Urbanization and plant pathogen infection interact to affect the outcome of ecological interactions in an experimental multitrophic system

Urbanization can change interactions in insect communities, and the few studies of tritrophic interactions in urban settings focus on interactions between plants, herbivorous insects and their mutualists and natural enemies. Plant pathogen infection is also widespread and common, and infection may also alter such interactions, but we have no understanding of whether the ecological consequences of pathogen infection vary with urbanization. Using replicated aphid colonies on experimental plants, we investigated how infection by the plant pathogen Botrytis cinerea influences interactions between plants, aphids and the aphid natural enemies and ant mutualists in highly urbanized, suburban and rural study sites. Aphid and natural enemy abundance were highest in the suburban site, while mutualist ants were most abundant in the urban site, reversing the usual positive density-dependent relationship between natural enemies and aphids. The effect of pathogen infection varied with trait and site, mediated by natural enemy preference for hosts or prey on uninfected plants. The effect of infection on aphid abundance was only seen in the suburban site, where natural enemies were most abundant on uninfected plants and aphid numbers were greatest on infected plants. In the urban site, there was no effect of infection, while in the rural site, aphid numbers were lower on infected plants. Uninfected plants were smaller than infected plants and differed between locations. This study suggests that the effects of urbanization on ecological interactions may become more complex and difficult to predict as we study ecological assemblages and communities at greater levels of structural complexity.

Social and environmental correlates of rat complaints in Chicago

Urban rats are widely distributed pests that have negative effects on public health and property. It is crucial to understand their distribution to inform control efforts and address drivers of rat presence. Analysing public rat complaints can help assess urban rat distribution and identify factors supporting rat populations. Both social and environmental factors could promote rat complaints and must be integrated to understand rat distributions. We analysed rat complaints made between 2011 and 2017 in Chicago, a city with growing rat problems and stark wealth inequality. We examined whether rat complaints at the census tract level are associated with factors that could influence rat abundance, rats’ visibility to humans, and the likelihood of people making a complaint. Complaints were significantly positively correlated with anthropogenic factors hypothesized to promote rat abundance (restaurants, older buildings, garbage complaints, and dog waste complaints) or rat visibility (building construction/demolition activity), and factors hypothesized to increase the likelihood of complaining (human population density, more owner-occupied homes); we also found that complaints were highest in the summer. Our results suggest that conflicts between residents and rats are mainly driven by seasonal variation in rat abundance and human activity and could be mitigated with strategies such as securing food waste from residential and commercial sources. Accounting for social factors such as population density, construction and demolition activity, and home ownership versus rental can also help cities more accurately predict blocks at higher risk of rat conflicts.

Landscape design approaches to enhance human–wildlife interactions in a compact tropical city

Urban landscapes have the potential to conserve wildlife. Despite increasing recognition of this potential, there are few collaborative efforts to integrate ecology and conservation principles into context-dependent, spatial and actionable design strategies. To address this issue and to encourage multi-disciplinary research on urban human–wildlife interactions, we ask the following questions. To what extent should design and planning actions be aligned with urban ecology in the context of a compact city? How can wildlife conservation meet the seemingly conflictual demands of urban development and public preference? To answer these questions, we refer to the relevant literature and a number of design projects. Using the compact tropical city of Singapore as a case study, we propose 12 design strategies. We encourage designers and planners to strengthen the links between wildlife and urban dwellers and promote wildlife conservation within cities.

Urban waste no replacement for natural foods—Marabou storks in Botswana

We compared diets of marabou storks Leptoptilos crumenifer foraging from urban landfills and natural areas in northern Botswana using stable isotope analyses and inductively coupled plasma mass spectrometry on moulted feathers. There were significant differences in the diet of marabous foraging from natural areas compared to urban waste sites, reflected by lower δ13C and less enriched δ15N concentrations in those feeding at landfills, suggesting a shift in trophic niche. Feathers from birds foraging at landfills also had significantly higher concentrations of chromium, lead, nickel, and zinc and lower levels of cadmium and potassium than feathers sampled from natural areas. We also analysed marabou regurgitant (42 kg, naturally expelled indigestible food resources) from the Kasane landfill site. More than half was plastic, with single regurgitants weighing up to 125 g. Urban waste stored in open air landfills is altering some marabou diets, affecting their natural trophic niche, resulting in the consumption (and regurgitation) of large amounts of plastic, and exposing marabou to potentially chronic levels of trace metals. Despite the marabou’s apparent resilience to this behavioural shift, it could have long-term effects on the population of the marabou stork, particularly considering Botswana has some of the few regular marabou breeding colonies in southern Africa.

Lower socioeconomic status neighborhoods in Puerto Rico have more diverse mosquito communities and higher Aedes aegypti abundance

Mosquito community dynamics in urban areas are influenced by an array of both social and ecological factors. Human socioeconomic factors (SEF) can be related to mosquito abundance and diversity as urban mosquito development sites are modified by varying human activity, e.g., level of abandoned structures or amount of accumulated trash. The goal of this study was to investigate the relationships among mosquito diversity, populations of Aedes aegypti, and SEF in a tropical urban setting. Mosquitoes were collected using BG Sentinel 2 traps and CDC light traps during three periods between late 2018 and early 2019 in San Juan, Puerto Rico, and were identified to species. SEFs (i.e. median household income, population density, college-level educational attainment, unemployment, health insurance coverage, percentage of households below the poverty line, amount of trash and level of abandoned homes) were measured using foot surveys and U.S. Census data. We found 19 species with the two most abundant species being Culex quinquefasciatus (n = 10 641, 87.6%) and Ae. aegypti (n = 1558, 12.8%). We found a positive association between Ae. aegypti abundance and mosquito diversity, which were both negatively related to SES and ecological factors. Specifically, lower socioeconomic status neighborhoods had both more Ae. aegypti and more diverse communities, due to more favorable development habitat, indicating that control efforts should be focused in these areas.

An automated classification system for urban areas matching the ‘city country fingers’ pattern: the cases of Kamakura (Japan) and Acireale (Italy) cities

The uncontrolled expansion of urban areas is one of the main factors that reduce the liveability of cities. In recent years, to contrast urban sprawl, several nations have promoted policies aimed at developing urban green spaces. The importance of green oases within cities had already been highlighted, in 1977, by the architect Christopher Alexander who had developed a series of patterns including ‘City Country Fingers’ claiming that city development should consider the prolongation of country land in to the urban area. In several cities, especially in Japan, it is possible to recognize the imprint of urban development based on country fingers. This term refers to extensive urban intersections of agricultural land or wooded hills which, from the peripheral areas, penetrate the city. Inside them, there are urban windows, called city fingers, whose development direction is opposite to those of the country fingers. To recognize and analyze, in an automated way, these particular structures, a Python-based application was created. Starting from the original high-resolution image of Google Earth, a complete analysis was performed, labeling and delimiting urban and vegetational areas and extrapolating the main geometric parameters of the country and city fingers. The finalization of the results obtained was carried out through a classification model whose criteria were based on Alexander’s pattern. Thanks to this classification scheme, the distinction between Active Green Areas (country fingers) and Passive Green Areas (gardens and public parks) have been revealed for the analyzed cities. The tests performed showed almost ideal conditions for the city of Kamakura and a limited match for the urban area of Acireale. The proposed method is suitable for fields of application that require a qualitative and quantitative determination of the vegetation cover present within the city, an essential condition for correct territorial planning.

Economic assessment of urban space and blue-green infrastructure in Singapore

The urban conglomeration has accentuated the role of urban greenery as a determinant factor for sustainable living, especially in highly dense cities. The country of Singapore has consistently attempted to develop and rehabilitate urban greenery by attempting to align the green space policy with the pursuit of better life quality. In this study, we assess the benefits arising from the rehabilitated Bishan-Ang Mo Kio (AMK) Park in north Singapore and the effects on economic welfare. The Bishan-AMK Park was initially constructed in the late 70 s as a drainage area for the avoidance of flooding incidents. In 2012, a pilot project was introduced to create a blue-green infrastructure (BGI) space for the provision of drainage and flood prevention but also for recreational and environmental improvement in the area. Yet, the benefits emerging from BGI are not well explored and still underestimated. To this extent, we evaluate selected services related to recreational, socio-cultural and tourism-related values by indicating the economic benefits from the introduction of BGI in condensed urban environments like Singapore. The findings indicate that the benefits deriving from the selected services could be within the range of US$100 million to US$220 million with a mean value of US$160 million per year by substantially contributing to human well-being. The assessment of environmental services can raise the awareness of residents and local authorities on the contribution of urban greenery to livelihoods and economic development in Singapore and similar densely populated areas.

Winter bird abundance, species richness and functional guild composition at Delhi’s ponds: does time of day and wetland extent matter?

Urbanisation can limit species persistence and bias composition of functional guilds with serious consequences for ecosystem functioning and conservation planning. Standardised biodiversity surveys are missing at most tropical urban cities where biodiversity levels are high alongside rapidly increasing rates of urbanisation. We explored the utility of time-bound surveys to document winter birds at ponds (wetlands ≤ 5 ha) in Delhi, India at two different times of the day (morning and evening) and in areas with varying extents of wetlands. Systematic surveys at 39 ponds during January–March 2020 yielded an estimated 173 ± 22 bird species (∼37% of Delhi’s birds). The total bird species assemblage at ponds did not vary significantly with time of day, but β-diversity increased marginally with increasing extent of wetlands. Total bird abundance and species richness varied substantially with time of day, with differences apparent across several species rich functional feeding and habitat guilds. Abundance and species richness of some guilds, including species-poor guilds, varied in ponds located in areas with differing extent of wetlands. Reliable and comparable measures of species abundance and species richness (both total and across functional guilds)— metrics commonly used to set research and conservation priorities—in urban habitats can be obtained after appropriately standardising field effort. Such standardised efforts can help underscore the importance of maintaining and improving erstwhile-ignored habitats such as unprotected ponds that are providing refugia to hundreds of bird species in mega-cities like Delhi.

Thinking outside the park: recommendations for camera trapping mammal communities in the urban matrix

Urbanization is increasing globally, fragmenting habitats and prompting human–wildlife conflict. Urban wildlife research is concurrently expanding, but sampling methods are often biased towards large and intact habitats in public green spaces, neglecting the far more abundant, but degraded, habitats in the urban matrix. Here, we introduce the Five P’s of Urban Ecology—Partnerships, Planning, Placements, Public participation and Processing—as a path to overcoming the logistical barriers often associated with camera-trapping in the urban matrix. Though the Five P’s can be applied to a variety of urban sampling methods, we showcase the camera-trapping efforts of the DC Cat Count project in Washington, DC, as a case study. We compared occupancy models for eight urban mammal species using broad categorizations of land cover and local land use to determine drivers of mammal occurrence within the urban matrix as compared with urban habitat patches. Many native species maintained a strong association with large, semi-natural green spaces, but occupancy was not limited to these locations, and in some cases, the use of private yards and the built environment were not notably different. Furthermore, some species exhibited higher occupancy probabilities in developed areas over green spaces. Though seemingly intuitive, we offer advice on how to greatly reduce habitat-biased sampling methods in urban wildlife research and illustrate the importance of doing so to ensure accurate results that support the formation of effective urban planning and policy.

Relationship between lake area and distance from the city centre on lake-dependent resident and migratory birds in urban Bangalore, a tropical mega-city in Southern India

Urbanization is one of the major causes of biodiversity loss worldwide. Some species are able to adapt to urbanization, whereas others perish. Studies on long-term effects of the impact of urbanization on species diversity and abundance patterns are especially lacking from tropical cities. We seek to assess the relationship between urbanization and species richness of lake-dependent birds in Bangalore, a tropical mega-city in Southern India. We specifically ask: (i) How is bird species richness related to the size of the lake? (ii) How is bird species richness in Bangalore’s lakes related to the degree of urbanization? We used data from 2014 to 2019, collected from eBird—an online database that collates information on bird observations globally. Both lake area and distance from the city centre are correlated to species richness, with larger lakes supporting more bird species. As distance from the city centre increased (i.e. urbanization decreases), bird richness increased. Overall, in the city of Bangalore, migratory birds have declined while many lake-dependent resident birds seem to be increasing over the past 5 years. We hypothesize that birds that roost and nest in trees appear to be increasing. To confirm this, further research taking a trait-based approach is required. Urbanization appears to have species-specific impacts on lake-dependent birds in this tropical city, with certain groups of birds faring better than others. This research adds to the significant paucity of studies of the impact of urbanization on biodiversity in the urban tropics.