Gene flow and pathogen transmission among bobcats (Lynx rufus) in a fragmented urban landscape

Urbanization can result in the fragmentation of once contiguous natural landscapes into a patchy habitat interspersed within a growing urban matrix. Animals living in fragmented landscapes often have reduced movement among habitat patches because of avoidance of intervening human development, which potentially leads to both reduced gene flow and pathogen transmission between patches. Mammalian carnivores with large home ranges, such as bobcats (Lynx rufus), may be particularly sensitive to habitat fragmentation. We performed genetic analyses on bobcats and their directly transmitted viral pathogen, feline immunodeficiency virus (FIV), to investigate the effects of urbanization on bobcat movement. We predicted that urban development, including major freeways, would limit bobcat movement and result in genetically structured host and pathogen populations. We analysed molecular markers from 106 bobcats and 19 FIV isolates from seropositive animals in urban southern California. Our findings indicate that reduced gene flow between two primary habitat patches has resulted in genetically distinct bobcat subpopulations separated by urban development including a major highway. However, the distribution of genetic diversity among FIV isolates determined through phylogenetic analyses indicates that pathogen genotypes are less spatially structured-exhibiting a more even distribution between habitat fragments. We conclude that the types of movement and contact sufficient for disease transmission occur with enough frequency to preclude structuring among the viral population, but that the bobcat population is structured owing to low levels of effective bobcat migration resulting in gene flow. We illustrate the utility in using multiple molecular markers that differentially detect movement and gene flow between subpopulations when assessing connectivity.     

Habitat connectivity analysis for conservation implications in an urban area

In urbanized areas, habitat loss and fragmentation resulting from urban growth and human activities may threaten the biological diversity. It is essential to maintain the connectivity in some isolated and fragmented habitat patches. In 2005, the orchard-based conservation with the legal binding was implemented in Shenzhen to mitigate the ecological threats from forest destruction and to protect the ecological diversity. It is critical to evaluate the efficiency of orchard habitat from the species’ perspective for providing the reference for the habitat management. Based on graph-theoretic methods, we compared the habitats with or without orchards and evaluated the contribution of orchards to the whole network connectivity and its three fractions (intra, flux and connector), and then analyzed the species that could benefit the most from the habitat supplement. We identified the important landscape elements for serving the prioritized conservation. The results showed that orchard-based conservation was an efficient way in maintaining the functional connectivity, which mainly contributed to the intrapatch connectivity and species dispersal flux. The value of orchard incorporation was strongly related with the dispersal ability of threatened species. Our findings indicated that the orchard conservation would be more valuable for species with relatively weak dispersal abilities. We showed the key patches and links that most contribute to uphold functional connectivity in the reserve network. We believe that the assessment based on habitat functional connectivity can effectively serve the practical guidelines of habitat conservation and management in urban areas.     

Species‐habitat relationships and ecological correlates of butterfly abundance in a transformed tropical landscape

Tropical butterfly conservation strategies often focus on total and/or common species richness to assess the conservation value of a patch or habitat. However, such a strategy overlooks the unique dynamics of rare species. We evaluated the species‐habitat relationships of 209 common, intermediate, and rare butterfly species (including morphospecies) across four habitat types (mature, degraded, or fragmented forest, and urban parks) and two patch sizes (<400 ha, ≥400 ha) in Singapore. Common species richness was consistent across habitat types. Intermediate species richness declined by more than 50 percent in urban parks (relative to all forest habitats), and rare species richness was reduced by 50 percent in degraded and fragmented forest and by 90 percent in urban parks (relative to mature forest). Large patches had comparable overall richness to small patches, but they supported more rare species and three times as many habitat‐restricted species over a similar area. Importantly, a number of rare species were confined to single small patches. Mixed‐effects regression models were constructed to identify habitat and ecological/life history variables associated with butterfly abundance. These models revealed that species with greater habitat specialization, rare larval host plants, few larval host plant genera, and narrow global geographic ranges were more likely to be rare species. Overall, these results demonstrate that the richness of habitat‐restricted and rare species do not follow the same spatial distribution patterns as common species. Therefore, while conserving mature forests is key, effective butterfly conservation in a transformed landscape should take into account rare and habitat‐restricted species.     

Using theoretical models to explore dispersal variation and fragmentation in urban environments

Cities are fundamentally changing the environment that plants inhabit, most notably through habitat fragmentation. Urban plant habitat patches are separated by impervious surfaces like buildings and roads and may vary from small, isolated green spaces to large green spaces like parks. Understanding the consequences of this urban fragmentation on seed dispersal is essential to both maintain urban biodiversity and mitigate the spread of unwanted weeds or invasive species but we currently lack enough empirical data to draw generalities. Theoretical reasoning (via both verbal and mathematical models) is well positioned to contribute to this knowledge gap in dispersal by providing useful predictions when empirical data are lacking. Variation in dispersal can easily be captured by models by incorporating different dispersal kernel shapes, and multiple habitat configurations can be examined. Urban environments are rarely considered by mathematical models, and our literature review indicates that most models that include dispersal variation via a dispersal kernel use only one or two shapes, suggesting a gap in the theoretical literature as well. We present a proof-of-concept model of fragmentation in an urban environment illustrating how varying habitat width can lead to different outcomes depending on the dispersal kernel. We also provide some thoughts for future directions on the application of mathematical models in urban areas.     

Investigating the distribution of prairie dogs in an urban landscape

Habitat fragmentation is a prevalent threat to biological diversity, and urbanization is a primary agent of fragmentation and a leading cause of species endangerment. Landscape biogeographic and local habitat characteristics can be important determinants of the distribution of species in habitat patches in urban landscapes. However, the specifics of which characteristics are most critical to maintaining biological diversity are not fully known for prairie ecosystems, especially in fragmented urban habitat. This study focuses on black-tailed prairie dogs along an urban gradient in Denver, CO. Prairie dogs have declined precipitously throughout the region and are an essential part of the prairie ecosystem, making them excellent study subjects. We identified a series of habitat fragments along a gradient of urbanization in the fully urbanized areas and south suburbs of Denver, CO, both containing and not containing prairie dogs. Local characteristics, including fragment slope and vegetative cover, and landscape characteristics, including fragment size, age and connectivity, were measured on each fragment. We used likelihood-based methods to explore which variables most accurately predicted prairie dog occurrence within our study area. Multiple factors influenced the distribution of prairie dogs in urban settings, with colony connectivity the strongest predictor of occupancy. Large and recently isolated fragments near other prairie dog colonies, flat areas and those with high graminoid cover were most likely to support prairie dog populations. Our study provides the first attempt to model prairie dog occurrence in highly fragmented urban habitat and has important implications for the management and conservation of prairie dogs.     

Noise pollution and decreased size of wooded areas reduces the probability of occurrence of Tawny Owl Strix aluco

At present, urban areas cover almost 3% of the Earth's land surface, and this proportion is constantly increasing along with human population growth. Although urbanization leads to biodiversity decline, at the same time it creates a novel and extensive environment that is exploited by whole assemblages of organisms. These include predators, which use the matrix of different habitat types within the urban environment for breeding and/or foraging. This study investigated how attributes of the urban landscape influence the distribution pattern of a nocturnal acoustic predator, the Tawny Owl Strix aluco. The probability of occurrence of this species was correlated with the presence of natural forests, and the increasing size of wooded habitat patches within the urban landscape; however, Tawny Owls were less likely to occur at sites with high noise levels at night. Our study suggests that the distribution pattern of acoustic predators is shaped by the availability of primary habitat but reduced by noise intensity (which may decrease hunting efficiency). The Tawny Owl is a top predator in the urban environment and its presence/absence may therefore affect populations of other species; this provides clear evidence of the indirect effect of noise pollution on animal populations inhabiting urban environments.     

Biodiversity in cities needs space: a meta‐analysis of factors determining intra‐urban biodiversity variation

Understanding varying levels of biodiversity within cities is pivotal to protect it in the face of global urbanisation. In the early stages of urban ecology studies on intra‐urban biodiversity focused on the urban–rural gradient, representing a broad generalisation of features of the urban landscape. Increasingly, studies classify the urban landscape in more detail, quantifying separately the effects of individual urban features on biodiversity levels. However, while separate factors influencing biodiversity variation among cities worldwide have recently been analysed, a global analysis on the factors influencing biodiversity levels within cities is still lacking. We here present the first meta‐analysis on intra‐urban biodiversity variation across a large variety of taxonomic groups of 75 cities worldwide. Our results show that patch area and corridors have the strongest positive effects on biodiversity, complemented by vegetation structure. Local, biotic and management habitat variables were significantly more important than landscape, abiotic or design variables. Large sites greater than 50 ha are necessary to prevent a rapid loss of area‐sensitive species. This indicates that, despite positive impacts of biodiversity‐friendly management, increasing the area of habitat patches and creating a network of corridors is the most important strategy to maintain high levels of urban biodiversity.     

城市扩张导致京津冀区域生境质量下降

城镇化发展极大地改变了区域生境分布格局和功能,从而影响区域生态安全。因此,开展生境质量的评估,对于城市生态安全保障具有重要作用。基于In VEST生境质量模型,评估了京津冀区域2005—2015年生境质量时空变化格局。研究结论如下:1)2005—2015年,京津冀生境面积减少7134.2 km~2,占2005年生境面积的3.7%。耕地、草地和水域生境面积分别减少5081.0、1695.1、421.6 km~2,占对应类型生境面积的4.7%,4.9%和7.2%。2)京津冀生境质量从0.88降至0.83,下降幅度达5.69%。其中,耕地生境质量下降最为严重,其次为水域生境质量。3)生境质量下降区域主要沿北京-保定-石家庄-邢台-邯郸等经济发展迅速的区域分布,表现为城市扩张侵占原有生境。4)京津冀高生境质量斑块破碎度增加,低生境质量斑块集聚度增加。整体上看,京津冀区域生境斑块破碎度增加。     

Biogenic habitat creation affects biomass–diversity relationships in plant communities

Biogenic habitat creation refers to the ability of some organisms to create, maintain or destroy habitats. These habitat changes affect species diversity of natural communities, but it remains to be elucidated if this process also affects the link between ecosystem functions and species diversity. Based on the widely accepted positive relationships between ecosystem functions and species diversity, we hypothesize that these relationships should be different in biogenically created habitat patches as compared to unmodified habitat patches. We tested this hypothesis by assessing the effects of a high-Andean cushion plant, Azorella madreporica, which creates habitat patches with different environmental conditions than in the surrounding open areas with reduced vegetation cover. We used observational and experimental approaches to compare the plant biomass–species richness relationships between habitat patches created by A. madreporica cushions and the surrounding habitat without cushion plants. The observational assessment of these relationships was conducted by counting and collecting plant species within and outside cushion patches. In the experiment, species richness was manipulated within and outside cushion patches. The cushion plant itself was not included in these approaches because we were interested in measuring its effects. Results of both approaches indicated that, for a given level of species richness, plant biomass within cushions was higher than in the surrounding open areas. Furthermore, both approaches indicated that the shape of plant biomass–species richness curves differed between these habitat types. These findings suggest that habitat modifications performed by A. madreporica cushions would be positively affecting the relationships between ecosystem functions and species diversity.     

Urban amphibian assemblages as metacommunities

1. Urban ecosystems are expanding throughout the world, and urban ecology is attracting increasing research interest. Some authors have questioned the value of existing ecological theories for understanding the processes and consequences of urbanization. 2. In order to assess the applicability of metacommunity theory to urban systems, I evaluated three assumptions that underlie the theory - the effect of patch area, the effect of patch isolation, and species-environment relations - using data on assemblages of pond-breeding amphibians in the Greater Melbourne area of Australia. I also assessed the relative impact of habitat fragmentation, habitat isolation, and changes to habitat quality on these assemblages. 3. Poisson regression modelling provided support for an important increase in species richness with patch area (pond size) and a decrease in species richness with increasing patch isolation, as measured by surrounding road cover. Holding all other variables constant, species richness was predicted to be 2.8-5.5 times higher at the largest pond than at the smallest, while the most isolated pond was predicted to have 12-19% of the species richness of the least isolated pond. Thus, the data were consistent with the first two assumptions of metacommunity theory evaluated. 4. The quality of habitat at a pond was also important, with a predicted 44-56% decrease in the number of species detected at ponds with a surrounding vertical wall compared with those with a gently sloping bank. This demonstrates that environmental differences between habitat patches were also influencing amphibian assemblages, providing support for the species-sorting and/or mass-effect perspectives of metacommunity theory. 5. Without management intervention, urbanization may lead to a reduction in the number of amphibian species persisting in urban ponds, particularly where increasing isolation of ponds by roads and associated infrastructure reduces the probability of re-colonization following local extinction. Journal of Animal Ecology (2006) 75, 757-764 doi: 10.1111/j.1365-2656.2006.01096.x.     

土地利用变化对鸟类栖息地连通性的影响——以鄂州市为例

土地利用变化是造成栖息地破碎、缺失与退化的重要原因。生态网络能保护重要栖息地,促进栖息地之间的物质与能量流动,对区域土地利用规划和生物多样性保护具有重要意义。以鄂州市为研究区,基于CLUE-S模型预测现状延续、生态保护和城市扩张3种土地利用情景,将生境质量作为遴选生境斑块的依据之一,以鸟类最大迁徙距离为阈值构建生态网络,从连通概率指数PC和斑块重要性指数dPC两方面,探讨土地利用变化对鸟类栖息地连通性的影响。结果表明：(1)不同情景的地类数量和空间结构均有差异,与生态保护相比,城市扩张情景的建设用地增加11603.52 hm~2,林地、耕地和水体减少5041.8 hm~2、2540.16 hm~2、3385.8 hm~2,新城区、山地风景区与水体周边是主要变化区域;(2)现状延续和城市扩张情景的生境斑块降至235块和216块,网络出现破碎化,生态保护情景增至367块,网络结构完整但空间位置改变;(3)2004—2024年PC表现为先上升后下降再上升的趋势,生态保护的PC高于现状延续和城市扩张,且利于保护短距离迁徙鸟类;(4)生态保护情景边缘型和关键小型斑块得到保护,第一等级斑块增加,城...     

生态保护区外斑块对景观连接度的影响评价

快速的城市化过程带来的生境斑块破碎化及损失会影响物种迁移、捕食等生态活动,对生物多样性构成威胁。然而,现有生态保护区可能无法覆盖其内生物的必要活动范围。生态保护区外的生境斑块对于维持生态过程也具有重要作用,因此识别生态保护区外的关键斑块并加以保护非常重要。以北京市延庆区为研究区,划分两种生境斑块,即核心生境斑块和潜在生境斑块,并基于图论构建生境网络。考虑地表覆盖类型、坡度、人类活动等因素构建生境阻力面。结合未来土地利用类型变化的模拟,研究城市化过程对区域生境网络和景观连接度的影响,选用CLUE-S模型模拟土地利用类型变化的格局。结合生境斑块特征和未来城市土地利用变化情况设计了3种未来生境变化情景。利用连接概率指数(PC)和网络连接度变化率(dI)评价不同生境变化情景下生态保护区外潜在生境斑块的景观连接度重要性,判断保护优先顺序,并分析景观格局变化对不同迁移能力物种的影响。结果表明：生态保护区外的全部潜在生境斑块对维持生境整体景观连接度有最大2.15%的影响,单个潜在生境斑块对维持景观连接度有最大0.28%的影响。此外,景观格局及其变化对不同迁移能力物种的影响差异显著,因此需针对保护物种和城市生境特征设计保护方案,研究区需要优先保护大中型斑块和位于关键位置的小型斑块。为了满足对生物多样性保护的需求,建议在区分生境斑块保护优先顺序时考虑生境斑块对景观连接度的贡献和城市化扩展过程的压力。研究为城市生物多样性保护和生境管理提供了方法参考。     

Precise direct tracking and remote sensing reveal the use of forest islands as roost sites by Purple Martins during migration

Direct tracking methods in combination with remote sensing data allow examination of habitat use by birds during migration. Species that roost communally during migration, such as some swallows, form large aggregations that can attract both avian and terrestrial predators. However, the extent to which they might use patchy habitats that could reduce predation risk during migration is unknown. We tested the hypothesis that Purple Martins (Progne subis) use forest islands (patches of suitable forest habitat surrounded by unsuitable habitat) as roost sites during migration between breeding sites in North America and overwintering sites in South America. We used high‐precision (< 10 m), archival GPS units deployed and retrieved during the 2015 and 2016 breeding seasons, respectively, at 12 colonies located across eastern North America. We found that Purple Martins roosted in forest islands more often than expected based on availability during both spring and fall migration. Despite an apparent association with urban habitats by Purple Martins based on observational and radar data in North America during the fall, the roost locations we identified during spring and fall migration were not more closely associated with urban areas than random locations. The use of forest islands during both spring and fall migration suggest that Purple Martins may use these habitats to reduce predation risk during migration. Our results suggest that some species of birds may use similar habitats as stopover sites during migration and that patches of forest habitat may be important conservation targets for Purple Martins and other species. Identifying habitat use during migration represents an important advance in support of full annual‐cycle conservation of Purple Martins and other migratory species with declining populations.     

城市周边农田景观中非农生境与土壤动物的协同关系——以沈阳市沈北新区为例

农田景观中非农生境对生物多样性保护、耕地多功能性和农业产量等具有重要影响.本文选择中国城市化过程中生物多样性保护与农业高产需求相互冲突的典型地区沈阳市沈北新区为研究区,采用信息熵模型划分为城市近郊、城市边缘区和乡村区域,采用手捡法和Baermann 法调查,鉴定了节肢动物和土壤线虫,并通过线性回归分析确定了非农生境类型、结构及数量与土壤动物的协同关系.结果表明： 沈北新区农田景观的非农生境斑块面积均小于1 hm².随着与城市中心距离的增加,非农生境类型和比例逐渐增加,面积比例呈倒“U”型变化,斑块数量比例从8.6%增加到27.8%;土壤动物个体数呈现“U”型变化,物种量无明显变化规律.乡村和城市近郊的非农生境斑块数量比与土壤动物个体数呈正向协同关系,城市边缘区无明显规律;非农生境面积比与土壤动物个体数均呈反向协同关系;非农生境斑块数量比和面积比与土壤动物物种量均无明显协同关系.     

The response of herpetofauna to urbanization: Inferring patterns of persistence from wildlife databases

Urbanization involves the conversion of natural habitats into human‐modified ecosystems and is known to reduce the diversity and abundance of indigenous plant and animal communities. Urbanization may lead to the extinction of indigenous species or facilitate the establishment of non‐indigenous communities in cities and towns. We analysed sighting records held in wildlife databases to infer the probability of persistence of reptiles and amphibians (‘herpetofauna’) within Melbourne, Victoria, Australia. Throughout greater Melbourne, 81% (13) of the 16 frog species recorded had ≥95% probability of being extant in 2006, compared with 56% (22) of the 39 species of reptiles recorded. The number of frog species that had ≥95% probability of being extant in inner local government areas (LGAs) within 10 km of the centre of Melbourne was higher (86%) than in the outer LGAs (69%). Conversely, only 46% of reptile species had ≥95% probability of being extant in inner and outer LGAs. The proportion of reptile species with <50% probability of being extant in inner LGAs was higher than for frog species (25% and 7%, respectively), suggesting that reptiles have been negatively affected by urbanization to a much greater extent than frogs. Based on the probability of species being extant, frogs and reptiles exhibited variations in their response to urbanization between species that persisted (urban‐adapters) and species that did not (urban‐sensitive or urban‐avoiders). These differences in response were likely related to individual species' life‐history and their requirements for habitat, space and dispersal. To conserve herpetofauna in urban areas we need to maintain structural complexity in remnant habitat patches, and implement strategic policies and management actions that protect habitat remnants and habitat corridors.     

State‐space modeling reveals habitat perception of a small terrestrial mammal in a fragmented landscape

相似文献   

Reef fish and habitat relationships in a Caribbean seascape: the importance of reef context

Marine protected area (MPA) effectiveness is contingent on understanding key ecological patterns and processes at appropriate spatial scales and may depend upon maintaining critical linkages among essential habitat patches to conserve reef-fish communities. Hypotheses were tested to investigate the importance of habitat linkages in the US Virgin Islands. As expected, reef context (the spatial pattern of surrounding habitat patches) was a strong predictor of reef fish assemblage structure. Specific relationships were functionally consistent with the ecology of the fishes of interest. For example, reefs with large amounts of seagrass nearby harbored the greatest numerical abundance of fishes, particularly mobile invertebrate feeders and the exploited fish families of Haemulidae (grunts) and Lutjanidae (snappers). Species richness for the entire fish community and within these fish groups was also strongly associated with reef context. Furthermore, reef fish mobility influenced how fishes related to reef context. Fish-habitat relationships were detected as far as 1 km from study reefs, suggesting that fish movements result in habitat encounter rates that may influence their patterns of distribution. Consequently, functional habitat connectivity of habitat patches appears important in structuring reef-fish assemblages, and suggests that landscape-scale metrics may provide insights useful to managers in the design of MPAs.     

Environmental drivers of spider community composition at multiple scales along an urban gradient

Broad-scale modification of natural ecosystems associated with urbanisation often leads to localised extinctions and reduced species richness. Despite this, habitats within the urban matrix are still capable of supporting biodiversity to varying degrees. As species have different responses to anthropogenic habitat modification, the species composition of urban areas can depend greatly on the habitat characteristics of the local and surrounding areas. The aim of this study was to compare the community composition of spiders in private gardens, urban parks, patches of remnant vegetation and continuous bushland sites, so as to identify habitat variables associated with variation in spider populations along and within the urban gradient and matrix. Overall spider abundances and richness were highest in remnant vegetation patches and were associated with increased vegetation cover at microhabitat and landscape-scales. While gardens were not as diverse as remnant patches, they did support a surprisingly high diversity of spiders. We also found that species composition differed significantly between gardens and other urban green spaces. Higher richness within gardens was also associated with greater vegetation cover, indicating the importance of private management decisions on local biodiversity. Differences in community composition between land-use types were driven by a small number of urban-tolerant species, and spider guilds showed different responses to habitat traits such as vegetation cover and human population densities. This study demonstrates that urban land-uses support unique spider communities and that maintaining vegetation cover within the urban matrix is essential in order to support diverse spider communities in cities.     

湖南省城市群生态网络构建与优化

大型生境斑块为区域生物多样性保护提供了重要的空间保障。然而,快速城市化使得大型生境斑块变得日益破碎化、岛屿化,连接性不断下降,且日益受到周边土地利用变化的强烈影响,已严重威胁着区域生物多样性的保护。通过生态廊道建立或修复破碎生境斑块之间的连接,将非常有利于生态网络生态服务功能的有效发挥。基于景观生态学和保护生物学的相关原理,以湖南省城市群为例,在RS和GIS技术的支撑下,采用最小费用路径和情景分析方法,定量模拟了研究区的潜在生态廊道,基于重力模型对重要生态廊道进行了识别与提取,并就消费面模型对潜在生态网络结果产生的影响进行了分析,在此基础上有针对性地提出了生态网络优化的对策。研究结果表明,林地和耕地是组成研究区生态网络的优势景观要素类型;不同生境斑块间的相互作用强度差异显著,总体上西高东低,南高北低;消费面模型能够在较大程度上影响到生态网络的分析结果,因而进行情景分析十分重要和必要。研究结果可为研究区生态网络的构建和优化提供科学依据,同时可为其他城市群区域生态网络的构建提供参考和借鉴。     

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.