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1.
To assay the effect of area and predators on invasion success, spiders were introduced onto islands that were large, with lizard predators; large, without lizard predators; or small, without lizard predators. Short-term survival was greater on islands without than with predators; area had no effect. Spiders initially increased substantially on both groups of islands without lizards, but after 5 years they nearly died off on small islands while persisting on most large islands; populations in the presence of predators never increased above initial sizes. Results show how predators as well as area are important in determining invasion success. 相似文献
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Which species affect one another, how intensely, and the mechanisms of those effects are crucial data for understanding how ecological communities work. Tropical islands without lizards, the major top predators, have about ten times as dense web spider populations as those with lizards; processes responsible for this effect were experimentally simulated by removing lizards from randomly selected mainland plots. Spider densities in removal plots averaged 2.5 times as high as controls. Spider survival, prey abundance, and prey consumption were all negatively affected by lizards. Contrary to most studies, predator removal caused an increase in the number of spider species. 相似文献
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研究青海湖景区旅游干扰下沙化草地群落的植物多样性,利用主要物种重要值、α多样性、功能群重要值和β多样性比较分析不同干扰后群落植物多样性及结构功能的变化。结果表明：随着干扰强度的增加,群落物种组成从以不耐旅游干扰的物种为主逐渐发展到以耐旅游干扰的物种为主,群落的重要值有向少数物种集中的趋势;Pat-rick丰富度指数和Shannon-Wiener指数均随着干扰强度的增加而呈下降趋势,均匀度指数则在中度干扰下最大,生态优势度的变化与α多样性的变化存在一定的负关联;功能群丰富度在中度干扰下最高;中度-重度干扰阶段群落间的物种替代速率最快。青海湖景区沙化草地群落稳定与群落自身的物种多样性、功能群功能特性及结构特点密切相关。 相似文献
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JB Losos TR Jackman A Larson K Queiroz L Rodriguez-Schettino 《Science (New York, N.Y.)》1998,279(5359):2115-2118
The vagaries of history lead to the prediction that repeated instances of evolutionary diversification will lead to disparate outcomes even if starting conditions are similar. We tested this proposition by examining the evolutionary radiation of Anolis lizards on the four islands of the Greater Antilles. Morphometric analyses indicate that the same set of habitat specialists, termed ecomorphs, occurs on all four islands. Although these similar assemblages could result from a single evolutionary origin of each ecomorph, followed by dispersal or vicariance, phylogenetic analysis indicates that the ecomorphs originated independently on each island. Thus, adaptive radiation in similar environments can overcome historical contingencies to produce strikingly similar evolutionary outcomes. 相似文献
5.
林火干扰对广东省杉木林土壤有机碳及其组分的影响 总被引：2，自引：1，他引：1
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Theory predicts that the approach of catastrophic thresholds in natural systems (e.g., ecosystems, the climate) may result in an increasingly slow recovery from small perturbations, a phenomenon called critical slowing down. We used replicate laboratory populations of the budding yeast Saccharomyces cerevisiae for direct observation of critical slowing down before population collapse. We mapped the bifurcation diagram experimentally and found that the populations became more vulnerable to disturbance closer to the tipping point. Fluctuations of population density increased in size and duration near the tipping point, in agreement with the theory. Our results suggest that indicators of critical slowing down can provide advance warning of catastrophic thresholds and loss of resilience in a variety of dynamical systems. 相似文献
7.
Wardle DA Yeates GW Barker GM Bellingham PJ Bonner KI Williamson WM 《Science (New York, N.Y.)》2003,301(5640):1717-1720
Although island attributes such as size and accessibility to colonizing organisms can influence community structure, the consequences of these for ecosystem functioning are little understood. A study of the suspended soils of spatially discrete epiphytes or treetop "islands" in the canopies of New Zealand rainforest trees revealed that different components of the decomposer community responded either positively or negatively to island size, as well as to the tree species that the islands occurred in. This in turn led to important differences between islands in the rates of ecosystem processes driven by the decomposer biota. This system serves as a model for better understanding how attributes of both real and habitat islands may affect key ecosystem functions through determining the community structure of organisms that drive these functions. 相似文献
8.
上海市无居民岛土地资源开发适宜性研究 总被引：5，自引：1，他引：4
无居民岛的土地资源的开发利用受到人们越来越多的关注,根据对上海市无居民岛的实地调查,结合文献数据,参考相关土地资源的分类体系,作为评价的框架,从保护和开发两个角度分别进行指标的选取,选择层次分析法(AHP)和德尔菲法(Delphi)相结合的赋值方式,建立上海市无居民岛土地资源开发利用评价体系,计算上海无居民岛土地资源生态保护和开发利用指数,分析上海市6个河口冲积无居民岛开发适宜性等级,建议九段沙和青草沙限制开发,东风西沙、扁担沙和黄瓜沙应适宜开发,除青草沙的开发方向为岛陆资源,其余海岛的开发方向均为岛陆和滩涂资源。 相似文献
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对不同干扰梯度下的植被特征、土壤含水量、重要值和多样性等指标进行比较分析。结果表明:随着干扰程度的加大,多年生植物的种类不断减少,植物适口性以中度干扰为最高;植被的盖度、高度及密度均是中度干扰>重度干扰>轻度干扰,生物量调查结果是重度干扰>中度干扰>轻度干扰;中度干扰和重度干扰的主要优势种重要值分布相对均匀,而轻度干扰下只是极少数几个物种有较高的重要值;多样性结果显示:中度干扰>轻度干扰>重度干扰,表明进行围封的同时进行适当的放牧干扰,才更有利于研究区植被朝多样化方向发展。综合以上分析,中度干扰(半封育措施)显然是农牧交错区植被恢复的最好方式。 相似文献
10.
A deposit of fossil seabirds from the late Pliocene of Florida includes more than 130 skeletons of an extinct cormorant that is related phylogenetically to Recent species currently restricted to the eastern north Pacific. Evidence suggests the birds died in a single catastrophic event, perhaps a red tide. The fossil cormorant, along with other extinct seabirds and marine mammals, supports molluscan evidence for cold-water upwelling along the Florida Gulf Coast during the Pliocene. A decline in species richness of marine vertebrates throughout the Pliocene of Florida coincides with cessation of upwelling after emergences of the Panamanian Land Bridge. 相似文献
11.
政策性农业保险巨灾风险准备金制度研究——以北京市政策性农业保险为例 总被引：2，自引：0，他引：2
农业保险的巨灾风险准备金作为一种特殊的准备金,是为了应付巨灾风险事故发生后,责任准备金不足以支付赔款的一种准备。以北京市政策性农业保险为例,运用农业经济学、计量经济学、数值计算方法等相关理论与方法,利用SPSS等相关统计软件,在已有研究的基础上,根据1983-2009年北京市农业生产及灾害损失等相关资料,采取定性研究和定量分析相结合的方法,重点对北京市农业巨灾风险准备金进行了规模测算和推论分析。从测算结果和实际需求出发,建议可以取消已经建立的巨灾风险准备金;如果继续保留该巨灾准备金,则需要从运行机制和政策环境两方面对现行制度进行优化和完善。 相似文献
12.
大兴安岭兴安落叶松林火烧迹地群落演替状况 总被引：4，自引：0，他引：4
采用由植被空间序列推断时间系列的方法,分析了大兴安岭地区兴安落叶松(Larix gmelinii)林不同火强度火烧迹地群落演替状况。研究结果显示,重度火干扰后,兴安落叶松林群落演替趋势规律为:杂草丛或灌草丛→白桦山杨混交林→阔叶兴安落叶松林→兴安落叶松林;中度火干扰后,兴安落叶松林的群落演替趋势为:杨桦林或以阔叶树为主的针阔混交林→兴安落叶松林;轻度火干扰后,对兴安落叶松群落的影响较小,不能改变原有的树种组成,林分群落结构变化主要表现在灌木层和草本层中一些旱生物种与中湿生物种的替代过程。 相似文献
13.
放牧干扰对东祁连山高寒草地植物群落物种多样性的影响 总被引：10，自引：2，他引：10
放牧干扰是改变草地植物群落物种多样性的主要因素之一。通过研究东祁连山高寒草地放牧干扰梯度对植物群落物种多样性的影响,结果表明,放牧过程中,牲畜的啃食、践踏等作用干扰了草地环境,改变了群落内物种的竞争力和环境条件,使群落类型和种群组成与分布发生变化,物种优势地位发生更替,从而引起植物群落多样性的变化。随着放牧强度的增大,群落丰富度逐渐下降。多样性指数在中牧或重牧阶段达最大值,过牧阶段也较高,略有所增加, 主要是由于群落均匀度的增加。生活型功能群也表现出了明显的变化。放牧干扰对草地生态系统是一种常见现象,是推动草地生态系统进化和演变的外在驱动力。其利弊取决于干扰本身的性质、强度以及草地群落的结构特征,适度的放牧干扰可以促进物种多样性的维持与保护。 相似文献
14.
为了解人为干扰对河涌沿岸植物景观特征的影响,选取广州市南沙区4条河涌作为研究对象,采用ANOVA单因素方差分析轻度、中度以及重度人为干扰强度下河涌沿岸植物景观特征的差异及不同植物景观特征因子之间的相互关联作用。结果表明：1)不同人为干扰强度下河岸植物景观在数量特征、生活型特征、功能特征以及绿量特征方面存在显著差异。与轻度干扰相比,中度干扰和重度干扰下的河岸植物种类平均多1种、乔木占比平均高26.8%和18.5%,草本占比平均低25.6%和20.8%、生态植物占比平均低17.0%和24.8%。中度干扰下食用植物占比较高,重度干扰下观赏植物占比较高。2)从河岸总体植物景观特征来看,生态植物占比随建筑物盖度增加而降低,食用植物占比和观赏植物占比随建筑物盖度增加而增加,植物绿量随风水植物占比增加而增加。3)不同人为干扰强度下河岸植物景观特征要素之间的相互关系存在差异。轻度干扰下,植物种类、乔木占比、风水植物占比随建筑物盖度增加而增加,植物绿量随建筑物盖度、风水植物占比增加而增加;中度干扰下,生态植物占比随建筑物盖度增加而降低,食用植物占比随建筑物盖度增加而增加,绿化覆盖率随植物数量、生态植物占... 相似文献
15.
Coral islands drown when sea level rise exceeds the maximum potential of coral reefs to grow upward (about 10 millimeters per year). During the Holocene transgression (18,000 years ago to present) sea levels rose at rates of up to 10 to 20 millimeters per year, and most coral island reefs situated deeper than a critical depth of30 to 40 meters below present day sea level drowned. Coral islands that did not drown during the Holocene transgression apparently all developed on antecedent foundations shallower than critical depth. During low stands in sea level during the Pleistocene, these islands were elevated and subject to subaerial erosion. Today, in the Hawaiian Archipelago, the depth of drowned banks is inversely related to summit area; smaller banks are progressively deeper, evidently because of erosional truncation during low sea level stands. Bank summit area may therefore be an important factor determining the failure or success of coral islands. 相似文献
16.
Tail removal from dominant juvenile Uta stansburiana resulted in a decrease in social status in dyadic encounters. Most lizards were affected after removal of two-thirds of their tails. In some pairs, dominant lizards lost status after removal of one-third of their tails but regained dominance after the other member of the pair lost two-thirds of its tail. Tail loss in nature may impose a social handicap to successful home range acquisition and thereby increase risk of death. 相似文献
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18.
不同干扰程度对金佛山方竹林土壤物理特性及其水源涵养功能的影响 总被引：3，自引：0，他引：3
本文对贵州遵义地区金佛山方竹(Chimonobambusa utilis)林3种不同干扰程度的土壤物理特性及其水源涵养功能等进行了研究,结果表明:干扰对方竹林的土壤容重及土壤孔隙度有比较大的影响,土壤容重均随土层深度的增加而增加,土壤总孔隙度与非毛管孔隙度基本上都是随着土层深度的增加而减小;不同干扰程度枯落物的持水率为:中度干扰>轻度干扰>重度干扰,而总持水量则为:中度干扰>重度干扰>轻度干扰;其平均最大蓄水量为:中度干扰(1237.84t/hm)2>轻度干扰(1198.21t/hm)2>重度干扰(1173.38t/hm2);非毛管蓄水量为:轻度干扰(141.06t/hm)2>中度干扰(114.81t/hm2)>重度干扰(102.67t/hm)2;平均土壤稳渗速率为:轻度干扰(2.20mm/min)>中度干扰(1.77mm/min)>重度干扰(1.00mm/min);从综合情况来看:林地的水源涵养能力(土壤最大蓄水量+枯落物最大持水量)的变化顺序为:总蓄水量中度干扰(1250.56t/hm)2>轻度干扰(1207.33t/hm)2>重度干扰(1184.78t/hm)2。在相同的立地条件下,中度干扰的方竹林的水... 相似文献
19.
以大兴安岭根河地区兴安落叶松林为研究对象,在1987年、2003年和2015年受到火干扰区域选取中度、重度火干扰样地,并设置未受火干扰的对照样地,运用树轮数据和样地调查数据,分析火干扰下林分结构特征及其空间分布格局动态。结果表明:3~5 m尺度上不同火干扰强度下林分空间格局存在差异且具有阶段性。中度火干扰的兴安落叶松林,恢复5 a趋向均匀分布,恢复15 a和31 a后呈聚集分布;而重度火干扰的兴安落叶松林,恢复5 a趋向聚集分布,恢复15 a呈随机分布,恢复31 a呈聚集分布。不同树种空间分布格局有所不同,重度火干扰的白桦林,恢复初期由随机分布变为不显著聚集分布,恢复10 a后呈显著聚集分布,恢复31 a后,在3 m以上的尺度上又变为不显著聚集分布甚至趋向随机分布。因此,火干扰样地林分空间格局研究应考虑物种差异以及响应的滞后性。 相似文献
20.
Castilla JC 《Science (New York, N.Y.)》1988,242(4877):440-443
The coastal uplift(approximately 40 to 60 centimeters) associated with the Chilean earthquake of 3 March 1985 caused extensive mortality of intertidal organisms at the Estación Costera de Investigaciones Marinas, Las Cruces. The kelp belt of the laminarian Lessonia nigrescens was particularly affected. Most of the primary space liberated at the upper border of this belt was invaded by species of barnacles, which showed an opportunistic colonization strategy. Drastic modifications in the environment such as coastal uplift, subsidence, or the effects of the El Ni?o phenomenon are characteristic of the southern Pacific. Modifications in the marine ecosystem that generate catastrophic and widespread mortalities of intertidal organisms can affect species composition, diversity, or local biogeography. 相似文献