Urban biodiversity management using evolutionary tools

Urban wall lizards are resilient to high levels of blood lead

Living in urban environments presents many challenges to wildlife, including exposure to potentially toxic pollutants. For example, the heavy metal lead (Pb) introduces numerous health problems to all animals, including humans. The little work that has been conducted on lead toxicity in reptiles suggests that lizards may be extraordinarily resilient to very high levels of lead pollution, by either avoiding or mitigating the toxicity. To assess the impact of lead exposure, we measured field blood levels and tested for the effects on ecologically-relevant performance measures in common wall lizards (Podarcis muralis) - a small reptile particularly capable of thriving in urban environments. We captured lizards from roadside and park habitats across Cincinnati, Ohio, USA and quantified the concentration of lead in blood samples (n = 71 adult lizards). Lizards from roadside populations had higher blood lead concentrations than lizards from park populations, and females had higher blood lead concentrations than males regardless of habitat type. We then tested two aspects of lizard performance important for survival: (1) balance, a cognitively-demanding task, to assess the effect of lead on cognition (n = 41), and (2) running endurance, an aerobic exercise dependent on oxygen (n = 43), to assess the impact of lead on blood oxygen-carrying capacity. We then used correlation analyses to quantify the relationship between lead levels and these ecologically-relevant performance measures. There was no effect of blood lead levels on running endurance, but contrary to our predictions there was a slight positive effect on balance performance, whereby lizards with higher blood lead concentrations slipped less often than lizards with lower blood lead concentrations. Understanding the effects of lead toxicity and resilience in a particularly resistant animal could help us better respond to public health and environmental pollution concerns.

Drivers of urban biodiversity in Mexico and joint risks from future urban expansion, climate change, and urban heat island effect

Urbanization is a phenomenon where humans concentrate in high densities and consume more per capita energy than in rural areas, imposing high pressures on biodiversity and ecosystem services. Although Mexico is recognized as a megadiverse country and there is an understanding of ecological and evolutionary processes underlying this high diversity, only some efforts have been devoted to understanding how urban biodiversity has been shaped. Here, we compiled a set of socioeconomic and ecological variables to explore macroecological patterns in urban biodiversity across Mexican municipalities. Specifically, we tested the species-area relationships (SAR) between rural and urban areas across municipalities and evaluated the relative role of different socioeconomic and ecological variables driving urban species richness for terrestrial vertebrates. Finally, we explored the exposure of Mexican municipalities to future urban expansion, the urban heat island (UHI) effect, and climate change. Urban and rural settlements show differences in the shape of SAR models. We found that urban area, size of the network of urban protected areas, the number of ecoregions, and GDP explained the urban total species richness relatively well. Mexican cities in the northeast region may be at a higher risk than others. Based on our analyses, policymakers should identify priority urban conservation sites in cities with high species richness and low urbanization development. These actions would alleviate future urban biodiversity loss in these growing cities.

Urbanization alters the relative importance of local and landscape factors affecting plant communities in the Tokyo megacity

Plant communities are impacted by local factors (related to environmental filtering) and landscape factors (related to dispersal limitation). While many studies have shown that the relative importance of these factors in understanding plant community dynamics due to urbanization, little is known about how they are altered by urbanization-a significant threat to biodiversity. This study evaluates the relative importance of local environmental (local factors), landscape, and spatial (landscape factors) variables that influence plant communities in 34 urban green spaces comprising two different habitats (forests and grasslands) along the urban-rural gradients in the Tokyo megacity, Japan. To continuously assess the relative importance of each factor along the urban-rural gradients, we extracted 1000 landscapes within a certain range that contained several sites. Subsequently, the relative importance of each factor and urbanization rate (proportion of artificial built-up area) were estimated for each landscape. Our study found that the relative importance of both local and landscape factors decreased, while that of local factor for native species in forest habitats and that of landscape factors for native species in grassland habitats increased. Collectively, these findings suggest that city size and habitat characteristics must be considered when predicting changes in plant communities caused by urbanization.

Effects of urban-induced mutations on ecology, evolution and health

Increasing evidence suggests that urbanization is associated with higher mutation rates, which can affect the health and evolution of organisms that inhabit cities. Elevated pollution levels in urban areas can induce DNA damage, leading to de novo mutations. Studies on mutations induced by urban pollution are most prevalent in humans and microorganisms, whereas studies of non-human eukaryotes are rare, even though increased mutation rates have the potential to affect organisms and their populations in contemporary time. Our Perspective explores how higher mutation rates in urban environments could impact the fitness, ecology and evolution of populations. Most mutations will be neutral or deleterious, and higher mutation rates associated with elevated pollution in urban populations can increase the risk of cancer in humans and potentially other species. We highlight the potential for urban-driven increased deleterious mutational loads in some organisms, which could lead to a decline in population growth of a wide diversity of organisms. Although beneficial mutations are expected to be rare, we argue that higher mutation rates in urban areas could influence adaptive evolution, especially in organisms with short generation times. Finally, we explore avenues for future research to better understand the effects of urban-induced mutations on the fitness, ecology and evolution of city-dwelling organisms.

Constructing urban ecological corridors to reflect local species diversity and conservation objectives

Ensuring bird diversity can secure key ecosystem services within cities. Building ecological corridors into urban planning is an effective way to protect urban birds, but existing corridor construction methods often ignore locality and diversity of species, leading to homogenization of corridor construction results and orientation. We proposed a corridor construction model that combines local bird surveys and bird threat levels. After constructing differentiated corridors for each bird species by assessing their habits and flight abilities, we used three weighted scenarios (original, weighted abundance, weighted abundance, and phylogeny) to assess the conservation priorities of birds and overlaid them to derive a comprehensive bird corridor model. Our results show significant differences in conservation priority and corridor pattern among different bird species, thus demonstrating the importance of local bird surveys and knowledge of threat levels in accurate corridor simulations. This study provides differential simulation of corridors for each bird species and the identification of important conservation species, and uses these to extend the theory of ecological corridor planning to urban bird populations. These results can be applied to guide biodiversity management, evaluate green space policies, and provide practical assistance for sustainable urban development and management.

Cities of the Anthropocene: urban sustainability in an eco-evolutionary perspective

Cities across the globe are driving systemic change in social and ecological systems by accelerating the rates of interactions and intensifying the links between human activities and Earth's ecosystems, thereby expanding the scale and influence of human activities on fundamental processes that sustain life. Increasing evidence shows that cities not only alter biodiversity, they change the genetic makeup of many populations, including animals, plants, fungi and microorganisms. Urban-driven rapid evolution in species traits might have significant effects on socially relevant ecosystem functions such as nutrient cycling, pollination, water and air purification and food production. Despite increasing evidence that cities are causing rapid evolutionary change, current urban sustainability strategies often overlook these dynamics. The dominant perspectives that guide these strategies are essentially static, focusing on preserving biodiversity in its present state or restoring it to pre-urban conditions. This paper provides a systemic overview of the socio-eco-evolutionary transition associated with global urbanization. Using examples of observed changes in species traits that play a significant role in maintaining ecosystem function and resilience, I propose that these evolutionary changes significantly impact urban sustainability. Incorporating an eco-evolutionary perspective into urban sustainability science and planning is crucial for effectively reimagining the cities of the Anthropocene. This article is part of the theme issue 'Evolution and sustainability: gathering the strands for an Anthropocene synthesis'.

Urbanization and a green corridor do not impact genetic divergence in common milkweed (Asclepias syriaca L.)

Urbanization is altering landscapes globally at an unprecedented rate. While ecological differences between urban and rural environments often promote phenotypic divergence among populations, it is unclear to what degree these trait differences arise from genetic divergence as opposed to phenotypic plasticity. Furthermore, little is known about how specific landscape elements, such as green corridors, impact genetic divergence in urban environments. We tested the hypotheses that: (1) urbanization, and (2) proximity to an urban green corridor influence genetic divergence in common milkweed (Asclepias syriaca) populations for phenotypic traits. Using seeds from 52 populations along three urban-to-rural subtransects in the Greater Toronto Area, Canada, one of which followed a green corridor, we grew ~ 1000 plants in a common garden setup and measured > 20 ecologically-important traits associated with plant defense/damage, reproduction, and growth over four years. We found significant heritable variation for nine traits within common milkweed populations and weak phenotypic divergence among populations. However, neither urbanization nor an urban green corridor influenced genetic divergence in individual traits or multivariate phenotype. These findings contrast with the expanding literature demonstrating that urbanization promotes rapid evolutionary change and offer preliminary insights into the eco-evolutionary role of green corridors in urban environments.

Urban insect bioarks of the 21st century

Insects exhibit divergent biodiversity responses to cities. Many urban populations are not at equilibrium: biodiversity decline or recovery from environmental perturbation is often still in progress. Substantial variation in urban biodiversity patterns suggests the need to understand its mechanistic basis. In addition, current urban infrastructure decisions might profoundly influence future biodiversity trends. Although many nature-based solutions to urban climate problems also support urban insect biodiversity, trade-offs are possible and should be avoided to maximize biodiversity-climate cobenefits. Because insects are coping with the dual threats of urbanization and climate change, there is an urgent need to design cities that facilitate persistence within the city footprint or facilitate compensatory responses to global climate change as species transit through the city footprint.

Home ranges of box turtles in a rural woodland and an urban park in Saint Louis, MO; implications for turtle conservation

The negative consequences of fragmentation, infrastructure development, and urbanization onbiodiversity are well known. However, careful urban planning can provide viable habitat for some species and communities. Generally, r-selected species are more likely to persist in urbanizing landscapes, while long lived, mobile species, such as turtles, are likely to decline toward extinction. Understanding species responses across urban gradients is important for developing mitigation planning. We used VHF telemetry to quantify ranging behavior of three-toed box turtles in fragmented urban forest patches and a semi-contiguous large rural forest in Saint Louis, Missouri. We then simulated movement trajectories based on empirical data from the two turtles with the largest and smallest home ranges, overlaid on forest cover and road network maps of Missouri, to quantify the state-wide probability of turtles encountering roads. Home range (HR) size varied from 1–250Ha. The mean home range estimate of rural turtles was > 9 times larger than that of urban turtles. Simulations indicated that the least mobile turtle (HR 1Ha) would have a 22% likelihood of encountering a road if placed randomly in suitable habitat anywhere in the state. The likelihood increased to 90% for the most mobile turtle (HR 250Ha), with 10 road crossings per year. High turtle mortality, range restriction and population fragmentation are likely even in rural areas. In urban cityscapes, large, roadless forest patches offer the highest conservation potential for this species.

Are really Nature-Based Solutions sustainable solutions to design future cities in a context of global change? Discussion about the vulnerability of these new solutions and their probable unsustainable implementation

The urban ecosystem is a very challenging environment that faces many problems such as various pollutions, higher temperatures than its surroundings or flooding risks due to soil sealing. Nature-based solutions (NBS) seem to be good option to address these problems, while simultaneously offering benefits for facing climate change and the biodiversity crisis. Despite their potential, NBS can be threatened by various urban disturbance, namely: land use change, pollution, or invasive species. These disturbances can have multiple consequences on urban NBS, such as causing changes in plant characteristics/traits, altering the services they provide, and even make certain plant populations disappear, etc. In turn, these consequences may even jeopardize the solutions themselves, which then may no longer solve the problems they originally targeted. To avoid this, NBS should be eco-designed, i.e. designed in function of their environment. Their management should be adaptive and should also take into consideration the evolution of climatic and anthropogenic factors. The choice of species should not be left to chance or random: In this sense, is it better to plant native species for biodiversity conservation or exotic species that are more likely to resist global changes? Is it better to find resistant or ruderal species that have proven themselves in the face of certain disturbances? In any case, it would be good to diversify any NBS to have a better chance of survival in the face of global changes.

Anthropogenic Transformations of Vegetation in the Kuyalnik Estuary Valley (Ukraine, Odesa District)

Human influence on the steppe ecosystems of Ukraine caused irreversible loss of biodiversity in the natural zone. Currently, this problem is aggravated by military operations which cover almost half of the steppe zone and are unprecedented in the entire history of their existence. This actualizes the study of vegetation dynamic processes under the influence of the novel anthropogenic factors, and serves as the scientific basis for restoring and preserving steppe vegetation and maintaining its functional stability. The paper highlights anthropogenic changes in vegetation of the Kuyalnik Estuary valley based on long-term comparative phytocenotic surveys and uses of the method of succession series for reconstruction. These changes are representative of the river valleys of the estuaries in the Northern Black Sea region. This work examines vegetation changes induced by runoff overregulation of estuary rivers within the basin, quarrying of sand and limestone, ploughing, grazing, burning, terracing of slopes and their afforestation, excessive mowing of grass stands, and uncontrolled recreation. Subject to the existing anthropogenic impact combined with global climate changes, further vegetation degradation was predicted to occur in the direction of xerophitization and halophitization, reduction in shrubby vegetation areas, degradation of steppe vegetation, and intensification of desertification processes.

Behavioral plasticity can facilitate evolution in urban environments

Plasticity-led evolution is central to evolutionary theory. Although challenging to study in nature, this process may be particularly apparent in novel environments such as cities. We document abundant evidence of plastic behavioral changes in urban animals, including learning, contextual, developmental, and transgenerational plasticities. Using behavioral drive as a conceptual framework, our analysis of notable case studies suggests that plastic behaviors, such as altered habitat use, migration, diurnal and seasonal activity, and courtship, can have faciliatory and cascading effects on urban evolution via spatial, temporal, and mate-choice mechanisms. Our findings highlight (i) the need to incorporate behavioral plasticity more formally into urban evolutionary research and (ii) the opportunity provided by urban environments to study behavioral mechanisms of plasticity-led processes.

Genetic population structure defines wild boar as an urban exploiter species in Barcelona, Spain

Urban wildlife ecology is gaining relevance as metropolitan areas grow throughout the world, reducing natural habitats and creating new ecological niches. However, knowledge is still scarce about the colonisation processes of such urban niches, the establishment of new communities, populations and/or species, and the related changes in behaviour and life histories of urban wildlife. Wild boar (Sus scrofa) has successfully colonised urban niches throughout Europe. The aim of this study is to unveil the processes driving the establishment and maintenance of an urban wild boar population by analysing its genetic structure. A set of 19 microsatellite loci was used to test whether urban wild boars in Barcelona, Spain, are an isolated population or if gene flow prevents genetic differentiation between rural and urban wild boars. This knowledge will contribute to the understanding of the effects of synurbisation and the associated management measures on the genetic change of large mammals in urban ecosystems. Despite the unidirectional gene flow from rural to urban areas, the urban wild boars in Barcelona form an island population genotypically differentiated from the surrounding rural ones. The comparison with previous genetic studies of urban wild boar populations suggests that forest patches act as suitable islands for wild boar genetic differentiation. Previous results and the genetic structure of the urban wild boar population in Barcelona classify wild boar as an urban exploiter species. These wild boar peri-urban island populations are responsible for conflict with humans and thus should be managed by reducing the attractiveness of urban areas. The management of peri-urban wild boar populations should aim at reducing migration into urban areas and preventing phenotypic changes (either genetic or plastic) causing habituation of wild boars to humans and urban environments.

Microflora Influence: The Aquatic Environment Changes Grouping Risk and Development Speed of Toad Tadpoles

In addition to habitat loss and fragmentation, behavioral traits and the deterioration of water environments also contribute to the local extinction of amphibians. Abundant microflora in urban ponds may cause fatal diseases, whereas symbiotic bacteria may protect the host from pathogens; these effects may vary with group size. In this study, I monitored the growth of Japanese common toad (Bufo japonicus) larvae in Tokyo using three different group sizes: 1 (solitary), 2 (pair), and 15. Although there was no genetic bias in the major histocompatibility complex (MHC) class II genes or microsatellite loci to the survival of the larvae, the mortality risk of the larvae reared in pond water was higher than that of those reared in tap water. According to the survival analysis, the risk was more significant when the group size was 15. This result would be unwelcomed for the B. japonicus tadpoles, which have habits of social aggregation. Furthermore, larval metamorphosis took longer to complete in pond than tap water without any difference in body length or mass. These findings provide fundamental insight into the impact of the aquatic environment and the effect of the group size on animal health and conservation.

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale.

Biodiversity at disequilibrium: updating conservation strategies in cities

Greenspaces represent an ark for urban biodiversity, but understanding their carrying capacity to sustain species remains challenging. Old greenspaces that were fragmented from natural habitats are now overcrowded, while revegetated new greenspaces remain vacant. This is because they have different processes leading towards biodiversity equilibrium, and conservation management needs to differentiate between fragmented and revegetated greenspaces.

Small Prey Animal Habitat Use in Landscapes of Fear: Effects of Predator Presence and Human Activity Along an Urban Disturbance Gradient

Human activity can impose additional stressors to wildlife, both directly and indirectly, including through the introduction of predators and influences on native predators. As urban and adjacent environments are becoming increasingly valuable habitat for wildlife, it is important to understand how susceptible taxa, like small prey animals, persist in urban environments under such additional stressors. Here, in order to determine how small prey animals’ foraging patterns change in response to habitat components and distances to predators and human disturbances, we used filmed giving-up density (GUD) trials under natural conditions along an urban disturbance gradient. We then ran further GUD trials with the addition of experimentally introduced stressors of: the odors of domestic cat (Felis catus)/red fox (Vulpes vulpes) as predator cues, light and sound as human disturbance cues, and their combinations. Small mammals were mostly observed foraging in the GUD trials, and to a lesser degree birds. Animals responded to proximity to predators and human disturbances when foraging under natural conditions, and used habitat components differently based on these distances. Along the urban disturbance gradient situation-specific responses were evident and differed under natural conditions compared to additional stressor conditions. The combined predator with human disturbance treatments resulted in responses of higher perceived risk at environments further from houses. Animals at the urban-edge environment foraged more across the whole site under the additional stressor conditions, but under natural conditions perceived less risk when foraging near predators and further from human disturbance (houses). Contrastingly, at the environments further from houses, foraging near human disturbance (paths/roads) when close to a predator was perceived as lower risk, but when foraging under introduced stressor conditions these disturbances were perceived as high risk. We propose that sensory and behavioral mechanisms, and stress exposure best explain our findings. Our results indicate that habitat components could be managed to reduce the impacts of high predation pressure and human activity in disturbed environments.

Evolution in Cities

Although research performed in cities will not uncover new evolutionary mechanisms, it could provide unprecedented opportunities to examine the interplay of evolutionary forces in new ways and new avenues to address classic questions. However, while the variation within and among cities affords many opportunities to advance evolutionary biology research, careful alignment between how cities are used and the research questions being asked is necessary to maximize the insights that can be gained. In this review, we develop a framework to help guide alignment between urban evolution research approaches and questions. Using this framework, we highlight what has been accomplished to date in the field of urban evolution and identify several up-and-coming research directions for further expansion. We conclude that urban environments can be used as evolutionary test beds to tackle both new and long-standing questions in evolutionary biology.

Wealth and urbanization shape medium and large terrestrial mammal communities

Urban biodiversity provides critical ecosystem services and is a key component to environmentally and socially sustainable cities. However, biodiversity varies greatly within and among cities, leading to human communities with changing and unequal experiences with nature. The "luxury effect," a hypothesis that predicts a positive correlation between wealth, typically measured by per capita income, and species richness may be one indication of these inequities. While the luxury effect is well studied for some taxa, it has rarely been investigated for mammals, which provide unique ecosystem services (e.g., biological pest control) and exhibit significant potential for negative human-wildlife interactions (e.g., nuisances or conflicts). We analyzed a large dataset of mammal detections across 20 North American cities to test whether the luxury effect is consistent for medium- to large-sized terrestrial mammals across diverse urban contexts. Overall, support for the luxury effect, as indicated by per capita income, was inconsistent; we found evidence of a luxury effect in approximately half of our study cities. Species richness was, however, highly and negatively correlated with urban intensity in most cities. We thus suggest that economic factors play an important role in shaping urban mammal communities for some cities and species, but that the strongest driver of urban mammal diversity is urban intensity. To better understand the complexity of urban ecosystems, ecologists and social scientists must consider the social and political factors that drive inequitable human experiences with nature in cities.

Human‐induced evolution: Signatures, processes and mechanisms underneath anthropogenic footprints on natural systems

The impact of human activities on the global environment has increased to such an extent that the current geological era has been coined the Anthropocene. Studies dedicated to understanding the evolutionary consequences of human‐induced selection on all levels of diversity (species, populations, traits, genes) provide direct knowledge about the mechanisms underlying species' responses and their evolutionary potential. A better understanding of the effects of human‐induced selection is needed to leverage evolved mechanisms to develop appropriate conservation programmes to guarantee the maintenance of healthy systems. In this special issue, we focus on different types of human‐mediated selection pressures, from the direct harvesting of individuals (e.g. hunting, fishing), to the more pervasive effects of climate change. Contributions highlight the diversity of human‐induced selection pressures ranging from fisheries, trophy‐hunting, poaching and domestication to climate change, and pollution. With those, we question whether there are parallel evolutionary solutions across fisheries systems, whether hunting pressures alter population dynamics and population structure, and whether climate change is an evolutionary dead‐end. The contributions reflect the direction of travel of the field and the solutions to mitigate the impact of human activities.

Phenotypic variation in urban environments: mechanisms and implications

In the past decade, numerous studies have explored how urbanisation affects the mean phenotypes of populations, but it remains unknown how urbanisation impacts phenotypic variation, a key target of selection that shapes, and is shaped by, eco-evolutionary processes. Our review suggests that urbanisation may often increase intraspecific phenotypic variation through several processes; a conclusion aligned with results from our illustrative analysis on tit morphology across 13 European city/forest population pairs. Urban-driven changes in phenotypic variation will have immense implications for urban populations and communities, particularly through urbanisation's effects on individual fitness, species interactions, and conservation. We call here for studies that incorporate phenotypic variation in urban eco-evolutionary research alongside advances in theory.

Discovering and Applying the Urban Rules of Life to Design Sustainable and Healthy Cities

The city and its urban biome provides an extreme laboratory for studying fundamental biological questions and developing best practices for sustaining biodiverse and well-functioning ecological communities within anthropogenic built environments. We propose by studying urban organisms, urban biotic communities, the urban biome, and the interactions between the urban biome and peri-urban built and natural environments, we can (1) discover new 'rules of life' for the structure, function, interaction, and evolution of organisms;(2) use these discoveries to understand how novel emerging biotic communities affect and are affected by anthropogenic environmental changes in climate and other environmental factors; and (3) apply what we have learned to engage residents of the urban biome, and design cities that are more biologically diverse, are provided with more and better ecosystem services, and are more equitable and healthier places to live. The built environment of the urban biome is a place that reflects history, economics, technology, governance, culture, and values of the human residents; research on and applications of the rules of life in the urban biome can be used by all residents in making choices about the design of the cities where they live. Because inhabitants are directly invested in the environmental quality of their neighborhoods, research conducted in and about the urban environment provides a great opportunity to engage wide and diverse communities of people. Given the opportunity to engage a broad constituency - from basic researchers to teachers, civil engineers, landscape planners, and concerned citizens - studying the translation of the rules of life onto the urban environment will result in an integrative and cross-cutting set of questions and hypotheses, and will foster a dialogue among citizens about the focus of urban biome research and its application toward making more equitable, healthy, livable, sustainable, and biodiverse cities.

Designing (for) Urban Food Webs

Interest is growing in designing resilient and ecologically rich urban environments that provide social and ecological benefits. Regenerative and biocentric designs fostering urban ecological habitats including food webs that provide ecosystem services for people and wildlife increasingly are being sought. However, the intentional design of urban landscapes for food webs remains in an early stage with few precedents and many challenges. In this paper, we explore the potential to design (for) urban food webs through collaborations between designers and ecologists. We start by examining the ecology and management of Jamaica Bay in New York City as a case study of an anthropogenic landscape where ecosystems are degraded and the integrity of extant food webs are intertwined with human agency. A subsequent design competition focusing on ecological design and management of this large-scale landscape for animal habitat and ecosystem services for people illustrates how designers approach this anthropogenic landscape. This case study reveals that both designing urban landscapes for food webs and directly designing and manipulating urban food webs are complicated and challenging to achieve and maintain, but they have the potential to increase ecological health of, and enhance ecosystem services in, urban environments. We identify opportunities to capitalize on species interactions across trophic structures and to introduce managed niches in biologically engineered urban systems. The design competition reveals an opportunity to approach urban landscapes and ecological systems creatively through a proactive design process that includes a carefully crafted collaborative approach to constructing ecologically functioning landscapes that can integrate societal demands. As designers increasingly seek to build, adapt, and manage urban environments effectively, it will be critical to resolve the contradictions and challenges associated with human needs, ecosystem dynamics, and interacting assemblages of species. Ecologists and designers are still discovering and experimenting with designing (for) urban food webs and fostering species interactions within them. We recommend generating prototypes of urban food webs through a learning-by-doing approach in urban development projects. Design and implementation of urban food webs also can lead to research opportunities involving monitoring and experiments that identify and solve challenges of food-web construction while supporting and encouraging ongoing management.

Physiological adaptation to cities as a proxy to forecast global-scale responses to climate change

Cities are emerging as a new venue to overcome the challenges of obtaining data on compensatory responses to climatic warming through phenotypic plasticity and evolutionary change. In this Review, we highlight how cities can be used to explore physiological trait responses to experimental warming, and also how cities can be used as human-made space-for-time substitutions. We assessed the current literature and found evidence for significant plasticity and evolution in thermal tolerance trait responses to urban heat islands. For those studies that reported both plastic and evolved components of thermal tolerance, we found evidence that both mechanisms contributed to phenotypic shifts in thermal tolerance, rather than plastic responses precluding or limiting evolved responses. Interestingly though, for a broader range of studies, we found that the magnitude of evolved shifts in thermal tolerance was not significantly different from the magnitude of shift in those studies that only reported phenotypic results, which could be a product of evolution, plasticity, or both. Regardless, the magnitude of shifts in urban thermal tolerance phenotypes was comparable to more traditional space-for-time substitutions across latitudinal and altitudinal clines in environmental temperature. We conclude by considering how urban-derived estimates of plasticity and evolution of thermal tolerance traits can be used to improve forecasting methods, including macrophysiological models and species distribution modelling approaches. Finally, we consider areas for further exploration including sub-lethal performance traits and thermal performance curves, assessing the adaptive nature of trait shifts, and taking full advantage of the environmental thermal variation that cities generate.

Socio-ecological drivers of vertebrate biodiversity and human-animal interfaces across an urban landscape

Urbanization can have profound impacts on the distributional ecology of wildlife and livestock, with implications for biodiversity conservation, ecosystem services and human health. A wealth of studies have assessed biotic responses to urbanization in North America and Europe, but there is little empirical evidence that directly links human activities to urban biodiversity in the tropics. Results from a large-scale field study conducted in Nairobi, Kenya, are used to explore the impact of human activities on the biodiversity of wildlife and livestock with which humans co-exist across the city. The structure of sympatric wildlife, livestock and human populations are characterized using unsupervised machine learning, and statistical modelling is used to relate compositional variation in these communities to socio-ecological drivers occurring across the city. By characterizing landscape-scale drivers acting on these interfaces, we demonstrate that socioeconomics, elevation and subsequent changes in habitat have measurable impacts upon the diversity, density and species assemblage of wildlife, livestock and humans. Restructuring of wildlife and livestock assemblages (both in terms of species diversity and composition) has important implications for the emergence of novel diseases at urban interfaces, and we therefore use our results to generate a set of testable hypotheses that explore the influence of urban change on microbial communities. These results provide novel insight into the impact of urbanization on biodiversity in the tropics. An understanding of associations between urban processes and the structure of human and animal populations is required to link urban development to conservation efforts and risks posed by disease emergence to human health, ultimately informing sustainable urban development policy.

Socio-eco-evolutionary dynamics in cities

Cities are uniquely complex systems regulated by interactions and feedbacks between nature and human society. Characteristics of human society-including culture, economics, technology and politics-underlie social patterns and activity, creating a heterogeneous environment that can influence and be influenced by both ecological and evolutionary processes. Increasing research on urban ecology and evolutionary biology has coincided with growing interest in eco-evolutionary dynamics, which encompasses the interactions and reciprocal feedbacks between evolution and ecology. Research on both urban evolutionary biology and eco-evolutionary dynamics frequently focuses on contemporary evolution of species that have potentially substantial ecological-and even social-significance. Still, little work fully integrates urban evolutionary biology and eco-evolutionary dynamics, and rarely do researchers in either of these fields fully consider the role of human social patterns and processes. Because cities are fundamentally regulated by human activities, are inherently interconnected and are frequently undergoing social and economic transformation, they represent an opportunity for ecologists and evolutionary biologists to study urban "socio-eco-evolutionary dynamics." Through this new framework, we encourage researchers of urban ecology and evolution to fully integrate human social drivers and feedbacks to increase understanding and conservation of ecosystems, their functions and their contributions to people within and outside cities.

The evolutionary consequences of human-wildlife conflict in cities

Human-wildlife interactions, including human-wildlife conflict, are increasingly common as expanding urbanization worldwide creates more opportunities for people to encounter wildlife. Wildlife-vehicle collisions, zoonotic disease transmission, property damage, and physical attacks to people or their pets have negative consequences for both people and wildlife, underscoring the need for comprehensive strategies that mitigate and prevent conflict altogether. Management techniques often aim to deter, relocate, or remove individual organisms, all of which may present a significant selective force in both urban and nonurban systems. Management-induced selection may significantly affect the adaptive or nonadaptive evolutionary processes of urban populations, yet few studies explicate the links among conflict, wildlife management, and urban evolution. Moreover, the intensity of conflict management can vary considerably by taxon, public perception, policy, religious and cultural beliefs, and geographic region, which underscores the complexity of developing flexible tools to reduce conflict. Here, we present a cross-disciplinary perspective that integrates human-wildlife conflict, wildlife management, and urban evolution to address how social-ecological processes drive wildlife adaptation in cities. We emphasize that variance in implemented management actions shapes the strength and rate of phenotypic and evolutionary change. We also consider how specific management strategies either promote genetic or plastic changes, and how leveraging those biological inferences could help optimize management actions while minimizing conflict. Investigating human-wildlife conflict as an evolutionary phenomenon may provide insights into how conflict arises and how management plays a critical role in shaping urban wildlife phenotypes.

Urban evolution comes into its own: Emerging themes and future directions of a burgeoning field

Urbanization has recently emerged as an exciting new direction for evolutionary research founded on our growing understanding of rapid evolution paired with the expansion of novel urban habitats. Urbanization can influence adaptive and nonadaptive evolution in urban-dwelling species, but generalized patterns and the predictability of urban evolutionary responses within populations remain unclear. This editorial introduces the special feature "Evolution in Urban Environments" and addresses four major emerging themes, which include: (a) adaptive evolution and phenotypic plasticity via physiological responses to urban climate, (b) adaptive evolution via phenotype-environment relationships in urban habitats, (c) population connectivity and genetic drift in urban landscapes, and (d) human-wildlife interactions in urban spaces. Here, we present the 16 articles (12 empirical, 3 review, 1 capstone) within this issue and how they represent each of these four emerging themes in urban evolutionary biology. Finally, we discuss how these articles address previous questions and have now raised new ones, highlighting important new directions for the field.

Long-term urbanization impacts the eastern golden frog (Pelophylax plancyi) in Shanghai City: Demographic history, genetic structure, and implications for amphibian conservation in intensively urbanizing environments

Understanding the mechanisms of how urbanization influences the evolution of native species is vital for urban wildlife ecology and conservation in the Anthropocene. With thousands of years of agriculture-dominated historical urbanization followed by 40 years of intensive and rapid urbanization, Shanghai provides an ideal environment to study how the two-stage urbanization process influences the evolution of indigenous wildlife, especially of anuran species. Therefore, in this study, we used mitochondrial Cyt-b gene, microsatellite (SSR), and single nucleotide polymorphism (SNP) data to evaluate the demographic history and genetic structure of the eastern golden frog (Pelophylax plancyi), by sampling 407 individuals from 15 local populations across Shanghai, China. All local populations experienced bottlenecks during historical urbanization, while the local populations in urban areas maintained comparable contemporary effective population sizes (N e) and genetic diversity with suburban and rural populations. Nevertheless, the rapid modern urbanization has already imposed significant negative effects to the integrity of populations. The 15 local populations were differentiated into eight genetic clusters, showing a spatial distribution pattern consistent with the current urbanization gradient and island-mainland geography. Although moderate gene flow still occurred from the rural peripheral cluster to urban and suburban clusters, population fragmentation was more serious in the urban and suburban populations, where higher urbanization levels within 2-km radius areas showed significant negative relationships to the N e and genetic diversity of local populations. Therefore, to protect urban wildlife with limited dispersal ability, improving conditions in fragmented habitat remnants might be most essential for local populations living in more urbanized areas. Meanwhile, we highlight the need to preserve large unfragmented rural habitats and to construct corridor networks to connect discrete urban habitat remnants for the long-term wildlife conservation in intensively urbanizing environments.

Adaptive Evolution in Cities: Progress and Misconceptions

Current narratives suggest that urban adaptation - the adaptive evolution of organisms to cities - is pervasive across taxa and cities. However, in reviewing hundreds of studies, we find only six comprehensive examples of species adaptively evolving to urbanization. We discuss the utility and shortcomings of methods for studying urban adaptation. We then review diverse systems offering preliminary evidence for urban adaptation and outline a research program for advancing its study. Urban environments constitute diverse, interacting selective agents that test the limits of adaptation. Understanding urban adaptation therefore offers unique opportunities for addressing fundamental questions in evolutionary biology and for better conserving biodiversity in cities. However, capitalizing on these opportunities requires appropriate research methods and dissemination of accurate narratives.

If you build it, they will come: rapid colonization by dragonflies in a new effluent-dependent river reach

Background

Aquatic ecosystems are greatly altered by urban development, including the complete loss of natural habitat due to water diversions or channel burial. However, novel freshwater habitats also are created in cities, such as effluent-dependent streams that rely on treated wastewater for flow. It is unclear how diverse these novel ecosystems are, or how quickly aquatic species are able to colonize them. In this study, we (1) quantify odonate (Insecta, Odonata) colonization of a novel effluent-dependent river reach, (2) examine how drying events affect odonates in these novel habitats, and (3) explore whether effluent-dependent streams can support diverse odonate assemblages.

Methods

We conducted monthly odonate surveys at three sites along the Santa Cruz River (Tucson, AZ, USA) between June 2019 and May 2020. One site was in a long-established effluent-dependent reach (flowing since the 1970s) that served as a reference site and two sites were in a newly-established reach that began flowing on June 24, 2019 (it was previously dry). We compared odonate species richness, assemblage composition, and colonization patterns across these reaches, and examined how these factors responded to flow cessation events in the new reach.

Results

Seven odonate species were observed at the study sites in the new reach within hours of flow initiation, and species rapidly continued to arrive thereafter. Within 3 months, species richness and assemblage composition of adult odonates were indistinguishable in the new and reference reaches. However, drying events resulted in short-term and chronic reductions in species richness at one of the sites. Across all three sites, we found over 50 odonate species, which represent nearly 40% of species known from the state of Arizona.

Discussion

Odonates were surprisingly diverse in the effluent-dependent Santa Cruz River and rapidly colonized a newly established reach. Richness levels remained high at study sites that did not experience drying events. These results suggest that consistent discharge of high-quality effluent into dry streambeds can be an important tool for promoting urban biodiversity. However, it remains to be seen how quickly and effectively less vagile taxa (e.g., mayflies, caddisflies) can colonize novel reaches. Effluent-dependent urban streams will always be highly managed systems, but collaboration between ecologists and urban planners could help to maximize aquatic biodiversity while still achieving goals of public safety and urban development.

Decline in Distribution and Abundance: Urban Hedgehogs under Pressure

Simple Summary

Hedgehogs have been found in higher densities in urban compared to rural areas. Recent dramatic declines in rural hedgehog numbers lead us to pose the question: how are hedgehogs faring in urban areas? In this study, we examined how hedgehog numbers have changed in the city of Zurich, Switzerland, in the last 25 years. We compared data collected through citizen science projects conducted in 1992 and 2016–2018, including: observations of hedgehogs, data from footprint tunnels, and capture-mark recapture studies. We found that hedgehog numbers have declined by 41%, from the former average of more than 30 individuals per km², in the last 25 years. In the same time span, hedgehogs have lost 18% of their former urban distribution. The reasons for this decline are still unknown. Intensification of urban buildup, reduction of green space quality, the use of pesticides, parasites, or diseases, as well as increasing numbers of badgers, which are hedgehog predators, in urban areas are discussed as potential causes. Worryingly, these results suggest that hedgehogs are now under increasing pressure not only in rural but also in urban areas, their former refuges.

Abstract

Increasing urbanization and densification are two of the largest global threats to biodiversity. However, certain species thrive in urban spaces. Hedgehogs Erinaceus europaeus have been found in higher densities in green areas of settlements as compared to rural spaces. With recent studies pointing to dramatically declining hedgehog numbers in rural areas, we pose the question: how do hedgehogs fare in urban spaces, and do these spaces act as refuges? In this study, recent (2016–2018) and past (1992) hedgehog abundance and distribution were compared across the city of Zurich, Switzerland using citizen science methods, including: footprint tunnels, capture-mark recapture, and incidental sightings. Our analyses revealed consistent negative trends: Overall hedgehog distribution decreased by 17.6% ± 4.7%, whereas abundance declined by 40.6% (mean abundance 32 vs. 19 hedgehogs/km², in past and recent time, respectively), with one study plot even showing a 91% decline in this period (78 vs. 7 hedgehogs/km², respectively). We discuss possible causes of this rapid decline: increased urban densification, reduction of insect biomass, and pesticide use, as well as the role of increasing populations of badgers (a hedgehog predator) and parasites or diseases. Our results suggest that hedgehogs are now under increasing pressure not only in rural but also in urban areas, their former refuges.

The Complexity of Urban Eco-evolutionary Dynamics

Urbanization is changing Earth's ecosystems by altering the interactions and feedbacks between the fundamental ecological and evolutionary processes that maintain life. Humans in cities alter the eco-evolutionary play by simultaneously changing both the actors and the stage on which the eco-evolutionary play takes place. Urbanization modifies land surfaces, microclimates, habitat connectivity, ecological networks, food webs, species diversity, and species composition. These environmental changes can lead to changes in phenotypic, genetic, and cultural makeup of wild populations that have important consequences for ecosystem function and the essential services that nature provides to human society, such as nutrient cycling, pollination, seed dispersal, food production, and water and air purification. Understanding and monitoring urbanization-induced evolutionary changes is important to inform strategies to achieve sustainability. In the present article, we propose that understanding these dynamics requires rigorous characterization of urbanizing regions as rapidly evolving, tightly coupled human–natural systems. We explore how the emergent properties of urbanization affect eco-evolutionary dynamics across space and time. We identify five key urban drivers of change—habitat modification, connectivity, heterogeneity, novel disturbances, and biotic interactions—and highlight the direct consequences of urbanization-driven eco-evolutionary change for nature's contributions to people. Then, we explore five emerging complexities—landscape complexity, urban discontinuities, socio-ecological heterogeneity, cross-scale interactions, legacies and time lags—that need to be tackled in future research. We propose that the evolving metacommunity concept provides a powerful framework to study urban eco-evolutionary dynamics.