Landscape-level toxicant exposure mediates infection impacts on wildlife populations

Anthropogenic landscape modification such as urbanization can expose wildlife to toxicants, with profound behavioural and health effects. Toxicant exposure can alter the local transmission of wildlife diseases by reducing survival or altering immune defence. However, predicting the impacts of pathogens on wildlife across their ranges is complicated by heterogeneity in toxicant exposure across the landscape, especially if toxicants alter wildlife movement from toxicant-contaminated to uncontaminated habitats. We developed a mechanistic model to explore how toxicant effects on host health and movement propensity influence range-wide pathogen transmission, and zoonotic exposure risk, as an increasing fraction of the landscape is toxicant-contaminated. When toxicant-contaminated habitat is scarce on the landscape, costs to movement and survival from toxicant exposure can trap infected animals in contaminated habitat and reduce landscape-level transmission. Increasing the proportion of contaminated habitat causes host population declines from combined effects of toxicants and infection. The onset of host declines precedes an increase in the density of infected hosts in contaminated habitat and thus may serve as an early warning of increasing potential for zoonotic spillover in urbanizing landscapes. These results highlight how sublethal effects of toxicants can determine pathogen impacts on wildlife populations that may not manifest until landscape contamination is widespread.     

Integrative population genetics and metagenomics reveals urbanization increases pathogen loads and decreases connectivity in a wild bee

As urbanization continues to increase, it is expected that two-thirds of the human population will reside in cities by 2050. Urbanization fragments and degrades natural landscapes, threatening wildlife including economically important species such as bees. In this study, we employ whole genome sequencing to characterize the population genetics, metagenome and microbiome, and environmental stressors of a common wild bee, Ceratina calcarata. Population genomic analyses revealed the presence of low genetic diversity and elevated levels of inbreeding. Through analyses of isolation by distance, resistance, and environment across urban landscapes, we found that green spaces including shrubs and scrub were the most optimal pathways for bee dispersal, and conservation efforts should focus on preserving these land traits to maintain high connectivity across sites for wild bees. Metagenomic analyses revealed landscape sites exhibiting urban heat island effects, such as high temperatures and development but low precipitation and green space, had the highest taxa alpha diversity across all domains even when isolating for potential pathogens. Notably, the integration of population and metagenomic data showed that reduced connectivity in urban areas is not only correlated with lower relatedness among individuals but is also associated with increased pathogen diversity, exposing vulnerable urban bees to more pathogens. Overall, our combined population and metagenomic approach found significant environmental variation in bee microbiomes and nutritional resources even in the absence of genetic differentiation, as well as enabled the potential early detection of stressors to bee health.     

Urbanization drives unique latitudinal patterns of insect herbivory and tree condition

Urban landscapes are characterized by high proportions of impervious surface resulting in higher temperatures than adjacent natural landscapes. In some cities, like those at cooler latitudes, trees may benefit from warmer urban temperatures, but trees in many cities are beset with problems like drought stress and increased herbivory. What drives patterns of urban tree health across urbanization and latitudinal temperature gradients? In natural systems, latitude–herbivory relationships are well‐studied, and recent temperate studies have shown that herbivory generally increases with decreasing latitudes (warmer temperatures). However, the applicability of this latitude–herbivory theory in already‐warmed urban systems is unknown. In this study, we investigated how the interaction of urbanization, latitudinal warming and scale insect abundance affected urban tree health. We predicted that trees in warmer, lower latitude cities would be in poorer health at lower levels of urbanization than trees at cooler, higher latitudes due to the interaction of urbanization, latitudinal temperature and herbivory. To evaluate our predictions, we surveyed the abundance of scale insect herbivores on a single, common tree species Acer rubrum in eight US cities spanning 10° of latitude. We estimated urbanization at two extents, a local one that accounted for the direct effects on an individual tree, and a larger one that captured the surrounding urban landscape. We found that urban tree health did not vary with latitudinal temperature but was best predicted by local urbanization and herbivore abundance. We did not observe increased herbivore abundance in warmer, lower latitudes cities, but instead herbivore abundance peaked in the mid latitudes of our study. This study demonstrates that urban landscapes may deviate from classical theory developed in natural systems and reinforces the need for research reconciling ecological patterns in urban landscapes.     

The relationship between wealth and biodiversity: A test of the Luxury Effect on bird species richness in the developing world

The Luxury Effect hypothesizes a positive relationship between wealth and biodiversity within urban areas. Understanding how urban development, both in terms of socio‐economic status and the built environment, affects biodiversity can contribute to the sustainable development of cities, and may be especially important in the developing world where current growth in urban populations is most rapid. We tested the Luxury Effect by analysing bird species richness in relation to income levels, as well as human population density and urban cover, in landscapes along an urbanization gradient in South Africa. The Luxury Effect was supported in landscapes with lower urbanization levels in that species richness was positively correlated with income level where urban cover was relatively low. However, the effect was reversed in highly urbanized landscapes, where species richness was negatively associated with income level. Tree cover was also positively correlated with species richness, although it could not explain the Luxury Effect. Species richness was negatively related to urban cover, but there was no association with human population density. Our model suggests that maintaining green space in at least an equal proportion to the built environment is likely to provide a development strategy that will enhance urban biodiversity, and with it, the positive benefits that are manifest for urban dwellers. Our findings can form a key contribution to a wider strategy to expand urban settlements in a sustainable way to provide for the growing urban population in South Africa, including addressing imbalances in environmental justice across income levels and racial groups.     

Key lessons for achieving biodiversity‐sensitive cities and towns

Australia's urban landscapes offer opportunities to marry socio‐economic and biodiversity conservation objectives. Yet, information is needed on what urban landscape and habitat features are important for wildlife. In this article, we draw together our research from southeastern Australia to describe key lessons for biodiversity‐sensitive cities and towns. Lesson 1: The effects of urbanization on wildlife extend into adjacent habitats. We recommend retaining large, undisturbed areas of habitat away from development, avoiding intensive development adjacent to important conservation areas, prioritizing areas of ecological and social significance, screening light and noise pollution at the urban fringe and around large nature reserves, and planting appropriately provenanced locally native species for public streetscapes, parks and gardens. Lesson 2: Strategic enhancement of urban greenspace offers biodiversity gains. We recommend increasing the total amount of greenspace cover, maintaining ecological structures as habitat islands, using landscaping techniques to minimize risks to human safety, and gardening with low‐flowering native shrubs. Lesson 3: Large old trees need to be managed for long‐term sustainability. We recommend retaining large old trees in new developments, increasing the maximum standing life of urban trees, protecting regenerating areas and planting more seedlings, supplementing habitat features associated with large trees, and ensuring that young trees have space to grow through time. Lesson 4: Education and engagement connects residents with nature and raises awareness. We recommend education programs to enhance opportunities for residents to experience and learn about biodiversity, engaging residents in the establishment and maintenance of wildlife habitat, providing ‘cues to care’, facilitating access to garden plants that benefit wildlife, and encouraging cat containment. These lessons provide an evidence‐base for implementing conservation and management actions to improve the capacity of our cities and towns to support a diverse and abundant biota.     

Blood-sucking ticks (Acarina,Ixodoidea) as an essential component of the urban environment

The problem of urban ticks has arisen from the increased rate of urbanization since WWII. Expansion of municipal boundaries encompasses adjacent territories, so that large areas of wilderness together with all their inhabitants get incorporated into city limits. Current strategies of biodiversity conservation include the creation of green corridors and other forms of connectivity between wilderness and urban areas as well as between green patches within cities. All this allows various mammals and birds to migrate from their native habitats into and between various parts of the cities and to establish permanent urban populations. Medium-sized and larger animals provide adult ticks with blood meal, thus creating suitable conditions for the establishment and persistence of tick populations. Independent tick populations can exist in urban forests, parks, private properties, old cemeteries, etc. Over the last decades, the tick populations that originated from those in natural habitats around the cities have become a permanent component of urban fauna. Among such ticks, the castor bean tick Ixodes ricinus is the most important species for European cities, while the deer tick I. scapularis is of great significance for the East Coast of the United States. The taiga tick I. persulcatus is the most important species for the Russian cities and towns within its range. All these and some other ticks aggressively attack humans and their pets inside cities. The tick species especially well adapted to urban life are those which can live and reproduce in buildings. The brown dog tick Rhipicephalus sanguineus (family Ixodidae), the pigeon ticks from the reflexus group of the genus Argas, and Ornithodoros ticks (family Argasidae), which form urban and semi-urban populations, are the main urban tick pests and vectors. House infestation by ticks can lead to human infection with tick-borne pathogens or severe allergic reactions. Some tick hosts, mammals as well as birds, maintain tick-transmitted pathogens and serve as competent reservoir hosts. Urban populations of these animals can participate in the circulation of some pathogens within cities. Thus, the enlargement of urban green areas followed by their population by wild mammals and birds create good opportunities for the establishment of urban populations of tick vectors with the resulting threat to the health of urban dwellers and their pets. At the same time, our understanding of the real scope and complexity of the problem of urban ticks is far from being sufficient. Finding the ways of protecting the environment without increasing the risk to human health in modern cities is a pressing and challenging problem of our time.     

Permeability of the urban matrix to arboreal gliding mammals: Sugar gliders in Melbourne,Australia

Habitat corridors that facilitate functional connectivity are a fundamental component of wildlife conservation in fragmented landscapes. However, the landscape matrix separating suitable habitat is not uniformly impermeable to movement and management to increase matrix permeability could be an alternative means to maintain connectivity. Gliding mammals are particularly sensitive to fragmentation because their movements are constrained by glide distance thresholds. Populations of gliders in cities are at risk of being isolated by increasing habitat loss and urban development, yet little is known about how the urban matrix affects glider movement. Here we investigate how the level of urbanization and tree cover in the matrix influence matrix permeability to sugar gliders (Petaurus breviceps) within suburban forest reserves. Twenty‐two sugar gliders were radio‐tracked over winter and summer at four reserves. Boundary crossing behaviour was measured as the number of times each glider crossed into the matrix, and matrix permeability was determined as the maximum distance travelled by gliders into the matrix. The majority of gliders (81%) were located in the matrix at least once, and rates of boundary crossing were consistent across urbanization and tree cover levels. Matrix permeability was negatively affected by matrix urbanization, but not by matrix tree cover, and no interaction effects were found. Although distances travelled by gliders into the matrix did not exceed 180 m, they were comparable with typical movement distances by gliders in reserves. Our results demonstrate that the urban matrix can provide suitable habitat for gliding mammals to move and forage, but that increased urbanization may inhibit glider use of the matrix irrespective of tree cover. This finding has implications for conservation planning and suggests that structurally connected areas may not be used if movement behaviour is inhibited. Conversely, management of matrix permeability could be used to maintain connectivity without needing to construct physical corridors.     

快速城市化背景下广西典型城市景观空间格局动态比较研究

随着城市化的快速发展与城市规模日益扩张,城市景观空间结构不断地被人为改变着,不合理的景观空间格局既削弱了区域的经济和社会发展功能,影响着城市生态环境质量的不断提高,也进一步制约着城市的可持续发展进程。以广西3座典型中心城市——南宁、柳州和桂林市为研究对象,利用6景Landsat5 TM和Landsat8 OLI/TIRS影像数据,通过遥感影像分类技术提取研究区的土地利用景观信息,对典型城市1990—2015年的景观空间格局特征与生态过程进行对比分析,旨在揭示快速城市化阶段重点城市核心景观要素的时空演化规律。结果表明:(1)在城市化进程加快的背景下,广西各典型城市的景观空间格局均发生了剧烈的变化。受人为影响强烈的土地利用景观类型变动最为显著,建设用地景观的不断扩张与耕地、林地景观的缩减是城市化发展的基本特征。(2)在水平空间上,城市建筑景观逐渐由核心圈层向外围圈层扩展,外围区的自然景观受人工干扰强度加大,景观类型逐渐丰富,但破碎化程度加剧。(3)在垂直空间上,城市景观类型呈现较显著的海拔分异特征,中、低海拔区是城镇化最集中的地带,建设用地的景观优势度增长最为显著。高海拔区因但受城市扩张与农业开发活动的胁迫,自然景观的优势度与团聚性呈下降趋势。(4)从城市功能定位来看,南宁、柳州和桂林市作为广西3座不同功能类型的中心城市,它们在区域社会经济发展方面起到重要的辐射和引领作用。该研究为科学开展城市景观规划、实施城市生态环境管理和推进广西城市化健康有序发展提供参考依据。     

Restoration of Fragmented Landscapes for the Conservation of Birds: A General Framework and Specific Recommendations for Urbanizing Landscapes

Humans fragment landscapes to the detriment of wildlife. We review why fragmentation is detrimental to wildlife (especially birds), review the effects of urbanization on birds inhabiting nearby native habitats, suggest how restoration ecologists can minimize these effects, and discuss future research needs. We emphasize the importance of individual fitness to determining community composition. This means that reproduction, survivorship, and dispersal (not simply community composition) must be maintained, restored, and monitored. We suggest that the severity of the effects of fragmentation are determined by (1) the natural disturbance regime, (2) the similarity of the anthropogenic matrix to the natural matrix, and (3) the persistence of the anthropogenic change. As a result, urbanization is likely to produce greater effects of fragmentation than either agriculture or timber harvest. Restoration ecologists, land managers, and urban planners can help maintain native birds in fragmented landscapes by a combination of short‐ and long‐term actions designed to restore ecological function (not just shape and structure) to fragments, including: (1) maintaining native vegetation, deadwood, and other nesting structures in the fragment, (2) managing the landscape surrounding the fragment (matrix), not just the fragment, (3) making the matrix more like the native habitat fragments, (4) increasing the foliage height diversity within fragments, (5) designing buffers that reduce penetration of undesirable agents from the matrix, (6) recognizing that human activity is not compatible with interior conditions, (7) actively managing mammal populations in fragments, (8) discouraging open lawn on public and private property, (9) providing statutory recognition of the value of complexes of small wetlands, (10) integrating urban parks into the native habitat system, (11) anticipating urbanization and seeking creative ways to increase native habitat and manage it collectively, (12) reducing the growing effects of urbanization on once remote natural areas, (13) realizing that fragments may be best suited to conserve only a few species, (14) developing monitoring programs that measure fitness, and (15) developing a new educational paradigm.     

Diseases of humans and their domestic mammals: pathogen characteristics, host range and the risk of emergence

Pathogens that can be transmitted between different host species are of fundamental interest and importance from public health, conservation and economic perspectives, yet systematic quantification of these pathogens is lacking. Here, pathogen characteristics, host range and risk factors determining disease emergence were analysed by constructing a database of disease-causing pathogens of humans and domestic mammals. The database consisted of 1415 pathogens causing disease in humans, 616 in livestock and 374 in domestic carnivores. Multihost pathogens were very prevalent among human pathogens (61.6%) and even more so among domestic mammal pathogens (livestock 77.3%, carnivores 90.0%). Pathogens able to infect human, domestic and wildlife hosts contained a similar proportion of disease-causing pathogens for all three host groups. One hundred and ninety-six pathogens were associated with emerging diseases, 175 in humans, 29 in livestock and 12 in domestic carnivores. Across all these groups, helminths and fungi were relatively unlikely to emerge whereas viruses, particularly RNA viruses, were highly likely to emerge. The ability of a pathogen to infect multiple hosts, particularly hosts in other taxonomic orders or wildlife, were also risk factors for emergence in human and livestock pathogens. There is clearly a need to understand the dynamics of infectious diseases in complex multihost communities in order to mitigate disease threats to public health, livestock economies and wildlife.     

The effect of habitat and human disturbance on the spatiotemporal activity of two urban carnivores: The results of an intensive camera trap study

With rising urbanization, the presence of urban wildlife is becoming more common, increasing the need for wildlife‐friendly spaces in urban planning. Despite this, understanding is limited to how wildlife exploits urban environments and interacts with human populations, and this is vital to our ability to manage and conserve wildlife in urban habitats. Here, we investigate how two urban mammal species, the red fox (Vulpes vulpes) and the European badger (Meles meles), exploit urban environments. Using intensive camera trap surveys, we assessed how habitat and human disturbance influenced the spatiotemporal activity of these species across south‐west London. Firstly, we found elevated activity levels of both species at boundaries and within built‐up areas, suggesting movement paths follow anthropogenic features. However, badgers were most active in woodland, indicating the importance of high cover habitats suitable for setts and foraging. Secondly, we found badger activity levels were negatively affected by human activity, whilst foxes were unaffected. Further investigation suggested foxes may adapt their activity patterns to avoid human disturbance, with badger activity patterns less plastic. Whilst the results of this study are useful for both the conservation and management of urban wildlife populations, these results also show potential factors which either facilitate or limit wildlife from fully exploiting urban environments.     

Avian productivity in urban landscapes: a review and meta-analysis

There is an urgent need to thoroughly review and comprehend the effects of urbanization on wildlife in order to understand both the ecological implications of increasing urbanization and how to mitigate its threat to biodiversity globally. We examined patterns in comparative productivity of urban and non-urban passerine birds, using published estimates from paired comparisons, and by reviewing and developing explanations in terms of resources, competitors, predators and other specifically urban environmental factors. The most consistent patterns were for earlier lay dates, lower clutch size, lower nestling weight and lower productivity per nesting attempt in urban landscapes; these were supported by a formal meta-analysis. Nest failure rates did not show consistent patterns across the species considered. We suggest that food availability is a key driver of differences in passerine demography between landscapes. In urban habitats, human-provided food may improve adult condition over winter, leading to earlier lay dates and, in some species, to higher survival and higher breeding densities, but paucity of natural food may lead to lower productivity per nesting attempt. We demonstrate that additional comparative research is needed on a wider range of species, on the effects of natural and human-provided food availability, and on the differences in survival and dispersal between urban and non-urban populations. Importantly, better-targeted research and monitoring is needed in areas that are at greatest threat from urbanization, especially in the developing world.     

A habitat island approach to conserving birds in urban landscapes: case studies from southern and northern Europe

Wildlife conservation in urban habitats is increasingly important due to current urbanization trends. We review the different approaches to studying birds in urban landscapes, and point out the importance of the habitat island ecological theory as a research framework for the management and conservation of urban birds. Based on two comprehensive research projects conducted at urban parks in Spain (Madrid) and Finland (Oulu and Rovaniemi), several different issues related to bird conservation in cities are discussed, main findings of these projects are presented, and future research needs are suggested. Urban parks are important biodiversity hotspots in cities. Fragmentation conditions have the same deleterious effects to urban birds as in other fragmented landscapes. Park size accounts for species accumulation in urban parks; this pattern being highly nested. Urban parks of 10–35 ha would contain most of the species recorded in cities, but other indicators related to the probabilities of persistence of the target species should be obtained. Wooded streets can increase urban landscape connectivity by providing alternative habitat for feeding and nesting during the breeding season. Because increasing the size of parks is difficult in cities, enhancement of habitat diversity and resource availability for birds within parks (e.g. nest boxes, winter feeding tables, etc.) appears to be a straightforward way of increasing urban bird diversity. However, human disturbance (pedestrians) should be controlled since it can negatively influence many urban birds. We present a conceptual model for urban bird conservation, which includes three aspects (management, environmental education and research) and new alternatives to promote the involvement of different sectors of the society.     

城市化对土壤动物群落结构和多样性的影响

城市化进程加快带来的环境挑战正威胁着地球上的生物多样性。土壤动物是生物多样性的重要组成部分, 对维持土壤健康及城市生态系统稳定性具有重要意义。近年来, 城市土壤动物群落结构和多样性的研究已经取得了一定进展, 但是仍缺乏系统的总结和综述。基于此, 本文梳理归纳了国内外已有的相关文献, 总结了城市化影响土壤动物的主要途径, 并阐述了城市中不同体型大小的优势土壤动物类群对城市化的响应。本文建议未来应利用分子生物学手段深入解析城市土壤动物多样性, 明晰城市土壤食物网的结构与功能, 关注土壤动物群落的保护与恢复, 揭示城市土壤动物肠道微生物组特征, 并挖掘城市土壤动物抑制人类致病菌的潜力, 以期为城市生物多样性保护、生态系统稳定和人类健康维持提供相关科学依据。     

Gene flow and genetic drift in urban environments

Evidence is growing that human modification of landscapes has dramatically altered evolutionary processes. In urban population genetic studies, urbanization is typically predicted to act as a barrier that isolates populations of species, leading to increased genetic drift within populations and reduced gene flow between populations. However, urbanization may also facilitate dispersal among populations, leading to higher genetic diversity within, and lower differentiation between, urban populations. We reviewed the literature on nonadaptive urban evolution to evaluate the support for each of these urban fragmentation and facilitation models. In a review of the literature with supporting quantitative analyses of 167 published urban population genetics studies, we found a weak signature of reduced within‐population genetic diversity and no evidence of consistently increased between‐population genetic differentiation associated with urbanization. In addition, we found that urban landscape features act as barriers or conduits to gene flow, depending on the species and city in question. Thus, we speculate that dispersal ability of species and environmental heterogeneity between cities contributes to the variation exhibited in our results. However, >90% of published studies reviewed here showed an association of urbanization with genetic drift or gene flow, highlighting the strong impact of urbanization on nonadaptive evolution. It is clear that species biology and city heterogeneity obscure patterns of genetic drift and gene flow in a quantitative analysis. Thus, we suggest that future research makes comparisons of multiple cities and nonurban habitats, and takes into consideration species' natural history, environmental variation, spatial modelling and marker selection.     

城市菌根真菌多样性、变化机制及功能应用

菌根真菌能够与大多数陆生植物的根系形成菌根共生体,具有改善宿主植物矿质营养、增强抗逆性、改良土壤结构等重要生态功能。城市化过程中气候、土壤、植被、土地利用等因素的改变,对菌根真菌的多样性产生了直接或间接的影响。目前城市菌根真菌的研究多侧重对其空间分布及群落组成的简单描述,缺乏针对城市典型生态现象及生态问题系统性的探讨。分别从城市菌根真菌的多样性变化、影响机制及功能应用等3方面进行了综述,全面揭示城市菌根真菌的研究现状及研究的复杂性,发现当前研究存在多样性评估简单化、研究层次单一化、内在机制现象化及功能应用停滞化等问题,认为今后应建立更为系统、综合、标准的研究体系以深刻而准确地认识与理解城市化对菌根真菌多样性的影响,为城市微生物资源的保存及绿地系统维持提供理论依据。     

Are house sparrow populations limited by the lack of cavities in urbanized landscapes? An experimental test

Current urban policies are associated with deep changes in urban structures, which may impoverish urban biodiversity. A major concern is the disappearance of nesting sites for wild vertebrate species living in urban areas. New urban structures without any cracks or cavities may especially preclude cavity nesters from breeding in cities and they may cause population declines. In that context, we experimentally investigated this question in an urban exploiter bird species (the house sparrow Passer domesticus), which is dramatically declining in most European cities. To test if the lack of cavities is limiting house sparrow populations in urban areas, we equipped 11 sites along an urbanization gradient with nest boxes and we then evaluated the rate of occupancy of these nest‐boxes. This urbanization gradient was characterized by very rural places (isolated farms) and moderately urbanized areas (town of medium size, i.e. 60 000 inhabitants). Surprisingly, rural nest boxes were more occupied than urban ones, suggesting that cavity availability is probably more constraining in rural areas relative to urban ones. Therefore, our study suggests that urban house sparrow populations are probably not constrained by a lack of nesting sites in medium size cities with urban designs similar to our city of interest (Niort, western France). This hypothesis definitely needs now to be tested in further urban landscapes (e.g. large cities and urban landscapes with other architecture and management policies).     

Land-use effects on prevalence of raccoon roundworm (Baylisascaris procyonis)

The raccoon (Procyon lotor) is the definitive host of Baylisascaris procyonis, a large intestinal roundworm that is zoonotic and can result in fatal or severe central nervous system disease in young children. Prevalence of infection among raccoon populations often is high, and in the midwestern United States, B. procyonis has been reported in 68-82% of raccoons. Raccoon populations have increased in response to changes in human land use, and often reach higher densities in urban and suburban landscapes than rural landscapes. However, shifts in foraging behavior among urban raccoons could impact the transmission of B. procyonis if small vertebrate intermediate hosts are not a significant part of the raccoon diet. The objective of this study was to compare prevalence of B. procyonis infection between urban and rural raccoon populations on a regional scale. Necropsy was done on 204 raccoons collected from September through February during 2000-2005 from seven states across the Midwest (regional sample). Baylisascaris procyonis was found in 54% of examined raccoons. Prevalence differed between land-use types (chi2=11.56, df=1, P=0.0007), and was higher among animals collected from rural locations (65%) than those collected in urban locations (41%). Intensity of infection also differed (F=5.52, df=1, P=0.02), with rural raccoons having greater worm burdens (x=29.63+/-36.42) than urban raccoons (x=13.85+/-18.47). Despite high densities of raccoons in urban landscapes, fewer urban raccoons were infected with B. procyonis, suggesting decreased dependence on intermediate hosts as a food source. This possible explanation was supported by a similar trend in prevalence among subsamples of raccoons collected from three Chicago-area populations (local samples) with differing levels of urbanization, population densities, and foraging behavior that had been intensively monitored during 1995-2002. Decreased transmission of B. procyonis in urban landscapes may be due to decreased predation of intermediate hosts, and contact of juvenile raccoons with B. procyonis eggs may be an important factor in maintaining infections within such populations.     

基于LSMM与MSPA的深圳市绿色景观连通性研究

基于线性光谱混合模型(LSMM,Linear Spectral Mixture Model),引入形态学空间格局分析(MSPA,Morphological Spatial Pattern Analysis)进行城市地域绿色景观连通性评价。根据城市绿色景观特点和MSPA方法中的7种连通性类型的涵义,定义了城市绿色景观连通性功能类型。以深圳市1986年、1995年、2000年、2005年及2010年五期Landsat TM影像为数据源,应用线性光谱混合模型提取植被覆盖率,得到深圳市植被覆盖图。在此基础上,提取出高、全植被覆盖作为目标像元进行MSPA处理,分析植被覆盖状况与绿色景观功能类型的时序总体特征及空间梯度动态。结果表明:深圳市绿色景观破碎程度较高,表现为对结构连通性贡献最小的斑块类型总数最大。城市内部东西部连通性呈现出不同变化的趋势;右侧外圈层的大鹏半岛结构连通性最佳;在同一城市化发展梯度上,东部的样带连通性水平比西部要好。在城市化过程中,深圳市高、全覆被植被像元连通性大小受以下因素的影响:城市化程度,地形因素及区域定位。在同一城市化程度上,地形因素对景观连通性的影响较大。从整体的时间变化和空间梯度动态分析可知,在快速城市化过程中植被覆盖率和连通性功能均下降,而到稳定城市化阶段植被覆盖率和连通性均得到改善。研究表明线性光谱混合模型与形态学空间格局分析相结合可以较好的表征城市绿色景观连通性类型时空分布特征,进而明晰城市化过程与区域内绿色景观数量及连通性动态变化关系。     

Ecological traits and landscape characteristics predicting bird sensitivity to urbanization in city parks

Habitat loss and fragmentation caused by urbanization often have negative impacts on wildlife in cities. There are considerable studies investigating the relationship between species traits and fragmentation vulnerability. However, so far, very few studies have examined the influence of species traits combined with landscape factors on vulnerability to urbanization in urbanized landscapes. In this study, we investigated how species traits and park characteristics influenced bird sensitivity to urbanization in the highly urbanized city of Nanjing, China. We used the line-transect method to survey birds in 37 urban parks. For each bird species, we collected data on nine life-history and ecological traits that are commonly assumed to influence urbanization vulnerability. For each park, we selected six landscape variables that are commonly considered to influence bird response to urbanization. After phylogenetic correction, the nine species traits were used separately and in combination to evaluate their associations with species abundance, an indicator of urbanization vulnerability. We then used the RLQ and fourth-corner analyses to test relationships between species traits and environmental variables. We found that the 75 species analyzed demonstrated considerable variation in vulnerability to urbanization. Using PGLS analyses and model averaging, we found that habitat specificity was the single best ecological predictor of urbanization vulnerability in birds in Nanjing city parks. The RLQ analysis showed that body size and habitat specificity were correlated with distance to city center and connectivity of the parks, reflecting strong effects of trait-mediated environmental filters that selectively benefit species with smaller body mass and lower habitat specificity in urbanized landscape. Therefore, conservation efforts giving priority to species with high habitat specificity and to parks with high connectivity and far away from the city center may prove effective for the preservation of bird diversity in our highly urbanized system. Meanwhile, preventing future habitat loss and destruction in existing city parks may also effectively conserve these vulnerable species.