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排序方式: 共有938条查询结果,搜索用时 31 毫秒
31.
D. L. Britton 《African Journal of Aquatic Science》2013,38(1-2):51-64
Summary The effects of a late-summer prescribed burn on the temperature and benthic macroinvertebrate fauna of a south-western Cape mountain stream were investigated over a period of 12 months. Temperature and discharge regimes appear well-defined and relatively predictable from year to year. As in other mediterranean-type ecosystems, seasonal changes in the structure of the invertebrate community and the relative abundance of different feeding groups appear to be associated primarily with changes in the physical environment. Distinctive summer and winter communities were identified, with chironomids dominating the fauna in summer and simuliids dominant in winter. Although the riparian vegetation was only slightly damaged by the fire, a heavy, aseasonal leaf-fall occurred shortly afterwards. The canopy remained sparse for approximately four months. Stream temperature in the post-burn year was not demonstrably affected by increased exposure to solar radiation, however, probably because the canopy remained open during the winter months. The fire appeared to have little effect on the invertebrate fauna. Apart from five rare elements of the biota, all species recorded in the pre-burn year were present in the post-burn year and in similar densities. It is concluded that the riparian vegetation is of major importance in maintaining the integrity of the stream environment. 相似文献
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Mean hemoglobin (Hb) concentration of about 3 500 subjects derived from 17 studies of Himalayan highlanders (Tibetans, Sherpas, and Ladakhis) was compared with lowlanders (Chinese Han, Indian Tamils) lived in the Himalayas, and European climbers during Everest expeditions as well as Andean natives. The results found that Hb concentration in Himalayan highlanders was systemically lower than those reported for Andean natives and lowland immigrants. These comparative data demonstrated that a healthy native population may successfully reside at high altitude without a significant elevation in Hb, and the lower Hb levels of Himalayan highlanders than those of migrated lowlanders and Andean natives are an example of favourable adaptation over the generations. In addition, excessive polycythemia has frequently been used as a marker of chronic mountain sickness (CMS). Altitude populations who have a higher Hb concentration also have a higher incidence of CMS. The low Hb in Himalayans suggested as showing adaptation over many generations in Tibetan stock. Recent work in Tibet, suggested that Tibetans there may have adapted to high altitude as a result of evolutionary pressure selecting for genes which give an advantage at altitude. All of the population genomic and statistical analysis indicated that EPAS1 and EGLN1 are mostly likely responsible for high altitude adaptation and closely related to low Hb concentration in Tibetans. These data supported the hypothesis that Himalayan highlanders have evolved a genetically different erythropoietic response to chronic hypoxia by virtue of their much longer exposure to high altitude. 相似文献
34.
Charlotte Ndiribe Loïc Pellissier Silvia Antonelli Anne Dubuis Julien Pottier Pascal Vittoz Nicolas Salamin 《Ecology and evolution》2013,3(15):4925-4939
The trend of closely related taxa to retain similar environmental preferences mediated by inherited traits suggests that several patterns observed at the community scale originate from longer evolutionary processes. While the effects of phylogenetic relatedness have been previously studied within a single genus or family, lineage‐specific effects on the ecological processes governing community assembly have rarely been studied for entire communities or flora. Here, we measured how community phylogenetic structure varies across a wide elevation gradient for plant lineages represented by 35 families, using a co‐occurrence index and net relatedness index (NRI). We propose a framework that analyses each lineage separately and reveals the trend of ecological assembly at tree nodes. We found prevailing phylogenetic clustering for more ancient nodes and overdispersion in more recent tree nodes. Closely related species may thus rapidly evolve new environmental tolerances to radiate into distinct communities, while older lineages likely retain inherent environmental tolerances to occupy communities in similar environments, either through efficient dispersal mechanisms or the exclusion of older lineages with more divergent environmental tolerances. Our study illustrates the importance of disentangling the patterns of community assembly among lineages to better interpret the ecological role of traits. It also sheds light on studies reporting absence of phylogenetic signal, and opens new perspectives on the analysis of niche and trait conservatism across lineages. 相似文献
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该研究在江西省瑞昌市设置9个淡竹林样地,调查和测定了淡竹林密度、淡竹各构件的生物量和总生物量,以及土壤含水率、土层厚度、林下裸岩率、pH、电导率、全氮和全磷等7个土壤环境因子,并对竹林密度、土壤环境因子和淡竹生物量分配指标进行了相关分析和回归分析。结果表明:(1)密度与淡竹蔸比重相关系数r达0.66( P=0.02<0.05),而与叶比重、枝比重、秆比重、鞭比重、根比重及根冠比均无显著相关关系;土壤环境因子与生物量分配指标有密切相关,环境主成分Z1与叶比重、秆比重及蔸比重均显著相关(P<0.05),Z2与鞭比重显著相关(P=0.034<0.05)。(2)密度与土壤环境因子密切相关(P<0.05),控制土壤环境因子的偏相关分析显示密度与淡竹生物量分配不显著相关( P>0.05),而控制密度时,土壤环境因子与淡竹生物量分配仍有显著相关关系(P<0.05);逐步回归分析也验证了偏相关分析的结果,密度被排除出回归方程。分析认为,土壤含水率、土层厚度及土壤养分等环境因子是影响石灰岩山地优势种淡竹生物量分配的主因,密度对生物量分配的影响实为土壤环境因子的间接作用。该研究结果为石灰岩地区植被恢复提供了理论支撑。 相似文献
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Rodney A. Chimner David J. Cooper Marcie D. Bidwell Anthony Culpepper Kay Zillich Koren Nydick 《Restoration Ecology》2019,27(1):63-69
Ditching is a common practice to dewater wetlands, including peatlands, and ditch blocking is a common method for restoring wetlands because substrate is often unavailable for filling the ditches. However, filling has many advantages compared to blocking ditches. Our goal was to test whether ditches could be filled in a Colorado sloping fen (Chattanooga Fen) using bales created from shredded aspen (Populus tremuloides) tree‐fiber. We monitored water table levels before and after we filled two ditches (combined length of approximately 165 m × 3 m wide) as well as an undisturbed reference portion of Chattanooga fen. The reference site had stable water tables that rarely dropped more than 20 cm below the soil surface. The ditches had been dewatering large areas of the fen for at least 100 years. Filling the ditches with fiber bales resulted in a water table increase between 2 and 22 cm in an area up to 150 m below the ditch. Native sedges now cover the area where we filled the ditches, with no erosion or compression/settling of the ground observed and no water backing up behind the filled ditches. Filling the ditches with shredded fiber bales is a good option for restoration in wilderness areas, or areas lacking peat or mineral soil fill because it is a natural material that is easily transported and placed in the ditches. 相似文献
39.
Soil erosion affects extensive areas worldwide and must be urgently reduced promoting plant cover and beneficial microorganisms associated with plants, including arbuscular mycorrhizal fungi (AMF). In mountain environments, plant cover is difficult to enhance due to harsh conditions during the dry season and steep slopes. Our objective was to evaluate the percentage of the soil surface covered by plants and the AMF community associated with trees 12.5 years after planting during forest restoration efforts in microsites at different levels of soil degradation. The study was performed in the first montane forest restoration initiative of Central Argentina, where one of the trials consisted of planting Polylepis australis saplings at microsites with different levels of soil degradation: high, intermediate, and low. After 12.5 years, percentage of bare soil cover was significantly reduced by 36 and 37% in the high and intermediate degradation microsites, respectively. Low degradation microsites were initially very low in bare soil and did not significantly change. Mycorrhizal colonization, hyphae, vesicles, arbuscules, AMF diversity, and community structure were similar among microsite types. Percentage of hyphal entry points was higher at microsites with low degradation, number of spores was higher in high and intermediate degradation, and species richness was higher in high degradation. Acaulospora and Glomus were the most abundant genera in all microsites. We conclude that even in the most degraded microsites around 2.8% of the bare soil is covered by vegetation each year and that the arbuscular mycorrhizal community is highly tolerant and adapted to soils with different disturbance types. 相似文献
40.
为了筛选适宜南京地区的优良城市绿化树种,在野外调查和问卷调查的基础上,利用层次分析法(AHP)建立江苏宁镇山脉乡土树种评价体系,对该区域的乡土树种进行客观的定量分析。结果表明:(1)乡土树种作为城市绿化树种应首先考虑抗逆性,其次是生态价值、美学价值和生物学特性;(2)参与评价的41种宁镇山脉乡土树种可分为4类,其中I类乡土树种应大力推广应用,Ⅱ类乡土树种可作为森林城市树种多样性的有益补充,Ⅲ类和Ⅳ类乡土树种作为城市绿化树种仍有一定的差距。13种Ⅰ类乡土树种作为城市绿化树种具有良好的应用前景。 相似文献