheltered, exposed, over unheated building) resulted in differential snow accumulation; deeper snow resulted in lower variability in heat flux. The benefits of green relative to conventional roofs were lower in extreme winter conditions when the substrate was frozen and/or had snow cover, but also during sunny conditions. Plant species differentially affected depth and duration of snow coverage. Substrate temperatures also differed according to plant growth form during both snow-covered and bare conditions. Net thermal benefits of green roofs in winter will depend on climate, plant choice, roof construction and location.

Summary 1. Green roofs are novel ecosystems that are increasingly common in cities. While their hydrologic and energy saving benefits are well-established, green roofs have also been proposed as having significant value for conserving biodiversity. 2. We evaluate six hypotheses that describe the purported biodiversity conservation benefits of green roofs. Green roofs largely support generalist species particularly insects, but their conservation value for rare taxa, and other taxonomic groups especially vertebrates, is poorly documented. Further, their ability to replicate biotic communities in the context of ecological restoration is largely untested, as is their potential to connect ground-level habitats. 3. Synthesis and applications. Given the evidence, green roof proponents should use restraint in claiming conservation benefits and it is premature for policymakers to consider green roofs equivalent to ground-level urban habitats. Ecologists need to work with the industry to evaluate green roof biodiversity and help design green roofs based on ecological principles to maximize biodiversity gains.

Numerous bee species were collected from a single green roof over the blooming period of the dominant exotic plant type, Sedum, a succulent stonecrop widely used in the green roof industry. As green roofs become more common in cities, an understanding of the potential positive and negative impacts of widespread use of this exotic but useful plant is needed. In this study we sampled bees visiting a green roof in downtown Toronto and compared the proportion of Sedum pollen in the loads they were carrying back to nesting locations. It was found that smaller bees (e.g. Lasioglossum, Hylaeus) were significantly less common on the roof compared with medium (e.g. Apis, Megachile) and large-sized bees (e.g. Bombus, Andrena). The proportion of Sedum pollen in the pollen loads of foraging bees collected was high amongst all bees (average of 80.5 % of total pollen load), but significantly greater for exotic bees compared to native bees. Moreover, native bees had significantly greater numbers of non-Sedum pollen types comprising more than >20 % of their pollen loads, meaning bees could be visiting flowers at ground level and on the roof in the same foraging bout. As the number of green roofs in cities increase, the characteristics of their designs, including the vegetation type and diversity, could have a significant impact in shaping local urban bee communities.

Artificial nests (e.g., nest boxes) for bees are increasingly being used to contribute to nesting habitat enhancement for bees that use preexisting cavities to provision brood. They usually incorporate additional nesting materials that vary by species. Cavity-nesting bees are susceptible to brood parasitoids that recognize their host(s) using visual and chemical cues. Understanding the range of cues that attract parasitoids to bee nests, including human-made analogues, is important if we wish to control parasitism and increase the potential value of artificial nests as habitat-enhancement strategies. In this study, we investigated the cues associated with the orientation of the generalist brood parasitoid Monodontomerus obscurus Westwood (Hymenoptera: Torymidae) to the nests of a common cavity-nesting resin bee Megachile campanulae (Robertson) (Megachilidae). The parasitoids were reared from previously infested M. campanulae brood cells and placed into choice trials where they were presented with pairs of different nest material cues. Among different materials tested, we found that Mo. obscurus was most attracted to fresh resin collected directly from Pinus strobus trees followed by previously used resin collected from the bee nest. The parasitoid also attacked other bee species in the same nest boxes, including those that do not use resin for nesting. Our findings suggest that M. campanulae could act as a magnet, drawing parasites away from other bee hosts co-occurring in nest boxes, or, as an attractant of Mo. obscurus to nest boxes, increasing attacks on co-occurring host bee species, potentially undermining bee diversity enhancement initiatives.

Occupancy modelling has received increasing attention as a tool for differentiating between true absence and non-detection in biodiversity data. This is thought to be particularly useful when a species of interest is spread out over a large area and sampling is constrained. We used occupancy modelling to estimate the probability of three phylogenetically independent pairs of native-introduced species [Megachile campanulae (Robertson)-Megachile rotundata (Fab.), Megachile pugnata Say-Megachile centuncularis (L.), Osmia pumila Cresson-Osmia caerulescens (L.)] (Apoidea: Megachilidae) being present when repeated sampling did not always find them. Our study occurred along a gradient of urbanization and used nest boxes (bee hotels) set up over three consecutive years. Occupancy modelling discovered different patterns to those obtained by species detection and abundance-based data alone. For example, it predicted that the species that was ranked 4th in terms of detection actually had the greatest occupancy among all six species. The native M. pugnata had decreased occupancy with increasing building footprint and a similar but not significant pattern was found for the native O. pumila. Two introduced bees (M. rotundata and M. centuncularis), and one native (M. campanulae) had modelled occupancy values that increased with increasing urbanization. Occupancy probability differed among urban green space types for three of six bee species, with values for two native species (M. campanulae and O. pumila) being highest in home gardens and that for the exotic O. caerulescens being highest in community gardens. The combination of occupancy modelling with analysis of habitat variables as an augmentation to detection and abundance-based sampling is suggested to be the best way to ensure that urban habitat management results in the desired outcomes.

University campuses often contain contiguous areas of urban green space (UGS) which are otherwise scarce in large cities and, thus, may provide critical habitat for numerous species. In this study, we evaluate butterfly and plant diversity at Chiba University in Japan from five UGS types, including intensive green roofs, meadows, roadsides, open spaces, and community gardens. Surveying non-destructively every two weeks from June to November 2010, we identified 707 individual butterflies to 25 species from five families, including red-listed species (e.g. Parantica sita Kollar, 1844). However, one species, Pseudozizeeria maha Kollar, 1848, represented over 50% of all individuals surveyed. Butterflies in the family Papilionidae showed strong preference for roadside habitat, indicating the importance of ‘butterfly flyways’ and contiguous habitat corridors on University campuses. Butterfly richness and abundance was significantly different between UGS types and highest in the community garden and roadsides. We recorded 70 garden plant species and 117 spontaneous plant species (which grew opportunistically, without design input), of which 58% were native. Total plant richness was positively correlated with butterfly species richness, and non-native spontaneous plant species richness was positively correlated with butterfly richness, abundance, diversity, and evenness. Additionally, 76% of the spontaneous species identified were determined to be used by butterflies as larval hosts or for adult feeding. Identification of spontaneous plant species and use of selective weeding should be included in landscape management planning on campuses to promote butterflies, which can act as ambassadors for biodiversity conservation and help connect people to nature.

Supplemental irrigation systems are often specified on green roofs to ensure plant cover and growth, both important components of green roof performance and aesthetics. Properties of the growing media environment too can alter the assemblage of plant species able to thrive. In this study we determine how plant cover, above ground biomass and species diversity are influenced by irrigation and growing media. Grass and forb vegetative cover and biomass were significantly greater in organic based growing media but there was no effect of supplemental irrigation, with two warm season grasses dominating in those treatments receiving no supplemental irrigation. On the other hand, plant diversity declined without irrigation in organic media, and having no irrigation in inorganic growing media resulted in almost a complete loss of cover. Sedum biomass was less in inorganic growing media treatments and species dominance shifted when growing media organic content increased. Our results demonstrate that supplemental irrigation is required to maintain plant diversity on an extensive green roof, but not necessarily plant cover or biomass. These results provide evidence that planting extensive green roofs with a mix of plant species can ensure the survival of some species; maintaining cover and biomass when supplemental irrigation is turned off to conserve water, or during extreme drought.

The pursuit for and production of fresh and local fruits and vegetables is gaining popularity among homeowners and community groups in cities. Cultivating crops allows one to connect to natural processes, invest in food security and gain crucial life skills. It’s also relaxing, provides exercise and is a lot of fun. Although gardening is one of the most common activities among homeowners, and many are aware of the role of pollinators in plant reproduction, the various needs of pollinating insects are often overlooked in garden design and maintenance.

Assessing plant species performance on extensive green roofs can inform about and improve green roof functioning, aesthetics, longevity and the diversity of plant palettes available for the green roof industry. In this study, we evaluate survival, cover, roof cooling and stormwater retention properties of 15 plant species native to coastal regions of Atlantic Canada in extensive green roof monocultures. After a complete growing season (May–October 2009), all but one species had greater than 80% survival, and 10 species reached greater than 90% groundcover. Over the growing season, the top performing species reduced roof surface temperature by an average of 3.44 °C and increased solar reflectivity by 22.2% over the growing-medium only controls. Moreover, the best species retained 75.3% of experimentally added stormwater. Our results demonstrate that several species (mainly graminoids) performed better than creeping shrubs and forbs for most functions, although significant variation existed within life-form groups.

While it is expected that green roofs support a wider variety of insects compared with conventional roof surfaces, few studies have quantified insect diversity on green roofs. Even fewer have attempted to determine whether green roofs can support insect communities comparable to level-ground urban habitats. In this study, insect richness, abundance and diversity indices were compared between five pairs of intensive green roofs and adjacent ground-level habitat patches in downtown Halifax, Nova Scotia. Pitfall traps were set at each site, collected bi-weekly between May-October 2009 and captured insects were identified to morphospecies (except where taxonomic expertise was available). No significant differences in richness, abundance or any of the indices (S, H’, Evar) were detected in analysis, which included plant species richness, site area and sampling effort as covariables. However, richness and abundance tended to be greater at ground level for all orders (except Heteroptera), and diversity appeared to increase away from the downtown core. Insect composition differed slightly between green roof and ground-level sites; only 17 species were collected from a single site type in numbers greater than five specimens. Nevertheless, a wide variety of insects, including many uncommon species were collected from green roofs, supporting the idea that these habitats can contribute to sustaining biodiversity in cities.

Insects and other invertebrates provide essential ecosystem functions in designed habitats including green roofs. Services offered by invertebrates in these novel environments include pollination for plant reproduction and yield in cultivated crops, pest control to reduce damage to green roof vegetation, decomposition to retain organic matter and cycle nutrients in the substrate, and contribution to food webs for species like birds that frequent green roofs.