Forest fragmentation predicts local scale heterogeneity of Lyme disease risk

Fragmentation of the landscape has been proposed to play an important role in defining local scale heterogeneity in Lyme disease risk through influence on mammalian host density and species composition. We tested this observed relationship in a suburban region around Lyme, Connecticut, where we collected data on the density of the tick vector, Ixodes scapularis and prevalence of the Lyme bacterium, Borrelia burgdorferi at 30 sites. Analysis of the landscape pattern of forest patches was performed using satellite imagery. The calculated landscape indices, which included patch size and isolation, revealed a positive link between fragmentation and both tick density and infection prevalence in ticks. In spite of higher entomologic risk, human incidence of Lyme disease is lower in fragmented contexts suggesting that entomologic risk is not the critical driver of human infections. These results represent a departure from the prior claims that fragmentation and human Lyme disease risk are positively linked. A complete understanding of the influence of landscape fragmentation will allow for improved risk mapping and potential environmental management of Lyme disease.     

Agricultural disturbance response models for invertebrate and algal metrics from streams at two spatial scales within the U.S.

As part of the USGS study of nutrient enrichment of streams in agricultural regions throughout the United States, about 30 sites within each of eight study areas were selected to capture a gradient of nutrient conditions. The objective was to develop watershed disturbance predictive models for macroinvertebrate and algal metrics at national and three regional landscape scales to obtain a better understanding of important explanatory variables. Explanatory variables in models were generated from landscape data, habitat, and chemistry. Instream nutrient concentration and variables assessing the amount of disturbance to the riparian zone (e.g., percent row crops or percent agriculture) were selected as most important explanatory variable in almost all boosted regression tree models regardless of landscape scale or assemblage. Frequently, TN and TP concentration and riparian agricultural land use variables showed a threshold type response at relatively low values to biotic metrics modeled. Some measure of habitat condition was also commonly selected in the final invertebrate models, though the variable(s) varied across regions. Results suggest national models tended to account for more general landscape/climate differences, while regional models incorporated both broad landscape scale and more specific local-scale variables.     

Consequences of landscape fragmentation on Lyme disease risk: a cellular automata approach

The abundance of infected Ixodid ticks is an important component of human risk of Lyme disease, and various empirical studies have shown that this is associated, at least in part, to landscape fragmentation. In this study, we aimed at exploring how varying woodland fragmentation patterns affect the risk of Lyme disease, through infected tick abundance. A cellular automata model was developed, incorporating a heterogeneous landscape with three interactive components: an age-structured tick population, a classical disease transmission function, and hosts. A set of simplifying assumptions were adopted with respect to the study objective and field data limitations. In the model, the landscape influences both tick survival and host movement. The validation of the model was performed with an empirical study. Scenarios of various landscape configurations (focusing on woodland fragmentation) were simulated and compared. Lyme disease risk indices (density and infection prevalence of nymphs) differed considerably between scenarios: (i) the risk could be higher in highly fragmented woodlands, which is supported by a number of recently published empirical studies, and (ii) grassland could reduce the risk in adjacent woodland, which suggests landscape fragmentation studies of zoonotic diseases should not focus on the patch-level woodland patterns only, but also on landscape-level adjacent land cover patterns. Further analysis of the simulation results indicated strong correlations between Lyme disease risk indices and the density, shape and aggregation level of woodland patches. These findings highlight the strong effect of the spatial patterns of local host population and movement on the spatial dynamics of Lyme disease risks, which can be shaped by woodland fragmentation. In conclusion, using a cellular automata approach is beneficial for modelling complex zoonotic transmission systems as it can be combined with either real world landscapes for exploring direct spatial effects or artificial representations for outlining possible empirical investigations.     

Integrated Assessment of Behavioral and Environmental Risk Factors for Lyme Disease Infection on Block Island,Rhode Island

Peridomestic exposure to Borrelia burgdorferi-infected Ixodes scapularis nymphs is considered the dominant means of infection with black-legged tick-borne pathogens in the eastern United States. Population level studies have detected a positive association between the density of infected nymphs and Lyme disease incidence. At a finer spatial scale within endemic communities, studies have focused on individual level risk behaviors, without accounting for differences in peridomestic nymphal density. This study simultaneously assessed the influence of peridomestic tick exposure risk and human behavior risk factors for Lyme disease infection on Block Island, Rhode Island. Tick exposure risk on Block Island properties was estimated using remotely sensed landscape metrics that strongly correlated with tick density at the individual property level. Behavioral risk factors and Lyme disease serology were assessed using a longitudinal serosurvey study. Significant factors associated with Lyme disease positive serology included one or more self-reported previous Lyme disease episodes, wearing protective clothing during outdoor activities, the average number of hours spent daily in tick habitat, the subject’s age and the density of shrub edges on the subject’s property. The best fit multivariate model included previous Lyme diagnoses and age. The strength of this association with previous Lyme disease suggests that the same sector of the population tends to be repeatedly infected. The second best multivariate model included a combination of environmental and behavioral factors, namely hours spent in vegetation, subject’s age, shrub edge density (increase risk) and wearing protective clothing (decrease risk). Our findings highlight the importance of concurrent evaluation of both environmental and behavioral factors to design interventions to reduce the risk of tick-borne infections.     

Effects of landscape and patch-level attributes on regional population persistence

Species responses are influenced by processes operating at multiple scales, yet many conservation studies and management actions are focused on a single scale. Although landscape-level habitat conditions (i.e., habitat amount, fragmentation and landscape quality) are likely to drive the regional persistence of spatially structured populations, patch-level factors (i.e., patch size, isolation, and quality) may also be important. To determine the spatial scales at which habitat factors influence the regional persistence of endangered Ord's kangaroo rats (Dipodomys ordii) in Alberta, Canada, we simulated population dynamics under a range of habitat conditions. Using a spatially-explicit population model, we removed groups of habitat patches based on their characteristics and measured the resulting time to extinction. We used proportional hazards models to rank the influence of landscape and interacting patch-level variables. Landscape quality was the most influential variable followed by patch quality, with both outweighing landscape- and patch-level measures of habitat quantity and fragmentation/proximity. Although habitat conservation and restoration priorities for this population should be in maximizing the overall quality of the landscape, population persistence depends on how this goal is achieved. Patch quality exerted a significant influence on regional persistence, with the removal of low quality road margin patches (sinks) reducing the risk of regional extinction. Strategies for maximizing overall landscape quality that omit patch-level considerations may produce suboptimal or detrimental results for regional population persistence, particularly where complex local population dynamics (e.g., source-sink dynamics) exist. This study contributes to a growing body literature that suggests that the prediction of species responses and future conservation actions may best be assessed with a multi-scale approach that considers habitat quality and that the success of conservation actions may depend on assessing the influences of habitat factors at multiple scales.     

Macroecological patterns of spider species richness across Europe

We analysed the pattern of covariation of European spider species richness with various environmental variables at different scales. Four layers of perception ranging from single investigation sites to the whole European continent were selected. Species richness was determined using published data from all four scales. Correlation analyses and stepwise multiple linear regression were used to relate richness to topographic, climatic and biotic variables. Up to nine environmental variables were included in the analyses (area, latitude, elevation range, mean annual temperature, local variation in mean annual temperature, mean annual precipitation, mean July temperature, local variation in mean July temperature, plant species richness). At the local and at the continental scale, no significant correlations with surface area were found, whereas at the landscape and regional scale, surface area had a significant positive effect on species richness. Factors that were positively correlated with species richness at both broader scales were plant species richness, elevation range, and specific temperature variables (regional scale: local variation in mean annual, and mean July temperature; continental scale: mean July temperature). Latitude was significantly negatively correlated with the species richness at the continental scale. Multiple models for spider species richness data accounted for up to 77% of the total variance in spider species richness data. Furthermore, multiple models explained variation in plant species richness up to 79% through the variables mean July temperature and elevation range. We conclude that these first continental wide analyses grasp the overall pattern in spider species richness of Europe quite well, although some of the observed patterns are not directly causal. Climatic variables are expected to be among the most important direct factors, although other variables (e.g. elevation range, plant species richness) are important (surrogate) correlates of spider species richness.     

Close to home: a history of Yale and Lyme disease

Yale scientists played a pivotal role in the discovery of Lyme disease and are credited as the first to recognize, name, characterize, and treat the affliction. Today, Lyme disease is the most commonly reported vector-borne illness in the United States, affecting approximately 20,000 people each year, with the incidence having doubled in the past 10 years [1]. Lyme disease is the result of a bacterial infection transmitted to humans through the bite of an infected deer tick, which typically results in a skin rash at the site of attack. While most cases, when caught early, are easily treated by antibiotic therapy, delayed treatment can lead to serious systemic side effects involving the joints, heart, and central nervous system. Here we review Yale's role in the discovery and initial characterization of Lyme disease and how those early discoveries are crucial to our current understanding of the disease.     

Metacommunity,mainland‐island system or island communities? Assessing the regional dynamics of plant communities in a fragmented landscape

Understanding the regional dynamics of plant communities is crucial for predicting the response of plant diversity to habitat fragmentation. However, for fragmented landscapes the importance of regional processes, such as seed dispersal among isolated habitat patches, has been controversially debated. Due to the stochasticity and rarity of among‐patch dispersal and colonization events, we still lack a quantitative understanding of the consequences of these processes at the landscape‐scale. In this study, we used extensive field data from a fragmented, semi‐arid landscape in Israel to parameterize a multi‐species incidence‐function model. This model simulates species occupancy pattern based on patch areas and habitat configuration and explicitly considers the locations and the shapes of habitat patches for the derivation of patch connectivity. We implemented an approximate Bayesian computation approach for parameter inference and uncertainty assessment. We tested which of the three types of regional dynamics – the metacommunity, the mainland‐island, or the island communities type – best represents the community dynamics in the study area and applied the simulation model to estimate the extinction debt in the investigated landscape. We found that the regional dynamics in the patch‐matrix study landscape is best represented as a system of highly isolated ‘island’ communities with low rates of propagule exchange among habitat patches and consequently low colonization rates in local communities. Accordingly, the extinction rates in the local communities are the main drivers of community dynamics. Our findings indicate that the landscape carries a significant extinction debt and in model projections 33–60% of all species went extinct within 1000 yr. Our study demonstrates that the combination of dynamic simulation models with field data provides a promising approach for understanding regional community dynamics and for projecting community responses to habitat fragmentation. The approach bears the potential for efficient tests of conservation activities aimed at mitigating future losses of biodiversity.     

No Observed Effect of Landscape Fragmentation on Pathogen Infection Prevalence in Blacklegged Ticks (Ixodes scapularis) in the Northeastern United States

Pathogen prevalence within blacklegged ticks (Ixodes scapularis Say, 1821) tends to vary across sites and geographic regions, but the underlying causes of this variation are not well understood. Efforts to understand the ecology of Lyme disease have led to the proposition that sites with higher host diversity will result in lower disease risk due to an increase in the abundance of inefficient reservoir species relative to the abundance of species that are highly competent reservoirs. Although the Lyme disease transmission cycle is often cited as a model for this “dilution effect hypothesis”, little empirical evidence exists to support that claim. Here we tested the dilution effect hypothesis for two pathogens transmitted by the blacklegged tick along an urban-to-rural gradient in the northeastern United States using landscape fragmentation as a proxy for host biodiversity. Percent impervious surface and habitat fragment size around each site were determined to assess the effect of landscape fragmentation on nymphal blacklegged tick infection with Borrelia burgdorferi and Anaplasma phagocytophilum. Our results do not support the dilution effect hypothesis for either pathogen and are in agreement with the few studies to date that have tested this idea using either a landscape proxy or direct measures of host biodiversity.     

Assessing multi-taxa sensitivity to the human footprint,habitat fragmentation and loss by exploring alternative scenarios of dispersal ability and population size: a simulation approach

Quantifying the effects of landscape change on population connectivity is compounded by uncertainties about population size and distribution and a limited understanding of dispersal ability for most species. In addition, the effects of anthropogenic landscape change and sensitivity to regional climatic conditions interact to strongly affect habitat fragmentation and loss. To further develop conservation theory and to understand the interplay between all of these factors, we simulated habitat fragmentation and loss across the Western United States for several hypothetical species associated with four biome types, and a range of habitat requirements and dispersal abilities. We found dispersal ability and population size of the focal species to be equally sensitive to habitat extent, while dispersal ability is more sensitive to habitat fragmentation. There were also strong critical threshold effects where habitat connectivity decreased disproportionately to decreases in life-history traits making these species near these thresholds more sensitive to changes in habitat loss and fragmentation. Overall, grassland and forest associated species are also most at risk from habitat loss and fragmentation driven by human related land-use. These two largest biome types were most sensitive at large contiguous patch sizes which is often considered most important for metapopulation viability and biodiversity conservation. Hypothetical simulation studies such as this can be of great value to scientists in further conceptualizing and developing conservation theory, and evaluating spatially-explicit scenarios of habitat connectivity. Our results are available for download in a web-based interactive mapping prototype useful for accessing the results of this study.     

Tropical tree species diversity in a mountain system in southern Mexico: local and regional patterns and determinant factors

Mechanisms explaining patterns of biodiversity along elevation gradients in tropical mountain systems remain controversial. We use a set of climatic, topographic, and soil variables encompassing regional, landscape, and local‐level spatial scales to explain the spatial variation of tree species diversity in the Sierra Madre of Chiapas, Mexico. We sampled 128 circular plots (0.1‐ha each) in four elevational bands along four elevation gradients or transects encompassing 100–2200 m. A total of 12,533 trees belonging to 444 species were recorded. Diversity patterns along the elevation gradient and the explanatory power of independent variables were dependent on spatial scale (regional vs transect) and functional group (total vs late‐successional or pioneer species). Diversity of all species and late‐successional species (1 – proportion of pioneer species) showed a constant pattern at the regional and transect scales, with low predictive power of climatic variables and/or elevation. A linear decrease in either number or proportion of pioneer species diversity was observed with increasing elevation, which was correlated with temperature, rainfall, and human disturbance trends. Total species diversity showed an increase with rainfall of the warmest quarter, indicating a regional‐level limiting effect of seasonality (drought duration). Yet the explanatory power of climatic and topographic variables was higher at the individual transect level than at the regional scale, suggesting the parallel but differential influence of evolutionary and geological history factors on diversification not so far studied to explain elevation patterns of species diversity in tropical mountain systems.     

Species richness patterns of amphibians in southwestern Ontario ponds

Abstract. In southwestern Ontario amphibian species richness (α-diversity) was investigated at 180 ponds from 1992 to 1994. Patterns of species richness were compared among regions and the relationship between species richness and local habitat and regional landscape variables was investigated. Patterns of incidence differed among regions, with species that use woodlands being rare in one of the regions. Repeated measures analysis of variance indicated that species richness differed significantly among regions but not among sub-regions nested within regions. Species richness did not change significantly over time and there was no region by year effect. Species richness was highly correlated with local variables related to fish predation and to regional variables related to forest cover. Multiple regression indicated that a combination of local and regional variables best accounted for the variance in species richness, but the amount of regional woodlands was the single most important variable. The pattern of species richness can be explained by historical deforestation as the primary process.     

景观历史对物种多样性的影响: 以内蒙古伊敏露天煤矿为例

矿产开采等人类活动极大地改变着生态环境和景观格局, 景观变化又是导致区域和全球物种多样性丧失的主要原因之一。然而, 物种多样性对周边景观变化响应的时间尺度问题往往被人们忽略。作者以内蒙古草原区伊敏露天煤矿为例, 从物种和功能群两个层次上, 探讨了不同的空间范围(1 km、2 km、3 km、4 km、6 km、8 km、10 km)内在不同时期(1975年、1990年、2000年、2010年)的景观格局(景观优势度指数、生境综合连接度指数和生境连接度概率指数)与生物多样性之间的关系。结果显示: 当前物种多样性与开矿前和开矿初期周边景观格局之间的相关性更高, 而且与4–8 km缓冲区范围内景观格局之间的关系更加密切。不同功能群物种丰富度与景观格局之间的关系不同, 其中, 多年生根茎禾草物种丰富度和当前小尺度(1–3 km)景观格局之间呈显著相关; 多年生杂类草和开矿前和开矿初期大尺度(4–10 km)景观格局之间相关显著; 多年生丛生禾草与景观格局的相关性并未达到显著水平, 但是随着空间尺度的增加出现单峰趋势, 在6 km范围上最高; 灌木、半灌木与景观格局的相关关系随着空间尺度的增加而增加; 一二年生草本与景观格局的相关性始终最低。为此, 本文得出如下结论: (1)物种多样性对周边景观格局变化的响应存在一定时间的滞后, 人类当前不合理的土地利用方式可能引起未来一段时间内该地区一些物种的消失; (2)区域种库决定小尺度物种多样性的大小, 研究区4–8 km范围内具有连通性的生境斑块是主要的种库资源; (3)植物的繁殖策略及种子传播方式是破碎化生境中物种多样性维持的重要机制。     

Fine-scale analysis reveals cryptic landscape genetic structure in desert tortoises

Characterizing the effects of landscape features on genetic variation is essential for understanding how landscapes shape patterns of gene flow and spatial genetic structure of populations. Most landscape genetics studies have focused on patterns of gene flow at a regional scale. However, the genetic structure of populations at a local scale may be influenced by a unique suite of landscape variables that have little bearing on connectivity patterns observed at broader spatial scales. We investigated fine-scale spatial patterns of genetic variation and gene flow in relation to features of the landscape in desert tortoise (Gopherus agassizii), using 859 tortoises genotyped at 16 microsatellite loci with associated data on geographic location, sex, elevation, slope, and soil type, and spatial relationship to putative barriers (power lines, roads). We used spatially explicit and non-explicit Bayesian clustering algorithms to partition the sample into discrete clusters, and characterize the relationships between genetic distance and ecological variables to identify factors with the greatest influence on gene flow at a local scale. Desert tortoises exhibit weak genetic structure at a local scale, and we identified two subpopulations across the study area. Although genetic differentiation between the subpopulations was low, our landscape genetic analysis identified both natural (slope) and anthropogenic (roads) landscape variables that have significantly influenced gene flow within this local population. We show that desert tortoise movements at a local scale are influenced by features of the landscape, and that these features are different than those that influence gene flow at larger scales. Our findings are important for desert tortoise conservation and management, particularly in light of recent translocation efforts in the region. More generally, our results indicate that recent landscape changes can affect gene flow at a local scale and that their effects can be detected almost immediately.     

Woody riparian plant distributions in western Oregon,USA: comparing landscape and local scale factors

We studied riparian forests along mountain streams in four large watersheds of western Oregon and far northern California, USA, to better understand the multiscale controls on woody riparian vegetation in a geographically complex region. In each of the four-study watersheds, we sampled woody riparian vegetation in161-ha sampling reaches that straddled the stream channel. Within each hectare, we sampled riparian vegetation and local environmental factors in 40 m² sampling plots arrayed along topographic transects. We also surveyed natural disturbance gaps in 6 ha in each watershed to explore the effects of fine scale disturbance on species distributions. We compared species composition across our study watersheds and used Nonmetric Multidimensional Scaling (NMS) and chi-squared analyses to compare the relative importance of landscape scale climate variables and local topographic and disturbance variables in explaining species distributions at sampling plot and hectare scales. We noted substantial turnover in the riparian flora across the region, with greatest numbers of unique species in watersheds at the ends of the regional gradient. In NMS ordinations at both scales, variation in woody riparian species composition showed strongest correlations with climatic variables and Rubus spectabilis cover, but the latter was only an important factor in the two northern watersheds. At the smaller scale, topographic variables were also important. Chi-squared analyses confirmed that more species showed landscape scale habitat preferences (watershed associations) than associations with topographic position (94.7% vs. 42.7% of species tested) or gap versus forest setting (94.7% vs. 24.6% of species tested). The woody riparian flora of western Oregon shows important biogeographic variation; species distributions showed strong associations with climatic variables, which were the primary correlates of compositional change between riparian sites at both scales analyzed. Additional local variation in composition was explained by measures of topography and disturbance.     

Avian taxonomic and functional diversity in early stage of longleaf pine (Pinus palustris) stands restored at agricultural lands: variations in scale dependency

In agricultural landscapes, the longleaf pine initiative (LLPI) and the Bobwhite Quail Initiative (BQI) aim to restore longleaf pine forests and early successional habitats, respectively. The early stage of longleaf pine stands and grass and forb vegetation produced by a combination of both restoration programs (LLPI‐BQI) may form habitat conditions favorable to early successional bird species and other birds, increasing avian diversity. We investigated how the LLPI and BQI programs affected taxonomic and functional diversity of birds and abundance of early successional birds (grassland and scrub/shrub species), and what environmental characteristics were associated with the diversity and abundance of birds. Our study was performed at 41 fields in Georgia, United States, during 2001–2002 by considering environmental characteristics at two spatial scales: local‐scale vegetation features and restoration program type (LLPI or LLPI‐BQI) and landscape‐scale vegetation features and landscape heterogeneity. Functional evenness, species richness, and abundance of grassland and scrub/shrub species did not show a clear association with local‐ or landscape‐scale variables. Shannon‐Wiener diversity was slightly influenced by restoration program type (local‐scale variable) with higher value at LLPI‐BQI stands than at LLPI stands despite no significant differences in local vegetation features between those stands. Functional divergence was strongly positively associated with landscape‐scale variables. That is, niche differentiation increased with increasing shrub coverage within a landscape, reducing competition between abundant bird species and others. Our results suggest that although a combination of BQI and LLPI program may have a positive effect on avian taxonomic diversity, it is important to consider shrub vegetation cover within a landscape to improve functional diversity.     

Climate refugia for Pinus spp. in topographic and bioclimatic environments of the Madrean sky islands of México and the United States

Climate refugia, or places where habitats are expected to remain relatively buffered from regional climate extremes, provide an important focus for science and conservation planning. Within high-priority, multi-jurisdictional landscapes like the Madrean sky islands of the United States and México, efforts to identify and manage climate refugia are hindered by the lack of high-quality and consistent transboundary datasets. To fill these data gaps, we assembled a bi-national field dataset (n?=?1416) for five pine species (Pinus spp.) and used generalized boosted regression to model pine habitats in relation to topographic variability as a basis for identifying potential microrefugia at local scales in the context of current species’ distribution patterns. We developed additional models to quantify climatic refugial attributes using coarse scale bioclimatic variables and finer scale seasonal remote sensing indices. Terrain metrics including ruggedness, slope position, and aspect defined microrefugia for pines within elevation ranges preferred by each species. Response to bioclimatic variables indicated that small shifts in climate were important to some species (e.g., P. chihuahuana, P. strobiformis), but others exhibited a broader tolerance (e.g., P. arizonica). Response to seasonal climate was particularly important in modeling microrefugia for species with open canopy structure and where regular fires occur (e.g., P. engelmannii and P. chihuahuana). Hotspots of microrefugia differed among species and were either limited to northern islands or occurred across central or southern latitudes. Mapping and validation of refugia and their ecological functions are necessary steps in developing regional conservation strategies that cross jurisdictional boundaries. A salient application will be incorporation of climate refugia in management of fire to restore and maintain pine ecology. Una versión en español de este artículo está disponible como descarga.

     

Conceptualization and Measurement of Habitat Fragmentation from the Primates’ Perspective

Habitat fragmentation is one of the principal threats to primates. Studies of primates in fragments usually conclude that fragmentation negatively affects some aspect of their biology or ecology. Nevertheless, the definition and quantification of fragmentation vary considerably among studies, resulting in contradictions and results that are difficult to interpret. We here 1) discuss the problems associated with the definition of habitat fragmentation and the ways of measuring it, 2) emphasize the importance of the concepts and methods from landscape ecology and metapopulation theory for the study of primates in fragmented landscapes, and 3) offer recommendations for more precise use of concepts associated with habitat fragmentation from the primates’ perspective. When specific knowledge of the study species/population is available, we suggest that the definition of the variables to be measured should be functional from the primates’ perspective, based, e.g., on their habitat requirements and dispersal capacity. The distance to the nearest fragment may not be the best way to measure the isolation between populations. Fragmentation per se is a landscape scale process and, hence, landscape scale studies are required to understand how species are distributed across heterogeneous landscapes. Finally, it is important to consider that what happens at the fragment scale could be the consequence of processes that interact at various spatial and temporal scales.     

Variation of a floral polymorphism at different spatial scales in the Mediterranean geophyte Narcissus assoanus

Aims Habitat fragmentation impacts the spatial extent and isolation of local populations and communities. Although the biological consequences of these impacts have been well studied at the site level, effects directly related to changes in the spatial configuration of populations in the landscape remain less clear. The objective of this study is to examine how changes in the spatial-scale configuration of populations are associated with variability in morph rations in the floral polymorphic Mediterranean geophyte Narcissus assoanus .Methods We performed a nested analysis of morph ratio variation at three spatial scales: a 50×50 km regional scale in SE France, in fourteen 1×1 km landscapes located in the same region, and within 12 spatially extensive population patches. We also quantified variation in the behaviour of pollinators in population patches of contrasting spatial configuration.Important findings At a regional scale, morph ratios show a geographic pattern of increasing isoplethy (1:1 morph ratio) away from centres of human population development and in upland pastures. At the landscape scale, isoplethy of local population patches is more correlated with decreased isolation among patches than with patch size. Finally, within local isoplethic populations, small patches can show significantly biased morph ratios. In small isolated patches, pollinators perform shorter flight distances among consecutive flower visits than in spatially extensive patches. This study of variation in a genetic polymorphism at multiple spatial scales provides new insights into the scale-dependent effects of habitat fragmentation and the potential occurrence of metapopulation dynamics in natural plant populations.     

陕北黄土高原景观破碎化的时空动态研究

景观破碎化受到自然环境背景及社会经济活动的影响,并限制区域发展.为揭示景观破碎化的时空变化特征,整合了MODIS(中分辨率成像光谱仪)影像逐旬数据与多时段景观类型数据,并对其进行了分析.比较1987～2002年景观破碎化的年际差异表明,陕北黄土高原的景观破碎化过程较缓慢,但具有区域差异,且与景观类型组成息息相关.结果表明,林地的破碎化水平变化显著,而农、草地的破碎化水平变化相对缓慢.年际变化分析有助于说明区域景观破碎化的趋势,而年内季节变化则能帮助认识景观破碎化过程的周期规律.