Household Debt and Adult Depressive Symptoms in the United States

This study used data from Waves 1 (1987–1989) and 2 (1992–1994) of the National Survey of Families and Households in the United States and a series of regression models, some of which included individual-specific fixed effects, to estimate associations of particular types and levels of debt with adult depressive symptoms. Results suggest that household debt is positively associated with greater depressive symptoms. However, this association appears to be driven by short-term (unsecured) debt; we found little evidence of associations with depressive symptoms for mid- or long-term debt. The link between short-term debt and depressive symptoms persisted with alternative estimation strategies, including defining debt in absolute and relative terms. Furthermore, this association was particularly concentrated among 51–64 year-old adults, those with a high school education or less, and those who were not stably married throughout the observation period. These findings suggest that short-term debt may have an adverse influence on psychological wellbeing, particularly for those who are less educated, approaching retirement age, or unmarried.     

Avian haemosporidian parasites in an urban forest and their relationship to bird size and abundance

Urbanization has been identified as a threat to biodiversity due to landscape modifications. Studies of parasite ecology in urbanized areas lagged behind those made on macro organisms. Here we studied infection prevalence of haemosporidian parasites in an avian community of an urban forest from Germany, and its relationship with bird abundance and body mass. We used PCR to amplify a fragment of the mtDNA cyt b gene to determine the infection status of birds, and bird point counts to determine bird relative abundances. The avifauna was dominated by two small sized insectivore passerines (Parus major, Cyanistes caeruleus), representing ~40 % of the total bird records. The highest haemosporidian prevalence was recorded for Turdus philomelos (100 %) and for Fringilla coelebs (75 %). Bird abundance and body mass were positively associated with infection status for two haemosporidian genera: Plasmodium and Leucocytozoon. Infection rate was lower in juveniles compared to adult birds. We recorded a total of 7 Plasmodium, 26 Haemoproteus, and 10 Leucocytozoon lineages. Avian malaria (P. relictum) was detected infecting 5 individuals of P. major, the most abundant species in the community. These results, together with those of previous studies at the same site, suggest that potentially any of the genetic haemosporidian lineages detected in this urban forest can be transmitted across native and pet bird species, and to species of conservation concern housed at aviaries.     

Large body size for metamorphic wood frogs in urban stormwater wetlands

Constructed wetlands in urban environments may be used by urban amphibian populations for breeding. Yet, few studies have examined the performance of young-of-the-year from created wetlands even though the success of terrestrial life stages is directly linked to the performance of individuals at the egg and larval stage. We assessed how early-stage amphibians developing within constructed stormwater wetlands compared in body size (one metric of performance) to those in nearby natural wetlands. We conducted surveys for wood frog, Lithobates sylvaticus, larvae and young-of-the-year metamorphs at 13 wetlands located in the City of Edmonton, Alberta, Canada and compared metamorph size (a useful metric for fitness and reproductive success) between constructed stormwater and two types of natural wetlands. We related body size to within-wetland parameters (reflecting water chemistry, thermal regimes and physical characteristics) and used an information-theoretic approach to identify predictors of metamorph body size. Abundances of egg masses, larvae and metamorphs were generally lower at stormwater than natural wetlands. Metamorphs exhibited larger body size in stormwater wetlands compared to natural wetlands. Low metamorph abundances and cool, stable water temperatures best explained large body size in stormwater metamorphs. We propose that with increasing urbanization and associated construction of artificial wetlands, size benefits in early developmental stages may help individuals cope with reduced habitat suitability in the terrestrial environment.     

Mangrove forests store high densities of carbon across the tropical urban landscape of Singapore

Tropical forested ecosystems provide multiple ecosystem services to rural and urban landscapes, with carbon storage gaining particular attention. Deforestation due to rural-urban transitions may lead to a reduction in carbon storage ability. Coastal mangrove forests are particularly at risk from deforestation due to their location in the rapidly urbanizing coastal zone, and the city state of Singapore is an extreme example, losing as much as 90 % of its original mangrove cover due to land reclamation and reservoir construction. Knowledge of mangrove ecosystem services may allow better conservation, restoration and incorporation of remaining mangrove patches into the urban landscape. Focusing on the regulating ecosystem service of carbon storage, mangrove carbon stocks have been estimated for Singapore using a combination of field and remote sensing techniques. Biomass carbon showed substantial spatial variation, with old, contiguous mangrove patches containing a higher density of biomass carbon than fragmented, river-fringing or restored mangroves. In total, national biomass carbon equated to 116,117.1 megagrams of carbon (Mg C), and a coarse estimate of the total carbon stock (including soil carbon) suggests that Singapore’s mangroves may store 450,571.7 Mg C. While lower than other regional estimates focused on natural, oceanic mangroves, this is a significant carbon stock for a disturbed, urban mangrove system, and may be equivalent to the average annual carbon emissions of 621,000 residents. This analysis, alongside a review of other urban forest studies, highlights the importance of forested ecosystems such as mangroves in providing a carbon storage ecosystem service to urban areas.     

Peeking into the past to plan the future: Assessing bird species richness in a neotropical city

Urbanization has been considered as a major threat to biodiversity, making its ecology of increasing interest. Many urban ecology studies have been developed in a short time-scale, measuring real-time patterns. However, long-term studies are imperative to understand the responses of some species to the urbanization process. In this study, we aimed to assess the information provided by a recent one-year citywide bird survey when compared to a published ‘historical’ bird list of a neotropical city (Xalapa, Mexico) that compiles information of the past three decades, mainly from urban greenspaces. Specifically, we contrasted species richness values and assessed differences in species composition between both lists. We recorded 51 species in the one-year citywide survey, representing ~15 % of those reported in the historical list. Nonetheless, the upper-bound confidence interval of the citywide survey richness prediction represented ~66 %. Most of the species recorded in the one-year citywide survey are insectivores and granivores, a pattern that agrees with previous findings that underline the importance of insectivores as part of urban bird communities in the Neotropics. Although we used robust methods to compare our one-year citywide bird list and the historical list for the city of Xalapa, we acknowledge the limitations of comparing them. However, our results shed some light on the kind and type of information that one-year citywide surveys can provide and the importance of long-term studies for comprehending the processes involved in biodiversity changes within urban areas over time. Undoubtedly, establishing long-term citywide surveys sampling birds and other biodiversity groups will allow us to better understand the response of biodiversity to urbanization over time.     

Persistence and survival of the spider <Emphasis Type="Italic">Nephila plumipes</Emphasis> in cities: do increased prey resources drive the success of an urban exploiter?

Species that successfully inhabit urban ecosystems are rare, and urbanisation often drives localised extinctions of native species. Nonetheless, some species take advantage of the novel conditions available in cities and increase in abundance. Trends in the abundance and distribution of species in urban areas have received much attention, but the precise elements of urban ecosystems that affect the survival of urban-dwelling species are largely unknown. Animals that successfully exploit urban environments may do so because of increases in the availability of resources or habitats. Here we assess the effects of anthropogenic landscapes and prey abundance on the persistence of an orb-weaving spider, Nephila plumipes. We assessed spider persistence for six months in situ along an urban gradient in Sydney. We then transplanted spiders from a common garden into sites along the gradient, monitored their persistence in the new environment and measured a suite of environmental variables at local and landscape scales. The abundance of prey was closely linked with spider persistence, in both the survey and the transplant experiment, and was positively associated with anthropogenic habitats. The surveyed spiders survived longer when located closer to the coast and transplanted spiders persisted longer in smaller sites with more impervious surfaces and reduced vegetation cover. Our study shows that urbanisation has a strong effect on potential prey abundance and can lead to increased persistence of N. plumipes, demonstrating the broad impacts that habitat disturbance can have on the life history and trophic interactions of city-dwelling animals.     

Food in a row: urban trees offer valuable floral resources to pollinating insects

Urbanization affects the availability and diversity of floral resources (pollen and/or nectar) for wild pollinating insects. For example, urban green areas are characterized by an abundance of ornamental plant species. Increasingly, trees are planted to improve the aesthetics of urban streets and parks. These urban trees might offer important floral resources to pollinating insects. To examine the suitability of urban trees as resources for pollinating insects, we investigated the chemical composition of pollen and nectar as well as the amount of nectar produced by the nine major insect-pollinated tree species planted in cities of Western Europe, namely Acer pseudoplatanus, Aesculus carnea, A. hippocastanum, Robinia pseudoacacia, Tilia cordata, T. x euchlora, T. x europaea, T. platyphyllos and T. tomentosa. The analyses revealed that globally the Tilia trees provide pollen with lower contents of polypeptides, amino acids and phytosterols compared with the other species. Urban tree flowers offer abundant nectar with relatively high sugar contents (0.16–1.28 mg/flower); sucrose was the predominant sugar in all nectars. The investigated tree species could therefore be considered in future city plantings.     

Are plant communities mainly determined by anthropogenic land cover along urban riparian corridors?

Often used as a mitigation tool to landscape fragmentation, urban riparian corridors also suffered from the effects of the urban expansion. This study explored the relationships between plant riparian communities and two major environmental variables (land cover, soil characteristics) and analyzed the floristic change along an urbanization gradient. Fifteen sites were surveyed on both riverbanks of two riparian corridors characterized by contrasting water regimes in Strasbourg, North Eastern France. Data of spontaneous species abundance was collected from 180 quadrats using (i) all plant species, (ii) herbaceous stratum and (iii) ligneous stratum (bush and tree). The diversity and compositional patterns of riparian plant species were analyzed within each corridor according to three levels of urbanization (urban, suburban, peri-urban). Relationships between riparian communities, land cover and soil chemical properties (pH, nitrogen and carbon content, moisture) were established by between-class co-inertia analyses. Land cover emerged as the main factor explaining changes in riparian communities along the rural–urban gradient while soil chemical properties discriminate water stress and fluvial dynamics of the two corridors. Similar compositional patterns were found within the most urbanized sites with the establishment of ubiquitous species. The herbaceous stratum is best linked to the level of urbanization, whereas the tree stratum is primarily correlated with corridor attributes (hydrological regime, soil properties). Although riparian species and communities are mainly determined by land cover, urban riparian corridors maintain native biodiversity up to the urban center.     

Demography of a ground nesting bird in an urban system: are populations self-sustaining?

Urbanization poses threats to earth’s biota, and retention of remnant native habitat in protected areas within expanding urban boundaries may help alleviate threats to wildlife. However, it is unclear for nearly all nonsynanthropic (i.e., not benefiting from an association with humans) species whether vital rates in urban habitats can sustain populations or if populations persist only through immigration from outside the urban boundary. We conducted a three-year study of spotted towhees (Aves: Pipilo maculatus) breeding in four undeveloped parks in Portland, OR, USA, to measure park-specific seasonal reproductive output (F) and annual adult survival (S_A). We developed a stochastic model that combined F and S_A with an estimate of first-year survival to measure population growth rate (λ) in all parks assumed to be closed to immigration. F differed among parks but S_A did not. Relatively high F was possible because many pairs raised >1 brood/season. When combined with empirical estimates of survival through the 30-day period of post-fledging parental care (S_D = 0.645), only 2 of 4 parks were self-sustaining (i.e., λ > 1.0). However, S_D reflected substantial loss of fledglings to domestic cats (Felis catus). Assuming no loss to cats and either partial compensatory or additive mortality of fledglings substantially improved prospects of population persistence for declining (sink) populations. Moreover, allowing low levels of immigration to sinks reversed population declines in most parks even when vital rates were insufficient to maintain populations. Our results suggest that nonsynanthropic bird species can persist in urban landscapes, but also that offspring mortality in the post-fledging period may be a critical determinant of population viability.