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An analysis is introduced, based on the decomposition of relativegrowth rates, to examine the mode of competition (i.e. whethercompetition is symmetric or asymmetric), the size-dependenceof growth, and their interdependence. In particular, the basisfor two commonly held views is examined: (1) that the type ofresource limitation determines the mode of competition, and(2) that asymmetric competition always leads to size-divergencebetween unequal competitors. It is shown that in field-grownmillet plants, competition for light was symmetric at low densityand asymmetric at high density. However, size variation at lowdensity decreased during growth, because small plants had greaterrelative growth rates than larger plants. Size variation stayedconstant at high density, since plants of all sizes had equalaverage relative growth rates. Based on these results and ageneral discussion, it is proposed that the type of resourcelimitation does not determine the mode of competition. Competitionfor light can be symmetric, and foraging for heterogeneouslydistributed soil resources can produce asymmetric competitionbelow-ground. Furthermore, the mode of competition alone doesnot determine size structure dynamics. Size-dependence of resourceconversion efficiency and allocation can modify the effectsof resource uptake on growth. Pennisetum americanumCuster ; mode of competition; size structure dynamics; plant growth analysis 相似文献
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Improved Coated Vesicle Isolation Allows Better Characterization of Clathrin Polypeptides 总被引:1,自引:0,他引:1
DEMMER ANNETTE; HOLSTEIN SUSANNE E. H.; HINZ GISELBERT; SCHAUERMANN GABRIELE; ROBINSON DAVID G. 《Journal of experimental botany》1993,44(1):23-33
Postmicrosomal pellets from plant sources are grossly contaminatedwith nbosomes. Previous purifications of clathrin coated vesicles(CCV) from such subcellular fractions have therefore often involvedan RNase treatment. Performed at 30°C, this step inherentlycarries with it the dangers of proteolysis. We document herea method for CCV isolation which avoids this. Through the inclusionof suitable antiproteases in the homogenizing and subsequentisolation media, we have also been able to improve the qualityof CCV recovered from plant tissues. As a result we have tentativelybeen able to identify clathrin light chains from zucchini hypocotyland pea cotyledon CCV. Similar to light chains from bovine brainthese polypeptides are heat stable, can be solubilized fromneutralized TCA precipitates, bind calcium and clathrin heavychains. However, in contrast to brain CCV the two light chainsof plant CCV are some 10 kDa heavier. Key words: Antiproteases, Ca2+-binding, clathrin coated vesicles, clathrin heavy chains, clathrin light chain(s), heat stability, pea cotyledons, RNase, zucchini hypocotyls 相似文献
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THERESE F. MOE ANNE K. BRYSTING TOM ANDERSEN SUSANNE C. SCHNEIDER ØYVIND KASTE DAG O. HESSEN 《Freshwater Biology》2013,58(1):114-127
1. Invasive species can transform aquatic ecosystems, and the nuisance growth of the freshwater macrophyte Juncus bulbosus has become a problem in many lakes and rivers in northern Europe. It affects biodiversity strongly and conflicts with human uses, not least compromising the generation of hydroelectricity. The causes of the proliferation of these massive stands of J. bulbosus are not finally resolved, however. 2. In this study, a wide range of catchment, lake and sediment parameters (n = 34) were assessed for 139 lakes in Southern Norway, with the aim of explaining the presence or absence of J. bulbosus and to assess potential drivers behind its prolific growth. 3. Juncus bulbosus was more often present in lakes with lower pH and phosphate concentrations, and a higher element ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (DIN : TotP). 4. Despite the many parameters measured across substantial environmental gradients, none explained nuisance growth. Genetic screening (amplified fragment length polymorphism fingerprinting) of plants from a subset of lakes and additional river sites also showed no genetic differences between the various growth forms. A macrophyte trophic index, however, suggested that the most problematic growth occurred in the most oligotrophic lakes. 5. The lack of consistent patterns may reflect either factors not assessed in our survey, or that the current extension of stands represents a gradual cumulative response over time, not characterised effectively in our snapshot survey. Nevertheless, we can now exclude some putative causes of nuisance growth, including in particular genetics and N‐deposition. 相似文献
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A panel of untrained judges was asked to assess spreadability of selected solid edible fat samples (butter, margarine, low fat products) of different temperature with regard to hedonic preferences. Instrumental measurements were performed by cone penetration with constant load. The statistical analysis of the ranked sensory data showed significant spreadability optima in the apparent yield value range of approximately 30–60 kPa. Differences between the selected fats were not observed. 相似文献
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KATJA PUSCH BERNHARD SEIFERT SUSANNE FOITZIK JÜRGEN HEINZE 《Biological journal of the Linnean Society. Linnean Society of London》2006,88(2):223-234
The two sibling ant species Temnothorax nylanderi and Temnothorax crassispinus are widely distributed throughout deciduous forests in Europe. Their resemblance in morphology and similar ecological requirements suggest that they evolved from the same ancestral species in different glacial refugia and re-immigrated into Central Europe after the last ice age. Here, we show that the two species are parapatrically distributed in south-eastern Germany and hybridize along a narrow contact zone close to the continental divide. Phylogeographical data based on the mitochondrial genes cytochrome oxidase subunit I and cytochrome b suggest that the dominant haplotypes for T. nylanderi and T. crassispinus might have diverged already 1.5–2 Mya. Intraspecific variability is extremely low in both species, which might be explained by severe bottlenecks during rapid postglacial expansion into Central Europe. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 223–234. 相似文献
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Montane and alpine habitats in Europe remained relatively undisturbed until the beginning of the last century. Today, outdoor recreation activities are a major economic factor in alpine regions. Many tourism areas coincide with winter habitats of shy and endangered species. The Western Capercaillie Tetrao urogallus has suffered from rapid population declines during recent decades over much of its range. In central Europe, many Capercaillie are exposed to intensive human recreation activities in their habitats, which may contribute to this decline. However, little is known about their susceptibility to human recreation activities. This study assessed whether human recreation in winter evokes physiological stress responses in several populations of Capercaillie. During two winters, we sampled 1130 Capercaillie droppings in Germany and Switzerland of populations at various distances from winter recreation activities and measured concentrations of faecal corticosterone metabolites. Capercaillie in relatively dense and homogeneous mountain forests dominated by Norway Spruce Picea abies showed markedly increased stress hormone levels closer to locations with winter recreation activity. However, this physiological response to human recreation was not detectable in forests dominated by various pine species and a heterogeneous structure. Capercaillie may be particularly sensitive to recreation because any factor affecting their fine‐tuned physiological and behavioural adaptations to survive under harsh winter conditions may lead to harmful fitness costs. 相似文献