Search

Holobionts are dynamic ecosystems that may respond to abiotic drivers with compositional changes. Uncovering elevational diversity patterns within these microecosystems can further our understanding of community‐environment interactions. Here, we assess how the major components of lichen holobionts—fungal hosts, green algal symbionts, and the bacterial community—collectively respond to an elevational gradient. We analyse populations of two lichen symbioses, Umbilicaria pustulata and U. hispanica, along an elevational gradient spanning 2100 altitudinal metres and covering three major biomes. Our study shows (i) discontinuous genomic variation in fungal hosts with one abrupt genomic differentiation within each of the two host species, (ii) altitudinally structured bacterial communities with pronounced turnover within and between hosts, and (iii) altitude‐specific presence of algal symbionts. Alpha diversity of bacterial communities decreased with increasing elevation. A marked turnover in holobiont diversity occurred across two altitudinal belts: at 11°C–13°C average annual temperature (here: 800–1200 m a.s.l.), and at 7°C–9°C average annual temperature (here: 1500–1800 m a.s.l.). The two observed zones mark a clustering of distribution limits and community shifts. The three ensuing altitudinal classes, that is, the most frequent combinations of species in holobionts, approximately correspond to the Mediterranean, cool‐temperate, and alpine climate zones. We conclude that multitrophic microecosystems, such as lichen holobionts, respond with concerted compositional changes to climatic factors that also structure communities of macroorganisms, for example, vascular plants. [ABSTRACT FROM AUTHOR]

Antibiotic resistance genes (ARGs) have become an important public health problem. In this study, we used metagenomic sequencing to analyze the composition of ARGs in selected original habitats of northeast China, comprising three different rivers and riverbank soils of the Heilongjiang River, Tumen River, and Yalu River. Twenty types of ARG were detected in the water samples. The major ARGs were multidrug resistance genes, at approximately 0.5 copies/16S rRNA, accounting for 57.5% of the total ARG abundance. The abundance of multidrug, bacitracin, beta-lactam, macrolide-lincosamide-streptogramin, sulfonamide, fosmidomycin, and polymyxin resistance genes covered 96.9% of the total ARG abundance. No significant ecological boundary of ARG diversity was observed. The compositions of the resistance genes in the three rivers were very similar to each other, and 92.1% of ARG subtypes were shared by all water samples. Except for vancomycin resistance genes, almost all ARGs in riverbank soils were detected in the river water. About 31.05% ARGs were carried by Pseudomonas. Opportunistic pathogenic bacteria carrying resistance genes were mainly related to diarrhea and respiratory infections. Multidrug and beta-lactam resistance genes correlated positively with mobile genetic elements (MGEs), indicating a potential risk of diffusion. The composition of ARGs in three different rivers was similar, indicating that climate plays an important role in ARG occurrence. ARG subtypes in river water were almost completely the same as those in riverbank soil. ARGs had no significant geographical distribution characteristics. Many ARGs were carried by human pathogenic bacteria related to diarrhea and respiratory infections, such as Pseudomonas aeruginosa and Aeromonas caviae. In general, our results provide a valuable dataset of river water ARG distribution in northeast China. The related ecological and geographical distribution characteristics should be further explored. [ABSTRACT FROM AUTHOR]

Planetary boundaries have received considerable attention since they were first proposed, but applying various downscaling methods to the regional scale has certain limitations due to regional heterogeneity. The concept of ecological boundaries (EB) extends and complements planetary boundaries at a regional scale. However, previous studies have not considered the EB of multiple regions and the impact of interregional ecosystem service value (ESV) flows on EB. In this study, we optimized the EB accounting method and quantified the EB of 30 provinces in China from 2002 to 2017, then assessed the ecosystem unsustainability, and determined the impact of demand for goods and services on the consumption of local natural resources by each province in China using an ESV-extended multiregional input-output model. We found that EB increased in all provinces of China. The ecological unsustainability index of all 30 provinces was larger than 1, indicating a serious environmental unsustainability, but the magnitude of the index tends to decrease. Furthermore, the regions that have the greatest impact on exceeding EB in each province were concentrated in Guangdong and Henan. Guangdong had the highest total net imports in 2012 and 2015 (665.08 and 641.70 billion yuan, respectively), while Henan had the highest total net imports in 2017 (611.58 billion yuan). For the role of net exports, the rankings of the provinces differed in terms of the direct ESV and the boundary-exceeding ESV indicators. Our results reveal EB across provinces in China, underscoring the importance of considering the flow of ESV between regions in assessing the impact of exceeding EB. This study can assist policymakers in better allocating ecological resources within EB, which is critical for alleviating ecological pressures. [ABSTRACT FROM AUTHOR]

Context: Historically, habitat edges were thought to increase diversity by combining communities from two habitats, but empirical results are mixed. Variation in edge responses may be driven by lumping specialists and generalists with divergent responses. Objectives: We examined arthropod communities associated with a habitat edge in an intertidal salt marsh in New Jersey. We predicted that herbivores, largely specialists, would decline along the habitat edge due to their failure to expand across the boundary, and specialist natural enemies should track prey. Generalists should be less impacted by the edge if they use resources from both sides. Thus, habitat edges should affect species composition more than species diversity. Methods: We studied the edge responses of 115 arthropod species to the habitat edge formed between Spartina patens (SP) and Spartina alterniflora (SA) throughout the growing season. Results: We found that the edge between SA and SP affected the abundance and composition of the associated arthropod community, but not species richness. Composition of herbivores, epigeic feeders, specialist natural enemies, and generalist predators shifted not only between SA and SP interiors, but also the edges. Compositional shifts were driven by dietary or habitat specialists. Conclusions: We found that edges change community composition via divergent responses by species with different resource requirements. This change in composition is not between two disparate habitat types but two congeneric grass species. Our results demonstrate that biodiversity losses due to edge effects associated with habitat fragmentation will not be random but will be driven by specialization and resource use. [ABSTRACT FROM AUTHOR]

Questions: Spatial characteristics of ecotones can affect ecotone function and define their role in ecological systems. Identifying ecotone location is necessary to quantify the relationship between spatial characteristics and function, yet there is no standard approach, particularly for compositionally complex ecotones where binary classification for the two adjacent systems is difficult to assign. We tested a new approach for identifying ecotone location based on the co‐occurrence property, which recognizes ecotones as areas where species from adjacent systems co‐occur. We assessed whether the approach can objectively identify the location of the Tension Zone in Wisconsin. Location: Wisconsin, USA. Methods: Ecotone Co‐occurrence Mapping (ECoMap) is a multi‐step approach: (a) indicator species analysis identifies representative species of two adjacent systems; (b) a ratio map constructed from the spatial densities of the indicator species identifies high co‐occurrence areas; and (c) contour lines encapsulate highest co‐occurrence areas. We applied this approach to identify the Tension Zone location using point locations of witness trees from the mid‐1800s Public Land Survey. We assessed the approach by examining results of multiple permutations, testing sensitivity to different initial boundary configurations, and comparing it to a subjectively derived map, the Curtis Tension Zone. Results: The location of the Tension Zone was identified consistently in multiple permutations, though there is minor variability in certainty of final ecotone location. Ecotone width varied substantially along the Tension Zone. The location was similar to the Curtis Tension Zone but slightly farther north and more spatially detailed. Sensitivity to initial boundary configuration was low. Conclusions: The ECoMap approach was robust and identified a spatially detailed Tension Zone location. This approach is broadly applicable and can be used to identify the location of simple or compositionally complex ecotones where spatial data of species occurrences and modest prior knowledge of general boundary location are available. [ABSTRACT FROM AUTHOR]

Within a plant community, variation among species in their abilities to exploit different types of soil patches can promote increased species diversity. However, it also has been suggested that some species may be disproportionately abundant along the edges between soil patches (i.e. soil microedges). We investigated the potential mechanisms whereby microedges can offer distinct ecological niches. Desmodium canadense, a tallgrass prairie species observed anecdotally to be abundant along patch edges, was grown in homogenized sandy loam (low-quality patch), clay loam (high-quality patch), or along the microedge between these two substrates, both in the presence or absence of competitors (Andropogon gerardii and Solidago juncea). Treatment effects on the biomass and root foraging strategies of D. canadense were assessed and compared to the responses of Andropogon gerardii and Solidago juncea. Although D. canadense biomass was highest in the clay loam without competition, with competition D. canadense biomass was highest along the microedge, which was a pattern not observed in A. gerardii or S. juncea. D. canadense also exhibited disproportionate root proliferation along the microedge into the clay loam patch, regardless of competitor presence. Although D. canadense biomass can be limited in both low- and high-quality soil patches, the edges between these patches allow D. canadense to avoid intense aboveground competition yet still access beneficial soil patches through lateral root foraging, thus enabling soil patch microedges to serve as a unique ecological niche. [ABSTRACT FROM AUTHOR]

Boundaries are the most reactive nodes in landscapes and may be hypersensitive to global change in climate and land use. Investigations on how soils govern vegetation boundaries are scant, particularly in arid and semiarid ecosystems. The Tankwa Karoo National Park (TKNP) is a unique arid biodiversity hotspot with an unrivalled aridity gradient from < 100 mm MAP to about 700 mm in < 10 km. We investigated the abruptness of four soil‐vegetation boundaries separating eight communities. Two 50 m transects were established across four boundaries for 24 descending point transects, in which the cover‐abundance of each plant encounter at 1 m intervals was recorded. In addition, three soil samples were collected from the top 5 cm in each of the four boundaries and twelve patches. Soil and vegetation parameters altogether indicated three boundary syndromes that were context dependent: (a) a sharp boundary, (b) a gradual boundary or (c) no boundary exists. Soil respiration recorded here, and perhaps other ecosystem processes, was mediated by the soil‐vegetation boundaries. These nodes should be the focus of ecological studies since they reveal much more than the constituent patches themselves. [ABSTRACT FROM AUTHOR]

As key components of landscapes, edges have received considerable scientific attention in anthropogenic ecosystems. However, edges in natural and semi-natural forest-grassland mosaics have received less attention, despite the fact that they cover a considerable proportion of these mosaic ecosystems. We studied forest edges in a semi-natural forest-grassland mosaic ecosystem of the Samobor Mountains (Croatia). Our aim was to compare the species composition, diversity and ecological indicator values of forest edges to those of the interior parts of the adjacent forest and grassland habitats. The vegetation was studied in 80 plots established in forest patch interiors, north-facing forest edges, south-facing forest edges and grassland interiors. We found that edges had a unique species composition, containing species from both the forest and the grassland interiors plus their own edge-related species (i.e. species that significantly preferred the edge habitat). These local edge-related species did not correspond to regionally-identified edge-related species. Compared to the forest and the grassland interiors, we revealed increased species richness in north-facing edges but not in south-facing edges. The mean light availability and nutrient supply indicator values of the edges were intermediate between those of the forest interiors and the grasslands. The mean soil moisture indicator values of the edges were similar to those of the grasslands. Our results show that edges form a unique component of forest-grassland mosaics, and they contribute considerably to landscape complexity, which should be taken into account during conservation decisions and habitat management. [ABSTRACT FROM AUTHOR]

The agro-pastoral transitional zone (APTZ) in Northern China is one of the most important ecological barriers of the world. The commonly-used method to identify the spatial distribution of ATPZ is to apply a threshold rule on climatic or land use indicators. This approach is highly subjective, and the quantity standards vary among the studies. In this study, we adopted the spatial continuous wavelet transform (SCWT) technique to detect the spatial fluctuation in normalized difference vegetation index (NDVI) sequences, and as such identify the APTZ. To carry out this analysis, the Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI 1-month data (MODND1M) covering the period 2006⁻2015 were used. Based on the spatial variation in NDVI, we identified two sub-regions within the APTZ. The temporal change of APTZ showed that although vegetation spatial pattern changed annually, certain areas appeared to be stable, while others showed higher sensitivity to environmental variance. Through correlation analysis between the dynamics of APTZ and precipitation, we found that the mean center of the APTZ moved toward the southeast during dry years and toward the northwest during humid years. By comparing the APTZ spatial pattern obtained in the present study with the outcome following the traditional approach based on mean annual precipitation data, it can be concluded that our study provides a reliable basis to advance the methodological framework to identify accurately transitional zones. The identification framework is of high importance to support decision-making in land use management in Northern China as well as other similar regions around the world.

In this review paper, we highlight some of the trends and issues that have dominated ecotone research over the decade of 1996–2006. The terms and definitions of ecotone research in vegetation ecology are reviewed. We summarize the most important techniques and highlight the discrepancies between the definitions and their scientific application in vegetation ecology. We see a need for semantic uniformity with regard to the term and the definition of “the ecotone”, as the variable and the non-exclusive use of terms and definitions can be a source of confusion when interpreting and comparing different studies. To avoid further confusion, a unique definition of the term “ecotone” should be agreed upon, based upon a set of general characteristics. We therefore adapted and extended the definition from Holland et al. (Ecotones: the role of landscape boundaries in the management and restoration of changing environments, 1991) to “A multi-dimensional environmentally stochastic interaction zone between ecological systems with characteristics defined in space and time, and by the strength of the interaction”. We also advocate that (1) a shift in focus from one-dimensional to two-dimensional techniques in ecotone characterization is desirable and (2) more research into novel techniques, including multi-dimensional data and time series, is needed in view of local and global ecotone changes. [ABSTRACT FROM AUTHOR]

Abstract: Ecotones are gradual transitions between two adjacent ecological systems. Ecotones are characterized by their spatial properties which are reflected in an ecotone width and location and the temporal variation across time during succession or environmental change on both a local and a global scale. If only one main environmental factor drives this gradual change the shape of the ecotone is evident as a sigmoid wave. In this paper we explore a two-dimensional sigmoid wave curve fitting algorithm that describes an ecotone and validate it on classified remote sensing data of a forest-tundra ecotone in the Northwest Territories of Canada. The estimated location and width of the forest-tundra ecotone are validated with digital land cover data. We conclude that the algorithm was able to delineate the forest-tundra ecotone based upon the classified remote sensing image and is robust for various algorithm parameter settings. [Copyright &y& Elsevier]

Abstract: Ecological boundaries have been described as being multiscalar or hierarchical entities. However, the concept of the ecological boundary has not been explicitly examined in the context of hierarchy theory. We explore how ecological boundaries might be envisioned as constituents of scalar hierarchical systems. Boundaries may be represented by the surfaces of constituents or as constituents themselves. Where surfaces would correspond to abrupt transition zones, boundary systems might be quite varied depending on hierarchical context. We conclude that hierarchy theory is compatible with a functional vision of ecological boundaries where functions can be largely represented as the processing or filtering of ecological signals. Furthermore, we postulate that emergent ecological boundaries that arise on a new hierarchical level may contribute to the overconnectedness of mature ecosystems. Nevertheless, a thermodynamic approach to the emergence and development of boundary systems does indicate that in many situations, ecological boundaries would persist in time by contributing to the energy production of higher hierarchical levels. [Copyright &y& Elsevier]

Edge responses have been studied for decades and form a critical component of our understanding of how organisms respond to landscape structure and habitat fragmentation. Until recently, however, the lack of a general, conceptual framework has made it difficult to make sense of the patterns and variability reported in the edge literature. We present a test of an edge effects model which predicts that organisms should avoid edges with less-preferred habitat, show increased abundance near edges with preferred habitat or habitat containing complementary resources, and show no response to edges with similar-quality habitat that offers only supplementary resources. We tested the predictions of this model against observations of the edge responses of 15 butterfly species at 12 different edge types within a complex, desert riparian landscape. Observations matched model predictions more than would be expected by chance for the 211 species/edge combinations tested over 3 years of study. In cases where positive or negative edge responses were predicted, observed responses matched those predictions 70% of the time. While the model tends to underpredict neutral results, it was rare that an observed edge response contradicted that predicted by the model. This study also supported the two primary ecological mechanisms underlying the model, although not equally. We detected a positive relationship between habitat preferences and the slope of the observed edge response, suggesting that this basic life history trait underlies edge effects and influences their magnitude. Empirical evidence also suggested the presence of complementary resources underlies positive edge responses, but only when completely confined to the adjacent habitat. This multi-species test of a general edge effects model at multiple edge types shows that resource-based mechanisms can explain many edge responses and that a modest knowledge of life history attributes and resource availability is sufficient for predicting and understanding many edge responses in complex landscapes. [ABSTRACT FROM AUTHOR]

Ecological transition zones are increasingly recognized as systems that play a critical role in controlling or modifying flows of organisms, materials, and energy across landscapes. Many concepts describing transitional areas have been proposed over the years, such as the prevalent and durable ecotone concept. Confusion among ecologists and land managers about transition zone concepts and the isolation of studies that use only one transition concept can hinder unified progress in understanding these key systems. Currently, a movement toward conceptual synthesis under the umbrella concept of ‘ecological boundary’ is underway. Here we examine the history and theoretical baggage of the ecotone, riparian zone, and several other concepts. Subsequently, we present a conceptual cluster analysis, which facilitates a better understanding of the similarities and differences between boundary and transition concepts. We emphasize the hierarchical nature of these concepts: higher-level synthetic concepts can be used in the development of theory, whereas lower-level concepts allow more specificity and the formulation of operational definitions. Finally, we look briefly at the utility and future use of boundary and transition zone concepts. [ABSTRACT FROM AUTHOR]

1. The increased length of forest clear-cut edges is considered to be one of the main ecological consequences of silviculture. The effects vary over the landscape, and studies have shown that aspect is one important factor determining the extent of microclimatic edge effects across forest clear-cut boundaries. However, little is known about the relationship between contrasts in microclimate at edges and responses of ecological processes and biodiversity, such as growth, decomposition and species distributions.2. A field experiment was conducted in the boreal forest of northern Sweden to assess the effect of aspect at north- and south-facing edges using mosses as bioindicators. The growth of two species (Hylocomium splendensandHylocomiastrum umbratum) was evaluated during one growing season. Samples of each species were planted in pots at eight north- and eight south-facing forest clear-cut edges.3. Growth increased exponentially with distance from the edge to the interior, and there was a significant effect both in north- and south-facing edges. The percentage decline in growth at the edge was larger in the south- than in the north-facing edges.4. The spatial extent of the edge effect, when measured at the point of 90% of interior growth, was similar between north- and south-facing edges, although it differed between the two species evaluated.5. Synthesis and applications.The difference in exposure to sunlight between north- and south-facing edges was shown to modify the magnitude of the growth of a poikilohydric organism at the very edge, but not the depth of the edge influence. Aspect should be taken into account in management plans for conservation of boreal forests. In the northern hemisphere, wider buffers of uncut forest should be left at the south side than at the north side of retained forest patches. Those forest interior species that are most sensitive to alterations in microclimate will, however, need equal protection from edge effects at all aspects.Journal of Applied Ecology(2005)42, 518 –525doi: 10.1111/j.1365-2664.2005.01033.x [ABSTRACT FROM AUTHOR]

Natural habitats adjacent to human-modified areas often suffer edge effects stemming from physical disturbance, elevated predator densities, or invasive species. Although seldom documented, detrimental edge effects can also occur at natural ecological boundaries. Here I examine the spatial pattern and ecological effects of a biological invasion at well-delineated and abrupt edges between riparian corridors and coastal sage scrub at 10 sites in southwestern California. The invasive Argentine ant Linepithema humile thrives in moist riparian corridors but decreases greatly in number with increasing distance into adjacent dry scrub habitats. As L. humile numbers decrease, both the number of native ant workers and the number of native ant species captured in pitfall traps increase. Argentine ants appear to suppress native ants within at least 50 m of riparian corridors, but these effects diminish to undetectable levels by 200 m. At comparable uninvaded sites neither the number of native ant workers nor the number of native ant species captured in pitfall traps varies significantly across riparian-scrub edges. Areas subject to this edge effect may be sinks both for native ants and for organisms that depend on them for food or services. In general edge effects occurring at natural boundaries should receive increased attention as they might disrupt ecosystems not greatly altered by human activity. [Copyright &y& Elsevier]

The relationship between plant species richness and the space organization of the community at different small scales was studied. The study was based on 51 sites distributed along a belt from Central Spain to Portugal. Each site was analyzed with a transect cutting across the boundary between two neighboring patches of shrubland and grassland. Local spatial organization of vegetation was analyzed at different levels of detail and each transect was divided into successively smaller portions. The first division coincides with a physiognomic perception of the site in two patches (shrubland and grassland). The average spatial niche width of the species was used to calculate the spatial organization of the vegetation of each division in each site. The correlation between species richness and spatial organization depended on the block size under consideration. A physiognomic criterion, sectorizing the sites into patches of shrubland and grassland, determines noteworthy floristic changes but does not enable us to express satisfactorily the variability in plant richness. In order to account for this variation, other factors must be taken into account which act at a more detailed small-scale and which determine the internal variability of these patches. In the case studied, the species richness of the sites increases along with an increase in the percentage of species whose occupation of the space is relatively restricted within the site. Many of these species are, however, frequent within the whole of the territory studied. The results highlight the importance of the level of local scale at which the factors influencing occupation of the space, and consequentially, plant richness, preferentially act. This circumstance ought to be taken into consideration in strategies for the conservation of biological diversity, and based on the delimitation of protected spaces with criteria frequently linked to the physiognomy of the vegetation. [ABSTRACT FROM AUTHOR]

Edge effects have been studied for decades because they are a key component to understanding how landscape structure influences habitat quality. However, making sense of the diverse patterns and extensive variability reported in the literature has been difficult because there has been no unifying conceptual framework to guide research. In this review, we identify four fundamental mechanisms that cause edge responses: ecological flows, access to spatially separated resources, resource mapping, and species interactions. We present a conceptual framework that identifies the pathways through which these four mechanisms can influence distributions, ultimately leading to new ecological communities near habitat edges. Next, we ex-amine a predictive model of edge responses and show how it can explain much of the variation reported in the literature. Using this model, we show that, when observed, edge responses are largely predictable and consistent. When edge responses are variable for the same species at the same edge type, observed responses are rarely in opposite directions. We then show how remaining variability may be understood within our conceptual frameworks. Finally, we suggest that, despite all the research in this area, the development of tools to extrapolate edge responses to landscapes has been slow, restricting our ability to use this information for conservation and management. [ABSTRACT FROM AUTHOR]

Edge effects are among the most extensively studied ecological phenomena, yet we lack a general, predictive framework to understand the patterns and variability observed. We present a conceptual model, based on resource distribution, that predicts whether organismal abundances near edges are expected to increase, decrease, or remain unchanged for any species at any edge type. Predictions are based on whether resources are found predominantly in one habitat (decreased abundance in preferred habitat, increase in non-preferred), divided between habitats (predicts an increase near both edges), spread equally among habitats (predicts a neutral edge response), or concentrated along the edge (increase). There are several implications of this model that can explain much of the variability reported in the edge literature. For instance, our model predicts that a species may show positive, negative, and neutral responses, depending on the edge type encountered, which explains some intraspecific variability observed in the literature. In addition, any predictable change in resource use (for example, by region or season) may explain temporal or spatial variability in responses even for the same species at the same edge type. We offer a preliminary test of our model by making predictions for 52 bird species from three published studies of abundance responses near forest edges. Predictions are based solely on general information about each species' habitat associations and resource use. Our model correctly predicted the direction of 25 out of 29 observed edge responses, although it tended to under-predict increases and over-predict decreases. This model is important because it helps make sense of a largely descriptive literature and allows future studies to be carried out under a predictive framework. [ABSTRACT FROM AUTHOR]

District energy systems, in particular combined cooling, heating and power (CCHP) systems, can provide cost-effective energy products, reduce fossil fuel consumption and emissions. A gas-fired CCHP system is considered here employing an internal combustion engine, whose exhaust gas is split between an organic Rankine cycle unit and absorption heat pump. A simulation model of the system is constructed and validated. An emergy based exergo-environmental cost method is proposed here to optimize the exhaust gas allocation ratio based on specific working conditions considering the equivalent emissions of the whole life-cycle chain from an ecological view. The emergy consumption in each process stage is evaluated accompanied with a sensitivity analysis. The results show that the minimize specific system cost is 310050 seJ/J when 63% of the exhaust gas flows to the ORC-unit. The ICE and AHP are responsible for >98% of the emergy consumption, dominated by the operation of the system. The sensitivity analysis shows that heating is the most sensitive of all products against key parameter variations, while electricity is the least. Increasing the service period and the operating hours, the economic performance could be improved, while the transformity of emission enlarges the cost. • A novel natural gas-fired CCHP system allocating exhaust gas to drive ORC and AHP units. • Emergy based exergo-environmental optimization with ecological boundary. • Equivalent CO 2 and SO x emissions in life-cycle chain. • Sensitivity analysis against crucial parameters. [ABSTRACT FROM AUTHOR]

Generalist predators are thought to be less vulnerable to habitat fragmentation because they use diverse resources across larger spatial scales than specialist predators. Thus, it has been suggested that generalist predators may respond positively to habitat edges or demonstrate no edge response, because they can potentially use prey resources equally well on both sides of the habitat edge. However, most predictions about generalist predator responses to the habitat edge are based solely on prey resources, without consideration of other potential drivers. For instance, structural resources are essential for some species to build webs to capture prey or to avoid intraguild predation and cannibalism. In this study, we used both prey and structural resources to predict the response of four predator functional groups (hunting spiders, web‐building spiders, aerial predators, and epigeic predators that feed on the detrital/algal food web) to a habitat edge between two salt‐marsh grasses (Spartina alterniflora and Spartina patens). We found that generalist predators largely demonstrated negative responses to the habitat edge and had distinct habitat associations. Positive edge responses were only observed in one functional group (hunting spiders), and this pattern was driven by the two most abundant species. Negative responses to the habitat edge were more common among taxa and were better explained by structural resources rather than prey resources in the two habitats. Although it is generally acknowledged that specialists decline in fragmented habitats, generalists are thought to be more resilient. However, our research demonstrates that even generalists have habitat structural or food resource requirements that may limit their resilience to habitat loss and fragmentation. [ABSTRACT FROM AUTHOR]

The agro-pastoral transitional zone (APTZ) in Northern China is one of the most important ecological barriers of the world. The commonly-used method to identify the spatial distribution of ATPZ is to apply a threshold rule on climatic or land use indicators. This approach is highly subjective, and the quantity standards vary among the studies. In this study, we adopted the spatial continuous wavelet transform (SCWT) technique to detect the spatial fluctuation in normalized difference vegetation index (NDVI) sequences, and as such identify the APTZ. To carry out this analysis, the Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI 1-month data (MODND1M) covering the period 2006–2015 were used. Based on the spatial variation in NDVI, we identified two sub-regions within the APTZ. The temporal change of APTZ showed that although vegetation spatial pattern changed annually, certain areas appeared to be stable, while others showed higher sensitivity to environmental variance. Through correlation analysis between the dynamics of APTZ and precipitation, we found that the mean center of the APTZ moved toward the southeast during dry years and toward the northwest during humid years. By comparing the APTZ spatial pattern obtained in the present study with the outcome following the traditional approach based on mean annual precipitation data, it can be concluded that our study provides a reliable basis to advance the methodological framework to identify accurately transitional zones. The identification framework is of high importance to support decision-making in land use management in Northern China as well as other similar regions around the world. [ABSTRACT FROM AUTHOR]