Effects of urbanisation on the parasitoid community of a leafminer

Urbanisation may have detrimental effects on communities of parasitoids, affecting their species richness, abundance, and species dominance. Here we investigated the influence of the degree of urbanisation on parasitoid communities of Liriomyza commelinae (Frost) (Diptera: Agromyzidae), a leafminer of Commelina erecta L. (Commelinaceae), in the city of Córdoba, Argentina. To study changes in species richness, the specific composition of parasitic complexes and their degree of impact on the leafminer, 18 sampling sites from the centre to the outskirts of the city were selected and different variables indicative of urbanisation were quantified in each site. During January and February of 2005 and 2006, all mined leaves found in each plant patch were collected and the following variables were estimated: proportion of mined patches, abundance of the leafminer, total parasitoid species richness, total parasitism rates and parasitism due to the most abundant parasitoid species. The percentage of mined patches and leafminer abundance increased with urbanisation degree. Estimates of parasitoid species richness were not influenced by urbanisation degree but increased with species richness of mined plants. Changes in the specific composition of species along the urbanisation gradient were observed. Although parasitism by one of the species studied was higher in more urbanised sites of the city, the total parasitism rate of L. commelinae was not affected by urbanisation degree, species richness of mined plants or leafminer abundance. It appears that urbanisation benefits the herbivore species here studied but not through altering parasitoid activity. Changes in parasitoid community composition reflex dissimilar tolerance to environmental conditions displayed by different parasitoid species.     

Monitoring urban environments on the basis of biological traits

Urbanization induces changes in species abundance and richness that are beginning to be extensively described. However, the functional structure of urban communities still requires attention to provide a basis for a more accurate understanding of urban ecosystems’ functioning. This study has been performed in order to assess functional changes in ecological communities related to changes of urban landscape features along an urbanization gradient. Species abundance and richness of birds and butterflies in the city parks of Marseille (south-east France) have been used to assess these changes. On the basis of easily accessible traits (reproduction parameters, size, feeding habits), we have examined whether different contexts of urbanization favour some strategies more than others. Some differences occur between butterflies and birds in terms of species abundance and richness through the urbanization gradient, showing that at least some species of birds manage to colonize city centre and/or exploit urban resources better than butterflies. But our results also clearly reveal general patterns in biological traits for both birds and butterflies that further reflect the gradient of urban features from outskirts to city centre. Species associated with the city centre tolerate a wide range of conditions whereas species associated with city outskirts have more specialized abilities. Urbanization acts as an environmental filter for bird and butterfly communities selecting species able to colonize and settle in the city centre on the basis of their biological traits. In our context, environmental filters induce a biotic homogenization with urbanization through loss of species (taxonomic homogenization) and over-representation of generalist species (functional homogenization). This homogenization reflects an underlying process of disruption of biotic interactions for butterflies and birds. This study has enabled us to identify a combination of biological traits sensitive to urban features that may represent useful indicators for both theoretical and applied purposes in order to understand the impact of urbanization on animal communities.     

Bird Richness and Abundance in Response to Urban Form in a Latin American City: Valdivia,Chile as a Case Study

There is mounting evidence that urban areas influence biodiversity. Generalizations however require that multiple urban areas on multiple continents be examined. Here we evaluated the role of urban areas on avian diversity for a South American city, allowing us to examine the effects of urban features common worldwide, using the city of Valdivia, Chile as case study. We assessed the number of birds and their relative abundance in 152 grid cells of equal size (250 m²) distributed across the city. We estimated nine independent variables: land cover diversity (DC), building density (BD), impervious surface (IS),municipal green space (MG),non-municipal green space (NG), domestic garden space (DG), distance to the periphery (DP), social welfare index (SW), and vegetation diversity (RV). Impervious surface represent 41.8% of the study area, while municipal green, non-municipal green and domestic garden represent 11.6%, 23.6% and 16% of the non- man made surface. Exotic vegetation species represent 74.6% of the total species identified across the city. We found 32 bird species, all native with the exception of House Sparrow and Rock Pigeon. The most common species were House Sparrow and Chilean Swallow. Total bird richness responds negatively to IS and MG, while native bird richness responds positively to NG and negatively to BD, IS DG and, RV. Total abundance increase in areas with higher values of DC and BD, and decrease in areas of higher values of IS, SW and VR. Native bird abundance responds positively to NG and negatively to BD, IS MG, DG and RV. Our results suggest that not all the general patterns described in previous studies, conducted mainly in the USA, Europe, and Australia, can be applied to Latin American cities, having important implications for urban planning. Conservation efforts should focus on non-municipal areas, which harbor higher bird diversity, while municipal green areas need to be improved to include elements that can enhance habitat quality for birds and other species. These findings are relevant for urban planning in where both types of green space need to be considered, especially non-municipal green areas, which includes wetlands, today critically threatened by urban development.     

Spider communities in urban green patches and their relation to local and landscape traits

Urbanization and urban landscape characteristics greatly alter plant and animal species richness and abundances in negative and positive directions. Spiders are top predators, often considered to be sensitive to habitat alteration. Studies in urban environments frequently focus on ground-dwelling spiders or on spiders in built structures, leaving aside foliage spiders. Effects of habitat, landscape type and structure and local characteristics on spider species composition, richness and relative abundance were evaluated in urban green patches in a temperate city of South America. We also assess whether Salticidae could be an indicator group for the broader spider community in the urban environment. Spiders were sampled with a G-VAC (aspirator) in urban green patches in Córdoba city, Argentina, in urban, suburban and exurban habitats (18 sites; six per habitat) and local and landscape traits were assessed. Overall, the exurban was richer than the urban habitat, however, at the site level Salticidae richness and abundance (but not the total spider assemblage) were significantly lower in urban sites. Species composition moderately differed between urban and exurban sites. Results indicate that on urban green spaces a low impervious surface cover, a coverage of trees, herbaceous vegetation and a vertical structure of vegetation at least up to 1 m in height contribute to higher richness and abundance of spiders, Salticidae being more sensitive than the overall spider community to local effects. In addition, Salticidae richness can predict 74% of the total spider richness recorded and may be used as spider diversity bio-indicators in this climatic region.     

Decreasing Abundance,Increasing Diversity and Changing Structure of the Wild Bee Community (Hymenoptera: Anthophila) along an Urbanization Gradient

Background

Wild bees are important pollinators that have declined in diversity and abundance during the last decades. Habitat destruction and fragmentation associated with urbanization are reported as part of the main causes of this decline. Urbanization involves dramatic changes of the landscape, increasing the proportion of impervious surface while decreasing that of green areas. Few studies have investigated the effects of urbanization on bee communities. We assessed changes in the abundance, species richness, and composition of wild bee community along an urbanization gradient.

Methodology/Principal Findings

Over two years and on a monthly basis, bees were sampled with colored pan traps and insect nets at 24 sites located along an urbanization gradient. Landscape structure within three different radii was measured at each study site. We captured 291 wild bee species. The abundance of wild bees was negatively correlated with the proportion of impervious surface, while species richness reached a maximum at an intermediate (50%) proportion of impervious surface. The structure of the community changed along the urbanization gradient with more parasitic species in sites with an intermediate proportion of impervious surface. There were also greater numbers of cavity-nesting species and long-tongued species in sites with intermediate or higher proportion of impervious surface. However, urbanization had no effect on the occurrence of species depending on their social behavior or body size.

Conclusions/Significance

We found nearly a third of the wild bee fauna known from France in our study sites. Indeed, urban areas supported a diverse bee community, but sites with an intermediate level of urbanization were the most speciose ones, including greater proportion of parasitic species. The presence of a diverse array of bee species even in the most urbanized area makes these pollinators worthy of being a flagship group to raise the awareness of urban citizens about biodiversity.     

Warm-temperate, immense, and sprawling: plant diversity drivers in urban Beijing, China

Urbanization is one of the most environmentally damaging of human activities, producing large alterations in ecosystem structure, function, species composition and interactions. In this study, we performed a systematic investigation of the plant species richness and density in the city of Beijing, China. We also assessed which socio-economic factors have most influence on plant diversity. Within the city, we found 551 plant species of 313 genera and 103 families, of which 118 were trees, 99 shrubs, and 296 herbs. Nearly half (48.3?%) of the total plant species were aliens. Species richness and density were positively correlated both for tree/shrub and herb taxa, which indicate that although some species predominate in our study area, there is an important array of species in relation to their densities. As expected, most of the socio-economic variables studied showed to be related to at least one of the four plant diversity variables (i.e., herb richness, herb density, tree/shrub richness, and tree/shrub density). Land-use showed a significant relationship in all four cases, which generally had lower values in cultural and education areas (areas that in Beijing are generally characterized by large extensions of urbanized land). The year of establishment was also largely related to plant diversity, with higher values for recently developed areas. This was an expected result given the dynamics of the urban development of Beijing during the last 60?years, which consisted of intense urban sprawling, followed by more environmentally-friendly urbanization practices during the 2000s related to the greening of the city for the olympic games. This dynamics also explained the negative relationship found between the distance to the city center and both tree/shrub species richness and density.     

Contrasting patterns in species richness of birds,butterflies and plants along riparian corridors in an urban landscape

Aim Urbanization is a major driver of global land‐use change, substantially modifying patterns of biodiversity. Managing these impacts has become a conservation priority. The creation and maintenance of greenways, such as river corridors, is frequently promoted as a strategy for mitigating habitat fragmentation in urban areas by bringing semi‐natural habitat cover into city centres. However, there is little evidence to support this assertion. Here, we examine whether riparian zones maintain semi‐natural habitat cover in urban areas and how species richness varies along such zones. Location Sheffield, Northern England. Methods Multiple taxonomic groups (birds, butterflies, plants) were surveyed at 105 sites spanning seven riparian corridors that transect the study system. For all groups, we model the relationships between species richness and environmental variables pertinent to an urban system. To test whether riparian zones can act to maintain semi‐natural habitats within a city, we modelled the proportion of semi‐natural land cover within 250 m grid squares that do, and do not, contain a river. Results Species richness varied markedly in relation to distance from the urban core. Trends differed both between taxonomic groups and between rivers, reflecting the complex patterns of environmental variation associated with cities. This suggests that biodiversity surveys that focus on a single group or transect cannot reliably be used as surrogates even within the same city. Nonetheless, there were common environmental predictors of species richness. Plant, avian and butterfly richness all responded positively to Habitat Diversity and the latter two declined with increases in sealed surface. Main conclusions Multiple transects and taxonomic groups are required to describe species richness responses to urbanization as no single pattern is evident. Although riparian zones are an important component of the mosaic of urban habitats, we find that river corridors do not disproportionately support tree and Natural Surface Cover when compared to non‐riverine urban areas.     

Native and alien floras in urban habitats: a comparison across 32 cities of central Europe

Aim To determine relative effects of habitat type, climate and spatial pattern on species richness and composition of native and alien plant assemblages in central European cities. Location Central Europe, Belgium and the Netherlands. Methods The diversity of native and alien flora was analysed in 32 cities. In each city, plant species were recorded in seven 1‐ha plots that represented seven urban habitat types with specific disturbance regimes. Plants were classified into native species, archaeophytes (introduced before ad 1500) and neophytes (introduced later). Two sets of explanatory variables were obtained for each city: climatic data and all‐scale spatial variables generated by analysis of principal coordinates of neighbour matrices. For each group of species, the effect of habitat type, climate and spatial variables on variation in species composition was determined by variation partitioning. Responses of individual plant species to climatic variables were tested using a set of binomial regression models. Effects of climatic variables on the proportion of alien species were determined by linear regression. Results In all cities, 562 native plant species, 188 archaeophytes and 386 neophytes were recorded. Proportions of alien species varied among urban habitats. The proportion of native species decreased with increasing range and mean annual temperature, and increased with increasing precipitation. In contrast, proportions of archaeophytes and neophytes increased with mean annual temperature. However, spatial pattern explained a larger proportion of variation in species composition of the urban flora than climate. Archaeophytes were more uniformly distributed across the studied cities than the native species and neophytes. Urban habitats rich in native species also tended to be rich in archaeophytes and neophytes. Main conclusions Species richness and composition of central European urban floras are significantly affected by urban habitat types, climate and spatial pattern. Native species, archaeophytes and neophytes differ in their response to these factors.     

The proportion of impervious surfaces at the landscape scale structures wild bee assemblages in a densely populated region

Given the predicted expansion of cities throughout the world, understanding the effect of urbanization on bee fauna is a major issue for the conservation of bees. The aim of this study was to understand how urbanization affects wild bee assemblages along a gradient of impervious surfaces and to determine the influence of landscape composition and floral resource availability on these assemblages. We chose 12 sites with a proportion of impervious surfaces (soil covered by parking, roads, and buildings) ranging from 0.06% to 64.31% within a 500 m radius. We collected using pan trapping and estimated the landscape composition of the sites within a 500 m radius and the species richness of plant assemblages within a 200 m radius. We collected 1104 bees from 74 species. The proportion of impervious surfaces at the landscape scale had a negative effect on wild bee abundance and species richness, whereas local flower composition had no effect. Ground‐nesting bees were particularly sensitive to the urbanization gradient. This study provides new evidences of the impact of urbanization on bee assemblages and the proportion of impervious surfaces at the landscape scale emerged as a key factor that drives those assemblages.     

Structure of Littoral-zone Fish Communities in Relation to Habitat, Physical, and Chemical Gradients in a Southern Reservoir

How the distribution and abundance of organisms vary across environmental gradients can reveal factors important in structuring aquatic communities. We sampled the littoral-zone fish community in a large reservoir (Lake Texoma) on the Texas–Oklahoma (U.S.A.) border that has pronounced environmental gradients from up- to downlake and between major tributary arms. Our objective was to evaluate the predictability of the littoral-zone fish-community structure from a suite of environmental variables. A stepwise multiple-regression model, with environmental factors at independent variables, explained 64% of the variation in fish species richness across sample sites. The number of species was positively associated with water-column productivity and total Kjedahl nitrogen, and negatively associated with Secchi depth and benthic productivity. Canonical correspondence analysis, with environmental factors as independent variables, explained 63% of the variation in fish-community structure across sites. Equal proportions of the variation in community structure were explained by variables that have strong gradients within the reservoir (e.g., Secchi depth and water-column productivity) and those that represent local habitat variables (e.g., shoreline aspect and substrate type).     

Relationship Between Testate Amoeba (Protist) Communities and Atmospheric Heavy Metals Accumulated in <Emphasis Type="Italic">Barbula indica</Emphasis> (Bryophyta) in Vietnam

We studied the relationships between testate amoeba communities and heavy metal (Pb, Cd, Zn, Ni, Cu, Mn, and Fe) concentrations in the moss Barbula indica sampled at 29 sites in and around the city of Hanoi (Vietnam). Our first approach was to compare the heavy metal concentrations and testate amoeba variables between the city (zone 1) and the surrounding (zone 2). Mean moss concentrations of Pb, Cd, Zn, Ni, and Cu were significantly higher and testate amoeba species richness and abundance were significantly lower in zone 1 and the abundance of eight taxa differed significantly between the two zones. We then studied the correlation between heavy metals and testate amoebae. Species richness and abundance were correlated negatively to Pb concentration. Shannon H′ was negatively correlated to both Pb and Cd. The abundance of several species was negatively correlated with Pb, Cd, Zn, and Ni; however, at the community level, Pb emerged as the only significant variable in a redundancy analysis. Our results suggest that testate amoebae are sensitive to and may be good bioindicators for heavy metal pollution, especially lead. Further research is needed to understand the causal relationships underlying the observed patterns.     

Wild bee species abundance and richness across an urban–rural gradient

Long-term and widespread monitoring programs are essential to understanding the role of human-dominated landscapes in supporting wild bee populations. Urbanization results in increased impervious surfaces throughout the landscape, fragmentation of green space, and a loss of naturally occurring floral vegetation. All of these changes have a negative impact on pollinator diversity. The objective of this study was to assess the abundance and richness of wild bee species throughout a small city in northwest Pennsylvania and identify how management of land throughout the city may influence bee communities. Seventeen sites across a land use gradient, moving from areas with large open spaces and mainly permeable surfaces, to sites in the city center consisting of mainly impermeable surfaces, were sampled over a 2-year period. During this time, 106 known species were identified with four state records and 1 undescribed species. Bee species richness was greatest at sites with the largest amount of permeable surface and naturally-occurring, native vegetation. Richness decreased on the college campus and city center where landscapes were highly managed and impermeable surfaces were most abundant. While floral richness was not related to bee abundance and richness, the number of open blooms near traps did have a positive impact on bee species richness. Overall, this survey revealed considerable richness never before recorded for northwest Pennsylvania, suggesting the importance of conservation management in homeowner and community yard space.     

Urban domestic gardens (VI): environmental correlates of invertebrate species richness

Domestic gardens associated with residential zones form a major component of undeveloped land in towns and cities. Such gardens may play a vital role in maintaining biodiversity in urban areas, but explanations for the variation in the richness of species assemblages in gardens are lacking. We report the results from a case study of 12 invertebrate groups in 61 domestic gardens in the city of Sheffield, UK. The mean number of species within a taxon, recorded per garden, was no greater than 3, 10, and 20 species in litter, pitfall trap and Malaise trap samples, respectively. Relatively speciose groups exhibited high turnover between gardens, with typically 50% of the group occurring only once. In contrast, several species-poor taxa were virtually ubiquitous. Species richness was analysed by multiple regression and hierarchical tree analysis in relation to garden and landscape variables. In general, the two methods of analysis corroborated one another. In total, 22 explanatory variables entered into regression models, although 12 of them only did so once. The amount of variation in species richness explained in models was generally quite high, with the factors involved operating over a range of scales. However, the patterns that emerged were not consistent across taxa. The most important predictors of species richness, of relevance to land use planners, were components of garden vegetation, especially the abundance of trees. Likely reasons for inconsistencies in the relationships are discussed in the context of sampling and species biology.     

Assessing the impact of local habitat variables and landscape context on riparian birds in agricultural,urbanized, and native landscapes

Large tracts of natural habitat are being replaced by agriculture and urban sprawl in Mediterranean regions worldwide. We have limited knowledge about the effects of human activities on native species in these landscapes and which, if any, management practices might enhance the conservation of native biodiversity within them. Through a citizen volunteer bird-monitoring project, we compared bird abundance and species richness in northern Californian riparian zones surrounded by vineyards, urban areas, and natural areas. We assessed both local and landscape-level variables that may enhance native bird diversity in each land use type. We also demonstrate a new statistical approach, generalized estimating equations, to analyze highly variable data, such as that collected by volunteers. Avian abundance was highly correlated with both landscape context and local habitat variables, while avian richness was correlated with local habitat variables, specifically shrub richness, and percent of tree cover. In particular, shrub species richness has a strong positive correlation with riparian-preferring bird species. This suggests that active local management of riparian zones in human-dominated landscapes can increase our ability to retain native bird species in these areas.     

Urban domestic gardens (VIII) : environmental correlates of invertebrate abundance

Domestic gardens associated with residential zones form a major component of vegetated land in towns and cities. Such gardens may play a vital role in maintaining biodiversity in urban areas, but variation in the abundance of organisms in gardens has been little explored. We report the results from a case study of 61 domestic gardens in the city of Sheffield, UK. Across 22 invertebrate groups, the median number of individuals recorded per garden was 49, 178, and 1012 in litter collections, pitfall and Malaise trap samples, respectively. Abundance was analysed by stepwise multiple regression and hierarchical tree analysis in relation to garden and landscape variables. The amount of variation explained in regression models ranged from 4 to 56%, for data based on pitfall and litter samples, and from 16 to 92% for data from Malaise traps. In total, 31 out of 36 explanatory variables entered into stepwise regression models, and 29 of them did so more than once. Although there was strong evidence only for approximately half of such relationships, in these cases the two methods of analysis corroborated one another. General correlates of invertebrate abundance were lacking, and likely reasons for inconsistencies in the relationships are discussed in the context of sampling and species biology. Correlates of the greatest significance occurred at both landscape (e.g. altitude) and garden scales (e.g. area of canopy vegetation). These factors were associated with species richness as well as abundance.     

Ants on a mountain: spatial, environmental and habitat associations along an altitudinal transect in a centre of endemism

Mountains are biodiversity hotspots and provide spatially compressed versions of regional and continental variation. They might be the most cost effective way to measure the environmental associations of regional biotic communities and their response to global climate change. We investigated spatial variation in epigeal ant diversity along a north–south elevational transect over the Soutpansberg Mountain in South Africa, to see to what extent these patterns can be related to spatial (regional) and environmental (local) variables and how restricted taxa are to altitudinal zones and vegetation types. A total of 40,294 ants, comprising 78 species were caught. Ant richness peaked at the lowest elevation of the southern aspect but had a hump-shaped pattern along the northern slope. Species richness, abundance and assemblage structure were associated with temperature and the proportion of bare ground. Local environment and spatially structured environmental variables comprised more than two-thirds of the variation explained in species richness, abundance and assemblage structure, while space alone (regional processes) was responsible for <10%. Species on the northern aspect were more specific to particular vegetation types, whereas the southern aspect’s species were more generalist. Lower elevation species’ distributions were more restricted. The significance of temperature as an explanatory variable of ant diversity across the mountain could provide a predictive surrogate for future changes. The effect of CO₂-induced bush encroachment on the southern aspect could have indirect impacts complicating prediction, but ant species on the northern aspect should move uphill at a rate proportional to their thermal tolerance and the regional increases in temperature. Two species are identified that might be at risk of local extinction.     

Macroclimate associated with urbanization increases the rate of secondary succession from fallow soil

To examine the impact of projected climate changes on secondary succession, we exposed the same fallow soil with a common seed bank to an in situ gradient of urban to rural macroenvironments that differed in temperature and CO₂ concentration ([CO₂]). This gradient was established at three locations: Baltimore city center (urban), a city park on the outskirts of Baltimore (suburban), and an organic farm 87 km from the Baltimore city center site (rural). Over a five-year period, the urban site averaged 2.1°C warmer and had a [CO₂] that was ~20% higher than at the rural location, indicating that this gradient was a reasonable surrogate for projected changes in those variables for this century. Previous work had demonstrated that other abiotic variables measured across the transect, including tropospheric ozone and nitrogen deposition, did not differ consistently. The first year of exposure resulted in (two- to threefold) greater aboveground biomass in the urban relative to the rural site, but with uniform species composition across sites. Simple regression of abiotic variables indicated that temperature and vapor pressure deficit (VPD) were the best predictors of plant biomass among locations. Stepwise multiple regressions were also performed to analyze the effect of more than one macroenvironmental variable on total plant biomass. The combination of daily CO₂ concentration and nighttime temperature explained 87% (P < 0.01) of the variability in total biomass between sites. After five years, the species demography of the plant communities had changed significantly, with a greater ratio of perennials to annuals for the urban relative to the rural location. Greater first-year biomass and litter accumulation at the urban site may have suppressed the subsequent seed germination of annual species, accelerating changes in species composition. If urban macroenvironments reflect future global change conditions, these data suggest a faster rate of secondary succession in a warmer, higher [CO₂] world.     

Garden bird feeding predicts the structure of urban avian assemblages

Households across the developed world cumulatively spend many millions of dollars annually on feeding garden birds. While beneficial effects on avian assemblages are frequently claimed, the relationships between levels of garden bird feeding and local avian populations are unknown. Using data from a large UK city, we show that both avian species richness and abundance vary across different socioeconomic neighbourhood types. We examined whether patterns in bird feeding could explain this variation. The density of bird feeding stations across the urban environment was strongly positively related to avian abundance, after controlling for differences in habitat availability. This effect was almost exclusively driven by the abundance of those species known to utilize garden feeding stations frequently. In contrast, the density of feeding stations had no effect on avian species richness. We also examined variation in the proportion of households in different communities that provide food for birds, a factor that is not correlated with feeder density. The prevalence of bird feeding across different neighbourhoods declined as socioeconomic deprivation increased, and increased with avian species richness and abundance. Our results suggest that the provision of supplementary food for birds by multiple landowners across a city can impact the status of urban bird populations. The potential for harnessing these actions for conservation needs to be explored.     

Urban sprawl and species movement may decimate natural plant diversity in an Afro-tropical city

Although urban sprawl is increasingly becoming a worldwide problem, the effects associated with urbanization on local biodiversity particularly in the developing countries, is still poorly understood. We investigated plant species richness along urban–rural gradients in an Afro-tropical metropolitan Morogoro city in Tanzania, and examined patterns of species movement by humans within and outside the city and its potential impact on habitat homogenization of urban ecosystems. Biodiversity information was assessed in 120 sample plots (25 × 25 m) distributed in core urban, sub-urban and peri-urban (rural) zones, while patterns of plant resource use and species movement were surveyed from 120 households in the study area. We found the highest tree species richness in the urban core (82.6 ± 1.4 species) whereas tree density decreased from peri-urban (465.60 ± 152.03 tree/ha) to urban core (244.00 ± 120.86 tree/ha) and species diversity decreased from urban core (α = 2.82 ± 0.01) to peri-urban area (α = 2.61 ± 0.23). Further, the proportion of exotic species was significantly higher (75.6 %) than that of native species in the study area (p = 0.001). Tree community assemblages showed least differences among the study zones (dissimilarity = 10 %) and appear to have been influenced by local cultural differences, species movement as well as local resource use. Furthermore, species movement exhibited a random and multi-directional pattern perpetuated by human and nonhuman factors. Movements were significantly higher between backyard gardens within the city than from outside. Alien species by far outnumbered native plant species moving across urban landscapes, potentially increasing species homogenization. Conservation awareness is needed to avoid habitat homogenization due to problems associated with urban sprawl and to maintain heterogeneous habitats for the urban wildlife.     

Climate stability is more important than water–energy variables in shaping the elevational variation in species richness

Changes in climate variables have an important impact on the prediction and protection of elevational biodiversity. Gaps exist in our understanding of the elevational distribution patterns in seed plant species richness. Our study examines the importance of climate variables in shaping the elevational variation in species richness. The importance of boundary constraint was also taken into account. Model selection based on Akaike's information criterion was used to select the best explaining climate models. Variation partitioning was used to assess the independent and joint effects of water–energy, physiological tolerance, and environmental stability variables on species richness. Our results revealed that: (a) Both raw (boundary constraint unreduced) and estimated (boundary constraint reduced) species richness showed large elevational variation, with the peak species richness seen at midelevations. The environmental variables were better at explaining the distribution pattern of species richness along the elevation, when the effect of boundary constraint was reduced; (b) the physiological tolerance and environmental stability variables explained more variation in raw and estimated species richness compared with the water–energy variables. Estimated species richness was better explained (98.6%) by the environmental variables than raw species richness (94%); (c) the water‐related variables generally had the highest independent effect on raw and estimated species richness and were dominant in shaping the elevational variation in species richness. Our findings quantify the influence of boundary constraint on the distribution pattern of species along an altitudinal gradient and compare the relative contributions of environmental stability and water–energy in explaining the altitude gradient distribution pattern of plant seed species.