Urban Gradient Research Articles

Urban scavenging: vertebrates display greater sensitivity to land-cover and garden vegetation cover than invertebrates

Scavenging removes carrion or littered food waste from the environment, promoting nutrient cycling, and reducing waste management costs. These ecosystem services are important in urban environments, where high human population densities result in increased littered food waste. It is unclear how the magnitude of scavenging across urban-rural gradients is influenced by agent, land-cover type, and patch size. We investigated scavenging provision by vertebrates and invertebrates across a gradient of urbanisation, based on impervious surface cover, in woodlands and gardens in Liverpool, UK. The percentage dry weight loss of bait after 48 h, deployed within vertebrate exclusion cages or exposed to vertebrates and invertebrates, was used to quantify scavenging provision. General linear mixed effects models were used to assess the relative contributions of vertebrates and invertebrates across an urban-rural gradient, variation in scavenging between woodlands and gardens, and the effects of semi-natural vegetation cover on scavenging in gardens. We consider patch size as a preliminary assessment of how fragmentation influences scavenging. Vertebrates contributed substantially more to scavenging than invertebrates across the urbanisation gradient. Vertebrate scavenging was greater in woodlands than gardens, while invertebrate scavenging remained consistent. Scavenging increased with patch size in gardens, but not woodlands. Vertebrate scavenging increased with patch size and garden semi-natural vegetation cover. Urban woodlands and gardens make important contributions to scavenging-mediated ecosystem services. There is a need to increase the cover of semi-natural vegetation in gardens to increase their contributions, and protect and expand woodlands, especially in areas with a high demand for scavenging-mediated ecosystem services.

Bee community response to multiple stressors along a tropical urban-peri urban gradient

Bee community response to multiple stressors along a tropical urban-peri urban gradient

Long-term directional changes in urban bird communities of Mar del Plata City, Argentina

Urban environments have been characterized by their temporal stability of resources, which could promote stability in bird composition. Several studies have found that bird communities in urban environments persist over the years, showing a similar species composition in the short term. However, studies analyzing continuous changes in urban communities over the long term are scarce. This study aimed to analyze the stability or directional changes (instability) in bird communities along an urban gradient. Bird counts were conducted in urban, suburban, and periurban areas over 8-10 years in 2002-2019. Changes in species composition were analyzed over periods ranging from one year to the next, to changes from one year to the seventeenth. Urban bird communities were more similar between years than suburban and periurban communities. Compositional changes were greater as time lags increased, indicating directional compositional shifts. The magnitude of these changes was similar across the urban gradient. The Chimango Caracara (Milvago chimango), the Picazuro Pigeon (Patagioenas picazuro), the Rufous Hornero (Furnarius rufus), and the Red-bellied Thrush (Turdus rufiventris) significantly increased their abundances during the period, while the House Sparrow (Passer domesticus) significantly decreased its abundance. Regional changes in species abundance, urban vegetation succession, and biotic interactions could explain the changes in bird communities.

Spatial and Temporal Characteristics of Fractional Vegetation Cover and Its Response to Urbanization in Beijing

Exploration of the spatiotemporal changes in fractional vegetation cover （FVC） and its response characteristics to urbanization is of great significance for urban ecological protection and planning in Beijing. This study analyzed the spatiotemporal characteristics of vegetation cover changes in Beijing from 2000 to 2020 using the Theil-Sen Median and Mann-Kendall methods based on a long-term time series vegetation cover dataset. Then, this study used the urbanization index as a key indicator of spatial urbanization and utilized the transect line and global grid analysis methods to investigate the response characteristics of FVC to different urbanization gradients. The results indicated that： ① FVC changes showed spatial and temporal heterogeneity. From 2000 to 2020, Beijing was predominantly covered by high vegetation, accounting for 65.22% of the total area, which was mainly distributed in ecological conservation areas consistent with the Jundu, Xishan, and Yaji Mountain ranges. The FVC presented an overall positive development trend, with a decreasing trend of areas with low FVC. The increase in FVC was significant （by 28.68%）, mainly distributed in ecological conservation areas and within a range of 10-12 km in concentric circles centered around Tiananmen Square. The urbanization index and FVC change rate were relatively high in Haidian District, Chaoyang District, Fengtai District, Shijingshan District, and Changping District. ② The artificial land surface in 2000, 2010, and 2020 was 9.69%, 13.64%, and 21.19%, respectively, with significant spatial agglomeration and strong spatial heterogeneity. During the urbanization process in Beijing, the increase in artificial land surface reached 11.5%, with the conversion from arable land to artificial land surface accounting for 53.83% of the total land use conversion area. ③ There was a significant negative correlation between FVC and the urbanization index, indicating that urbanization had a negative impact on regional FVC. However, as the urbanization process stabilized, this negative correlation tended to gradually weaken. Although the central urban areas were mainly characterized by low FVC, there was a significant increasing trend in the FVC, indicating a positive development in the FVC and an improvement in regional ecological quality, which was closely related to the governance of the mountain-water-forest-field-lake-grass-sand system. The results of the study can provide a basis for the development of vegetation restoration programs and ecological management measures in Beijing.

Effects of Urbanization on Soil Quality in the Rural‒Urban Gradient of Bengaluru, India

Understanding the impact of urbanization on soil quality is crucial for sustainable land management practices. This study was conducted in Bengaluru, India, to estimate the soil quality index (SQI) under different rural‒urban gradient (RUG) zones. Twenty-four sampling sites were identified along the RUG, and soil samples were collected monthly over five months during the October to February of 2020-2021. The soil quality assessment involved selecting the minimum data set (MDS) via principal component analysis (PCA) and correlation, scoring soil indicators, and combining these scores to create the soil quality index (SQI). PCA was used to identify key soil properties, which included microbial biomass carbon (MBC), SOC, N, manganese (Mn), and urease for different RUG zones derived from the MDS. The rural zones had the highest SQI (0.57), followed by the peri-urban (0.47 and 0.48) and urban (0.45 and 0.47) zones. These findings emphasize the importance of sustainable land management practices to preserve and boost soil quality across diverse regions, particularly in the face of rapid urbanization and industrialization.

Anthropogenic nesting materials and reproductive performance of Chinese Bulbuls (Pycnonotus sinensis) along the urbanization gradient in Hangzhou, China

Urbanization induced by human activities presents both challenges and adaptive opportunities for wildlife. One notable impact of urban sprawl is the vast amount of waste it produces, which has discernible effects on wildlife. Interestingly, an emerging trend has been observed that birds are incorporating anthropogenic materials into their nests. However, the relationship between anthropogenic nesting materials (ANMs) and the reproductive performance of urban birds is unclear. In this study, we investigated the relationship between the incorporation of ANMs into nests and the reproductive performance of Chinese Bulbuls (Pycnonotus sinensis) by monitoring and collecting data on 136 breeding nests in Hangzhou, China. We gathered data on seven reproductive traits of Chinese Bulbuls, including laying date, incubation period, nestling period, clutch size, egg volume, hatching success rate, and fledging success rate. We then calculated the urbanization synthetic index as a measure of the level of urbanization and examined its relationship with the proportion and weight of ANMs. Through examination of nest components, we observed significant increase in the proportion and weight of ANMs with the urbanization synthetic index. Notably, we found a higher hatching success rate of Chinese Bulbuls with an increasing proportion of ANMs. However, the inclusion of ANMs in nests was not correlated with other reproductive traits of Chinese Bulbuls. Overall, the use of ANMs by Chinese Bulbuls seems to be consistent with the adaptive hypothesis and the availability hypothesis. Further studies should use controlled experiments to investigate the impact of ANMs on avian reproductive success.

Taxonomic, Functional, and Phylogenetic Diversity of Bats in Urban and Suburban Environments in Southern México

Urbanization is one of the leading causes of habitat loss, which has increased significantly in tropical regions in recent years, leading to the loss of species, their ecological functions, and evolutionary history. To determine the effect of urbanization on the diversity of bat communities in urban and suburban environments, we analyzed the α and β taxonomic, functional, and phylogenetic diversities at four sites along urbanization gradients surrounding a rapidly expanding city (Oaxaca City) in southern Mexico. We recorded bats using conventional techniques such as mist nets and acoustic monitoring. We calculated the diversity of bats in four sites with different urbanization conditions: urban (1), suburban (1), and rural (2). To assess the degree of total differentiation and components of bat turnover and nestedness between sites, we calculated the β taxonomic, functional, and phylogenetic diversities. A total of 33 bat species were recorded. The highest taxonomic and functional diversity was observed in the Center of Oaxaca (the site with the highest level of urbanization). In contrast, the highest phylogenetic diversity was found in the West (the site with the lowest level of urbanization). The total β taxonomic diversity was higher than the functional and phylogenetic diversity. Regarding the contributions of turnover and nestedness, turnover made a more significant contribution than nestedness to the taxonomic and phylogenetic β diversity. In contrast, functional nestedness contributed more to the functional β diversity than turnover. Tadarida brasiliensis, Desmodus rotundus, Sturnira hondurensis, and S. parvidens were recorded in all three urbanization conditions. In the most urbanized site, four Myotis species were recorded: M. fortidens, M. keaysi, M. thysanodes, and M. velifer. We suggest that the analysis of different dimensions of diversity is essential and should be considered to strengthen conservation strategies; moreover, we suggest the preservation of native vegetation mosaics and water bodies within the city to maintain bat diversity.

Combined Application of Multiple Global Change Factors Negatively Influences Key Soil Processes across an Urban Gradient in Berlin, Germany

Urbanization is a growing phenomenon affecting soils worldwide. Urban centers have been highlighted as hotspots for global change factors due to heightened anthropogenic activity. However, few studies have investigated the multifaceted impacts of global change factors (GCFs) acting in concert with urban soils. Thus, the objective of this study was to add GCFs in different combinations (0, 1, 2, 5, and 8 simultaneously) in three high-urbanity and three low-urbanity soils in Berlin and to evaluate their effects on soil parameters and functions. We hypothesized four potential outcomes of soil process responses to GCF exposure, Site-Specific Resistance, General Susceptibility, Low-Urbanity Resistance, and High-Urbanity Resistance. We provide evidence for the negative impacts of individual and multiple GCF application on litter decomposition, water repellency, and water-stable aggregates. Additionally, we highlight the General Susceptibility of litter decomposition to GCF exposure regardless of urbanity, as well as the Low-Urbanity Resistance of water repellency and High-Urbanity Resistance of water-stable aggregates under increased exposure to GCFs. This study expands on evidence of the growing threat of global change factors in urban settings and highlights some potential consequences regarding soil function.

Exploring black kite (Milvus migrans) dynamics: Seasonal abundance and habitat preferences in an urban gradient

Urban expansion globally has altered biodiversity by transforming urban habitats, leading to habitat loss and changes in ecological systems. Black kites (Milvus migrans) are adaptable raptors across diverse landscapes, from natural to highly urbanized areas. This study focuses on Gujranwala City, Pakistan, a unique habitat offering insights into black kite ecology along an urban gradient. The research assesses seasonal abundance, temperature and humidity impacts, behavioral activities, and habitat preferences of black kites. Results show higher abundance in urban areas, influenced by environmental factors and food availability from anthropogenic sources. Black kites exhibit time-dependent associations with temperature and humidity, especially before sunset. Additionally, a significant correlation is observed between black kite abundance and solid waste components, particularly food and plastic waste, in the urban area. These findings contribute to understanding urban ecology, highlighting the adaptability of black kites to human-modified environments and the potential implications for conservation and management strategies.

Portable Sensors for Dynamic Exposure Assessments in Urban Environments: State of the Science.

This study presents a fit-for-purpose lab and field evaluation of commercially available portable sensor systems for PM, NO2, and/or BC. The main aim of the study is to identify portable sensor systems that are capable of reliably quantifying dynamic exposure gradients in urban environments. After an initial literature and market study resulting in 39 sensor systems, 10 sensor systems were ultimately purchased and benchmarked under laboratory and real-word conditions. We evaluated the comparability to reference analyzers, sensor precision, and sensitivity towards environmental confounders (temperature, humidity, and O3). Moreover, we evaluated if the sensor accuracy can be improved by applying a lab or field calibration. Because the targeted application of the sensor systems under evaluation is mobile monitoring, we conducted a mobile field test in an urban environment to evaluate the GPS accuracy and potential impacts from vibrations on the resulting sensor signals. Results of the considered sensor systems indicate that out-of-the-box performance is relatively good for PM (R2 = 0.68-0.9, Uexp = 16-66%, BSU = 0.1-0.7 µg/m3) and BC (R2 = 0.82-0.83), but maturity of the tested NO2 sensors is still low (R2 = 0.38-0.55, Uexp = 111-614%) and additional efforts are needed in terms of signal noise and calibration, as proven by the performance after multilinear calibration (R2 = 0.75-0.83, Uexp = 37-44%)). The horizontal accuracy of the built-in GPS was generally good, achieving <10 m accuracy for all sensor systems. More accurate and dynamic exposure assessments in contemporary urban environments are crucial to study real-world exposure of individuals and the resulting impacts on potential health endpoints. A greater availability of mobile monitoring systems capable of quantifying urban pollutant gradients will further boost this line of research.

Collaborative Changes between Soil Fauna and Urbanization Gradients in Guangzhou’s Remnant Forests

Collaborative Changes between Soil Fauna and Urbanization Gradients in Guangzhou’s Remnant Forests

Wild or neat? Personal traits affect public preference for wildness of urban lakeshores in France and China

Urban natural spaces with high wildness degrees could harbor greater biodiversity and provide more experiences of nature for urbanites than green–blue spaces that are perfectly manicured and regularly maintained. Existing empirical studies have suggested that people tend to prefer moderately wild landscapes. However, urbanites’ preferences for varying wildness degrees of urban landscapes have rarely been studied in developing countries with fast-growing cities. Using a photograph-based survey, this study compared citizens’ preferences for an urban wildness gradient of urban lakeshores between developed (Tours, France) and developing (Wuhan, China) contexts. In Tours and Wuhan, respectively, 120 and 295 questionnaires were collected, focusing on lakeshore visitors only. Bootstrapping and thematic analysis of the survey responses affirmed that urban lakeshores with medium-degree wildness are consistently preferred across developed and developing contexts, a result that can be attributed to the perceived balance between landscape coherence/legibility and complexity/mystery. Moreover, some respondents (25.8 % from Tours and 32.6 % from Wuhan) showed a strong preference for complex and unstructured lakeshore landscapes with high wildness for different reasons. In Tours, respondents’ preference for high wildness degree was associated with more frequent visits to lakeshore areas. In Wuhan, a similar preference was associated with increasing age. While increasing the wildness of urban lakeshores from low to medium could adequately meet public preferences, attracting more frequent visits and helping younger residents to appreciate urban wildness should be considered for successfully restoring/enriching biodiversity and mobilizing public support for wild urban landscapes.

Heat vulnerability: health impacts of heat on older people in urban and rural areas in Europe.

Exposure to extreme heat is associated with both increased morbidity and mortality, especially in older people. Health burdens associated with heat include heat stroke, diabetes mellitus, hypertension, ischemic heart diseases, heart failure and arrhythmia, pulmonary diseases but also injuries, problems with activities of daily living, and mental disorders. In Europe, there are remarkable spatial differences in heat exposure between urban and less populated areas. In Austria, for example, there is asignificant gradual association between population density and the number of heat days, where the gradient of urbanization also follows the gradient of sea level. The European population is continuously ageing, especially in rural areas. Older adults are especially vulnerable to negative health consequences resulting from heat exposure, due to a lack of physiological, social, cognitive, and behavioral resources. Older people living in urban areas are particularly at risk, due to the urban heat island effect, the heat-promoting interplay between conditions typically found in cities, such as alack of vegetation combined with ahigh proportion of built-up areas; however, older people living in rural regions often have less infrastructure to cope with extreme heat, such as fewer cooling centers and emergency services. Additionally, older adults still engaged in agricultural or forestry activities may be exposed to high temperatures without adequate protection or hydration. More research is required to examine factors responsible for heat vulnerability in older adults and the interactions and possibilities for increasing resilience in older urban and rural populations to the health consequences of heat.

Variation in insect herbivory across an urbanization gradient: The role of abiotic factors and leaf secondary metabolites

Urbanization impacts plant-herbivore interactions, which are crucial for ecosystem functions such as carbon sequestration and nutrient cycling. While some studies have reported reductions in insect herbivory in urban areas (relative to rural or natural forests), this trend is not consistent and the underlying causes for such variation remain unclear. We conducted a continental-scale study on insect herbivory along urbanization gradients for three European tree species: Quercus robur, Tilia cordata, and Fraxinus excelsior, and further investigated their biotic and abiotic correlates to get at mechanisms. To this end, we quantified insect leaf herbivory and foliar secondary metabolites (phenolics, terpenoids, alkaloids) for 176 trees across eight European cities. Additionally, we collected data on microclimate (air temperature) and soil characteristics (pH, carbon, nutrients) to test for abiotic correlates of urbanization effects directly or indirectly (through changes in plant secondary chemistry) linked to herbivory. Our results showed that urbanization was negatively associated with herbivory for Q. robur and F. excelsior, but not for T. cordata. In addition, urbanization was positively associated with secondary metabolite concentrations, but only for Q. robur. Urbanization was positively associated with air temperature for Q. robur and F. excelsior, and negatively with soil nutrients (magnesium) in the case of F. excelsior, but these abiotic variables were not associated with herbivory. Contrary to expectations, we found no evidence for indirect effects of abiotic factors via plant defences on herbivory for either Q. robur or F. excelsior. Additional biotic or abiotic drivers must therefore be accounted for to explain observed urbanization gradients in herbivory and their interspecific variation.

Utilizing spontaneous plants for sustainable development in residential green spaces: Insights from environmental drivers and niche analysis in Fuzhou City, China

This study, aimed at exploring low-maintenance, high-diversity, and sustainable greening strategies for residential areas, conducted a comprehensive survey and analysis of spontaneous plants in residential green spaces in Fuzhou City, documenting 361 species. Employing methods such as variance partitioning, Canonical Correspondence Analysis (CCA), and ecological niche analysis, we investigated the environmental factors influencing the distribution and composition of these plants, as well as their interrelationships. The study found that the composition of spontaneous plants in residential green spaces differs from other urban environments, with a high proportion of alien species (43.77%) due to influences such as resident activities, including a large number of ornamental and edible plants. Maintenance level, urbanization gradient, and green space ratio are common factors affecting the composition and distribution of spontaneous plants in urban environments, while unique residential socio-economic factors like building age, housing prices, and population density significantly affect the spontaneous plants in residential green spaces. The overall dominant plant community shows a significant positive association, indicating a relatively stable stage of succession. Although competition among most species is not significant and interspecific connectivity is weak, the presence of seven dominant invasive species intensifies competition. Based on these findings, the study proposes several specific sustainable management measures: adopting the concept of New Naturalistic Ecological Planting Design, selecting native spontaneous plants with strong adaptability, and constructing plant communities that are ecologically stable and have ornamental value by mimicking natural ecosystems. Additionally, specific methods for managing specific invasive species in residential green spaces using competitive replacement control methods are proposed. These measures aim to promote the health and sustainable development of urban residential green spaces.

Impacts of an urban density gradient on land-atmosphere turbulent heat fluxes across seasonal timescales

Impacts of an urban density gradient on land-atmosphere turbulent heat fluxes across seasonal timescales

Effects of Land Use on the Community Structure of Aquatic Invertebrate in Subtropical Streams

Streams constitute the water supply of the watersheds and provide the transfer of energy along the course of water, ensuring water biodiversity. Due to the different uses of the earth, the benthic community is being suppressed. The objective of this study is to investigate the effects of changes in land use on the abundance, richness, and diversity of benthic macroinvertebrates in subtropical streams, considering the physical and chemical variables of streams seasonally. In total, 144 samples were collected between February 2022 and November 2023 at 12 sites distributed in a watershed in southern Brazil, four sites for each land use. Herein, 83.520 individuals were identified, comprising 67 taxa. There was a decrease in richness along the forested–rural–urban gradient and a greater abundance in the urban environment, without the significant influence of seasonality. We conclude that the diversity of benthic macroinvertebrate in the streams is influenced not only by environmental variables but also by the spatial distribution between streams. The proximity of the streams generates a similarity in dominance. This study contributed to understanding the relationships of the environment with the benthic community and considering the spatial distribution among the streams sampled in future investigations.

Disentangling associations of human wellbeing with green infrastructure, degree of urbanity, and social factors around an Asian megacity

ContextOften called a ‘Garden city’, Bengaluru is renowned for its green infrastructure. However, the association of human wellbeing with the amount of tree cover (as an example of green infrastructure), degree of urbanization, and local people's socio-demographics has not been explored.ObjectiveWe investigated how human wellbeing is related to the amount of tree cover at household and neighborhood levels, the degree of urbanity, and underlying social factors among respondents.MethodsThe study was conducted in 61 towns along the rural–urban gradient of Bengaluru, surveying 836 respondents in total. Data on multiple dimensions of respondents’ wellbeing was collected between December 2016 and May 2017. The percentage of tree cover at the household and neighborhood levels was obtained based on WorldView-3 images. Logistic regression models were applied to assess correlations between human wellbeing and tree cover. Kruskal–Wallis tests, Mann–Whitney tests, and cross tabulation with chi-square tests were conducted to investigate relations of human wellbeing with the degree of urbanity, and with social factors.ResultsWe found that several variables of human wellbeing were positively associated with tree cover. Measures of wellbeing also differed along the rural–urban gradient and among social groups.ConclusionsThough urbanization is often considered to promote material wellbeing, non-material aspects (e.g., community activities and social relationships) are also important components of overall human wellbeing in urbanizing landscapes. Holistic interactions among natural, spatial, and social factors should be considered while designing interventions for equitable urban landscapes that promote human wellbeing and ecological restoration.

Phenotypic plasticity as the main driver of alien plant trait variation in urban versus rural microclimate for the model species Veronica persica.

Urban environments are warmer than the rural surroundings, impacting plant phenotypic traits. When plants are present over areas with contrasted conditions such as along urbanization gradients, their phenotypes may differ, and these differencesdepend on different processes, including phenotypic plasticity, maternal environmental effects and genetic differentiation (local adaptation and/or genetic drift). Successful establishment of alien species along environmental gradients has been linked to high phenotypic plasticity and rapid evolutionary responses, which are easier to track for species with a known residence time. The mechanisms explaining trait variation in plants in urban versus rural microclimatic conditions have received little attention. Using the alien Veronica persica as model species, we measured leaf traits in urban and rural populations and performed a reciprocal common-garden experiment to study how germination, leaf, growth, and flowering traits varied in response to experimental microclimate (rural or urban) and population origin environment (rural or urban). Veronica persica displayed phenotypic plasticity in all measured traits, with reduced germination, development, and flowering under urban microclimate which suggests more stressful growing conditions in the urban than in the rural microclimate. No significant effect of the rural or urban origin environment was detected, providing no evidence for local adaptation to urban or rural environments. Additionally, we found limited signs of maternal environmental effects. We noted the importance of the mother plant and the population identities suggesting genetically based differences. Our results indicate that urban environments are more hostile than rural ones, and that V. persica does not show any adaptation to urban environments despite genetic differences between populations.

Insect herbivory on Acer rubrum varies across income and urbanization gradients in the D.C. metropolitan area

Urbanization has increased wealth disparity within the United States, impacting the urban landscape and species interactions. In particular, the interactions between street trees and the arthropod communities that live among them may be modified by both human population densities across urban to suburban locations, as well as income levels within these areas. We examined the effect of land use type (urban vs. suburban) and median household income on variation in leaf damage and arthropod abundance of red maples (Acer rubrum) in the District of Columbia metropolitan region. We compared these levels of leaf damage to rates observed in a nearby temperate deciduous forest. We predicted leaf damage would be positively correlated with urbanization (forested < suburban < urban) and negatively correlated with neighborhood income level (low > medium > high). Instead, we observed higher levels of leaf damage on trees in the forest environment compared to the urban and suburban areas. Leaves from urban medium and high-income areas were less likely to exhibit herbivore damage than those from suburban areas. Of the leaves with damage, those in urban high-income and suburban low-income areas exhibited the most leaf area missing. These trends may be related to specific factors associated with urbanization and income level, such as impervious surface coverage and tree coverage. This study highlights differences in biotic interactions across individual neighborhoods and the importance of including socio-economic variables when examining species interactions in urban environments.