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191.
Landscape modification and habitat fragmentation are key drivers of global species loss. Their effects may be understood by focusing on: (1) individual species and the processes threatening them, and (2) human-perceived landscape patterns and their correlation with species and assemblages. Individual species may decline as a result of interacting exogenous and endogenous threats, including habitat loss, habitat degradation, habitat isolation, changes in the biology, behaviour, and interactions of species, as well as additional, stochastic threats. Human-perceived landscape patterns that are frequently correlated with species assemblages include the amount and structure of native vegetation, the prevalence of anthropogenic edges, the degree of landscape connectivity, and the structure and heterogeneity of modified areas. Extinction cascades are particularly likely to occur in landscapes with low native vegetation cover, low landscape connectivity, degraded native vegetation and intensive land use in modified areas, especially if keystone species or entire functional groups of species are lost. This review (1) demonstrates that species-oriented and pattern-oriented approaches to understanding the ecology of modified landscapes are highly complementary, (2) clarifies the links between a wide range of interconnected themes, and (3) provides clear and consistent terminology. Tangible research and management priorities are outlined that are likely to benefit the conservation of native species in modified landscapes around the world. 相似文献
192.
The retreating edge hypothesis for species responding to climate change predicts severe bottlenecks and eventual extinction. The disjunct Lost Pines population at the westernmost edge of the widespread Pinus taeda range is well suited for testing this prediction. The occurrence of one or more genetic bottlenecks in the Lost Pines population was tested using 34 nuclear microsatellite markers and a control sample from the larger, more continuous east Texas P. taeda forests. The Lost Pines population has undergone drastic contractions in effective population size between 3000 and 30 000 years bp. These results were supported by: (i) detection of transient heterozygosity excess, (ii) a mode-shift indicator of allele frequencies, and (iii) a ratio of allele number to allele size range. No bottleneck was detected for the east Texas control using any of the three methods. The distribution of allele frequencies was skewed for the Lost Pines population compared to the control, indicating a loss of rare alleles. However, allelic diversity was similar between the Lost Pines population and its east Texas control; the mean allele number per locus was 5.29 and 5.38, respectively. It is proposed that the Lost Pines population was the western refugium for P. taeda during Pleistocene glaciation and that East Texas P. taeda forests descended from the bottlenecked Lost Pines population. 相似文献
193.
Eustrate Uzabaho;Noel Kwizera;Jennifer Frances Moore;Donat Nsabimana; 《African Journal of Ecology》2024,62(1):e13238
People, livestock and carnivores are constantly interacting especially at the interface between community and protected areas. The carnivore guild category in Volcanoes National Park is important, and if well studied, could lead to additional research opportunities for improved wildlife management. We used single season occupancy models with multi-species data, to understand the factors affecting species occurrence, detection and distribution among native carnivores of Volcanoes National Park while accounting for imperfect detection and the effects of site variables on the observed trends. Our findings showed that six native carnivores use the park edge, where the side-striped jackal (Canis adustus) and serval (Leptailurus serval) are the most widespread with ψ = 0.904 (SE 0.051) and ψ = 0.415 (SE 0.086), respectively, followed by African golden cat (Caracal aurata) with ψ = 0.198 (SE 0.066), while the servaline genet (Genetta servalina), slender mongoose (Herpestes sanguineus) and spotted hyaena (Crocuta Crocuta) have very low probability of occupancy with ψ = 0.087 (SE 0.045), ψ = 0.044 (SE 0.032) and ψ = 0.022 (SE 0.022) respectively. In addition, there is high occurrence of feral dogs and human presence in the park edge. Overall, the occupancy of native carnivores increases as distance from settlements increase (β = 0.559 [SE 0.195]) except for hyaena and mongoose which showed a decrease in occupancy as distance to settlements increased. In general, native carnivores preferred sites located close to pasture areas, compared to areas used for agriculture and agroforestry. High overlapping activity between native carnivores and other wildlife varied greatly between species. This study provides the baseline information for the understanding of native carnivores using the park edge and insights on their interactions with other wildlife, livestock and human activities at the interface between the park and local communities. The co-occurrence of livestock, feral dogs and humans, and native wildlife is a challenge for both wildlife conservation inside the protected area and local communities who might be negatively affected in different ways including interspecific competition, disease exposure and increased conflicts. We anticipate that some of the current livestock keeping are hindered by the challenges of having native carnivores dwelling along the park edge and community interface. 相似文献
194.
Tomoki Sakiyama;Jorge García Molinos; 《Journal of Biogeography》2024,51(7):1199-1212
Despite warming temperatures, some species are found persisting at the trailing edge of their distribution. Microclimates provided by complex topography are considered a key factor in these cases of range stationarity, buffering stress from exposure to warming and enabling persistence. However, for species with trailing-edges located in human-modified landscapes, refugial conditions provided by microclimates could be disrupted by human activities. Here, we aimed to understand the determinants of trailing-edge occupancy for a small lagomorph found in rocky patches harbouring cool microclimates. 相似文献
195.
Licong Liu;Jin Chen;Miaogen Shen;Xuehong Chen;Ruyin Cao;Xin Cao;Xihong Cui;Wei Yang;Xiaolin Zhu;Le Li;Yanhong Tang; 《Global Change Biology》2024,30(1):e17005
Climate change has induced substantial shifts in vegetation boundaries such as alpine treelines and shrublines, with widespread ecological and climatic influences. However, spatial and temporal changes in the upper elevational limit of alpine grasslands (“alpine grasslines”) are still poorly understood due to lack of field observations and remote sensing estimates. In this study, taking the Tibetan Plateau as an example, we propose a novel method for automatically identifying alpine grasslines from multi-source remote sensing data and determining their positions at 30-m spatial resolution. We first identified 2895 mountains potentially having alpine grasslines. On each mountain, we identified a narrow area around the upper elevational limit of alpine grasslands where the alpine grassline was potentially located. Then, we used linear discriminant analysis to adaptively generate from Landsat reflectance features a synthetic feature that maximized the difference between vegetated and unvegetated pixels in each of these areas. After that, we designed a graph-cut algorithm to integrate the advantages of the Otsu and Canny approaches, which was used to determine the precise position of the alpine grassline from the synthetic feature image. Validation against alpine grasslines visually interpreted from a large number of high-spatial-resolution images showed a high level of accuracy (R2, .99 and .98; mean absolute error, 22.6 and 36.2 m, vs. drone and PlanetScope images, respectively). Across the Tibetan Plateau, the alpine grassline elevation ranged from 4038 to 5380 m (5th–95th percentile), lower in the northeast and southeast and higher in the southwest. This study provides a method for remotely sensing alpine grasslines for the first-time at large scale and lays a foundation for investigating their responses to climate change. 相似文献
196.
Jacek K. Pijanka Petar P. Markov Dan Midgett Neil G. Paterson Nick White Emma J. Blain Thao D. Nguyen Harry A. Quigley Craig Boote 《Journal of biophotonics》2019,12(5)
Second harmonic generation (SHG) microscopy is widely used to image collagen fiber microarchitecture due to its high spatial resolution, optical sectioning capabilities and relatively nondestructive sample preparation. Quantification of SHG images requires sensitive methods to capture fiber alignment. This article presents a two‐dimensional discrete Fourier transform (DFT)–based method for collagen fiber structure analysis from SHG images. The method includes integrated periodicity plus smooth image decomposition for correction of DFT edge discontinuity artefact, avoiding the loss of peripheral image data encountered with more commonly used windowing methods. Outputted parameters are as follows: the collagen fiber orientation distribution, aligned collagen content and the degree of collagen fiber dispersion along the principal orientation. We demonstrate its application to determine collagen microstructure in the human optic nerve head, showing its capability to accurately capture characteristic structural features including radial fiber alignment in the innermost layers of the bounding sclera and a circumferential collagen ring in the mid‐stromal tissue. Higher spatial resolution rendering of individual lamina cribrosa beams within the nerve head is also demonstrated. Validation of the method is provided in the form of correlative results from wide‐angle X‐ray scattering and application of the presented method to other fibrous tissues. 相似文献
197.
Laura Super;Robert D. Guy; 《植被学杂志》2024,35(2):e13251
Do nitrogen deposition and climate warming affect tree seedlings and plant communities in different habitats? In these habitats, how do microenvironments, including soil properties and, when applicable, edge effects relate to plant performance? 相似文献
198.
Linda Söderberg Gaston Lavén Marcin Kalek Professor Jacek Stawinski 《Nucleosides, nucleotides & nucleic acids》2013,32(7-8):552-564
31P NMR spectroscopy was used to investigate a stereochemical course of a nitrite-promoted conversion of phosphoramidate diesters into the corresponding phosphotriesters. It was found that this reaction occurred with almost complete epimerization at the phosphorus center and at the C1 atom in the amine moiety. On the basis of the 31P NMR data, a plausible mechanism for the reaction was proposed. The density functional theory calculation of the key step of the reaction, i.e., breaking of the P–N bond and formation of the P–O bond, suggested a one-step SN2(P) process with retention of configuration at the phosphorus center. 相似文献
199.
Gelareh Valadi Javad Eshaghi Rad Yahia Khodakarami Mostafa Nemati Peykani Karen A. Harper 《Journal of Plant Ecology》2022,15(2):413
伊朗稀疏橡木林片段对草本植物物种多样性和土壤特性的边缘影响温带和热带森林中的森林边缘现象已经得到了很好的研究,但在稀疏的橡木林片段中的相关研究却较为缺乏。本文研究了稀疏橡木林片段对植物物种多样性和土壤特性的边缘影响。本研究沿着伊朗克尔曼沙赫省3个小型(<10 ha)和3个大型(>10 ha)橡木林片段的3个横断面收集了从边缘到内部的相 关数据,测量了0(森林边缘)、25、50、100和150 m处的草本植物(高度<0.5 m)和土壤特性。使用香农指数量化了物种多样性,使用稀疏标准化方法比较了两个大小不同片段中的物种丰富度,并应用了非度量多维测度排序研究了物种组成的变化。通过随机化测试估算了边缘影响的距离,并利用Tukey HSD事后检验法的广义线性混合模型评估了距边缘距离和片段大小对多样性和土壤特性的影响。研究结果表明,大小片段边缘具有较高的物种丰富度、多样性和均匀度,而大片段边缘的土壤氮和有机碳含量则较内部更低(边缘50 m范围内的变化最大)。大小片段的物种组成、土壤有机碳和氮总量都存在显 著差异。本研究关于这些稀疏森林对草本植物和土壤特性产生显著边缘影响的发现,对于边缘研究,尤其是边缘和草本植物的相关研究具有重大贡献。 相似文献
200.
新疆白杨河流域特征及生态植被需水分析 总被引：1，自引：0，他引：1
新疆白杨河流域地跨上游乌鲁木齐市达坂城及下游吐鲁番市托克逊县两个行政区,上游达坂城区位于天山博格达峰山前冲击、洪积山间盆地干旱区,源于天山多支源流汇集于盆地南端峡口,基于峡口形成下游并由有多支流沿程补给白杨河干流,穿越极端干旱戈壁荒漠区的托克逊县直至末端吐鲁番市境内尾闾-艾丁湖,是我国典型少有的跨越干旱与极端干旱叠加型流域灌区,水资源有效利用及水生态环境保护具有重要作用。遵循流域各河流水系形成的自然生态环境属性及河道取水工程节点,采用Penman-Monteith法生态需水定额和卫星遥感面积识别及水文年内展布方法,分析评估流域内上下游绿洲生态环境植被需水量和河流生态基流及其调控断面。结果表明,上游达坂城区黑沟河年生态需水量、生态基流、年均径流占比和控制断面,分别为921万m3、0.29m3/s、18%和黑沟渠首;阿克苏河为1048万m3、0.33m3/s、12%和阿克苏渠首;高崖子河为862万m3、0.27m3/s、12%和高崖子渠首;下游托克逊境内由白杨河干流调节,艾丁湖等生态需水量分别为4256万m3、1.35m3/s、32%和小草湖渠首。白杨河流域年生态需水7880万m3,生态基流2.50m3/s,生态水占年均径流量17%,分析结果为流域生态环境管理保护提供依据。 相似文献