The effect of landscape structure on dispersal distances of the Eurasian red squirrel

Landscape structure can affect dispersal and gene flow in a species. In urban areas, buildings, roads, and small habitat patches make the landscape highly fragmented and can inhibit movement and affect dispersal behavior. Similarly, in rural forested areas, large open areas, such as fields, may act as barriers to movement. We studied how landscape structure affects natal dispersal distances of Eurasian red squirrels (Sciurus vulgaris) in an urban area and a rural area in Finland, by monitoring juvenile red squirrels with radio telemetry. We observed extremely long dispersal distances—up to 16 km—in the rural study area, but shorter distances—on average only half a kilometer—in the urban study area. The landscape structure affected the eventual dispersal paths; in the rural landscape, dispersers favored spruce dominated areas and avoided fields along their dispersal route, although they occasionally even crossed wide fields. In the urban landscape, squirrels preferred areas with deciduous or coniferous trees. The movement steps made by dispersers were longer in the more hostile landscape compared to forested areas. Despite these effects on movement path, the landscape structure only had a minor effect on straight line dispersal distances moved from the natal nest. In other words, individuals moved longer distances and were likely to circumvent barriers in their path, but this did not affect how far they settled from their natal home. This result indicates that, although landscape structure has obvious effects on movement, it still may have only a small effect on other aspects of the population, for example, gene flow.     

不同空间尺度景观特征对南流江水质的影响差异

流域景观特征决定了非点源污染物来源与地表景观削减消纳能力,但尚缺乏全流域不同空间尺度对二者关联性的认识。以广西北部湾南流江为例,分别在子流域、河岸缓冲带以及监测点圆形缓冲区三种尺度上,基于2020年Landsat 8 OLI遥感影像解译的土地利用类型特征,结合水质监测数据,运用数理统计和GIS空间分析方法,探讨了流域景观特征在不同空间尺度上对河流水质的影响。结果表明：(1)在子流域尺度,土地利用类型以林地为主,而在河岸缓冲带与监测点圆形缓冲区均以耕地为主;(2)水质指标高锰酸盐指数、生化需氧量与景观特征相关性最为显著,耕地、建设用地、其他用地和园地与其呈正相关,是南流江水质污染负荷的重要来源区;景观格局指数中,斑块密度、蔓延度指数、多样性指数、均匀度指数是引起河流水质指标变化的主要景观因子;(3)受流域内或不同子流域间景观特征差异,景观组成面积占比和景观格局指数均在河岸缓冲带尺度对水质状况影响最大,分别可解释57.0%和64.7%的水质指标变化;子流域尺度次之,圆形缓冲区尺度最小,且景观格局指数对水质状况的影响大于景观组成面积占比。建议在河岸带50 m范围内严格控制耕地面积,建设河岸缓...     

Assessing the spatial ecology and resource use of a mobile and endangered species in an urbanized landscape using satellite telemetry and DNA faecal metabarcoding

The conservation of highly mobile species presents challenges to managers for assessment of threats to survival, given the difficulties in locating and observing such species. Here we evaluate satellite telemetry, DNA faecal metabarcoding and traditional field observations as three complementary techniques to acquire critical management information for an endangered species, Carnaby's Cockatoo Calyptorhynchus latirostris. Satellite telemetry of 23 birds resulted in 6026 location fixes accurate to within 500 m, and combined with extensive field observations and DNA faecal metabarcoding resulted in a more detailed understanding of how this species survives in an urbanized landscape. We identified 168 night roosts, 75% of which were previously unknown, which will contribute towards a more accurate population size estimate based on annual counts of roosting birds. We also determined the scale of daily movements (morning 5.4 ± 3.4 km from roost, afternoon 5.5 ± 3.3 km to roost; maximum distance between consecutive roosts 69.7 km) and the size of foraging areas around roosts (range 17–276 km²), and identified dependence on a variety of native and exotic food sources. Field observations identified 11 food‐plant families, but combined with DNA faecal metabarcoding this was extended to 21 food‐plant families. The three techniques were compared to assess their individual and collective values. By combining spatial ecology information from satellite telemetry with ecological knowledge from field observation and DNA faecal analysis, we gained deeper insights into the ecology of the species than would have been possible from any one technique alone. This information will lead to more strategic conservation planning to allow this species to persist within a rapidly expanding urban environment.     

景观破碎化对东北虎主要猎物种群动态影响的模拟

以完达山东部地区的现实景观为背景,采用空间直观种群模型LAPS和情景模拟相结合的"虚拟实验"途径,模拟了在10个不同破碎化程度的景观情景中东北虎的主要猎物于1992-2011年间的种群动态,评价了完达山东部地区当前的景观破碎化程度对东北虎主要猎物种群动态的影响。结果表明:LAPS模型准确刻画了研究区东北虎主要猎物种群数量急剧下降的趋势,2002年模拟的东北虎主要猎物的种群数量和实测值之间没有显著差异,马鹿、野猪和狍子的P值分别为0.8651、0.9534和0.2836;不同生境类型的种群密度数据与实测值之间均没有显著差异,其中阔叶林生境中的马鹿、野猪和狍子的P值分别为0.8521、0.9447和0.3152;在灌丛生境中的马鹿、野猪和狍子的P值分别为0.8846、0.9576和0.2415。斑块类型和景观水平上的格局指标变化趋势表明由于农田扩张导致10个景观情景的破碎化程度逐渐增加,景观水平的破碎化程度低于斑块类型水平。方差分析显示10个景观情景中的种群数量没有显著差异,马鹿、野猪和狍子的P值分别为0.8516、0.2624和0.7636,说明研究区当前的景观破碎化程度对种群动态影响并不显著。完达山东部地区存在盗猎等人为干扰,导致了东北虎主要猎物的数量远低于环境容纳量,景观破碎化虽然在局部地区较为严重,但完达山东部地区整体上景观破碎化并不强烈,该地区景观破碎化的效应尚未显现。认为控制盗猎等人为干扰是增加该地区东北虎主要猎物的数量、实现东北虎种群恢复所应优先采取的措施。     

Using isolation‐by‐distance‐based approaches to assess the barrier effect of linear landscape elements on badger (Meles meles) dispersal

As the European badger (Meles meles) can be of conservation or management concern, it is important to have a good understanding of the species’ dispersal ability. In particular, knowledge of landscape elements that affect dispersal can contribute to devising effective management strategies. However, the standard approach of using Bayesian clustering methods to correlate genetic discontinuities with landscape elements cannot easily be applied to this problem, as badger populations are often characterized by a strong confounding isolation‐by‐distance (IBD) pattern. We therefore developed a two‐step method that compares the location of pairs of related badgers relative to a putative barrier and utilizes the expected spatial genetic structure characterized by IBD as a null model to test for the presence of a barrier. If a linear feature disrupts dispersal, the IBD pattern characterising pairs of individuals located on different sides of a putative barrier should differ significantly from the pattern obtained with pairs of individuals located on the same side. We used our new approach to assess the impact of rivers and roads of different sizes on badger dispersal in western England. We show that a large, wide river represented a barrier to badger dispersal and found evidence that a motorway may also restrict badger movement. Conversely, we did not find any evidence for small rivers and roads interfering with badger movement. One of the advantages of our approach is that potentially it can detect features that disrupt gene flow locally, without necessarily creating distinct identifiable genetic units.     

The effect of landscape features on population genetic structure in Yunnan snub-nosed monkeys (Rhinopithecus bieti) implies an anthropogenic genetic discontinuity

The Tibetan Plateau is one of the top 10 biodiversity hotspots in the world and acts as a modern harbour for many rare species because of its relatively pristine state. In this article, we report a landscape genetic study on the Yunnan snub-nosed monkey ( Rhinopithecus bieti ), a primate endemic to the Tibetan Plateau. DNA was extracted from blood, tissue and fecal samples of 135 wild individuals representing 11 out of 15 extant monkey groups. Ten microsatellite loci were used to characterize patterns of genetic diversity. The most striking feature of the population structure is the presence of five subpopulations with distinct genetic backgrounds and unique spatial regions. The population structure of R. bieti appears to be shaped by anthropogenic landscape features as gene flow between subpopulations is strongly impeded by arable land, highways and human habitation. A partial Mantel test showed that 36.23% ( r  =   0.51, P  =   0.01) of the genetic distance was explained by habitat gaps after controlling for the effect of geographical distance. Only 4.92% of the genetic distance was explained by geographical distance in the partial Mantel test, and no significant correlation was found. Estimation of population structure history indicates that environmental change during the last glacial maximum and human impacts since the Holocene, or a combination of both, have shaped the observed population structure of R. bieti . Increasing human activity on the Plateau, especially that resulting in habitat fragmentation, is becoming an important factor in shaping the genetic structure and evolutionary potential of species inhabiting this key ecosystem.     

Assessing the effect of management changes and environmental features on the spatio- temporal pattern of fire in an African Savanna: Fire spatio-temporal pattern

Spatio-temporal variability of the fire regime in the Kruger National Park (KNP) has been analyzed for the 1957–2011 period. Generalized linear mixed models have been used to assess the variability of fire metrics, such as the burnt area, the fire frequency and intensity for the entire area as well as for the main environmental classification systems (geology, soil, vegetation) and fire management zones. This analysis supports the hypothesis that the spatial pattern of fire regime is strongly influenced by the environmental template defined by climatic, geological, pedological and vegetation features. Moreover, contrary to some previous studies, together with the precipitation trend, fire management changes had a significant role in determining the temporal variability of the fire regime at the scale of KNP, particularly regarding the burnt area and the fire frequency.The complex interaction between the environmental template and management in determining the variability of the fire regime, as underscored by our study, defends the merit of adopting an adaptive planning/management based approach supported by quantitative analytic tools.     

Assessing edge effect on the spatial distribution of selected forest biochemical properties derived using the Worldview data in Dukuduku forests,South Africa

This work explores the potential of the high‐resolution WorldView‐2 sensor in quantifying edge effects on the spatial distribution of selected forest biochemical properties in fragmented Dukuduku forest in KwaZulu‐Natal, South Africa. Specifically, we sought to map fragmented patches within forested areas in Dukuduku area, using very high spatial resolution WorldView‐2 remotely sensed data and to statistically determine the effect of these fragmented patches on the spatial distribution of selected forest biochemical properties. Edge effects on carbon, LAI and foliar nitrogen were quantified based on the models derived by Omer et al. (IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015, 8, 4825). Edge effect statistical results on the spatial distribution of carbon, LAI and nitrogen showed significant (α = 0.05) variations with change in distance from fragmented patches (>150 m²). Forest foliar carbon concentrations significantly (p‐value = 0.016) increased from 44.8% to 45.3% with increasing distance (25–375 m) from fragmented patches. A similar trend was observed for LAI. Nevertheless, for nitrogen the results show that its concentration significantly (p = 0.016) decreased with increase in distance from the fragmented patches. Overall, the findings of this work underscore the invaluable potential and strength of WorldView‐2 data set in assessing edge effect on the spatial distribution of selected forest biochemical properties.     

A gradient analysis based on the buffer zones of urban landscape pattern of the constructed area in Guigang City, Guangxi, China

Over the last century urbanization on the landscape has increased and intensified. Urban development has a great impact on the environment at the local, regional and even global levels. As a driving force in global change, the need to understand the dynamics of urban pattern and its change in an accurate and efficient manner is ever more pressing. Based on aerial color infrared photography in 1985 and QuickBird satellite imagery in 2004 and according to the standard for plan and construction of city land use, the landscape of Guigang City was divided into 11 types. In the landscape classification maps, 31 buffer zones, each being 200 m wide, were divided. With the aid of GIS software ArcView 3.2 and landscape pattern analysis software FRAGSTATS 3.3, the landscape spatial patterns of each buffer zone were analyzed at the landscape level and class level. The landscape indices, such as patch size, patch fractal dimension, diversity index and evenness index, were calculated. The results indicated the following: The total area of the residential land and the communal land in 2004 covered 46.3% of the entire constructed area of Guigang City and the sum of the patch number of the two patch types occupied about 39.7% of the total patch number, while the percentages were respectively 48.2% and 45.4% in 1985. This showed that the mosaic landscape with the residential land and communal facilities land became increasingly unclear following urban development and landscape diversity. Based on the gradient analysis with the landscape-level index and the class-level index, there were two business and finance centers in the constructed area. One was located in the urban center with a range of 0.8 km; the other was from the 10^th to the 16^th zone. In each buffer zone, the mean patch size was larger and the landscape shape was more regular in 2004 than in 1985. Furthermore, the Shannon diversity index of each buffer zone rose in 2004 with patch richness and evenness increasing. The landscape index computed for the main landscape types (communal facilities land, industrial estate land, residential land and farmland) in the middle of the buffer zones clearly indicated the changes taking place in urbanization. The patch size and the patch number of industrial estate land and farmland also pointed to these changes, while communal facilities land and residential land assumed another similar tendency towards changes. In each gradient zone, industrial estate land had the most complex shape, the lowest area percentage of each zone and the biggest mean patch size, whereas communal facilities land and residential land were opposite to industrial estate land. Farmland had a steady percentage along the buffer zone and its continuous distribution had an important impact on the urban eco-environment. The question of how to relate the pattern of changing characteristics along the buffer zone to the urban ecological process and urban ecological planning remains to be studied further in the future.     

Assessing the agronomic and environmental effects of the application of cattle manure compost on soil by multivariate methods

Multivariate analysis was used for interpreting data from a pot experiment using samples of three Spanish soils. Samples of soil fertilized with compost were compared with untreated control samples. We also compared the effect of adding the compost to soil with a controlled moisture content of 50% of its water holding capacity (WHC), and to a near-saturated soil (95% WHC). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used; they perfectly differentiated sample groups both as a function of the treatment applied and by sampling date. The compost samples were characterized by higher pH, electrical conductivity (EC), organic matter (OM) content and cation exchange capacity (CEC), together with nutrient concentrations than the control pots. The pots with a soil–compost mixture at 95% WHC presented lower values of EC, CEC, inorganic N, K, Na and B than the mixtures at 50% WHC. Multivariate methods may therefore be useful for the analysis and interpretation of a large number of data in soil research.     

地形对大兴安岭北坡林火迹地森林景观格局影响的梯度分析

198 7年大兴安岭“5 .6”特大森林火灾 ,过火面积 1.33× 10 6 hm2 。火后 ,不同的火烧强度区和岛状的未火烧区形成了一个异质镶嵌体 ,然而在自然演替和人为干扰作用下 ,十几年过去之后这种异质镶嵌体格局已经发生了明显变化。以大兴安岭北坡 ,图强林业区的育英和奋斗两个林场为研究区 ,总面积 1.2× 10 5hm2 ,在景观尺度上 ,以遥感和地理信息系统为技术手段 ,将地形因子进行梯度划分 ,并运用分布指数和偏相关分析探讨了大兴安岭在 1987年大火后森林景观在地形梯度上的变化情况。研究结果表明 :森林景观在地形梯度上的格局发生了明显的变化 ,但是不同的景观斑块类型变化幅度不同 ,不同的地形因子对不同森林景观斑块类型变化的影响强度也迥异 ;偏相关分析表明地形对主要森林景观斑块类型之间的变化影响最大的是坡度 ,其次是海拔 ,坡向的影响不明显。     

Influence of the surrounding landscape on crop colonization by a polyphagous insect pest

Landscape composition plays an important, but poorly understood, role in the population dynamics of agricultural pest species with broad host ranges including both crops and weeds. One such pest, the generalist plant bug Lygus hesperus Knight (Hemiptera: Miridae), is a key cotton pest that feeds on various hosts differing in quality in California's San Joaquin Valley (USA). We investigated the effects of 15 common crops and uncultivated agricultural land on L. hesperus populations, by correlating the densities of L. hesperus in focal cotton fields with the areas of the 16 crops in surrounding rings. Insect counts were provided by private pest‐control advisors, and spatial data were obtained from Kern County records. We first calculated Spearman's partial correlation coefficients on an annual basis for each crop separately, and then performed a meta‐analysis of these correlations across years to describe the overall effect of a particular crop on L. hesperus after the effects of the 15 other crops are removed. Consistent with studies conducted in other areas, L. hesperus density was positively correlated with safflower, and negatively with cotton. Lygus hesperus density was also correlated with several other crops that are often not considered in pest management, including grape, oat, and onion (positive correlations), and almond, pistachio, and potato (negative correlations). Lygus hesperus density was also found to be negatively correlated with alfalfa and positively correlated with uncultivated habitats, a relationship that receives mixed support in the literature. Several other crops tested were not significantly correlated with L. hesperus densities in focal cotton fields, suggesting a neutral role for them in L. hesperus dynamics. The improved understanding of the effects of a greater variety of crops on L. hesperus population dynamics will be useful in the design of agricultural landscapes for enhanced management of this important polyphagous pest.     

Deciphering the effect of climate warming on an emerging poplar pest using spatial extrapolation of population parameters

1. The woolly poplar aphid Phloeomyzus passerinii Signoret (Aphididae: Phloeomyzinae) is a major pest of poplar plantations. We hypothesized that recent temperature increases may have contributed to the emergence and subsequent northward expansion of outbreaks in France.
2. We reared P. passerinii at four temperatures to estimate its thermal requirements. We used experimental data to parametrize a mechanistic and temperature-driven physiologically-based demographic model. The model was used to simulate the effect of temperature on aphid dynamics and to assess the role of climate warming on the spatiotemporal dynamics of outbreaks.
3. The lower developmental threshold was estimated at 6.4 °C and the development degree-days at 171.
4. Our model supports the hypothesis that recent warming may have promoted outbreaks in northern France. During recent exceptionally warm years, more than 70% of the northern poplar area was favourable for outbreaks.
5. Our model suggests that climate warming is not the sole factor involved. The dominance of resistant poplar genotypes such as ‘Robusta’ or ‘Beaupré’ may have preserved plantations from outbreaks before 1996 in southern France and until 2000 in the central part. Other factors, including biological characteristics, biotic interactions, or precipitation should be investigated.

     

Studying the effect of a charged surface on the interaction of bleomycin with DNA using an atomic force microscope

The cleavage of DNA caused by the antitumoral drug bleomycin has been investigated using atomic force microscopy (AFM). This work deals with the effect that adsorbing DNA onto a positively- or negatively-charged surface has on the double-strand cleavage of DNA by Fe(III)/bleomycin. Quantitative analysis of the number of breaks per DNA molecule, in bulk and at the surface of the mica substrate, has been performed by analyzing AFM images. It turns out that the cleavage of DNA is strongly inhibited by a positively-charged surface. Our experiments can be interpreted using a simple electrostatic model. This paper is a first step in the study of DNA accessibility to ligand such as bleomycin, using AFM in liquids.Olivier Piétrement and David Pastré have contributed equally to the work.     

The effect of warmer winters on the demography of an outbreak insect is hidden by intraspecific competition

Warmer climates are predicted to increase bark beetle outbreak frequency, severity, and range. Even in favorable climates, however, outbreaks can decelerate due to resource limitation, which necessitates the inclusion of competition for limited resources in analyses of climatic effects on populations. We evaluated several hypotheses of how climate impacts mountain pine beetle reproduction using an extensive 9‐year dataset, in which nearly 10,000 trees were sampled across a region of approximately 90,000 km², that was recently invaded by the mountain pine beetle in Alberta, Canada. Our analysis supports the hypothesis of a positive effect of warmer winter temperatures on mountain pine beetle overwinter survival and provides evidence that the increasing trend in minimum winter temperatures over time in North America is an important driver of increased mountain pine beetle reproduction across the region. Although we demonstrate a consistent effect of warmer minimum winter temperatures on mountain pine beetle reproductive rates that is evident at the landscape and regional scales, this effect is overwhelmed by the effect of competition for resources within trees at the site level. Our results suggest that detection of the effects of a warming climate on bark beetle populations at small spatial scales may be difficult without accounting for negative density dependence due to competition for resources.     

Floristic homogenization by native ruderal and alien plants in north-east Spain: the effect of environmental differences on a regional scale

Aim To evaluate the relative potential contribution of native ruderals and aliens to plant homogenization at a regional scale, after taking into account the effect of diverse environmental distances. Location Catalonia (north‐east Spain) Methods We have used the flora module of the BDBC project (Catalonian Database of Biodiversity), which provides information on plant species distribution per 10 × 10 km Universal Transverse Mercator (UTM) cell. Pairwise floristic similarities of: (1) total, (2) native non‐ruderal, (3) native ruderal, and (4) alien vascular plant species have been calculated for a particularly well‐sampled subset of UTM cells, using a modified version of the Simpson index. These similarities have been compared per UTM pair using Mantel tests, before and after considering their relative association with geographical, climatic and landscape distances from linear regression models. The floristic similarity of both total and native non‐ruderal species was also correlated with the proportion of alien and native ruderal species after discounting the effects of environmental distances. Results The proportion of variance explained by environmental correlates was highest for the floristic similarity of native non‐ruderal plants and lowest for that of aliens. In all plant groups, climatic distance was the main significant variable of species similarity. Geographical distance was only significant for total and native non‐ruderal species and was of secondary importance in both cases. Landscape distance was not significant in any case. Similarities among both aliens and native ruderals were significantly higher than among native non‐ruderals, but these differences disappeared after removing the effect of environmental distances. Main conclusions Species similarity between sites may depend on differences in environmental factors other than geographical distance. This has to be taken into account when exploring the implications for biotic homogenization. In the case of Catalonian flora, the potentially homogenizing effect of native ruderal and alien species seems to be associated with their lower dependence on geographical distance and climatic factors compared with those of native, non‐ruderal species.     

Field studies on the environmental fate of the Cry1Ab Bt-toxin produced by transgenic maize (MON810) and its effect on bacterial communities in the maize rhizosphere

Field studies were done to assess how much of the transgenic, insecticidal protein, Cry1Ab, encoded by a truncated cry1Ab gene from Bacillus thuringiensis (Bt), was released from Bt-maize MON810 into soil and whether bacterial communities inhabiting the rhizosphere of MON810 maize were different from those of the rhizosphere of nontransgenic maize cultivars. Bacterial community structure was investigated by SSCP (single-strand conformation polymorphism) of PCR-amplified 16S rRNA genes from community DNA. Using an improved extraction and detection protocol based on a commercially available ELISA, it was possible to detect Cry1Ab protein extracted from soils to a threshold concentration of 0.07 ng/g soil. From 100 ng of purified Cry1Ab protein added per gram of soil, only an average of 37% was extractable. At both field sites investigated, the amount of Cry1Ab protein in bulk soil of MON810 field plots was always lower than in the rhizosphere, the latter ranging from 0.1 to 10 ng/g soil. Immunoreactive Cry1Ab protein was also detected at 0.21 ng/g bulk soil 7 months after harvesting, i.e. in April of the following year. At this time, however, higher values were found in residues of leaves (21 ng/g) and of roots (183 ng/g), the latter corresponding to 12% of the Cry1Ab protein present in intact roots. A sampling 2 months later indicated further degradation of the protein. Despite the detection of Cry1Ab protein in the rhizosphere of MON810 maize, the bacterial community structure was less affected by the Cry1Ab protein than by other environmental factors, i.e. the age of the plants or field heterogeneities. The persistence of Cry1Ab protein emphasizes the importance of considering post-harvest effects on nontarget organisms.