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51.
Ethan P. White 《Ecology letters》2004,7(4):329-336
The species–time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analysed STRs for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two‐phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two‐phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most community dynamics were dominated by ecological processes over scales <5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes. 相似文献
52.
Aim Local‐regional (LR) species diversity plots were conceived to assess the contribution of regional and local processes in shaping the patterns of biological diversity, but have been used also to explore the scaling of diversity in terms of its alpha, beta, and gamma components. Here we explore the idea that patterns in the geographical ranges of species over a continent can determine the shape of small region to large region (SRLR) plots, which are equivalent to LR plots when comparing the diversity of sites at two regional scales. Location To test that idea, we analysed the diversity patterns at two regional scales for the mammals of North America, defined as the mainland from Alaska and Canada to Panama. Method We developed a theoretical model relating average range size of species over a large‐scale region with its average regional point species diversity (RPD). Then, we generated a null model of expected SRLR plots based on theoretical predictions. Species diversities at two scales were modelled using linear and saturation functions for Type I and Type II SRLR relationships, respectively. We applied the models to the case of North American mammals by examining the regional diversity and the RPD for 21 large‐scale quadrats (with area equal to 160,000 km2), arranged along a latitudinal gradient. Results Our model showed that continental and large‐scale regional patterns of distribution of species can generate both types of SRLR relationship, and that these patterns can be reflected in LR plots without invoking any kind of local processes. We found that North American nonvolant mammals follow a Type I SRLR relationship, whereas bats follow a Type II pattern. This difference was linked to patterns in which species of the two mammalian groups distribute in geographical space. Conclusion Traditional LR plots and the new SRLR plots are useful tools in exploring the scaling of species diversity and in showing the relationship between distribution and diversity. Their usefulness in comparing the relative role of local and regional processes is, however, very limited. 相似文献
53.
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
54.
A 2‐year study on epidemic progress of apple scab was conducted at Randwijk, the Netherlands, in 1998 and 1999. The summer epidemic caused by conidia was studied instead of the well‐described spring season epidemic originating from ascospores. The aim was to investigate relationships between disease measurements, i.e. disease incidence and severity measures of apple scab, and their implications for the development of predictive models and threshold levels. The study characterized good relationships between the measurements on cultivar Jonagold using regression analyses in three disease control regimes (untreated, organic and integrated). For fruit quality prediction, the relationship between fruit incidence (If) and leaf incidence (Il) in the organic control regime was given by If = 1.966 + 0.402 × (Il) (R2 = 0.92). As a result of low level of disease in the integrated control regime, shoot incidence (Is), with higher values than leaf incidence, was better suited for prediction. The relationship was given by If = ?0.162 + 0.028 × (Is) (R2 = 0.91). For the integrated control regime, disease threshold levels were constructed for timing of the final fungicide application. If an apple grower wants to keep fruit infection under 1% incidence (harvest scab threshold), the timing of the final fungicide application (action threshold) should correspond to 4% shoot scab incidence at the beginning of August. The results are compared with similar studies and their biological interpretation is discussed. 相似文献
55.
红原鸡与家鸡的亲缘关系研究 总被引:15,自引:2,他引:13
对中国红原鸡滇地亚种和海南亚种与我国茶花鸡,泰和鸡和寿光鸡等地方鸡种以及芦花鸡,洛岛红等外国鸡种进行了血型(3个位点,13个等位基因),蛋白质(酶)多态(5个位点,11个等位基因)和DNA指纹分析,结果表明,红原鸡与茶花鸡(原始型品种)的亲缘关系较近;与泰和鸡,寿光鸡,芦花鸡,洛岛红(进化型品种)的亲缘关系较远,呈红原鸡-茶花鸡-泰和鸡,寿光鸡或芦花鸡,洛岛红这样一个进化阶梯,以上结果与国外资料( 相似文献
56.
M. B. Ratnaparkhe V. S. Gupta M. R. Ven Murthy P. K. Ranjekar 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(6-7):893-898
Randomly amplified polymorphic DNA (RAPD) markers were used for the identification of pigeonpea [Cajanus cajan (L.) Millsp.] cultivars and their related wild species. The use of single primers of arbitrary nucleotide sequence resulted in the selective amplification of DNA fragments that were unique to individual accessions. The level of polymorphism among the wild species was extremely high, while little polymorphism was detected within Cajanus cajan accessions. All of the cultivars and wild species under study could be easily distinguished with the help of different primers, thereby indicating the immense potential of RAPD in the genetic fingerprinting of pigeonpea. On the basis of our data the genetic relationship between pigeonpea cultivars and its wild species could be established.NCL Communication No. 6062 相似文献
57.
Gernot Falkner Ferdinand Wagner John Victor Small Renate Falkner 《Journal of phycology》1995,31(5):745-753
The blue-green alga Anacystis nidulans Drouet (Synechococcus leopoliensis Raciborski) cultivated under phosphate-limited conditions adopts a threshold value in the nanomolar range below which uptake ceases. In this study, we investigated the influence of phosphate pulses on the regulation of uptake behavior during reestablishment of the threshold value. Short-term pulses had only a slight effect on uptake kinetics and, hence, on the threshold value, even if the population had been exposed several times to elevated concentrations above the steady-state level in the growth medium. The threshold value was also practically insensitive to the amount of phosphate stored during these short-term fluctuations. Long-term phosphate pulses resulted in a transition to a metastable state that was characterized by a severalfold higher threshold value. This transition, apparently an adaptation to the transiently elevated phosphate concentrations, was further studied by following the influx of 32 P-phosphate at constant external concentrations and was shown to be complete after a period of 10–20 min. After adaptation to pulses, the uptake behavior followed a linear flow-force relation over a wide range of external concentrations. This behavior was explained by the simultaneous operation of at least two uptake systems with different, but coordinated kinetic parameters. This linear flow-force relation facilitated a direct determination of the threshold value from uptake measurements. For applicability in the field the force-flow relation can be a diagnostic tool to assay for fluctuating phosphate and to establish threshold values below the normal measurable range . 相似文献
58.
Root to shoot ratio of crops as influenced by CO2 总被引:1,自引:0,他引:1
Hugo H. Rogers Stephen A. Prior G. Brett Runion Robert J. Mitchell 《Plant and Soil》1995,187(2):229-248
Crops of tomorrow are likely to grow under higher levels of atmospheric CO2. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO2 concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO2 concentration will affect roots and shoots of crop plants proportionally. Since elevated CO2 can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO2 on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability. Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO2 and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO2 enrichment will add substantially to the global change response data base.Abbreviations R:S
root to shoot ratio, dry weight basis 相似文献
59.
Actin is a highly conserved protein although many isoforms exist. In vertebrates and insects the different actin isoforms
can be grouped by their amino acid sequence and tissue-specific gene expression into muscle and nonmuscle actins, suggesting
that the different actins may have a functional significance. We ask here whether atomic models for G- and F-actins may help
to explain this functional diversity. Using a molecular graphics program we have mapped the few amino acids that differ between
isoactins. A small number of residues specific for muscle actins are buried in internal positions and some present a remarkable
organization. Within the molecule, the replacements observed between muscle and nonmuscle actins are often accompanied by
compensatory changes. The others are dispersed on the protein surface, except for a cluster located at the N-terminus which
protrudes outward. Only a few of these residues specific for muscle actins are present in known ligand binding sites except
the N-terminus, which has a sequence specific for each isoactin and is directly implicated in the binding to myosin. When
we simulated the replacements of side chains of residues specific for muscle actins to those specific for nonmuscle actins,
the N-terminus appears to be less compact and more flexible in nonmuscle actins. This would represent the first conformational
grounds for proposing that muscle and nonmuscle actins may be functionally distinguishable. The rest of the molecule is very
similar or identical in all the actins, except for a possible higher internal flexibility in muscle actins. We propose that
muscle actin genes have evolved from genes of nonmuscle actins by substitutions leading to some conformational changes in
the protruding N-terminus and the internal dynamics of the main body of the protein.
Received: 15 March 1996 / Accepted: 14 July 1996 相似文献
60.
利用自制的控温实验槽在暗室内进行医蛭科两种吸血水蛭对光闪烁和水扰动刺激的模拟个体生态实验,实验结果的统计分析表明,日本医蛭在16℃时与照度有极好的正相关关系,而在22℃时成负相关关系,0.2克体重的个体在两种温度对照度的敏感度均大于0.5-0.6克和1.0-1.3克体重的个体,湖北牛蛭在两种温度时与照度均成正相关关系;0.5克体重的个体在16℃时对照度的敏感度大于1.0-3.3克体重的个体9.5- 相似文献