Spatial distribution of populations of solitarious adult desert locust (Schistocerca gregaria Forsk.) on the coastal plain of Sudan

Abstract 1 Densities of solitarious adult desert locusts were measured on regular grids of up to 126 sample sites in the southern part of the coastal plain of Sudan during the winters of 1999/2000 and 2000/2001. Geostatistical procedures were used to characterize spatial dependence of locust density, to evaluate the possibility of estimating locust densities at unvisited sites, based on information obtained at surveyed sites, and to create density maps. 2 Sample variograms indicate that population densities were spatially correlated over ranges from 5 to 24 km. The range of spatial correlation decreased as dry conditions towards the end of the rainy season concentrated the locusts in contracting areas of sufficient humidity and availability of green vegetation. The rather small ranges of spatial correlation indicate that sampling needs to be conducted at a refined scale (< 24 km between sample points) to avoid missing hot spots of desert locust. 3 Locust densities were highly correlated with cover abundance of the wild plant Heliotropium arbainense and cultivated millet, Pennisetum typhoidum. The association of locusts with these host plants can be used to target sampling and enhance detection chance. 4 The relationship between sampling intensity and kriging variance was explored. Implications for monitoring of desert locust are discussed.     

Movement of outbreak populations of mountain pine beetle: influences of spatiotemporal patterns and climate

Insect outbreaks exert landscape-level influences, yet quantifying the relative contributions of various exogenous and endogenous factors that contribute to their pattern and spread remains elusive. We examine an outbreak of mountain pine beetle covering an 800 thousand ha area on the Chilcotin Plateau of British Columbia, Canada, during the 1970s and early 1980s. We present a model that incorporates the spatial and temporal arrangements of outbreaking insect populations, as well as various climatic factors that influence insect development. Onsets of eruptions of mountain pine beetle demonstrated landscape-level synchrony. On average, the presence of outbreaking populations was highly correlated with outbreaking populations within the nearest 18  km the same year and local populations within 6 km in the previous two years. After incorporating these spatial and temporal dependencies, we found that increasing temperatures contributed to explaining outbreak probabilities during this 15  yr outbreak. During collapse years, landscape-level synchrony declined while local synchrony values remained high, suggesting that in some areas host depletion was contributing to population decline. Model forecasts of outbreak propensity one year in advance at a 12 by 12  km scale provided 80% accuracy over the landscape, and never underestimated the occurrence of locally outbreaking populations. This model provides a flexible approach for linking temperature and insect population dynamics to spatial spread, and complements existing decision support tools for resource managers.     

天山中段主要植被类型中种群的空间分布格局与环境的关系

 用生物地理统计学的空间相关图及空间相关指数方法研究了天山中段主要植被类型中种群的空间分布格局及其影响种群空间分布格局的主要环境因子。主要考虑了山地荒漠、亚高山草甸和高山草甸3种植被类型,以及30年平均降水量和月平均气温、海拔、土壤pH值和有机质含量等9种环境及气象因子。结果表明：影响天山北坡荒漠植物种群空间分布格局的主要因子是海拔。结果表明：影响天山越高分布越少,而7月平均温度越高分布越广;影响南坡荒漠优势物种空间分布的因子较复杂,但土壤中N含量是其中一个重要因子。影响亚高山草甸优势种群空间分布的因子较多,但比较重要的因子包括土壤CaCO3含量及1月平均温度为负面因子,而降水量是比较重要的正影响因子;影响高山草甸优势种群空间分布的主要因子虽然很多,但是降水量、1月平均温度和7月平均温度等是主要影响因子。     

Outbreaks, gene flow and effective population size in the migratory locust, Locusta migratoria: a regional-scale comparative survey

The potential effect of population outbreaks on within and between genetic variation of populations in pest species has rarely been assessed. In this study, we compare patterns of genetic variation in different sets of historically frequently outbreaking and rarely outbreaking populations of an agricultural pest of major importance, the migratory locust, Locusta migratoria . We analyse genetic variation within and between 24 populations at 14 microsatellites in Western Europe, where only ancient and low-intensity outbreaks have been reported (non-outbreaking populations), and in Madagascar and Northern China, where frequent and intense outbreak events have been recorded over the last century (outbreaking populations). Our comparative survey shows that (i) the long-term effective population size is similar in outbreaking and non-outbreaking populations, as evidenced by similar estimates of genetic diversity, and (ii) gene flow is substantially larger among outbreaking populations than among non-outbreaking populations, as evidenced by a fourfold to 30-fold difference in F _ST values. We discuss the implications for population dynamics and the consequences for management strategies of the observed patterns of genetic variation in L. migratoria populations with contrasting historical outbreak frequency and extent.     

Season‐modulated responses of Neotropical bats to forest fragmentation

Seasonality causes fluctuations in resource availability, affecting the presence and abundance of animal species. The impacts of these oscillations on wildlife populations can be exacerbated by habitat fragmentation. We assessed differences in bat species abundance between the wet and dry season in a fragmented landscape in the Central Amazon characterized by primary forest fragments embedded in a secondary forest matrix. We also evaluated whether the relative importance of local vegetation structure versus landscape characteristics (composition and configuration) in shaping bat abundance patterns varied between seasons. Our working hypotheses were that abundance responses are species as well as season specific, and that in the wet season, local vegetation structure is a stronger determinant of bat abundance than landscape‐scale attributes. Generalized linear mixed‐effects models in combination with hierarchical partitioning revealed that relationships between species abundances and local vegetation structure and landscape characteristics were both season specific and scale dependent. Overall, landscape characteristics were more important than local vegetation characteristics, suggesting that landscape structure is likely to play an even more important role in landscapes with higher fragment‐matrix contrast. Responses varied between frugivores and animalivores. In the dry season, frugivores responded more to compositional metrics, whereas during the wet season, local and configurational metrics were more important. Animalivores showed similar patterns in both seasons, responding to the same group of metrics in both seasons. Differences in responses likely reflect seasonal differences in the phenology of flowering and fruiting between primary and secondary forests, which affected the foraging behavior and habitat use of bats. Management actions should encompass multiscale approaches to account for the idiosyncratic responses of species to seasonal variation in resource abundance and consequently to local and landscape scale attributes.     

Cyanobacterial ecology across environmental gradients and spatial scales in China's hot and cold deserts

Lithic photoautotrophic communities function as principal primary producers in the world's driest deserts, yet many aspects of their ecology remain unknown. This is particularly true for Asia, where some of the Earth's oldest and driest deserts occur. Using methods derived from plant landscape ecology, we measured the abundance and spatial distribution of cyanobacterial colonization on quartz stony pavement across environmental gradients of rainfall and temperature in the isolated Taklimakan and Qaidam Basin deserts of western China. Colonization within available habitat ranged from 0.37+/-0.16% to 12.6+/-1.8%, with cold dry desert sites exhibiting the lowest abundance. Variation between sites was most strongly correlated with moisture-related variables and was independent of substrate availability. Cyanobacterial communities were spatially aggregated at multiple scales in patterns distinct from the underlying rock pattern. Site-level differences in cyanobacterial spatial pattern (e.g. mean inter-patch distance) were linked with rainfall, whereas patchiness within sites was correlated with local geology (greater colonization frequency of large rocks) and biology (dispersal during rainfall). We suggest that cyanobacterial patchiness may also in part be self-organized - that is, an outcome of soil water-biological feedbacks. We propose that landscape ecology concepts and models linking desert vegetation, biological feedbacks and ecohydrological processes are applicable to microbial communities.     

Spatial structure and niche patterns of a rodent community in the south Bukhara desert (Middle Asia)

The distribution of niches in resource space and the niche patterns of a 13 species community of Middle Asian desert rodents were studied by use of discriminant function analysis Nineteen quantitative parameters of the environment (soil structure and vegetation), measured at 600 sample plots within twenty four one ha grids, were considered The first three canonical axes of resource space account for 83% of the variance, the first axis represents a general landscape gradient from sand to clay soils, the second axis reflects a gradient of increasing productivity, and the third axis reflects a gradient of increasing protectability of the environment The distribution of niches in resource space is not even, there are two distinct spatial guilds consisting of psammophilous and sclerophilous species There is a negative correlation between niche position (distance from species centroid to the center of the resource space) and maximal population biomass At the same time there are no correlations between the niche breadth and the niche position due to the absence of species with really broad niches Rodent biomass increases along the productivity axis and reaches a peak in the middle part of the substrate axis Rodent species diversity increases along the substrate axis from sand to clay soils Changes of species diversity along productivity axis have humpshaped patterns Maximum species diversity was recorded at low level of productivity on the sandy soils and shifted to intermediate levels of productivity on sandy-loam and clay soils     

Small-scale vegetation patterns in the parental environment influence the phase state of hatchlings of the desert locust

Desert locusts (Schistocerca gregaria Forskål (Orthoptera: Acrididae)) change phase in response to population density. Solitarious insects avoid one another; when crowded, they shift to the gregarious phase and aggregate. Laboratory experiments and individual‐based modelling have shown that small‐scale resource distribution can affect locust phase state via an influence on crowding. Laboratory work has also shown that parental phase state is transmitted to offspring via maternal inheritance. These effects had not been investigated in the field previously. We maintained small populations of adult desert locusts in semi‐field enclosures with different distribution patterns of a single plant species (Hyoscyamus muticus L. (Solanaceae)). The offspring of locusts exposed to more clumped patterns of vegetation exhibited more gregarious behaviour when tested in a behavioural phase assay than did progeny from parents left in enclosures with more scattered vegetation. These effects on nymphal behaviour appeared to be mediated by influences of resource distribution on adult phase state. Phase state in small semi‐field populations was influenced by small‐scale vegetation distribution. Phase differences engendered by environmental structure were maintained in time and transmitted to progeny.     

Land use changes affect distributional patterns of desert birds in the Baja California peninsula, Mexico

Reliable plans for desert bird conservation will depend on accurate prediction of habitat change effects on their distribution and abundance patterns. Predictive models can help highlight relationships between human‐related and other environmental variables and the presence of desert bird species. Presence/absence of 30 desert bird species of Baja California peninsula was modelled on the basis of explanatory variables taken from the field, maps, and digital imagery. Generalized linear models were fit to each bird species using both variables representing human activity and other environmental factors as predictors that might influence distribution. Probability of species presence was used as a habitat suitability index to evaluate the effect of human activity when the model contained a significant human activity variable. No differences were found in bird species richness between natural sites and those transformed by agriculture or urbanization. Of 59 bird species recorded in surveys, 34% were positively or negatively associated with human‐transformed habitats. Fourteen species seem to benefit from transformation of natural vegetation by agriculture or urbanization, while six were negatively affected. Sensitivity analyses of final models indicated all were robust. Results suggest that the occurrence of a large percentage of bird species inhabiting scrub habitats is sensitive to human habitat transformation. This finding has important conservation implications at regional scale as fragmentation and conversion of desert ecosystems into agricultural and urban areas affect the distribution of species that are highly selective for scrub habitat. Land use and anthropogenic activities seem to change ecological patterns at large spatial scales, but other factors could drive species richness distribution too (i.e. individual species response, species–energy relationships). The spatial modelling approach at regional scale used in this study can be useful for designing natural resource management plans in the Sonoran desert scrub.     

Spatial heterogeneity in resource distribution promotes facultative sociality in two trans-Saharan migratory birds

Background

Migrant populations must cope not only with environmental changes in different biomes, but also with the continuous constraints imposed by human-induced changes through landscape transformation and resource patchiness. Theoretical studies suggest that changes in food distribution can promote changes in the social arrangement of individuals without apparent adaptive value. Empirical research on this subject has only been performed at reduced geographical scales and/or for single species. However, the relative contribution of food patchiness and predictability, both in space and time, to abundance and sociality can vary among species, depending on their degree of flexibility.

Methodology/Principal Findings

By means of constrained zero-inflated Generalized Additive Models we analysed the spatial distribution of two trans-Saharan avian scavengers that breed (Europe) and winter (Africa) sympatrically, in relation to food availability. In the summering grounds, the probability of finding large numbers of both species increases close to predictable feeding sources, whereas in the wintering grounds, where food resources are widespread, we did not find such aggregation patterns, except for the black kite, which aggregated at desert locust outbreaks. The comparison of diets in both species through stable isotopes revealed that their diets overlapped during summering, but not during wintering.

Conclusions/Significance

Our results suggest that bird sociality at feeding grounds is closely linked to the pattern of spatial distribution and predictability of trophic resources, which are ultimately induced by human activities. Migrant species can show adaptive foraging strategies to face changing distribution of food availability in both wintering and summering quarters. Understanding these effects is a key aspect for predicting the fitness costs and population consequences of habitat transformations on the viability of endangered migratory species.     

Effect of woody vegetation at the landscape scale on the abundance of natural enemies in Australian vineyards

Undisturbed vegetation within agricultural areas, especially woody vegetation, has been documented to enhance natural invertebrate enemies within adjacent crops, particularly in northern Europe. To test this idea within the context of Australian vineyards, we considered 44 landscapes from two regions, and sampled invertebrates in vineyards central to each landscape five times at monthly intervals using canopy sticky traps. Landscape composition was characterized at 11 spatial scales from 95 m to 3 km radius. We found only weak relationships between woody vegetation and the abundance of invertebrate groups including coccinellids at any spatial scale, regardless of whether the contribution of each scale was considered independently or together using a multiple regression approach. The only consistent pattern was that several families of parasitoids were influenced by woody vegetation at the landscape scale; the abundance of Eulophidae increased with woody vegetation in the landscape, while two families of smaller parasitoids, Trichogrammatidae and Mymaridae, were negatively affected by woody vegetation. We discuss possible reasons for these apparent contrasting patterns between Australian and European studies.     

基于GIS和GS的东亚飞蝗卵块空间格局的研究

本文以沿渤海蝗区东亚飞蝗Locusta migratoria manilensis (Meyen) 越冬卵块为研究对象,野外采用450 m和50 m规则栅格取样,包括卵量、植被覆盖度、土壤含水量、含盐量、土壤pH和有机质等,利用地统计学方法,在GIS平台下,分析研究区域内影响蝗虫产卵选择的环境因子、蝗虫卵块的空间异质性及分布格局。结果表明, 植被覆盖度、土壤含盐量和土壤含水量在有卵和无卵的环境中存在极显著的差异,飞蝗产卵时最适宜的植被覆盖度、土壤含水量和盐度范围分别为0～30%、10.1%～20.0%和0.09%～1.99%,且当小环境植被覆盖度>50%、土壤含水量>30%或含盐量>3%时,飞蝗不再选择产卵。蝗虫卵块具有高度空间异质性,其空间自相关范围平均为390 m且呈斑块、聚集分布,蝗虫卵块变异函数曲线为球状模型。利用块段克立格法进行空间局部插值,得到研究区域卵块的空间分布格局图,可较准确地描述飞蝗卵块在研究区域内的空间分布、形状、地理位置及相对位置。研究结果可为地面卵块抽样调查、实时跟踪蝗卵胚胎发育进程、确定蝗灾早期发生点、片防治区域及蝗灾早期遥感预警提供科学依据。     

Changes in patch mosaics and vegetation structure of rural forested landscapes under shifting human impacts in South Korea

Landscape change in rural ecosystems is a major global issue because they are an important ecological and socio-cultural resource. The aim of this study was to demonstrate the driving forces behind landscape changes. Changes in the patterns and processes of landscape mosaics and vegetation community in two rural areas (Teokdong-ri, TD and Teokseong-ri, TS) in Korea were studied between 1988 and 2002. Quantitative data of vegetation community, landscape mosaics, and local statistics of the two study areas were analyzed. Agricultural efficiency increased even decreasing household population and the agricultural area. In both areas, as the human dependence on natural resources decreased, the patterns and processes of landscape mosaics and forest structure were changed due to changing human impacts on land use. Owing to the abandonment of forest management for 14 years, the spatial heterogeneity of TD significantly increased more than that of TS. In detrended correspondence analysis ordination, floristic compositions of forest patches of two areas were unevenly located on the ordination axes. Pinus densiflora communities of both areas in 1988 were separately located in 2002 as two directions according to management intensity. The species composition of P. densiflora in one direction of 1988 became similar to those of Quercus forests in 2002. This may be because species composition of P. densiflora has been influenced due to changed habitat environments. Finally, we concluded that the development of forest communities and vegetation succession predicted the spatial pattern of future landscape mosaics and due to the vegetation dynamics of rural ecosystems in Korea.Nomenclature: Miyawaki et al. (1994), Lee (1993), and Lee (1998) for identifying plant species.     

Small mammal abundance in Mediterranean post-fire habitats: a role for predators?

We studied patterns of small mammal abundance and species richness in post-fire habitats by sampling 33 plots (225 m² each) representing different stages of vegetation recovery after fire. Small mammal abundance was estimated by live trapping during early spring 1999 and vegetation structure was sampled by visual estimation at the same plots. Recently–burnt areas were characterised by shrubby and herbaceous vegetation with low structural variability, and unburnt areas were characterised by well developed forest cover with high structural complexity. Small mammal abundance and species richness decreased with time elapsed since the last fire (from 5 to at least 50 years), and these differences were associated to the decreasing cover of short shrubs as the post-fire succession of plant communities advanced. However, relationships between vegetation structure and small mammals differed among areas burned in different times, with weak or negative relationship in recently burnt areas and positive and stronger relationship in unburnt areas. Furthermore, the abundance of small mammals was larger than expected from vegetation structure in plots burned recently whereas the contrary pattern was found in unburned areas. We hypothesised that the pattern observed could be related to the responses of small mammal predators to changes in vegetation and landscape structure promoted by fire. Fire-related fragmentation could have promoted the isolation of forest predators (owls and carnivores) in unburned forest patches, a fact that could have produced a higher predation pressure for small mammals. Conversely, small mammal populations would have been enhanced in early post-fire stages by lower predator numbers combined with better predator protection in areas covered by resprouting woody vegetation.     

Estimation of climatic favourable areas for locust outbreaks in Spain: integrating species' presence records and spatial information on outbreaks

For millennia, locust swarms have recurrently devastated crop productivity across continents. In much of Europe, locust outbreaks have been considerably reduced by human pressure in recent decades, but important foci of outbreaks still exist in Spain. Distribution models are often used to derive spatial hypotheses and risk maps. Because insufficient information is available to include the extreme plasticity of the solitary and gregarious phases of locusts in large‐scale spatial models, we modelled the distribution either of Acrididae species or of outbreaks per se. Confirmed occurrences of Dociostaurus, Calliptamus and Chorthippus species were obtained from a field survey complemented by museum collection data and the published literature. The locations of confirmed or potential outbreaks covering two time periods of 20 years each were obtained from the literature and from Spanish autonomous community reports. Models were built with one topographic and eleven climatic predictors. We evaluated the ability of different models to predict outbreak recurrence and found that models based on Moroccan locust data or outbreak occurrence data performed the best. We generated a predictive map of the climatic favourability for locust outbreaks in Spain and found that the major foci of locust swarms were encompassed by those areas categorized by the models as areas of highest risk. Predictive maps of outbreak favourability can facilitate the more sustainable use of insecticides and more efficient integrated pest management.     

The relationship between pollen and extant vegetation across an arid urban ecosystem and surrounding desert in Southwest USA

Aim In this paper, we explore the relationship between pollen concentration in surface soil and extant perennial vegetation across a rapidly urbanizing arid ecosystem along with its surrounding agricultural and native Sonoran Desert land. We also investigate whether taxa behave as expected from known pollination characteristics (e.g. anemophilous vs. zoophilous) and whether the pollen–plant relationship differs between the undeveloped desert and agro‐urban regions. Location We used a probability‐based sampling scheme at 200, 900‐m² sites across the Central Arizona–Phoenix region, a 6400‐km² area of the south‐western USA. Methods Pollen–plant abundances were mapped across the study area using interpolation techniques, summary bar charts and scatterplots, then two statistical approaches were applied to examine the data quantitatively. Firstly, we used regression analysis of paired pollen concentration and plant cover data; secondly, pc‐ord was used on a cross‐matrix (contingency table) containing the presence/absence scores of both pollen and plants for each taxon at each site. Results Mapping and quantitative analysis revealed that pollen–plant relationships do vary both between anemophilous and zoophilous groupings and by individual taxon. They also revealed that distribution patterns of both pollen and plant abundance vary consistently across the three main landscape types (desert, urban, agricultural) and that pollen taxa groupings are consistent with pollination method and source plant distribution regardless of landscape type. Main conclusions These findings provide a broad range of comparative data to facilitate palynological reconstruction of past vegetation and aid in assessing types of prehistoric impacts on this vegetation. They also document that significant variation can occur in pollen rain across a city, even for taxa with widely distributed pollen, leading to the conclusion that forecasting pollen distribution patterns for allergy‐related pollen types using only one or a few pollen traps is likely to entail substantial error.     

Phase polyphenism and preventative locust management

The ecology of phase polyphenism plays a major role in locust swarm formation. We describe how recent advances in the understanding of phase polyphenism can be combined with existing management approaches as part of a preventative Desert locust management strategy. We start with a brief overview of phase polyphenism with particular emphasis on the role that resource distribution patterns play in the process of locust phase change. We then review current perspective on preventative locust management, and conclude by proposing a framework for quantitatively assessing the risk that phase change will occur in local locust populations. Importantly, the data required to implement this framework can be readily collected with little additional effort or cost just by slightly modifying locust habitat survey protocols that are already in operation. Incorporating gregarization risk assessment into existing preventative management strategies stands to make a considerable contribution toward realizing sustainable goals of reductions in the pesticide, manpower and financial support necessary to combat Desert locust upsurges, outbreaks and ultimately plagues.     

Distribution and abundance patterns of a newly colonizing species in Tunisian oases: the Common Blackbird Turdus merula

We investigated distribution and abundance patterns of a recently arrived species in the oases of southern Tunisia: the Common Blackbird Turdus merula . In this system, we expected that the vegetation structure and geographical locations of oases would have played an important part in shaping the patterns of oasis occupancy and local abundance. Using data collected at 53 oases during two breeding seasons, we found that Blackbird occurrence in a given oasis depended mainly on its presence at neighbouring oases. However, vegetation structure did not prove to be a relevant predictor of Blackbird occurrence. Within occupied oases, local abundance was associated with vegetation structure, namely with the diversity and abundance of the two lowest vegetation layers: fruit trees and herbaceous plants. The presence of Blackbirds at neighbouring oases was not found to account for local abundance. Overall, our results suggest that the distribution and abundance of this newly colonizing species in the southern Tunisian oasis system are influenced by processes acting at two different spatial scales. Landscape-scale processes (i.e. dispersal and colonization from nearby occupied oases) are likely to play an important role in shaping the pattern of oasis occupancy, whereas local-scale factors seem to be more relevant in determining the abundance of locally established populations.