Diversity and assemblage filtering in ground-dwelling spiders (Araneae) along an urbanisation gradient in Denmark

Urban Ecosystems - We studied the effects on spiders of a three-step rural-urban urbanisation gradient near a Danish town embedded in a historically forested landscape. Using pitfall traps set in...     

Trends in bird species richness,abundance and biomass along a tropical urbanization gradient

Impacts of urbanization on biodiversity are commonly studied using urbanization gradients which provide a space-for-time substitution in estimating consequences of urban expansion. Rates of urbanization and human population growth are high in tropical countries of the developing world, which also hold most of the world’s biodiversity hot-spots, yet few studies have considered biodiversity trends along urban gradients in these regions. Bird communities across a gradient of nine sites in Uganda, from the city centre of Kampala to outlying rural locations, were studied over a six year period. These sites were ordered along an urbanization gradient using Principle Components Analysis based on habitat variables estimated at each site. Bird species richness showed a decrease from rural to urban sites, a trend especially evident in forest birds. There was no clear pattern in total abundance, total biomass or biomass per individual along the gradient. However, this latter result was heavily influenced by a colony of Marabou Storks at one site. When this species was omitted, there was evidence of a positive trend with urbanization, showing that as species richness decreased, the bird community was increasingly dominated by larger species with increasing urbanization, which were mainly scavengers able to exploit human refuse. These results provide further support for the negative impacts of urbanization on species richness, but also demonstrate trends in abundance and biomass are variable across different regions. In particular, the increasing dominance of larger species in urban areas may be relevant to certain geographic and/or socioeconomic contexts.     

Dispersal-related traits of the snail Cornu aspersum along an urbanisation gradient: maintenance of mobility across life stages despite high costs

Urban Ecosystems - The extreme fragmentation of natural habitats due to urbanisation can influence the evolution of dispersal strategies in species persisting in cities. The brown garden snail...     

Analysis of breeding bird communities along an urban-rural gradient in Berlin,Germany, by Hasse Diagram Technique

Breeding bird communities in Berlin were investigated at five study sites, which represent an structural urban-rural gradient, from densely built-up areas with sealed ground to green areas such as large parks. In this paper, we tested the Hasse Diagram Technique (HDT), an approach belonging to partial order theory, for its appropriateness to extract information about changes in species composition from our data set. As expected, the overall number of bird species was positively correlated with the urban-rural gradient, increasing from 12 found in the city center to 28 in an urban park. By HDT analysis, four different sub-groups of birds could be identified, contributing differentially to the increase in species number: (1) ubiquists, i.e., species found at each study site, (2) a sub-group, the species’ number of which was positively correlated with the urban-rural gradient, increasing with increasingly green areas, (3) a sub-group, the species’ number of which was negatively correlated with the urban-rural gradient, decreasing with a declining density of buildings, and (4) species, the distribution of which did not show any correlation with the urban-rural gradient. The results show that HDT is a suitable tool for formalized analysis of the pattern of species’ communities along an environmental gradient.     

Forest bird communities across a gradient of urban development

This study examined native bird communities in forest patches across a gradient of urbanization. We used field data and multivariate statistical techniques to examine the effects of landscape context, roads, traffic noise, and vegetation characteristics on bird community composition in the North Carolina Piedmont (U.S.A.). Landscape-level variables, particularly those related to urbanization, were most important in structuring forest bird communities. Specifically, we found that road density and amount of urban land cover were the best predictors of species composition. We found that urban and rural bird communities were quite distinct from each other. Rural communities had more long-distance migrants and forest interior species but species richness did not differ between the communities. Our results suggest some specific guidelines to target bird species of interest both inside and outside of urban areas. For example, if increasing numbers of migratory species is of primary concern, then conservation areas should be located outside of urban boundaries or in areas with low road density. However, if maximizing species richness is the focus, location of the conservation area may not be as important if the conservation area is surrounded by at least 50 m of forest habitat in all directions.     

Understory plant species composition in remnant stands along an urban-to-rural land-use gradient

We examined the understory species composition of 24 remnant forest stands along an urban-to-rural gradient in the metropolitan Milwaukee, Wisconsin region to determine the relationships between plant community composition, human disturbance, and contrasting types of land use along a gradient of urbanization. A significant difference was found in shrub species community composition among three contrasting land-use categories but no significant difference was found in herbaceous community composition. Significant differences in human activity existed among rural, urban, and urbanizing land-use categories, but this index of disturbance was not significantly correlated to gradients in species composition. All stands in this study had been subjected to various types of human activity and environmental disturbances in the past. Our data suggest that differences in the relative importance of understory species exist among stands but these differences may not be caused by the impacts of urbanization alone. Changes in the natural disturbance regime of this landscape, along with the impacts associated with urbanization, have led to an individualistic response in the compositional dynamics of forest stands. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vascular plants along an urban-rural gradient in the city of Tampere,Finland

The aim of this study was to analyse the spatial distribution of vascular plants along a 21-kilometre rural–urban–rural transect in the city of Tampere, Finland. The study emphasised the distribution of native and non-native species, both in absolute numbers and proportionally. The observed differences are explained by the share of forest land, the number of detached houses, distance from the city centre, and human population. Non-natives showed the highest values in suburban areas. Still, the difference in number of non-natives between suburban and central areas was quite small. In the city of Tampere, there are not continuous large areas devoid of vegetation. The number of native species remained high until the urban core and natives dominated in the rural-type areas of the city. However, there was not a great difference in the number of native species between rural and suburban areas. In the suburban areas, the detached houses and block-of-flats have little effect on the general vegetation. Proportionally, the share of natives decreases in line with the urban traits of the city. Urbanisation therefore affects native species in Finland. Overall, the characteristic features of a Finnish city, such as dispersed urban structure, small population, late urbanisation, abundant natural vegetation (forest) and the qualities of Finnish forests, guarantee the continuing diversity of urban vascular plants.     

Bird and mammal use of vernal pools along an urban development gradient

Vernal pools in the northeastern US are of conservation concern primarily because of their role as habitat for specialized pool-breeding amphibians, but their use by birds and mammals may also be of interest, especially from the perspective of the impact of urbanization. We describe camera-trapped wildlife (CTW) at 38 vernal pools along an urban development gradient in greater Bangor, Maine, USA. We detected 20 mammal and 39 bird taxa (29 contacted pool water; 39 detected at >1 site). Land cover type within 1000 m (%), within-pool vegetation (%), and amphibian egg mass numbers explained a substantial portion of the variance (40.8%) in CTW assemblage composition. Submerged vegetation within pools and cover by water and impervious surfaces within 1000 m of pools were key site characteristics defining assemblages. We scored the urban-affiliation of taxa and modeled the relationship between weighted assemblage scores for each site and impervious cover. Impervious cover within 1000 m of pools was positively (p?<?0.01) related to site urban-affiliation scores. Use probability for red fox increased and snowshoe hare decreased with impervious cover at 1000 m. These results indicate that within-pool vegetation and land cover types at 1000 m influenced bird and mammal assemblages that used study pools and greater impervious cover at 100 and 1000 m was correlated with a shift in assemblages from being dominated by urban-avoider to urban-adapted species. We encourage land use planners and managers to consider the influence of land use practices within 1000 m of vernal pools on birds and mammals, especially near amphibian breeding pools.     

High species turnover shapes anuran community composition in ponds along an urban-rural gradient

Urban Ecosystems - The rapid expansion of urban areas in which natural and semi-natural areas are replaced by human infrastructure, is a major threat to biodiversity worldwide. However, little is...     

Litter decomposition and nitrogen mineralization in oak stands along an urban-rural land use gradient

We investigated litter mass loss and soil nitrogen (N)-transformation rates in oak stands along a 130-km, urban-rural transect originating in New York City to examine the relationship between changes in these parameters and previously documented differences in soil temperature, heavy metal and total salt concentrations, and soil biota. Reference litter from a rural site was placed in litterbags, and rates of mass loss and changes in N concentration in litter residues were measured over a 6-month period. Net N-mineralization and nitrification rates were measured in A horizon soils using laboratory incubations under constant moisture and temperature. Both mass loss (76%) and N release (65%) from litterbags reached their maximum in urban stands, whereas net N-mineralization rates were 2.3-fold higher than in rural A horizon soils. Litter fragmentation by earthworms and higher soil temperatures are potential causes of the higher mass loss rates observed in urban stands. The higher releases of N measured in the urban litterbags could be a result of their faster mass loss rates, exogenous inputs of N from atmospheric deposition, a relatively low heterotrophic demand for N, or a combination of these factors. The results of this study suggest that in comparison with rural stands, urban forests are characterized by comparatively high rates of litter decomposition, and may also be characterized by comparatively high rates of N mineralization. Additional studies are needed to test whether these effects are common to urban environments in general.     

Raptor nesting locations along an urban density gradient in the Great Basin,USA

Raptors are the most prevalent group of urban apex predators, and the majority of raptor genera in North America have been recorded using urban areas. Prior research assessments along urban-wildland gradients show that urban habitat preference varies by raptor species and that raptor nesting preferences within urban settings may vary. Attempts to understand the intra- and inter-specific nesting patterns along an urban gradient would advance extant knowledge. Here we present the locations of individual nest sites of nine raptor species along an urban gradient in Reno-Sparks, NV. We developed an urban density model based on the number of residents, number of employees, and building footprints and number of floors for built structures within each land parcel at four spatial scales, representing nest site, macrohabitat, average nearest-nest, and landscape scales. Cooper’s Hawks (Accipiter cooperii), Sharp-shinned Hawks (Accipiter striatus), and Red-tailed Hawks (Buteo jamaicensis) nested across the widest range of the urban spectrum and closest to the urban core, whereas Golden Eagles (Aquila chrysaetos) and Swainson’s Hawks (Buteo swainsonii) nested on the urban fringe. Urban density for all nest locations was lowest at the nest-site scale, and the highest at the average nearest-nest and landscape scales. Raptors tended to occupy a wide range of the building-area density spectrum but not the building-height or employee density spectrums indicative of the attractiveness of suburban habitat.

     

Allometry and photosynthetic capacity of poplar (Populus deltoides) along a metal contamination gradient in an urban brownfield

The value of urban green space has become an increasingly controversial issue. In particular, development of novel vegetative assemblages on vacant lands may have many formerly unrecognized benefits. However, questions remain regarding the functional impairment of these assemblages due to degraded soils. We investigated the effects of elevated concentrations of soil metals on allometry and photosynthetic capacity of naturally colonized poplars (Populus deltoides Michx.) growing at Liberty State Park, New Jersey. We found that allometries of harvested trees did not differ significantly between the low metal load (LML) and high metal load (HML) sites suggesting that metal contamination did not negatively affect carbon allocation patterns of the target species. Likewise, photosynthetic parameters did not differ significantly between the LML and HML sites, suggesting that soil metal contamination did not negatively affect photosynthetic capacity. However, trees from the LML site were significantly younger for a given size than trees from the HML site. Trees from the medium metal load site (MML) differed significantly in allometry and photosynthetic parameters from the other two sites suggesting other edaphic and ecological factors are a stronger driver for carbon allocation patterns and photosynthetic capacity in these trees. Taken together, this research suggests that sapling establishment and growth may be impaired by heavy metals and that trees in HML sites may incur more maintenance costs than trees in LML sites. However, given enough time, poplars can provide considerable rehabilitation of urban brownfields, particularly those that exhibit soil metal contamination.     

Biodiversity of ant species along a disturbance gradient in residential environments of Puerto Rico

One of the most effective ways to describe the successional gradient of an environment is by using measures of biodiversity. We investigated the biodiversity of ant communities (known tramp/structure invaders) in an environment undergoing urban succession to characterize how ant communities changed along a disturbance gradient. Ant community dynamics were examined within three Puerto Rican housing developments of different ages. Within each development, we assessed the ant community using biodiversity measures of richness, abundance, diversity and evenness. We also studied changes in biodiversity within each development over time as well as how biodiversity related to food preferences within the ant communities. In general, the biodiversity measures increased as the age of the housing development increased. Monthly changes in biodiversity indicated that month was a better predictor of biodiversity in the most recently disturbed development, while the biodiversity in the older developments was less predictable from month to month. The biodiversity measures also suggested that the ant community in the youngest development was comprised mostly of generalist feeders. However, the older sites’ ant species appeared to have more specific feeding preferences. Based on the biodiversity measures of these ant communities, our findings suggest that the housing developments of different ages represented advancing stages of secondary succession. Furthermore, this study indicated that the succession of ant species occurs rapidly (<10 years) in urban environments, resulting in a relatively diverse ant community.     

Intimate Partner Violence: Modifying an Internet-Based Safety Decision Aid to a New Zealand Context

Women experiencing intimate partner violence face complex decisions in navigating their safety. In a feasibility study, we examined the suitability of an intimate partner violence interactive online decision aid developed in the United States for its application in New Zealand, particularly with regard to cultural appropriateness. We conducted focus group sessions with women who experienced partner violence and focus group sessions with service providers. Women completed the U.S. online decision aid tool and provided feedback on the safety decision criteria, content, and design. Considering the findings from the focus group sessions the decision aid was modified. We reflect on the process of balancing women's stories with technical limitations and constraints of a replication study.     

The effect of artificial light on bat richness and nocturnal soundscapes along an urbanization gradient in an arid landscape of central Peru

Urbanization usually reduces bat richness; however, the presence of green areas within cities and peripheral rural areas in arid ecosystems may provide microhabitats for some species. Light pollution is a major feature of urbanization, but its impact on bat behavior appears to be species-specific and previous studies have documented contrasting responses. Moreover, the effect of urbanization on bat species has been poorly studied in arid regions. We assessed the effect of artificial night light intensity (as a proxy of urbanization) on both bat occupancy and the acoustic space used (ASU) in an urbanization gradient in Peruvian central coast, based on passive acoustic recorders. We collected 26,169 recordings from 19 sites which resulted in 579 independent detections of 15 bat species. Variation in both ASU and species richness was best explained by artificial night light intensity. Species-specific effects of the artificial night light intensity based on a multi-species occupancy modeling showed that this covariate had a negative effect on occupancy for most of the bat species (12 species). ASU and both observed and posterior bat species richness were positively correlated, suggesting that ASU can be used as a proxy of bat richness. This study provides evidence that both bat richness and occupancy decrease with artificial light intensity; nevertheless, eight species used urban areas, similar to results found in other cities around the world.

     

Short- and long-term effects of site factors on net N-mineralization and nitrification rates along an urban-rural gradient

Long- and short-term effects of urban site factors on net N-mineralization and nitrification rates were investigated in oak stands along an urban-rural land-use transect in the New York City metropolitan area. We used reciprocal transplants of undisturbed soil cores between urban and rural forests to determine the relative importance of long-term effects (mor vs. mull soils, quality of soil organic matter, and deposition of N) vs. short-term effects (soil temperature) of urban factors in controlling field N-transformation rates along the gradient. In addition, undisturbed soil cores from surface (A, Oe horizons) and subsurface (B horizon) soil were collected from urban, suburban, and rural stands and allowed to incubate in these respective sites to compare the net effect of all urban factors with transplanted-core results. The transplant experiment revealed that soil type (long-term) affected net N-mineralization and nitrification rates. Urban soils nitrified nearly 6.3 and 5.4 times more than rural soils incubating in urban and rural stands, respectively (p = 0.003 and p = 0.002, respectively). Similarly, in rural stands total accumulation of inorganic N was 87% higher in urban than in rural soils, whereas in urban stands, urban soils mineralized 83% more N than rural soils (p = 0.043 and 0.08, respectively). Comparing soils incubating in their native locations, urban soils incubating in urban stands mineralized more than 2.5 times the amount of N than rural soils incubating in the rural stands (p = 0.019). By contrast, urban soils incubating in urban stands exhibited a 8-fold increase in nitrification over rural soils incubating in rural stands (p = 0.008). As with the transplanted cores, the urban and suburban environments had a positive effect on net rates of N-mineralization and nitrification in both surface and subsurface layers of soil. The surface layer of suburban and urban stands had a 3- and 2.3-fold higher accumulation of net inorganic N than rural stands (ANOVA, p = 0.05). Similarly, in the subsurface layer both urban and suburban stands had 2.6-fold higher net N-mineralization rate than rural stands (ANOVA, p = 0.01). Along this urban-rural gradient, soils in oak stands exhibit higher net nitrification and, to a lesser extent, net N-mineralization rates in urban and suburban stands than in rural stands. Results from the transplant experiment and in situ measurements of surface and subsurface soil indicate that long-term effects (mor vs. mull soils, N deposition) contribute to the higher N-transformation rates in urban and suburban stands. As a result of these effects, urban and suburban stands have the potential for higher losses of N than rural stands.     

Changes in risky gambling prevalence among a New Zealand population cohort

Evidence suggests that problem gambling is an unstable state where gamblers move into and out of risk over time. This article looks at longitudinal changes in risky gambling and the factors associated with an increased risk (measured by the Problem Gambling Severity Index [PGSI]) in the current New Zealand context, which has experienced a doubling of the electronic gaming machine (EGM) market over the last two decades. Respondents from a nationally representative baseline sample (n = 2672) were recontacted two years later to assess changes in gambling behaviours. Among the 901 respondents reached at follow-up, average gambling risk increased over time, and the prevalence of those who had at least some level of gambling risk (i.e. low-risk or greater) more than doubled (from 4.7% to 12.4%). The majority (80.2%) of those who were at risk at follow-up had not been at risk at baseline. Multivariate linear regression analyses show that the predictors of low to moderate increased risk include Pacific ethnicity; high neighbourhood deprivation status; baseline frequent, continuous gambler type; baseline PGSI status; and playing EGMs. These findings highlight the need to develop theories of gambling addiction trajectories and to identify the earliest point along the trajectory where public health interventions should occur.     

Composition of the plant community in remnant patches of grassy woodland along an urban–rural gradient in Melbourne,Australia

The composition of the plant community in remnant patches of open grassy woodlands with an overstorey of Eucalyptus camaldulensis was investigated along an urban–rural gradient in Melbourne, Australia. The plant community showed very little difference between patches along the gradient, particularly in terms of the indigenous plant species. Average annual rainfall was the main factor contributing to patterns of indigenous plant species richness, while the level of urbanization in the surrounding landscape had a strong influence on the number of non-indigenous species recorded in the remnant plant community. Patterns of species richness were largely influenced by landscape-scale factors, while the percent cover of indigenous and non-indigenous plant species were more strongly influenced by patch scale factors. The findings of this study suggest that the plant communities investigated during this study appear to be relatively resilient to changes in the landscape associated with urbanization, but the plant community may be affected by predicted changes in average annual rainfall associated with climate change.