Variation in vegetative water use in the savannas of the North Australian Tropical Transect

Abstract. The decline in tree density on sandy soils in savannas is highly correlated with declining mean annual rainfall along the North Australian Tropical Transect (NATT). We reanalyse various data on water use by individual trees and argue that a common relationship can be used to estimate annual water use by tree stands along the NATT from ca. 600 mm mean annual rainfall to at least 1600 mm. Where rainfall is less than 600 mm, trees of a given size use less water than at sites where rainfall is higher. We use these relationships to relate water use at the stand scale with mean annual rainfall along the NATT. From this we show that the empirical data imply that the minimum depth of sandy soil that needs to be exploited by trees declines with increasing aridity along the NATT from more than 5 m to less than 1 m. This finding is consistent with other observations and the pattern that with increasing aridity, an increasing proportion of rainfall coming from isolated storms rather than from periods of extended monsoon activity.     

Demographic patterns of a widespread long‐lived tree are associated with rainfall and disturbances along rainfall gradients in SE Australia

Predicting species distributions with changing climate has often relied on climatic variables, but increasingly there is recognition that disturbance regimes should also be included in distribution models. We examined how changes in rainfall and disturbances along climatic gradients determined demographic patterns in a widespread and long‐lived tree species, Callitris glaucophylla in SE Australia. We examined recruitment since 1950 in relation to annual (200–600 mm) and seasonal (summer, uniform, winter) rainfall gradients, edaphic factors (topography), and disturbance regimes (vertebrate grazing [tenure and species], fire). A switch from recruitment success to failure occurred at 405 mm mean annual rainfall, coincident with a change in grazing regime. Recruitment was lowest on farms with rabbits below 405 mm rainfall (mean = 0–0.89 cohorts) and highest on less‐disturbed tenures with no rabbits above 405 mm rainfall (mean = 3.25 cohorts). Moderate levels of recruitment occurred where farms had no rabbits or less disturbed tenures had rabbits above and below 405 mm rainfall (mean = 1.71–1.77 cohorts). These results show that low annual rainfall and high levels of introduced grazing has led to aging, contracting populations, while higher annual rainfall with low levels of grazing has led to younger, expanding populations. This study demonstrates how demographic patterns vary with rainfall and spatial variations in disturbances, which are linked in complex ways to climatic gradients. Predicting changes in tree distribution with climate change requires knowledge of how rainfall and key disturbances (tenure, vertebrate grazing) will shift along climatic gradients.     

Evaluating ecohydrological theories of woody root distribution in the Kalahari

The contribution of savannas to global carbon storage is poorly understood, in part due to lack of knowledge of the amount of belowground biomass. In these ecosystems, the coexistence of woody and herbaceous life forms is often explained on the basis of belowground interactions among roots. However, the distribution of root biomass in savannas has seldom been investigated, and the dependence of root biomass on rainfall regime remains unclear, particularly for woody plants. Here we investigate patterns of belowground woody biomass along a rainfall gradient in the Kalahari of southern Africa, a region with consistent sandy soils. We test the hypotheses that (1) the root depth increases with mean annual precipitation (root optimality and plant hydrotropism hypothesis), and (2) the root-to-shoot ratio increases with decreasing mean annual rainfall (functional equilibrium hypothesis). Both hypotheses have been previously assessed for herbaceous vegetation using global root data sets. Our data do not support these hypotheses for the case of woody plants in savannas. We find that in the Kalahari, the root profiles of woody plants do not become deeper with increasing mean annual precipitation, whereas the root-to-shoot ratios decrease along a gradient of increasing aridity.     

Variation in the composition and structure of tropical savannas as a function of rainfall and soil texture along a large-scale climatic gradient in the Northern Territory, Australia

Abstract. Variation in structural and compositional attributes of tropical savannas are described in relation to variation in annual rainfall and soil texture along a subcontinental-scale gradient of rainfall in the wet-dry tropics of the Northern Territory, Australia. Rainfall varies along the gradient from over 1500 mm p.a. in the Darwin region ( c . 12° S) to less than 500 mm in the Tennant Creek region ( c . 18° S). Soils are patchy, and sands, loams and clays may occur in all major districts within the region. We utilized a large data set (1657 quadrats ° 291 woody species; with numerous measured and derived sample variables) covering an area of 0.5 million km². Correlations between floristic composition of woody species and environmental variables were assessed using DCA ordination and vector fitting of environmental variables. Vectors of annual rainfall and soil texture were highly correlated with variation in species composition. Multiple regression analyses incorporating linear and quadratic components of mean annual rainfall and topsoil clay content were performed on three structural attributes (tree height, tree cover, tree basal area) and two compositional attributes (woody species richness, deciduous tree species richness). Tree height declined with decreasing rainfall; cover, basal area, woody species richness and deciduous species richness all declined with decreasing rainfall and increasing soil clay content. Regression models accounted for between 17% and 45% of the variation in the data sets. Variation in other factors such as soil depth, landscape position and recent land-use practices (for which there were no data on an individual quadrat basis) are likely to have contributed to the large residual variation in the data set.     

The steppes and deserts of the Xizang Plateau (Tibet)

The Xizang Plateau (Tibet) covers a vast area over 4 000 m with a severe environment. Steppes and deserts are widely distributed on the plateau to the west of 91.5°E. Poaceae, Asteraceae, Fabaceae and Cyperaceae are the most important families in the composition of steppe communities. The steppe can be divided into high-cold steppe and montane steppe. The former one is characterized by the Stipa purpurea community, which occupies a vast area with a cold, dry climate: annual mean temperature 0 to –6°C, annual rainfall is 150–300 mm; The latter one is distributed in some limited regions, where the climate is less severe: annual mean temperature 0–7°C, annual rainfall is 150–400 mm. The representative communities here are the Stipa glareosa and S. bungeana communities. Chenopodiaceae and Asteraceae play a principal role in both high-cold and montane deserts. The high-cold desert is unique. Its major representative is the Ceratoides compacta community, which is found at about 5 000 m, in an extremely cold and very dry climate. The Ceratoides latens and Ajania fruticulosa communities are the common ones of the montane desert which mainly appears below 4 600 m in elevation, where the annual temperature is about 0°C and the rainfall is less than 100 mm. The distribution of the steppe and the desert communities shows a clear regional differentiation, and an equally clear vertical distribution pattern.     

Relationship between small-scale structural variability and simulated vegetation productivity across a regional moisture gradient in southern Africa

The observed variability in vegetation structure within landscapes was used as the basis for model estimates of the range of annual productivity of landscape patches at four sites along a moisture gradient in southern Africa ranging from 879 to 365 mm mean annual rainfall. Principal components of patch‐scale variability in leaf area, woody biomass and vertical leaf profiles were derived from intensive characterization of the small‐scale spatial structure of woody vegetation at each site. For each site, the mean and extremes of the principal component distribution parameterized an ecophysiology model of vegetation productivity. Vegetation was most heterogeneous at intermediate locations along the rainfall gradient. Variability in vegetation structure led to a range of annual productivity within one site (600 mm) that accounted for 68% of the total range in mean productivity across all sites. Patch‐scale estimates of tree productivity were found to be primarily correlated to annual rainfall (r²=0.66, P=0.001) and not woody leaf area (r²=0.01, P=0.75), while grass productivity was found to be related to values of woody leaf area (r²=0.77, P<0.001) and not annual rainfall (r²=0.11, P=0.29). This result indicates that life‐form interactions have a significant role in controlling vegetation productivity across the rainfall gradient. The findings of this study emphasize the importance of considering heterogeneity rather than mean structure when modeling productivity, particularly when considering dynamic vegetation structure, where differences between landscape patches may not be well represented in the mean structure.     

Effects of climate and local aridity on the latitudinal and habitat distribution of Arvicanthis niloticus and Arvicanthis ansorgei (Rodentia, Murinae) in Mali

Introduction The genus Arvicanthis (Lesson 1842) (Rodentia: Murinae), usually referred to as the unstriped grass rat, is mainly distributed in savanna and grassland habitats of Sub-Saharan Africa. Among the four chromosomal forms of Arvicanthis recently differentiated in Western and Central Africa, the one with a diploid chromosomal number (2n) of 62 and an autosomal fundamental number (NFa) of 62 or 64 is ascribed to Arvicanthis niloticus (Demarest 1822), while the one with 2n = 62 and a NFa between 74 and 76 is referred to A. ansorgei (Thomas 1910). Despite the broad area of sympatry recently uncovered along the inner delta of the Niger river in Mali [details in Volobouev et al. (2002) Cytogenetics and Genome Research, 96, 250–260], the distribution of the two species is largely parapatric and follows the latitudinal patterns of the West-African biogeographical domains, which are related to the latitudinal patterns of annual rainfall in this region. Here, we analyse the suggestion that the two species show specific adaptations to differences in climate aridity. Methods Karyologically screened animals were sampled in 19 localities in seasonally flooded regions located along the ‘Niger’ river in Mali and extending from 1100 to 200 mm of mean annual rainfall. The analysis of trapping success (TS) data allowed us to investigate the respective effects of climate (i.e. annual rainfall) and local (i.e. duration of the green herbaceous vegetation) aridity on the latitudinal and habitat distribution of the two species. Conclusions The broad zone of sympatry was found to correspond to a northward expansion of the recognized distribution area of A. ansorgei. TS values indicated that the two species responded very differently to climatic and local conditions of aridity. Arvicanthis ansorgei decreased in TS as regional conditions became more arid; a similar trend was also observed within regions where habitat occupancy decreased with local aridity. The higher TS observed in the most humid habitat relative to the others persisted throughout the latitudinal rainfall gradient. In contrast, TS of A. niloticus increased with latitudinal aridity. This species was present in more arid habitats than A. ansorgei from 1000 mm down to 400 mm of mean annual rainfall where a shift to the most humid habitat occurred. These opposite trends in TS distribution between species suggest that A. ansorgei is less adapted than A. niloticus to arid environments at both a regional and habitat level; thus, A. ansorgei would be able to invade dry regions only along the extensive floodplains bordering the inner delta of the ‘Niger’ river. Several biological traits that may be involved in limiting the southward distribution of A. niloticus are discussed.     

Lianas may be favoured by low rainfall: evidence from Ghana

We review the evidence in support of the hypotheses that (i) lianas are now increasing in tropical forests and (ii) lianas are more abundant in the drier tropical forests. There is good evidence to support both hypotheses, including a new analysis of data from Ghana. In this dataset, there is a linear increase in the percentage of species that are lianas, from 30% at a mean annual rainfall of 2,000 mm year⁻¹ to 43% at a mean annual rainfall of 1,000 mm year⁻¹. Both trends in lianas, one temporal, the other spatial, may be related to water availability, though parallel changes in canopy density (disturbance) may be contributory. It is also clear that most liana species in West Africa show restricted distribution along the rainfall gradient implying adaptation to different water availability. The reasons for the high sensitivity to rainfall may be that lianas have an especially effective water-transport system, with deep roots, large xylem vessels and a mechanism to avoid cavitation of water. As the climate of much of the tropics is becoming drier, we may expect increases in both liana abundance and their proportion in the flora over the future decades.     

Precipitation signal in pollen rain from tropical forests, South India

We have analyzed the pollen content of 51 surface soil samples collected in tropical evergreen and deciduous forests from the Western Ghats of South India sampled along a west to east gradient of decreasing rainfall (between 11 degrees 30-13 degrees 20'N and 75 degrees 30-76 degrees 30'E). Values of mean annual precipitation (Pann, mm/yr) have been calculated at each of the 51 sampling sites from a great number of meteorological stations in South India, using a method of data interpolation based on artificial neural network. Interpolated values at the pollen sites of Pann range from 1200 to 5555mm/yr, while mean temperature of the coldest month (MTCO) remains >15 degrees C and humidity factor (AET/PET, the actual evapotranspiration to potential evapotranspiration ratio) remains also included between 65 and 72%.Results are presented in the form of percentage pollen diagrams where samples are arranged according to increasing values of annual precipitation. They indicate that the climatic signal of rainfall is clearly evidenced by distinct pollen associations. Numerical analyses show that annual precipitation is an important parameter explaining the modern distribution of pollen taxa in this region. Pollen taxa markers of high rainfall (Pann >2500mm/yr) are Mallotus type, Elaeocarpus, Syzygium type, Olea dioica, Gnetum ula, and Hopea type, associated with Ixora type and Caryota. Pollen taxa markers of low rainfall (Pann <2500mm/yr) are Melastomataceae/Combretaceae, Maytenus type, Lagerstroemia and Grewia. The proportions of evergreen taxa and of arboreal taxa vary according to rainfall values. Indeed, when rainfall is <2500mm/yr, percentage of arboreal pollen (AP) is <50% and proportion of evergreen taxa is <20%. When rainfall exceeds 2500mm/yr, AP values average 70%, and proportion of evergreen taxa increases from 60 to 90%. Moreover, a good correlation between precipitation and proportion of evergreen taxa (0.85) presumes that precipitation can be estimated from pollen data.     

气候变化对杉木适生区和生态位的影响

杉木（Cunninghamia lanceolata）是我国主要的造林树种之一,具有重要的药用、经济和生态服务功能。在全球变暖趋势持续的背景下,气候成为制约物种生存和发展的重要因素,其中空间分布和生态位变化对生态过程的解释至关重要。基于211个杉木分布点和20个环境变量,利用MaxEnt模型和R语言的ecospat软件包对杉木适生区和生态位的变化进行研究,分析杉木对未来气候持续变暖的响应。结果表明杉木当前潜在适生区219.67万km²,约占国土总面积的22.88％,主要分布在我国800 mm等降水量线以东的地区,年均温、昼夜温差日均值和最干月降雨量是影响杉木分布的最主要环境变量。未来杉木适生区分布将沿着经纬度方向迁移,高度和低度适生区面积均不断减少。主成分分析（PCA）表明杉木气候生态位在不同时段不同代表性浓度路径下发生转移和扩展,气候生态位中心将向年均温和最暖季降雨量移动。生态位重叠指数均呈现不断下降的趋势,且RCP8.5情景下的生态位重叠率下降最为明显。结果表明全球气候变暖会改变物种的空间分布区域,并将对现存的生态系统产生不同程度的影响。杉木与气候变化关系的研究拓展了人们对气候变化与植物物种生态特征的认识,为杉木乃至乔木树种的保护和利用提供了理论依据。     

The differential responses of lianas and vines to rainfall gradients in distribution and abundance in Qinling Mountains, China

To clarify the differential responses of lianas and vines to rainfall, we investigated the distribution and abundance of climbers along the rainfall gradient in the Qinling Mountains of China. In our study, 28 climbing species were investigated across a rainfall gradient of 500?C1,200?mm. Results indicated that most lianas and vines show restricted distribution along the rainfall gradient, which imply their adaptation to different water availabilities. A significant increase in the percentage of the total climbing species with rainfall was observed. The abundance and richness of lianas increased significantly with rainfall, whereas the vines remained constant. This difference implies that lianas have a higher sensitivity to water availability than vines. During drought, lianas may be vulnerable because of the drought-induced embolism, whereas vines are drought-resistant because of their shorter life spans and safer nutrient storage. Further research on the ecophysiological differences between lianas and vines is needed to provide a mechanistic explanation for the patterns described here.     

Plant Functional Traits and the Distribution of West African Rain Forest Trees along the Rainfall Gradient

Plant morphological and physiological traits affect the way plants tolerate environmental stresses and therefore play an important role in shaping species distribution patterns in relation to environmental gradients. Despite our growing knowledge on the role of functional traits in structuring plant communities, few studies have tested their importance at large scales in the wet tropics. Here, we describe the distribution patterns of the most important West African rain forest timber species along the regional rainfall gradient and relate them to their functional traits. We found that the distribution patterns of 25 out of the 31 studied species (80%) were significantly related to mean annual rainfall. Shade tolerance and drought resistance were identified as the main strategy axes of variation. Wood density and leaf deciduousness emerged as the best predictor traits of species position along the rainfall gradient, explaining respectively 32 and 15 percent of the variation. Species traits tended to show stronger relationships with estimated optimum annual rainfall for each species than to the extreme rainfall conditions where they occur. The significant role of rainfall in shaping timber species distribution and the strong relationships between species traits and rainfall indicate that changes in climate, especially declining rainfall, could have strong effects on species composition and abundance in these tropical forests.     

中国森林生态系统林冠层降雨截留特征

森林生态系统作为陆地生态系统的主体,其发达的林冠层通过调节降水量、改变降水强度等深刻影响着流域全过程水文通量及水分输出。以中国广泛开展的典型森林降雨再分配过程的年尺度监测数据为基础,揭示中国不同类型森林生态系统的降雨再分配及林冠层降雨截留特征,阐明森林生态系统林冠层截留特征与降雨、植被要素的关系。结果表明:我国不同森林生态系统年穿透雨量处于141.4-2450.0 mm之间,年穿透雨率为36.3%-92.3%。5种典型森林生态系统多年平均穿透雨量((445.3±252.9)-(1230.6±479.6) mm)占同期多年平均降雨量的(72.6±9.2)%-(77.4±8.9)%。不同森林生态系统年树干茎流量介于0-508.2 mm之间,占同期年降雨量的0-25.8%。5种典型森林生态系统树干茎流量多年平均值((9.8±17.3)-(87.8±81.6) mm)占同期多年平均降雨量的(1.4±1.9)%-(5.4±4.6)%。不同森林生态系统林冠层年降雨截留范围在25.7-812.9 mm之间,占年降雨量的4.2%-55.6%。5种典型森林生态系统多年平均林冠截留量((154.2±81.6)-(392.2±203.5) mm)占同期年平均降雨量的(18.7±7.4)%-(25.9±8.3)%。进一步分析表明,我国森林生态系统穿透雨量、树干茎流量和林冠层截留量随观测区年降雨量的增加而呈显著增大(P<0.05),年穿透雨率、年树干茎流率随年降雨量的增加呈显著线性上升趋势(P<0.05),而年林冠截留率与年降雨量呈显著的负相关关系(P<0.01),降雨量、叶面积指数是深刻影响森林生态系统林冠层降雨截留率等特征的重要因素。整体上,不同类型森林生态系统林冠截留降雨能力存在明显差异,林冠层截留率突出表现为:落叶林大于常绿林、针叶林大于阔叶林。     

Within-island geographic variation of the dangerous Taiwanese snake, Trimeresurus stejnegeri, in relation to ecology

Multivariate analysis shows that geographic variation occurs in the scalation and body proportions of the dangerously venomous snake Tritneresurus stejnegeri , within the island of Taiwan. Canonical correlation analysis reveals a high correlation between constellations of morphological characters and ecological factors. Numerical hypothesis testing, using partial Mantel tests, provides evidence of a causal relationship with ecology. Head shape was found to be primarily associated with mean annual temperature and altitude, and head scalation with the annual range of temperature. Body scalation was found to be influenced by altitude, mean annual temperature and mean annual rainfall. Tail length is primarily associated with the range of temperature and rainfall and secondarily with the mean annual temperature and altitude. Geographic proximity was found to be less important in the explanation of the observed geographic pattern than some ecological factors, supporting the hypothesis of an ecogenetic origin of morphological variation.     

A study of the macro-environment at BenCat in southern Vietnam

Based on the meteorological data over a period of 4 years (1980–3), the macro-environment of BenCat Farm situated in the southern part of Vietnam (27 m above mean sea-level, 11° N and 106° E) was categorized as a “monsoon tropical climate”, due to heavy rainfall (annual mean 2028.96 mm) and about 32% wet days (annual mean 116.52 days) together with high air temperature (annual mean daily temperature 28.58, max. 32.33 and min 24.85° C). April was the hottest (monthly mean >35°C) and January the coldest month (monthly mean <22° C) of the year. The maximum number of wet days were during September and October (mean 18 days.month), whereas the minimum number of wet days were during January and February (mean <1 day/month). The months of December and January at Ben-Cat buffalo farm were categorized as the “comfortable (moderate-Dry) period” as the mean daily temperature was <27° C, while the remaining 10 months of the Calender year (February–November) were categorized as the “hot period” (mean daily temperature >27° C). On the basis of rainfall and the number of wet days, the hot period was further subdivided into a “hot-dry period” (February–April, mean of 1.67 wet days/month and mean rainfall 19.43 mm/month) and a “hot-humid period” (May–November, mean of 15.57 wet days/month and mean rainfall 276.28 mm/month).     

西藏不同生态型区苹果品质评价及其对气象因子的响应

通过对西藏4个不同生态型区‘金冠’苹果果实品质相关指标进行测定,并对果实品质与主要气象因子进行相关性分析及回归分析,以确定西藏‘金冠’苹果栽培主要气象因子评价体系。结果显示,在西藏4个不同生态型区‘金冠’苹果品质差异显著,其中,林芝‘金冠’综合表现较好。在西藏高海拔地区,年均温、7月均温、昼夜温差、≥10℃年均积温、年日照时数、年降水量及海拔是影响‘金冠’果实品质的主要气象因子。其中,海拔2857.9 m、年均气温13.2℃、7月平均气温15.9℃、年均昼夜温差12.7℃、≥10℃年均积温2310.5℃、年均日照时数2532.6 h、年均降水量636.7 mm是‘金冠’苹果形成最佳果实品质的适应气象因子,并且在一定范围内,昼夜温差越大,果实品质越好。本研究建立了西藏‘金冠’苹果栽培主要气象因子评价体系,并提出昼夜温差是影响西藏高海拔地区‘金冠’苹果品质的最主要评价因子。     

Bioclimatic analysis of the distribution of damage to native plants in Tasmania by Phytophthora cinnamomi

Climatic profiles were generated by the computer program BIOCLIM for three sets of sites in native vegetation in Tasmania: (i) 308 sites at which Phytophthora cinnamomi was isolated from diseased plants Pc+ ive; (ii) 322 sites in healthy plant communities from which P. cinnamomi could not be recovered Pc?ive; and (iii) 801 sites representing the climatic range across Tasmania. A discriminatory analysis comparing the first and third sets indicated that seven of the 16 climatic indices available for analysis were good discriminators of the distribution of damage by P. cinnamomi. The analysis suggests that damage to native vegetation due to P. cinnamomi is unlikely on sites where annual mean temperature does not exceed 7.5°C or annual mean rainfall is < 600 mm. Two maps were produced to indicate those areas of Tasmania that have climates suited to damaging interaction between P. cinnamomi and native vegetation. The first was based on those sites that had annual mean temperature more than 7.5°C and annual mean rainfall less than 600 mm. The second included those sites that matched the values of the Pc+ ive set for all seven good discriminators. The two approaches produced similar results. Areas in which even the most favourable microsites are unlikely to support pathogenic activity by P. cinnamomi constitute less than 20% of the land area. Twelve substantial areas of native vegetation that occur in climates suited to infection by P. cinnamomi. but for which no record of the fungus exists, have been identified.     

Comparative analysis of leaf angle and sclerophylly of Aspidosperma quebracho‐blanco on a water deficit gradient

Abstract Aspidosperma quebracho‐blanco is found throughout the Chaco (17°?33°S) in Argentina, and it is the dominant tree species in the arid Chaco. Under the hypothesis that morpho‐physiological features of A. quebracho‐blanco change as a function of its geographical position on a water deficit gradient, it was predicted that with increasing water stress, leaf angles (specifically horizontal) would be greater and mean values of the leaf mass per area would increase. These leaf characteristics were compared at three points on a water deficit gradient extending from the humid Chaco through semi‐arid Chaco to the arid Chaco of Argentina (south‐west to north‐east rainfall gradient, from 350 to 1200 mm annual mean precipitation). Twig and leaf positions were modified and water potentials were measured at the highest heating hour of the day at a site of the arid Chaco. Daily and seasonal water potential variations of untreated twigs were also observed. Leaf angle modification towards horizontal produced more negative twig water potentials with respect to those of leaves in non‐horizontal positions. The comparison of the three sites along the gradient showed contrasting patterns of leaf‐angle frequency distribution of adults. In Chancaní (mean annual temperature: 18–24°C, mean annual precipitation: 450 mm, arid) there was a higher frequency of angles near 90° for non‐pendulous and about 270° for pendulous trees. Leaf angles in Copo (semi‐arid) and Chaco National Park (mean annual temperature: 20–23°C, mean annual precipitation: 1300 mm humid) were widely distributed with higher frequency towards the angles near 0° and 180°. This sclerophyllous tree species showed plasticity in its leaf traits along the precipitation gradient. Plasticity in leaf mass per area and leaf position enables plants to develop efficiently in contrasting environmental conditions of humidity and aridity.     

Mapping distributions of chromosomal forms of Anopheles gambiae in West Africa using climate data

The mosquito Anopheles gambiae Giles sensu stricto (Diptera: Culicidae), the principal vector of malaria in West Africa, comprises several chromosomal forms (e.g. Bissau, Forest, Mopti, Savanna) associated with climatic zones. Here we show how climate data can be used to map the geographical distribution of these chromosomal forms. The climate at 144 sites surveyed for mosquitoes in West Africa between 1971 and 92 was determined using computerized climate surfaces. Forest and Bissau forms occurred at relatively wet sites: median annual precipitation 1325 mm and 1438 mm, respectively, interquartile ranges (IQR) 1144-1858 mm and 1052-1825 mm), whilst the Mopti form was found at dry sites (annual 938 mm, IQR 713-1047 mm) and the Savanna form at sites intermediate between the wet and dry forms (annual 1067 mm, IQR 916-1279). Logistic regression analyses of the climate variables were carried out on a stratified random sample of half the sites. The resulting models correctly classified over 80% of the sites for presence or absence of each chromosomal form. When these models were tested against excluded sites they were also correct at over 80% of sites. The combined data produced models that were correct at over 86% of sites. Mean annual precipitation, evapotranspiration, minimum temperature and maximum temperature were the most important climate variables correlated with the distribution of these forms of An. gambiae. We used the logistic models to map the distribution of each chromosomal form within the reported range for An. gambiae s.s. in West Africa employing a geographical information system. Our maps indicate that each chromosomal form favours particular climate envelopes in well-defined ecoclimatic zones, although these forms are sympatric at the edges of their ranges. This study demonstrates that climate can be used to map the distribution of chromosomal forms of insects across large areas.     

基于Maxent生态位模型的互花米草在我国沿海的潜在分布

以分布在我国沿海滩涂的96个互花米草分布记录点及覆盖东部沿海区域的海洋环境数据和气候环境数据为材料,利用Maxent生态位模型,研究外来物种互花米草在我国沿海的潜在分布情况.结果表明:互花米草适宜分布区占我国沿海区域的85%,其中高度适宜分布区占18%,中度适宜分布区占34%,低度适宜分布区占33%,不适宜分布区仅为15%.互花米草在我国沿海的地理分布主要受到年均最低海水温度、年均海水温度、年平均气温和1月最低气温4个环境因素的影响,而年均降水量、年均日较差、海水盐度、最高海水温度、7月最高气温及海流速度对互花米草地理分布的影响较小.互花米草高度适宜分布区的最低海水温度为0.62~24.81℃,平均海水温度为10.46~27.29℃,年均气温为9~25℃,1月最低气温为-13.5~16.7℃.互花米草地理分布概率在我国北部沿海区域达到20%以上,互花米草存在向我国北部进一步入侵的趋势,特别是在渤海湾地区,互花米草入侵潜力较大.互花米草在我国不适宜分布区主要集中在海南中部和南部海岸,以及台湾省大部分区域,依据当前我国分布记录及气候数据,这些区域互花米草入侵风险较小,但不排除未来入侵的可能性.