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101.
St Lucia Lake on the north coast of Natal, South Africa, has an area of 325 km2 and is the largest estuarine complex in Africa. It consists of a 20 km tidal channel, averagingca. 400 m in width, linking the sea with the non-tidal lake which is H-shaped with a maximum length ofca. 40 km and width ofca. 20 km. Except during flood periods the depth of the lake does not exceed 2 m. The salinity gradient depends on evaporation,
the configuration of the mouth and on the input of fresh water from four rivers which discharge into the northern and western
areas of the lake. If fresh water input is high, the lake and much of the channel may be fresh. An intermediate stage features
a normal salinity gradient while a third stage shows a reversed salinity gradient with salinities in excess of 100‰ in the
upper reaches of the system. Changing salinities have marked effects on the biota. Aquatic macrophytes show cycles of appearance
and disappearance depending on salinity tolerance and the presence of dormant stages. The resident benthic faunal species
go through cycles of range expansion and contraction depending on prevailing salinities and recolonisation by dispersal phases.
To date salinities in the southern part of the lake have approached, but not exceeded, lethal levels and this has therefore
acted as a reservoir area. Catchment degradation and water abstraction are anticipated to exacerbate future salinity extremes.
This has resulted in concern for the long term viability of this Ramsar site which has major southern African populations
of hippopotamus and crocodile, provides breeding sites for South African Red Data water bird species and plays an important
nursery role for marine fish and penaeid prawns. 相似文献
102.
A method has been developed for the isolation of RNA from apple skin. The method involves an adaptation of the Manning (1991)
method and includes a high-salt extraction step and a final purification step through a CsCl cushion. The RNA isolated was
of high quality and produced good hybridization signals in northern blot analyses. 相似文献
103.
Helen E. O'connor David R. Stevens Stuart V. Ruffle Jonathan H. A. Nugent Saul Purton 《Plant Molecular Biology Reporter》1993,11(3):207-211
The isolation of chloroplast DNA fromChlamydomonas reinhardtii requires the efficient separation of this AT-rich genome from the GC-rich nuclear genome by density-gradient centrifugation.
We describe a simple and efficient method for separating these DNA fractions by using a sodium iodide gradient in combination
with the DNA-binding dye, bisbenzimide. The yield of chloroplast DNA is close to the theoretical maximum and the DNA is suitable
for restriction enzyme analysis and cloning. This method is applicable to the isolation of AT-rich plastid genomes from other
organisms and may be appropriate as a general method for separating species of DNA that differ in their AT/GC ratios.
An erratum to this article is available at . 相似文献
104.
Isolation of polysaccharide-free DNA from plants 总被引:2,自引:2,他引:0
Benoît Rether Geneviève Delmas Abdelkrim Laouedj 《Plant Molecular Biology Reporter》1993,11(4):333-337
A quick procedure for the isolation of polysaccharide-free DNA from different plant species and cell suspension or callus
cultures is described. The originality of the method lies in the use of a mixture of glycoside hydrolases that leads, after
phenol and chloroform extraction, to the isolation of pure DNA without any polysaccharide contamination. The highly purified
DNA can be used for nucleotide analysis by HPLC, RFLP analysis and PCR amplification. 相似文献
105.
106.
Shao-Jun Ling Xiao-Lan Yao Juli Caujapé-Castells Jordi López-Pujol Ke Tan Ming-Xun Ren 《植物分类学报:英文版》2023,61(6):1020-1035
Disjunct distribution is a key issue in biogeography and ecology, but it is often difficult to determine the relative roles of dispersal vs. vicariance in disjunctions. We studied the phylogeographic pattern of the monotypic Conandron ramondioides (Gesneriaceae), which shows Sino-Japanese disjunctions, with ddRAD sequencing based on a comprehensive sampling of 11 populations from mainland China, Taiwan Island, and Japan. We found a very high degree of genetic differentiation among these three regions, with very limited gene flow and a clear Isolation by Distance pattern. Mainland China and Japan clades diverged first from a widespread ancestral population in the middle Miocene, followed by a later divergence between mainland China and Taiwan Island clades in the early Pliocene. Three current groups have survived in various glacial refugia during the Last Glacial Maximum, and experienced contraction and/or bottlenecks since their divergence during Quaternary glacial cycles, with strong niche divergence between mainland China + Japan and Taiwan Island ranges. Thus, we verified a predominant role of vicariance in the current disjunction of the monotypic genus Conandron. The sharp phylogenetic separation, ecological niche divergence among these three groups, and the great number of private alleles in all populations sampled indicated a considerable time of independent evolution, and suggests the need for a taxonomic survey to detect potentially overlooked taxa. 相似文献
107.
Douglas P. Swain 《Evolution; international journal of organic evolution》1992,46(4):987-997
Previous studies have demonstrated selective predation for vertebral traits of larvae in the stickleback Gasterosteus aculeatus. I tested the hypothesis that this selection results from a direct functional advantage to particular vertebral phenotypes by direct measurement of the burst swimming performance of larvae. Within a narrow window of lengths, burst speed did depend on vertebral phenotype. As in the previous predation experiments, performance was related more directly to the ratio of abdominal to caudal vertebrae (VR) than to the total number of vertebrae (VN), and the optimal VR decreased as larval length increased. Changes with length in the vertebral phenotype frequencies of wild larvae provided evidence of selection for VR and for VN in the wild. Larvae with particular VR increased in frequency in the wild at just those lengths when their relative performance was superior in the laboratory. The observed pattern of length-dependent selection for vertebral number provides an explanation for the widespread trends in vertebral number that occur among populations of related fishes. 相似文献
108.
109.
Ermias T. Azeria 《Global Ecology and Biogeography》2004,13(2):177-187
Aim This study aims to explain the patterns of species richness and nestedness of a terrestrial bird community in a poorly studied region. Location Twenty‐six islands in the Dahlak Archipelago, Southern Red Sea, Eritrea. Methods The islands and five mainland areas were censused in summer 1999 and winter 2001. To study the importance of island size, isolation from the mainland and inter‐island distance, I used constrained null models for the nestedness temperature calculator and a cluster analysis. Results Species richness depended on island area and isolation from the mainland. Nestedness was detected, even when passive sampling was accounted for. The nested rank of islands was correlated with area and species richness, but not with isolation. Idiosyncrasies appeared among species‐poor and species‐rich islands, and among common and rare species. Cluster analysis showed differences among species‐rich islands, close similarity among species‐poor and idiosyncratic islands, and that the compositional similarity among islands decreased with increasing inter‐island distance. Thus, faunas of species‐poor, smaller islands were more likely to be subsets of faunas of species‐rich, larger islands if the distance between the islands was short. Main conclusions Species richness and nestedness were related to island area, and nestedness also to inter‐island distances but not to isolation from the mainland. Thus, nestedness and species richness are not affected in the same way by area and distance. Moreover, idiosyncrasies may have been the outcome of species distributions among islands being influenced also by non‐nested distributions of habitats, inter–specific interactions, and differences in species distributions across the mainland. Idiosyncrasies in nested patterns may be as important as the nested pattern itself for conservation – and conservation strategies based on nestedness and strong area effects (e.g. protection of only larger islands) may fail to preserve idiosyncratic species/habitats. 相似文献
110.
Makoto Kato 《Population Ecology》1996,38(1):27-40
Population dynamics of a leafminer,Chromatomyia suikazurae (Agromyzidae, Diptera) and its parasitoid community were studied for ten years at seven natural populations along an altitudinal gradient in Japan. This species which mines leaves of a forest shrub,Lonicera gracilipes (Caprifoliaceae), was attacked by 25 hymenopterous parasitoid species. Annually, the parasitoid community structure varied less within a population than among populations. The seven parasitoid communities were clustered into three groups corresponding to the altitudinal gradient: (a) lowland communities dominated by late-attacking, generalist pupal idiobiont eulophids and with highest species diversity, (b) hillside communities dominated by an early-attacking, specialist larval-pupal koinobiont braconid and (c) highland communities dominated by an early-attacking, generalist larval idiobiont eulophid. Annual changes of the host larval densities among the local populations were largely synchronous rather than cyclic. Among these populations, host density levels and mortality patterns greatly varied. By analyzing these inter-populational differences of host mortality patterns, the following conclusions were drawn: (1) The host mortality patterns were determined by the host utilization patterns of the locally dominant species. (2) The host pupal mortality but not larval mortality was related to species diversity but not to species richness itself of each parasitoid community. (3) Density dependence was detected only in pupal mortality at a lowland population dominated by late-attacking pupal parasitoids. These results suggest that interspecific interactions of parasitoids add additive effects to host population dynamics dissimilarly among local populations with different parasitoid communities. 相似文献