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1.
《The Professional geographer》2013,65(3):346-347
Mapping patterns of species richness is a longstanding tradition in biogeography and more recently in conservation planning. This paper describes the effects of sampling unit size on patterns of vertebrate richness across landscapes in the Intermountain Sagebrush and Rocky Mountain Forest ecoregions in Idaho. Variability of richness decreased with increasing size of the spatial sampling units at both sites, with greater overall variability in the forested site. Richness in the sagebrush region was best explained by alpha diversity, whereas beta diversity accounted for more of the variability in richness in the forested site. 相似文献
2.
Kathleen C. Parker 《自然地理学》2013,34(4):320-333
Breeding bird censuses from 132 homogeneous sites representing a variety of habitats throughout North America are analyzed and a bird species diversity model based on environmental characteristics and sampling procedures is presented. Bivariate regression models relate the number of bird species detected in a site (NSPECIES) to plot size, latitude, and the number of bird pairs encountered during censusing. These models consistently overestimate NSPECIES in desert shrublands, grasslands, tundra, and scrub and underestimate NSPECIES in forested habitats, which indicates that the effects of the environmental and methodological variables on NSPECIES vary with respect to habitat. The expansion method of regression analysis is used to generate a multivariate model that accounts for this spatial variation in the influence of the independent variables on NSPECIES. With the exception of temperate wetlands, which have the third highest mean value for NSPECIES of nine habitat groups, forested sites and woodlands have higher mean NSPECIES values than more open habitats. Use of the expansion method to account for spatial variation in the effects exerted by independent variables introduces a geographically realistic element often lacking in broad-scale models. (Key words: avian diversity, sampling intensity, multiple regression analysis, vegetation structure, habitat types.) 相似文献
3.
The promotion and preservation of biodiversity in urban areas remains scant, especially in Asian cities. This study focuses on spatial pattern and diversity of landscape trees in compact Taipei. Aggregate species diversity of three urban habitats (streets, urban parks and riverside parks) exceeded the countryside's secondary forests. Urban parks with site heterogeneity and multiple functions accommodate the highest richness, and streets with acute site limitations the poorest represented by popular native species. More affinities exist between urban and riverside parks. Low diversity in riverside parks echoes natural site constraints and primary use for river discharge and flood control. The compact urban form has not stifled species diversity and spatial variability of urban forests. Development history and park area have no significant relationship with species diversity. Understanding species composition in urban ecosystems could frame conservation strategies to augment species richness, appropriate site selection, habit preservation and wildlife recruitment. 相似文献
4.
5.
Palaeolimnological records of shallow lake biodiversity change: exploring the merits of single versus multi-proxy approaches 总被引：1，自引：0，他引：1
Shallow lakes are among the most threatened ecosystems in the world and many contemporary studies have demonstrated declines in biodiversity due to anthropogenic forcing. Mostly, however, these studies have not covered the full period of human-induced diversity change in lakes which is typically over decades-centuries. Here we provide two examples of palaeoecological studies focussed on reconstructing biodiversity changes in contrasting shallow lake environments that demonstrate the efficacy of the approach—a shallow UK lake and a suite of floodplain lakes (called billabongs) in the Murray-Darling basin, Australia. In the Murray-Darling billabongs, complex sedimentary processes operate, sediment chronologies are less certain and replication of sites is needed to confirm patterns. The combination of sediment records from 10 billabongs showed that diatom diversity changes pre- and post-European (>1850) disturbance were inconsistent; however, reductions in diversity were more common and appear to reflect reductions in macrophyte abundance. At Felbrigg Lake, a multi-proxy study with strong chronological control demonstrated divergent responses of macrophyte, diatom, cladoceran and chironomid richness and diversity to a century of eutrophication. Eutrophication of the site was qualitatively inferred from changes in the macrophyte community in turn reconstructed from plant macrofossils. Benthic cladocerans showed a consistent decline in richness through the record, reflecting the gradual reduction in their macrophyte associated habitat over the past century. Diatom richness and diversity responses were complex, with increases in diversity and richness linked to both increases and decreases in macrophyte species richness and abundance. Chironomid richness and diversity patterns were less consistently linked to eutrophication. The loss of the dominant zooplanktivore (perch) in the 1970s was reflected in the richness and diversity profiles for all groups. Our study reveals clear potential for using sediment cores to infer biodiversity change in shallow lakes and shallow lake regions. However, given the contrasting patterns of diversity change for the different biological groups both in Felbrigg Lake and between Felbrigg and the billabongs, caution is required when interpreting whole-ecosystem biodiversity changes (or the absence of change) based on single as opposed to multi-proxy studies. 相似文献
6.
T.M. Wells A.S. Cohen L.E. Park D.L. Dettman B.A. McKee 《Journal of Paleolimnology》1999,22(3):259-276
We report here on the first detailed ostracode stratigraphic record to be obtained from late Holocene sediments of Lake Tanganyika. We analyzed four cores, three from the northern lake region and a fourth from a more southern lake locality, that collectively record ostracode assemblages under a variety of disturbance regimes. These cores provide a stratigraphic record of ostracode abundance and diversity, as well as depositional changes over time periods of decades to millennia. We have investigated the fossil ostracodes in these cores by looking at temporal changes of species diversity and population structure for the species present. All four cores provided distinct patterns of ostracode diversity and abundance. BUR-1, a northern lake core obtained close to the Ruisizi River delta, yielded a sparse ostracode record. Karonge #3, another northern core from a site that is closely adjacent to a river delta with high sediment loading, yielded almost no ostracodes. The third core 86-DG-14, taken from a somewhat less disturbed area of the lake, suggests that there have been recent changes in ostracode populations. Through most of the lower portion of this core, ostracode abundance is low and species richness is relatively constant. Above 7 cm there is a marked increase in ostracode abundance and a corresponding decrease in species richness, probably signaling the onset of a major community disturbance, perhaps due to human activities. The southernmost core, 86-DG-32, is from a site that is well removed from influent rivers. Ostracode abundance varies erratically throughout the core, whereas species richness is relatively constant and high throughout the core. The temporal variation evident in ostracode community makeup both within and between the studied cores may be a result of naturally patchy distributions among ostracodes, coupled with local extinctions and recolonizations, or it may reflect inadequate sampling of these high diversity assemblages. In either case, these cores illustrate the potential to obtain high resolution ostracode records from the rich, endemic fauna of Lake Tanganyika that can be used to address questions about the history of community structure and human impacts in this lake. 相似文献
7.
《Geomorphology》2003,49(1-2):109-124
The impacts of logging activities on mass wasting were examined in five watersheds in the coastal mountains of British Columbia. Historical aerial photos were used to document mass wasting events, and their occurrence was related to logging activities in the study basins. Logged and forested areas were compared in terms of mass wasting magnitude and frequency, with reference to site characteristics. The recovery time of the landscape after logging was assessed. Bedrock type and basin physiography had no identifiable effect on mass wasting frequency and magnitude. Mass wasting failure was primarily controlled by slope gradient. Basin vulnerability increased, following clearcutting relative to forested areas, in that mass wasting was initiated on gentler slopes. The volume of sediment produced from logged slopes is of the same order as that from forested areas, which are steeper by as much as 10°. In both logged and forested areas, the size distribution of mass wasting events follows an exponential distribution. However, the variability in mass wasting size in forested areas is much higher than that obtained for logged areas. The recovery time after forest harvesting is over 20 years, which confirms published estimates based on vegetation reestablishment. Continuous disturbance of the basin, however, may extend the recovery time for the whole basin well beyond 20 years. 相似文献
8.
Riparian plant species richness along lateral and longitudinal gradients of water stress and flood disturbance, San Pedro River, Arizona, USA 总被引：2，自引：0，他引：2
Diversity theory predicts that species numbers should be highest at intermediate levels of both disturbance and environmental stress. We examined woody and herbaceous plant species richness and cover in the San Pedro River flood plain, along lateral gradients of water availability (ground-water depth), flood disturbance (inundation frequency), and distance from and elevation above the channel, and along longitudinal gradients of water availability (ground-water depth, surface flow permanence, and rainfall) and flood disturbance (total stream power). Herbaceous species were recorded during four sampling periods, and spatial patterns for this group were time-dependent, reflecting temporal variation in limiting factors. During the summer dry season of a dry year, when overall richness was low, richness and cover of herbaceous species declined laterally from the stream channel with increasing ground-water depth, consistent with the idea that low resource levels can limit species richness. Following the summer monsoon rains and floods, when water was less limiting and annuals were seasonally abundant, lateral patterns shifted such that herbaceous species richness and cover increased with increasing plot location above or from the channel. The relationship of herbaceous species richness with tree canopy cover also varied seasonally, shifting from positive (greater richness under canopy) in dry seasons to negative (lesser richness under canopy) in wet seasons. Longitudinally, herbaceous species richness and cover were limited primarily by stream flow and/or ground-water availability during the summer dry season of a dry year. Following the summer monsoon rains and floods, patterns were weighted by the seasonally abundant annuals, and richness increased among sites primarily with distance upstream (and related rainfall gradients). Richness and cover patterns also varied between years with different flood conditions. During the two sampling seasons in the year following a large flood, herbaceous species richness increased with flood disturbance intensity but declined at the few most intensely disturbed sites, consistent with intermediate disturbance theory.For woody species, richness within plant functional groups varied in opposing ways along the lateral gradients: hydromesic pioneer species decreased and hydromesic and xeric competitors increased with distance from or above the channel, with no overall change in species richness. Among sites, woody species richness patterns were related to water availability, but not to flood disturbance. However, richness of woody hydromesic pioneer species increased with both increasing site moisture and flood disturbance. Woody and herbaceous species richness both increased among sites as a function of increasing flood-plain width, likely due to species–area effects. Overall, results indicate that flood disturbance and water availability both influence species richness of riparian plants in the flood plain of this semi-arid region river, with the relative influence of each factor varying among plant groups and over time. 相似文献
9.
Chironomid analysis was performed on late-glacial sediment from four New Brunswick lakes in order to gain basic ecological information regarding the richness and diversity of late-glacial chironomid assemblages, and to compare the pattern of succession at each site. At all sites, the richness and diversity of the larval assemblages were lowest immediately following deglaciation and during the Younger Dryas, corresponding to the coldest times of the late-glacial period. Although cold-stenothermous taxa are characteristic of sediments deposited immediately following deglaciation, as well as during the Killarney Oscillation and Younger Dryas cooling events, the constituent taxa are different at each site. During the intervening warm periods, the larval assemblages at each site are also dissimilar, with the more southern sites containing a greater variety of temperate littoral taxa. This raises the possibility that a north-south temperature gradient existed during the warm intervals of the late-glacial period in New Brunswick. 相似文献
10.
AbstractThe intermediate disturbance hypothesis (IDH) predicts highest species diversity in environments experiencing intermediate intensity disturbance, after an intermediate timespan. Because many landscapes comprise mosaics with complex disturbance histories, the theory implies that each patch in those mosaics should have a distinct level of diversity reflecting the magnitude of disturbance and the time since it occurred. We model changing patterns of species richness across a landscape experiencing varied scenarios of simulated disturbance in order to predict first the variation of richness through time in individual patches, based on their disturbance histories, and then the changing patterns of richness across the landscape through time, representing the cumulative impact of changing richness within the individual patches. Model outputs show that individual landscape patches have highly variable species richness through time, with the trajectory reflecting the timing, intensity and sequence of disturbances. When the results are mapped across the landscape, the resulting temporal and spatial complexity reveals a distribution of biodiversity that is strikingly contingent on the details of disturbance history. These results illustrate the danger of generalization (in either data interpretation or management decisions), as IDH actually imposes a highly variable pattern of diversity. 相似文献
11.
Spatial heterogeneity is an inherent characteristic of natural forest landscapes, therefore estimation of structural variability, including the collection and analyzing of field measurements, is a grow... 相似文献
12.
洪河自然保护区湿地主要植被类型物种多样性与表层土壤性质的相关性研究 总被引：1，自引：0，他引：1
对洪河湿地主要植被类型物种多样性特征、土壤性质特征及二者之间的相互关系进行了研究。结果表明:按沼泽—沼泽化草甸—湿草甸—灌丛草甸—岛状林的序列,物种丰富度呈逐渐增加的变化格局,物种多样性、均匀度呈先下降后上升的格局,优势度呈先上升后下降的格局;而土壤性质特征则呈不规则变化格局。植物物种多样性与土壤性质之间只有均匀度与速效氮之间存在着极显著正相关,其他均无显著相关。这说明在洪河湿地,土壤性质不是决定上述序列的植被类型的物种多样性的主要因素,而土壤速效氮含量是影响物种均匀度的关键因素,同时,对其他物种多样性特征也有一定影响。 相似文献
13.
Patterns of plant diversity were examined across 24 ironstone ranges in arid south western Australia. The high levels of beta diversity displayed between ranges primarily resulted from high turnover of perennial species and was not influenced by the lower species richness on the more arid ranges. The variance in composition of the vegetation across the ranges was evenly distributed between the broad spatial pattern and environmental factors measuring climate gradients, local site variables and soil chemistry. In contrast broad scale spatial and climatic gradients were most important in explaining the variance in perennial species richness. Ranges along the boundary of the Arid Zone appear to have acted as refugia during the climatic cycles of the Tertiary with several hotspots of species endemism and taxa with distributions centered on these ranges. On the more arid ranges these specialist ironstone taxa are largely absent. The variation in richness of these specialists taxa was strongly influenced by patterns in soil chemistry in addition to the broad scale spatial and climate gradients. The concentration of the ironstone specialist taxa is largely coincidental with the most prospective areas for iron ore mining and this will provide considerable challenges in conserving these unique ecosystems. 相似文献
14.
甘肃敦煌西湖荒漠湿地植物群落物种多样性特征研究 总被引：5，自引：1，他引：4
基于375个样方和150条样线的调查,对甘肃敦煌西湖荒漠-湿地生态系统植物群落物种多样性进行了研究。结果表明:①区内共记录植物26种,分属16科24属,芦苇（Phragmites australis）、多枝柽柳（Tamarix ramosissima）和胡杨（Populus euphratica）为绝对优势种,苏枸杞（Lycium ruthenicum）、疏叶骆驼刺（Alhagi sparsifolia）和胀果甘草（Glycyrrhiza inflata）为主要伴生种,其平均重要值依次为0.4728、0.4563、0.4342、0.2908、0.2594和0.2455。植物群落分多枝柽柳群落、胡杨群落、胀果甘草群落、疏叶骆驼刺群落、多枝柽柳沙包群落、苏枸杞群落、芦苇沼泽群落和芦苇群落8个类型。②植物群落物种多样性指数偏低（0.784～1.379）,多枝柽柳群落、胡杨群落和芦苇群落物种多样性指数最大（1.379、1.266和1.194）,群落之间差异显著（P＜0.05）;疏叶骆驼刺群落和苏枸杞群落次之（1.154、1.077）,胀果甘草群落、芦苇沼泽和多枝柽柳沙包群落最低（0.919、0.881、0.784）,各群落之间不存在显著差异。③灌（乔）木层是敦煌西湖植被主要层次,灌（乔）木层物种多样性指数（0.549～1.077）大于草本层（0.052～1.038）。④物种多样性指标H′、D、J和Ma随海拔梯度增加基本均显下降趋势,而指数C变化趋势则相反,表现为上升,均匀度指数变化幅度不显著。⑤物种多样性指标H′、D、J和Ma随经纬度升高变化趋势基本一致,均表现为先下降,后上升,再下降,而优势度指数C变化趋势则相反。 相似文献
15.
Impact of rainfall variability and grazing pressure on plant diversity in Mongolian grasslands 总被引：1，自引：0，他引：1
Climate and grazing are the main drivers of plant community composition and species richness in arid environments. This study aimed to examine the vegetation response to a spatial precipitation gradient, interannual rainfall variability, and grazing pressure in Mongolia. To examine the effect of a spatial precipitation gradient, we compared species richness among six sites. To investigate the effects of interannual rainfall variability and grazing pressure, we compared species richness for 2 years at two sites, in desert-steppe and steppe areas. The regional gradient in annual precipitation showed positive and negative relationships with grass richness and shrub richness, respectively, although total species richness did not vary significantly. The proportions of the different functional groups were affected by grazing pressure and rainfall variability in both zones. In the desert-steppe zone, species richness was lower in the drier year but did not vary with grazing pressure. In the steppe zone, species richness varied significantly with grazing pressure but did not vary between years. Precipitation would be more important than grazing pressure on vegetation changes in drier areas with high rainfall variability. 相似文献
16.
北固山湿地植物群落特征及其物种多样性研究 总被引：15，自引：4，他引：15
北固山湿地位于镇江市东北,由长江携带泥沙长期沉积形成,植被属原生裸地演替,植物种类丰富。但近年由于污染排放及渔民围网捕鱼,植被受到破坏,生态功能被削弱。采用样方法调查了镇江北固山湿地植物群落的组成,种类和外貌,并分析了其物种的多样性差异,从而为湿地的生态修复提供理论和技术依据。试验结果表明:群落物种组成较为丰富,有15科28属33种,但仅限于草本植物,生活型以地面芽植物和一年生植物占优势,物种出现频度上以D、C两个级别为主,表明群落内物种的分布较为均匀。从季相动态上看,季相明显,群落的优势种2~4月前是虉草(Phalarisarundinacea)单优种群,4~6月是虉草-芦苇(Phargnitescommunis)共优种群,6~11月是芦苇-酸模叶蓼(Polygonumlapathifolium)共优种群。随着基底高程的变化,植物呈现明显的平行于堤岸的带状分布,并形成区别明显的三个区域。其中,物种的丰度、多样性指数、群落的均匀度以及生物量均随基底高程的增加而增加,而生态优势度却随基底高程的增加减小。物种多样性指数受立地环境和人为因素的共同影响。其中,一定程度的人为干扰虽降低物种丰度,但由于其对优势种芦苇破坏较为严重,降低了群落的生态优势度而相应提高了群落的均匀度,最终对物种多样性指数有增加效应。在以上研究的基础上,提出了禁止污染排放及围网捕鱼等措施,并在裸露或物种稀少区域人工栽培土著物种以增加湿地生态系统物种的多样性和稳定性。 相似文献
17.
Arbuscular mycorrhizal fungi(AMF) are universally mutualistic symbionts that colonize the fine roots of most vascular plants. However, the biogeographical patterns and driving factors of AMF diversity of plant roots in grasslands are not well investigated. In this study, we used high-throughput sequencing techniques and bioinformatics to evaluate the AMF richness of 333 individual plant roots in 21 natural grassland ecosystems in northern China, including the Loess Plateau(LP), the Mongolian Plateau(MP), and the Tibetan Plateau(TP). The AMF richness showed a significant parabolic trend with increasing longitude. In regional situations, the AMF richness in the grasslands of the MP(60.4 ± 1.47) was significantly higher than those of the LP(46.4 ± 1.43) and TP(44.3 ± 1.64). Plant traits(including plant families, genera, and functional groups) explained the most variation in the AMF richness across China's grasslands, followed by energy and water; soil properties had the least effects. The results showed the biogeographical patterns of the AMF richness and the underlying dominant factors, providing synthetic data compilation and analyses in the AMF diversity in China's grasslands. 相似文献
18.
科尔沁沙地植物多样性对生产力的影响及分布格局 总被引：4，自引：3，他引：1
采用种丰富度和以Shannon-Wiener指数为计算方法的功能多样性和组成多样性为指标,探讨了植物多样性对科尔沁沙地草场生产力的影响以及其分布格局特征。结果表明,科尔沁沙地植被不同的物种多样性指数对系统生产力的影响以组成多样性最大,功能多样性次之,植物种丰富度最小。在小尺度上,组成多样性只存在一种格局且具有分形结构,其格局对干扰过程反应不明显;功能多样性有多种格局存在,对多种干扰过程反应敏感。从提高沙地草场生产力和增强系统的稳定性角度出发,草场改良的依据应建立在种的引进和引进种所产生的组成多样性上。 相似文献
19.
玉龙雪山植物物种多样性和群落结构沿海拔梯度的分布格局 总被引：15，自引：0，他引：15
生物多样性沿海拔梯度的变化是多样性环境梯度格局研究中的一个热点问题。在对滇西北玉龙雪山2 900 m~4 200 m间沿海拔梯度进行的群落调查基础上,对植物物种多样性和群落结构的垂直分异格局进行了分析。结果表明:1)在16个样地中共记录植物物种261种,分属78科,158属,其中木本植物36种,灌木植物71种,草本154种。2)沿海拔梯度,森林群落的最大树高、最大胸径、平均树高和平均胸径等群落结构指标均呈单峰分布格局。3)随着海拔的升高。木本和草本的物种丰富度,先增加后下降;而灌木层的物种丰富度随着海拔的上升呈明显下降格局。4)木本层和灌木层的β多样性(Cody指数)随海拔升高,总体呈减小趋势,而草本层β多样性显示出单峰分布的垂直格局。 相似文献
20.
JACOB BENDIX 《Geographical review》1997,87(4):468-483
ABSTRACT. Biodiversity varies considerably in Southern Californian riparian vegetation. The intermediate disturbance hypothesis posits greatest diversity in settings that are subject to moderate-intensity disturbance. Flood intensity tends to vary systematically in watersheds, potentially imposing patterns of biodiversity. In two study watersheds, species richness increases with flood severity. Diversity, or heterogeneity, is less predictable: Biodiversity patterns in these watersheds are complicated by atypical patterns of flood severity. Although riparian diversity may be intimately dependent on flood disturbance, the relationship is predictable only with due attention to the physiographic details of individual stream networks. 相似文献