Landscape Gradient Research Articles

Evidence for regional nitrogen stress on chlorophyll a in lakes across large landscape and climate gradients

AbstractNitrogen (N) and phosphorus (P) commonly stimulate phytoplankton production in lakes, but recent observations from lakes from an agricultural region suggest that nitrate may have a subsidy‐stress effect on chlorophyll a (Chl a). It is unclear, however, how generalizable this effect might be. Here, we analyzed a large water quality dataset of 2385 lakes spanning 60 regions across 17 states in the Northeastern and Midwestern U.S. to determine if N subsidy‐stress effects on phytoplankton are common and to identify regional landscape characteristics promoting N stress effects in lakes. We used a Bayesian hierarchical modeling framework to test our hypothesis that Chl a–total N (TN) threshold relationships would be common across the central agricultural region of the U.S. (“the Corn Belt”), where lake N and P concentrations are high. Data aggregated across all regions indicated that high TN concentrations had a negative effect on Chl a in lakes with concurrent high total P. This large‐scale pattern was driven by relationships within only a subset of regions, however. Eight regions were identified as having Chl a–TN threshold relationships, but only two of these regions located within the Corn Belt clearly demonstrated this subsidy‐stress relationship. N stress effects were not consistent across other intense agricultural regions, as we hypothesized. These findings suggest that interactions among regional land use and land cover, climate, and hydrogeology may be important in determining the synergistic conditions leading to N subsidy‐stress effects on lake phytoplankton.

The role of topography and plant functional traits in determining tropical reforestation success

Abstract Early establishment and sapling growth is a key phase in ensuring cost‐effective reforestation success in relation to biodiversity outcomes. Therefore, species selection must consider the interaction between plant functional traits and the often‐challenging and heterogeneous biophysical environment of degraded landscapes. In this study, we examine how microtopography (slope) results in spatial heterogeneity of soil nutrients, especially phosphorus (P) in a degraded tropical pasture landscape in Queensland, Australia. We then explore how this small‐scale heterogeneity influences the growth of two native tree species, Cardwellia (C.) sublimis (Proteaceae) and Flindersia (F.) brayleyana (Rutaceae), which differ in key nutrient‐acquisition strategies. The proteaceous C. sublimis was found to be buffered from possible P limitation in degraded soils due to its effective P acquisition by cluster roots. In contrast to C. sublimis, which showed no difference in growth after 5 years across a range of soil conditions, F. brayleyana was found to be highly responsive to soil conditions with increased growth in low‐slope, higher P availability areas. The ability of F. brayleyana to take advantage of high soil P levels, including the development of leaves with higher P concentrations, resulted in an apparent switch in competitive fitness between these two species across a landscape gradient. Synthesis and applications. In a detailed study of a landscape reforestation experiment in North Queensland, Australia, we demonstrate that site edaphic factors can vary within tens of metres due to topographic relief, and that species respond differently to these conditions. We therefore show the need to consider both the spatial heterogeneity of edaphic factors and the below‐ground functional traits of potential reforestation species when planning reforestation programmes.

OCO-2 advances photosynthesis observation from space via solar-induced chlorophyll fluorescence

Quantifying gross primary production (GPP) remains a major challenge in global carbon cycle research. Spaceborne monitoring of solar-induced chlorophyll fluorescence (SIF), an integrative photosynthetic signal of molecular origin, can assist in terrestrial GPP monitoring. However, the extent to which SIF tracks spatiotemporal variations in GPP remains unresolved. Orbiting Carbon Observatory-2 (OCO-2)'s SIF data acquisition and fine spatial resolution permit direct validation against ground and airborne observations. Empirical orthogonal function analysis shows consistent spatiotemporal correspondence between OCO-2 SIF and GPP globally. A linear SIF-GPP relationship is also obtained at eddy-flux sites covering diverse biomes, setting the stage for future investigations of the robustness of such a relationship across more biomes. Our findings support the central importance of high-quality satellite SIF for studying terrestrial carbon cycle dynamics.

Signal information of bird song changes in human-dominated landscapes

Communication systems rely upon specific social contexts and environments that permit effective transmission, and thus, are particularly vulnerable to disruption by anthropogenic disturbance. The acoustic environments of cities may affect conspecific interactions by altering the transmission or reception of song in ways that might ultimately influence fitness, however, the evolutionary and ecological consequences of altered songs remain poorly understood. We hypothesized that the relationship between bird song attributes and fitness metrics would be landscape-dependent, differing between urban and rural habitats. We investigated this hypothesis by measuring vocal and breeding behavior of 54 male Northern Cardinals (Cardinalis cardinalis) at nine sites distributed across a rural to urban landscape gradient in Columbus, Ohio in 2011. Interestingly, we found evidence that relationships between song attributes and male quality differed among landscapes. Shorter and slower songs were associated with larger males in more preferred territories (i.e. with denser vegetation), but only in rural landscapes. Across all landscapes, males that sang at high frequencies had nestlings in poorer condition, but otherwise song attributes were not associated with reproductive output or male provisioning ability. Our results suggest that urban landscapes change the function of song as a signal of quality and could reduce the usefulness of song as a predictor of reproductive performance. This is one of few studies to investigate signal relationships and potential fitness consequences of song variation in natural urban systems, thereby providing insight into micro-evolutionary processes operating within novel environments.

Patterns of Soil Bacterial Richness and Composition Tied to Plant Richness, Soil Nitrogen, and Soil Acidity in Alpine Tundra

ABSTRACTPatterns of soil bacterial richness using operational taxonomic units (OTUs) and abundance of bacterial groups (phylum or class) were studied in relation to plant richness and soil characteristics in the alpine at Niwot Ridge, Colorado, U.S.A. The study used a landscape gradient and snow fence in addition to plots amended with nitrogen (N). Bacterial richness was not correlated with total soil carbon (C) or total soil N, but showed strong positive correlations with pH and corresponding correlations with metallic cation concentrations. Bacterial richness showed a strong negative correlation (r = −0.86) with soil acidity and declined 30% over the pH gradient of 6.0–4.5. Plant richness correlated with acidity (r = −0.70) and declined 50% over this gradient. Bacterial OTU richness was sensitive to acidity but not to N amendments. However, abundance of five bacterial groups responded positively to N, four responded negatively, and three groups exhibited no changes. In plots with additional snow, snow additions reduced OTU richness. However, when snow was included in an ANCOVA model with N and soil acidity, OTUs were not affected, suggesting that snow effects were largely captured by soil acidity changes. Bacterial richness was correlated with forb richness and cover, but causal relationships remain unresolved.

Going beyond the green: senesced vegetation material predicts basal area and biomass in remote sensing of tree cover conditions in an African tropical dry forest (miombo woodland) landscape

In sub-Saharan Africa (SSA), tropical dry forests and savannas cover over 2.5 million km2 and support livelihoods for millions in fast-growing nations. Intensifying land use pressures have driven rapid changes in tree cover structure (basal area, biomass) that remain poorly characterized at regional scales. Here, we posed the hypothesis that tree cover structure related strongly to senesced and non-photosynthetic (NPV) vegetation features in a SSA tropical dry forest landscape, offering improved means for satellite remote sensing of tree cover structure compared to vegetation greenness-based methods. Across regrowth miombo woodland sites in Tanzania, we analyzed relationships among field data on tree structure, land cover, and satellite indices of green and NPV features based on spectral mixture analyses and normalized difference vegetation index calculated from Landsat 8 data. From satellite-field data relationships, we mapped regional basal area and biomass using NPV and greenness-based metrics, and compared map performances at landscape scales. Total canopy cover related significantly to stem basal area (r2 = 0.815, p < 0.01) and biomass (r2 = 0.635, p < 0.01), and NPV dominated ground cover (> 60%) at all sites. From these two conditions emerged a key inverse relationship: skyward exposure of NPV ground cover was high at sites with low tree basal area and biomass, and decreased with increasing stem basal area and biomass. This pattern scaled to Landsat NPV metrics, which showed strong inverse correlations to basal area (Pearson r = −0.85, p < 0.01) and biomass (r = −0.86, p < 0.01). Biomass estimates from Landsat NPV-based maps matched field data, and significantly differentiated landscape gradients in woody biomass that greenness metrics failed to track. The results suggest senesced vegetation metrics at Landsat scales are a promising means for improved monitoring of tree structure across disturbance and ecological gradients in African and other tropical dry forests.

Reproductive Contributions of Cardinals Are Consistent with a Hypothesis of Relaxed Selection in Urban Landscapes

Human activities are leading to rapid environmental change globally and may affect the eco-evolutionary dynamics of species inhabiting human-dominated landscapes. Theory suggests that increases in environmental heterogeneity should promote variation in reproductive performance among individuals. At the same time, we know that novel environments, such as our urbanizing study system, may represent more benign or predictable environments due to resource subsidies and ecological changes. We tested the hypothesis that reduced environmental heterogeneity and enhanced resource availability in cities relax selective pressures on birds by testing if urban females vary less than rural females in their demographic contributions to local populations. From 2004-2014, we monitored local population densities and annual reproductive output of 470 female Northern Cardinals (Cardinalis cardinalis) breeding at 14 forested sites distributed across a rural-to-urban landscape gradient in Ohio, USA. Reproductive contribution was measured as the difference between individual and site-averaged annual reproductive output across all nesting attempts, divided by the annual density at each site. We show that among-individual variation in reproductive contribution to the next year’s population declined with increasing urbanization, despite similar variability in body condition across the rural-urban gradient. Thus, female cardinals that bred in urban habitats within our study area were more similar in their contribution to the next generation than rural breeders, where a pattern of winners and losers was more evident. Within-individual variation in annual reproductive contribution also declined with increasing urbanization, indicating that performance of females was also more consistent among years in urban than rural landscapes. These findings are consistent with the hypothesis that urbanized environments offer more homogeneous or predictable conditions that may buffer individuals from environmental heterogeneity and relax natural selection.

Florally rich habitats reduce insect pollination and the reproductive success of isolated plants.

Landscape heterogeneity in floral communities has the potential to modify pollinator behavior. Pollinator foraging varies with the diversity, abundance, and spatial configuration of floral resources. However, the implications of this variation for pollen transfer and ultimately the reproductive success of insect pollinated plants remains unclear, especially for species which are rare or isolated in the landscape. We used a landscape‐scale experiment, coupled with microsatellite genotyping, to explore how the floral richness of habitats affected pollinator behavior and pollination effectiveness. Small arrays of the partially self‐compatible plant Californian poppy (Eschscholzia californica) were introduced across a landscape gradient to simulate rare, spatially isolated populations. The effects on pollinator activity, outcrossing, and plant reproduction were measured. In florally rich habitats, we found reduced pollen movement between plants, leading to fewer long‐distance pollination events, lower plant outcrossing, and a higher incidence of pollen limitation. This pattern indicates a potential reduction in per capita pollinator visitation, as suggested by the lower activity densities and richness of pollinators observed within florally rich habitats. In addition, seed production reduced by a factor of 1.8 in plants within florally rich habitats and progeny germination reduced by a factor of 1.2. We show this to be a consequence of self‐fertilization within the partially self‐compatible plant, E. californica. These findings indicate that locally rare plants are at a competitive disadvantage within florally rich habitats because neighboring plant species disrupt conspecific mating by co‐opting pollinators. Ultimately, this Allee effect may play an important role in determining the long‐term persistence of rarer plants in the landscape, both in terms of seed production and viability. Community context therefore requires consideration when designing and implementing conservation management for plants which are comparatively rare in the landscape.

Characterizing long-term soil and water erosion and their interactions with various conservation practices in the semi-arid Zulihe basin, Dingxi, Gansu, China

Located in a 200–400mm precipitation zone, the Zulihe basin (Zulihe River basin) in China is highly sensitive to climate change and land management. The relatively concentrated rainfall during the wet season (June-September) often leads to severe soil and water erosion. With a dataset collected at the outlet of the basin during 1955-2013, we first examined the trends in precipitation, runoff generation, and sediment transport with the Mann-Kendall (M-K) method. Then, we analyzed the impacts of various soil and water conservation practices on soil and water erosion with regression analysis. M-K results suggest overall downward trends in soil erosion and water runoff discharge from the basin with some similarity to the trends in precipitation. However, precipitation can only explain 30% of variability in sediment load and runoff discharge out of the basin. Various soil and water conservation practices were found to play a significant role in forming the downward trends in soil and water erosion. Multi-variate regression analysis confirmed that terraces construction, afforestation, grass land establishment, natural wildland preservation, and establishment of runoff-holding ponds together could explain up to 50% of variations in sediment load and runoff discharge. With an increase from 0 to 59% of land coverage protected by various soil and water conservation practices within the basin, sediment load reduced by at least five times and runoff by up to three times. It should be noted that the effects of soil and water conservation practices varied at both spatial and temporal scales, possibly due to interactions among different practices in terms of their distribution along the landscape and topographic gradients, and effectiveness of each practice. The findings from this study will not only explain the long-term variability in soil and water erosion changes over time but also provide insight for guiding future soil and water conservation programs in this basin and other regions with similar conditions.

Using environmental heterogeneity to plan for sea-level rise.

Environmental heterogeneity is increasingly being used to select conservation areas that will provide for future biodiversity under a variety of climate scenarios. This approach, termed conserving nature's stage (CNS), assumes environmental features respond to climate change more slowly than biological communities, but will CNS be effective if the stage were to change as rapidly as the climate? We tested the effectiveness of using CNS to select sites in salt marshes for conservation in coastal Georgia (U.S.A.), where environmental features will change rapidly as sea level rises. We calculated species diversity based on distributions of 7 bird species with a variety of niches in Georgia salt marshes. Environmental heterogeneity was assessed across six landscape gradients (e.g., elevation, salinity, and patch area). We used 2 approaches to select sites with high environmental heterogeneity: site complementarity (environmental diversity [ED]) and local environmental heterogeneity (environmental richness [ER]). Sites selected based on ER predicted present-day species diversity better than randomly selected sites (up to an 8.1% improvement), were resilient to areal loss from SLR (1.0% average areal loss by 2050 compared with 0.9% loss of randomly selected sites), and provided habitat to a threatened species (0.63 average occupancy compared with 0.6 average occupancy of randomly selected sites). Sites selected based on ED predicted species diversity no better or worse than random and were not resilient to SLR (2.9% average areal loss by 2050). Despite the discrepancy between the 2 approaches, CNS is a viable strategy for conservation site selection in salt marshes because the ER approach was successful. It has potential for application in other coastal areas where SLR will affect environmental features, but its performance may depend on the magnitude of geological changes caused by SLR. Our results indicate that conservation planners that had heretofore excluded low-lying coasts from CNS planning could include coastal ecosystems in regional conservation strategies.

Habitat use by barn owls across a rural to urban gradient and an assessment of stressors including, habitat loss, rodenticide exposure and road mortality

Urbanization and agricultural intensification resulting in habitat loss is having a profound negative effect on grassland and farmland birds worldwide. Barn owls (Tyto furcata), as a species, have been affected by this intensification. To evaluate how urbanization and agricultural intensification affects barn owls we sought to address: 1) how human land use influences barn owl hunting behavior and diet, and 2) do habitat and prey choice influence the likelihood of barn owls consuming anticoagulant rodenticide (AR) exposed prey. We radio tagged 11 owls across the rural-urban landscape gradient in the Lower Mainland, British Columbia, and collected sufficient location data on 10barn owls. We found that the 95% kernel home-ranges ranged from 1.0 to 28.5km2 (n=10) and were positively correlated with the proportion of urban land use within home-ranges. Barn owls across all landscapes selected roadside grass verges significantly more than other habitat types within home-ranges, which may reflect the loss of grassland associated agriculture in the region. The risk of consuming AR exposed prey was highest in roadside grass verges compared to other habitat types. However, the overall likelihood of consuming AR exposed prey significantly decreased when the proportion of grass patches within home-ranges increased, which suggests smaller linear grass sections are more likely to contain AR exposed small mammal prey. These results highlight the need to retain and enhance hunting habitat for barn owls during urban development and to mitigate the risk of barn owl road mortality along major highways.

Landscape‐scale interactions of spatial and temporal cropland heterogeneity drive biological control of cereal aphids

Summary Agricultural landscapes are characterised by dynamic crop mosaics changing in composition and configuration over space and time. Although semi‐natural habitat has been often shown to contribute to pest biological control, the effects of increasing landscape heterogeneity with cropland have been disregarded. Here, we examine how cereal aphids, their enemies and biological control are affected by the composition and configuration of the crop mosaic and its inter‐annual change due to crop rotation. We studied the abundance of cereal aphids, natural enemies and aphid parasitism over 2 years on 51 winter wheat fields. Arthropods were monitored at three distances (0, 10, 30 m) from field borders. Fields were embedded in landscapes of 1‐km diameter selected along orthogonal gradients of compositional crop heterogeneity (crop diversity), configurational heterogeneity (field border and grassy field boundary length) and inter‐annual change in cover of aphid host habitats (cereal, maize and grassland). We aimed to disentangle spatial and temporal heterogeneity effects through these independent landscape gradients. Aphid densities were lower in landscapes with smaller field size (more field borders) coupled with high amounts of grassy field boundaries. Aphid densities decreased also in landscapes with higher crop diversity when the cover of aphid host habitat had decreased from the year before. Aphid natural enemy densities decreased with smaller field size and high amounts of grassy field boundaries. Aphid parasitism decreased with the inter‐annual expansion in aphid host habitat, but only in landscapes with small field sizes. Synthesis and applications. Our study shows for the first time that cereal aphid numbers can be reduced by optimising the composition, configuration and temporal heterogeneity of the crop mosaic. We highlight the value of maintaining small field sizes in agricultural landscapes and high densities of grassy boundaries for reducing aphid abundance. Landscape‐wide crop diversification can reduce aphid densities as well.

Landscape and flux theory of non-equilibrium open economy

The economy is open and never in true equilibrium due to the exchanges with outside. However, most of the quantitative studies have been focused on the equilibrium economy. Despite of the recent efforts, it is still challenging to formulate a quantitative theory for uncovering the principles of non-equilibrium open economy. In this study, we developed a landscape and flux theory for non-equilibrium economy. We quantified the states of economy and identify the multi-stable states as the basins of attractions on the underlying landscape. We found the global driving force of the non-equilibrium economy is determined by both the underlying landscape gradient and the curl probability flux measuring the degree of non-equilibriumness through the detailed balance breaking. The non-equilibrium thermodynamics, the global stability, the optimal path and speed of the non-equilibrium economy can be formulated and quantified. In the conventional economy, the supply and demand usually has only one equilibrium. By considering nonlinear supply–demand dynamics, we found that both bi-stable states and limit cycle oscillations can emerge. By shifting the slope of demand curve, we can see how the bi-stability transforms to the limit cycle dynamics and vice versa. By parallel shifting the demand curve, we can also see how the monopoly, the competition, and the bistable monopoly and competition states emerge and transform to one other. We can also see how the mono-stable monopoly, the limit cycle and the mono-stable competition states emerge and transform to one another.

A hierarchy-based solution to calculate the configurational entropy of landscape gradients

The second law of thermodynamics is fundamental in landscape ecology, and Shannon entropy has been employed as an important means of analyzing landscape patterns. However, the thermodynamic basis of Shannon entropy has been recently questioned because such entropy considers only probability and not configurational information. As a result, Boltzmann entropy (also called configurational entropy), which is the basic measure in thermodynamics, has been revisited, and some thoughts on its calculation have been put forward. Nevertheless, a comprehensive calculation method is still lacking. The objective of this study is to propose a feasible solution for the calculation of configurational entropy for landscape gradients. To calculate the configurational entropy, the first step is to define a good macrostate and then to determine the number of microstates. The macrostate of a landscape gradient is defined as its abstract (i.e., upscaled) representation. The number of microstates is calculated by determining all the possible ways of downscaling from the macrostate to the original. Both simulated and real-life landscape patterns were used for experimental validation. The results show that the entropy calculated using the proposed method successfully captures the disorder of landscape gradients in terms of both composition and configuration. Configurational entropy, calculated using the proposed method, can serve as a thermodynamics-based metric to describe gradient-based landscapes and their changes across space and through time. With this metric, it becomes possible to interpret landscape ecological processes based on thermodynamic insights.

Continental‐scale variation in controls of summer CO2 in United States lakes

AbstractUnderstanding the broad‐scale response of lake CO2 dynamics to global change is challenging because the relative importance of different controls of surface water CO2 is not known across broad geographic extents. Using geostatistical analyses of 1080 lakes in the conterminous United States, we found that lake partial pressure of CO2 (pCO2) was controlled by different chemical and biological factors related to inputs and losses of CO2 along climate, topography, geomorphology, and land use gradients. Despite weak spatial patterns in pCO2 across the study extent, there were strong regional patterns in the pCO2 driver‐response relationships, i.e., in pCO2 “regulation.” Because relationships between lake CO2 and its predictors varied spatially, global models performed poorly in explaining the variability in CO2 for U.S. lakes. The geographically varying driver‐response relationships of lake pCO2 reflected major landscape gradients across the study extent and pointed to the importance of regional‐scale variation in pCO2 regulation. These results indicate a higher level of organization for these physically disconnected systems than previously thought and suggest that changes in climate and land use could induce shifts in the main pathways that determine the role of lakes as sources and sinks of atmospheric CO2.

Spreading and hole formation in natural oil films on aqueous solutions

The dynamics of a natural oil film on a free surface of the water has been studied experimentally. We examine the process of spreading and breakup of an oil film on water as well as on dilute aqueous solutions of Octanoic acid. Oil from Cocos Nucifera (Coconut) is used as the test fluid. A drop of this test fluid is introduced on to the free surface of the substrate fluid. The spatio-temporal evolution of the oil film is imaged and the features are investigated. The oil drop evolves into a film and spreads spontaneously because of the positive spreading coefficient. At a certain critical film thickness, holes, which are voids in the oil film, begin to nucleate. When the hole area fraction approaches the random packing limit, these holes begin to coalesce resulting in a coarser structure of the oil film. Coalescence occurs when the liquid bridge separating a pair of holes is ruptured due to Rayleigh–Plateau instability. This process is completely spontaneous since it is driven by gradients in the interfacial energy landscape. The oil film was observed to evolve through three phases viz., (i) spreading phase, (ii) hole nucleation and growth phase and (iii) hole coalescence phase. Quantitatively, the oil film diameter, number of holes in the oil film, diameter of each hole as well as the total triple line length has been measured. We also investigate the effect of Octanoic acid concentration in the substrate fluid on this dynamics. We show that increasing Octanoic acid concentration in the substrate fluid slows down the dynamics of film break up. This is possibly due to increased hydrophobic/hydrophilic interaction forces between the substrate fluid and the oil film.

Regression commonality analyses on hierarchical genetic distances

Landscape genetics is emerging as an important way of supporting decision‐making in landscape management, in response to the deterioration of matrix permeability due to habitat loss and fragmentation. In line with unremitting methodological developments in landscape genetics, a new analytical procedure was recently proposed as a way of evaluating the effects of landscape gradients on genetic structures. This procedure is based on the computation of inter‐individual hierarchical genetic distances (HGD), a metric of genetic differentiation taking into account the hierarchical structure in populations as inferred from clustering algorithms. HGD can be used as dependent variables in multivariate regressions to assess the effects of various landscape predictors on spatial patterns of genetic differentiation. However, multicollinearity may obscure the interpretation of multivariate regressions. We illustrate how regression commonality analyses (CA), a detailed variance partitioning procedure that can be used to deal with multicollinearity issues, can thoroughly improve our understanding of landscape connectivity when HGD are used as a dependent variable, with the red deer Cervus elaphus as an empirical example. Using logistic regression commonality analyses on HGD, we showed that semi‐natural open areas, transportation infrastructures and, to a lesser extent, urban areas and rivers, were associated with an increase in hierarchical genetic differentiation in red deer. Regressions based on HGD provided detailed results that could not have been obtained with regressions based on standard genetic distances, with notably additional insights as to the possible influence of linear features such as roads and highways on landscape connectivity. Furthermore, CA helped identify synergistic associations among variables as well as suppressors, thus resolving inconsistencies among hierarchical levels and revealing spurious correlations that may have gone unnoticed in the course of classical regression analyses. We thus recommend the use of regression commonality analysis on hierarchical genetic distances as a promising statistical tool for landscape geneticists.

Co‐varying impacts of land use and non‐native brown trout on fish communities in small streams

Summary Evaluating the biological integrity of stream ecosystems requires a clear understanding of biological responses to anthropogenic stressors. Co‐variation of stressors with natural landscape gradients has been shown to complicate the ability of biological assessments to detect community‐level responses to anthropogenic stressors. Similarly, the co‐varying occurrence of non‐native species would also likely confound the ability of biological assessments to accurately determine biological integrity, although these relationships have been less studied. We compared fish communities in 99 wadeable tributaries (with catchments of 10–35 km2) of the upper Allegheny River watershed, Pennsylvania, U.S.A., to disentangle the effects of human‐induced stressors associated with agricultural development, the presence of non‐native brown trout (Salmo trutta) and background variation in community composition associated with natural landscape features. Multivariate analyses using both taxonomic and trait‐based data revealed that environmental gradients sorted fish species into different thermal communities (coolwater versus warmwater). Layered over the shift in thermal communities was the presence of large‐bodied (piscivorous) brown trout, which along with agricultural land use, was a consistent determinant of community diversity and presence–absence of nine common native species. Small‐bodied taxa (minnows, darters) were the most responsive to the presence of these large non‐native predators. Our results highlight how the presence of a non‐native species can modify the interactions between natural and anthropogenic stressor gradients and therefore confound the ability to detect signals between land use stressors and local stream community composition. The complicated interaction between brown trout and other anthropogenic stressors documented herein is likely to be a widespread phenomenon given the global introductions of many salmonid species into systems with varying anthropogenic stressor gradients. Overall, understanding how non‐native species influence stream community composition should lead to biological assessments with greater capabilities for detecting non‐native effects on biological integrity relative to the more frequently evaluated land use stressors.

艾比湖区域景观格局空间特征与地表水质的关联分析

PDF HTML阅读 XML下载 导出引用 引用提醒 艾比湖区域景观格局空间特征与地表水质的关联分析 DOI: 10.5846/stxb201701100078 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41361045，41130531）；国家自然科学基金-新疆联合基金（U1503302）；新疆维吾尔自治区研究生教育改革创新项目（XJGRI2016014）；2016年新疆大学大学生创新训练计划重点项目（201610755057）资助 Correlation analysis between the spatial characteristics of land use/cover-landscape pattern and surface-water quality in the Ebinur Lake area Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为进一步明确区域土地利用/覆被-景观格局对河流水质影响的空间尺度。选择新疆艾比湖区域为研究对象，以25个水质采样点为中心，建立5种尺度的河流缓冲区并提取不同尺度下的土地利用/覆被-景观格局数据。首先，通过主成分分析获得水环境的主要水质变量。其次，利用冗余分析（RDA）方法探讨研究区不同宽度缓冲区土地利用/覆被-景观格局对河流水质的影响，获得水质管理的有效缓冲区。最后，引入突变点分析方法进一步寻找导致水质变量沿景观梯度突变的特定位置。结果表明：（1）土地利用/覆被-景观格局在不同宽度缓冲区内对河流水质的影响不同。4 km缓冲区土地利用/覆被-景观格局对区域水质有较强的分异解释能力，因此4 km缓冲区的景观格局合理配置对河流水质管理尤为重要。（2）通过偏RDA分析发现4 km缓冲区中，影响区域水质的主要环境变量为景观水平斑块密度、类型水平耕地斑块密度和森林聚集度。（3）在偏RDA分析的基础上，对4 km缓冲区内的景观指数进行突变点分析研究，发现区域景观水平斑块密度为90-105 m/hm2，类型水平耕地的斑块密度ED值在90-110 m/hm2、林草地的AI值在70%-90%，是艾比湖区域水质保护的最佳突变值，该值为艾比湖区域水质保护的阈值。本研究从多个角度对新疆艾比区域的土地利用/覆被-景观格局对区域水质的影响进行定量分析，揭示该地区景观生态变化的规律，为区域景观格局优化和土地合理规划提供理论依据，并对改善"丝绸之路经济带"生态环境、实现资源可持续利用具有重要的现实意义和理论价值。 Abstract:To understand the effect of land use/cover-landscape on water quality, this study selected the Xinjiang Ebinur Lake region as the study area. We took 25 water sampling points to build five buffer zones, and combined land use/cover types with water-quality monitoring data, selected land-use types, and landscape index (landscape level) to monitor water quality. We tried to study the effects of a wide range of buffer land use/cover-landscape patterns on water quality indexes using the redundancy analysis method. Subsequently, we analyzed the specific location of the water-quality variables along the landscape gradient using the change-point analysis method. The results indicated:(1) the landscape pattern has different effects on the river-water quality indexes in different buffer zones. A 4 km buffer of land use/cover landscape pattern seems to be a threshold for differentiating the regional water quality. (2) The major environmental variables affecting the water quality of the lake area are the patch density, the patch density, and the degree of aggregation in a buffer of 4 km. (3) When the edge density (ED), of cultivation was 90-105 m/hm2, and the aggregation of forest and grassland index of water was 70%-90%, and the water quality in this region appeared to be better protected. This study performed the quantitative analysis of the land use/landscape pattern changes from multiple perspectives in the Ebinur Lake area, revealing the main regularities of the landscape ecology variation in the region. This study provides the theoretical basis for the optimization of regional landscape pattern and reasonable land planning. It improves the "Silk Road Economic-One Belt and One Road" initiative of the ecological environment and sustainable utilization of resources in the Ebinur Lake area in Xinjiang. 参考文献 相似文献 引证文献

Electrical addressing and temporal tweezing of localized pulses in passively-mode-locked semiconductor lasers

We show that the pumping current is a convenient parameter for manipulating the temporal Localized Structures (LSs), also called localized pulses, found in passively mode-locked Vertical-Cavity Surface-Emitting Lasers. While short electrical pulses can be used for writing and erasing individual LSs, we demonstrate that a current modulation introduces a temporally evolving parameter landscape allowing to control the position and the dynamics of LSs. We show that the localized pulses drifting speed in this landscape depends almost exclusively on the local parameter value instead of depending on the landscape gradient, as shown in quasi-instantaneous media. This experimental observation is theoretically explained by the causal response time of the semiconductor carriers that occurs on an finite timescale and breaks the parity invariance along the cavity, thus leading to a new paradigm for temporal tweezing of localized pulses. Different modulation waveforms are applied for describing exhaustively this paradigm. Starting from a generic model of passive mode-locking based upon delay differential equations, we deduce the effective equations of motion for these LSs in a time-dependent current landscape.