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Many viral, bacterial and protozoan parasites of invertebrates first propagate inside their host without releasing any transmission stages and then kill their host to release all transmission stages at once. Life history and the evolution of virulence of these obligately killing parasites are modelled, assuming that within-host growth is density dependent. We find that the parasite should kill the host when its per capita growth rate falls to the level of the host mortality rate. The parasite should kill its host later when the carrying capacity, K, is higher, but should kill it earlier when the parasite-independent host mortality increases or when the parasite has a higher birth rate. When K(t), for parasite growth, is not constant over the duration of an infection, but increases with time, the parasite should kill the host around the stage when the growth rate of the carrying capacity decelerates strongly. In case that K(t) relates to host body size, this deceleration in growth is around host maturation. 相似文献
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Ingo Aldag Ulrike Bockau Jan Rossdorf Sven Laarmann Willem Raaben Lutz Herrmann Thomas Weide Marcus WW Hartmann 《BMC biotechnology》2011,11(1):11
Background
Tetrahymena thermophila possesses many attributes that render it an attractive host for the expression of recombinant proteins. Surface proteins from the parasites Ichthyophthirius multifiliis and Plasmodium falciparum and avian influenza virus antigen H5N1 were displayed on the cell membrane of this ciliate. Furthermore, it has been demonstrated that T. thermophila is also able to produce a functional human DNase I. The present study investigates the heterologous expression of the functional human intestinal alkaline phosphatase (hiAP) using T. thermophila and thereby presents a powerful tool for the optimization of the ciliate-based expression system. 相似文献5.
Markus Lange Wolfgang W. Weisser Martin M. Gossner Esther Kowalski Manfred Türke Fernando Joner Carlos Roberto Fonseca 《Biodiversity and Conservation》2011,20(10):2133-2147
Land use intensification in forests is a main driver of global biodiversity loss. Although historical state of land use differs
between subtropical and temperate zones, gradients of land-use intensities similarly range from unmanaged to very intensively
managed forests. Irrespective of similar land use forces in both climate zones, comparative studies on land use effects are
still rare. Such studies are, however, promising in discovering more general impacts and geographical specifics of land use
intensification. We studied litter-dwelling invertebrates along a gradient of increasing land use intensity in subtropical
forests in Southern Brazil and temperate forests in Central Europe using similar sampling designs. Effects of land use intensity
on the entire community were analyzed on the level of orders and feeding guilds. In both climate zones a similar number of
individuals were caught when standardizes to 100 pitfall trap days, but taxa richness was higher in the subtropics. Moreover,
community composition differed between both climate zones. In both regions, land use intensity did not affect taxa richness,
but invertebrate abundance was affected in opposite ways; while increasing land use intensity resulted in a decrease of invertebrate
abundance in the subtropics, an increase was observed in the temperate zone and this was mostly consistent regarding different
feeding guilds. Management practices should take into account that the effect of land use intensity on biodiversity can differ
drastically among climatic regions. 相似文献
6.
P. J. Weisser 《African Journal of Aquatic Science》2013,38(2):145-149
SUMMARY In shallow lakes a siltation system develops when wind driven water turbulence erodes the lake floor, silt is resuspended and transported by means of waterdrift into the littoral vegetation. Here, due to the resistance of the vegetation, the turbulence is reduced and the silt deposited. Through this mechanism, the prevailing winds have a major rôle in the erosion and siltation pattern, lake morphology, vegetation pattern and in the mixing of water and nutrients from the open water and the reedswamp and vice versa. The model explains the uneven distribution of vegetation at the lakes Neusiedlersee (Austria) and Chilwa (Malawi) satisfactorily, if one assumes a positive correlation between siltation and reedswamp growth and spread. 相似文献
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H. Pfestorf L. Weiß J. Müller S. Boch S.A. Socher D. Prati I. Schöning W. Weisser M. Fischer F. Jeltsch 《Perspectives in Plant Ecology, Evolution and Systematics》2013,15(1):1-11
Semi-natural grasslands, biodiversity hotspots in Central-Europe, suffer from the cessation of traditional land-use. Amount and intensity of these changes challenge current monitoring frameworks typically based on classic indicators such as selected target species or diversity indices. Indicators based on plant functional traits provide an interesting extension since they reflect ecological strategies at individual and ecological processes at community levels. They typically show convergent responses to gradients of land-use intensity over scales and regions, are more directly related to environmental drivers than diversity components themselves and enable detecting directional changes in whole community dynamics. However, probably due to their labor- and cost intensive assessment in the field, they have been rarely applied as indicators so far.Here we suggest overcoming these limitations by calculating indicators with plant traits derived from online accessible databases. Aiming to provide a minimal trait set to monitor effects of land-use intensification on plant diversity we investigated relationships between 12 community mean traits, 2 diversity indices and 6 predictors of land-use intensity within grassland communities of 3 different regions in Germany (part of the German ‘Biodiversity Exploratory’ research network). By standardization of traits and diversity measures, use of null models and linear mixed models we confirmed (i) strong links between functional community composition and plant diversity, (ii) that traits are closely related to land-use intensity, and (iii) that functional indicators are equally, or even more sensitive to land-use intensity than traditional diversity indices. The deduced trait set consisted of 5 traits, i.e., specific leaf area (SLA), leaf dry matter content (LDMC), seed release height, leaf distribution, and onset of flowering. These database derived traits enable the early detection of changes in community structure indicative for future diversity loss. As an addition to current monitoring measures they allow to better link environmental drivers to processes controlling community dynamics. 相似文献
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Background
Seed dispersal of ant-dispersed plants (myrmecochores) is a well studied ecosystem function. Recently, slugs have been found to act as seed dispersers of myrmecochores. The aim of our study was to (1) further generalize the finding that gastropods feed on seeds of myrmecochores and hence may act as seed dispersers, (2) to test whether gastropod body mass and the volume of diaspores have an influence on the seed dispersal potential.Methodology and Principal Findings
We assessed the seed dispersal potential of four slug and snail species with a set of seven myrmecochorous plant species from seven different plant families common to Central European beech forests. Diaspores differed in shape and size. Gastropods differed in their readiness to feed on diaspores and in the proportion of seeds that were swallowed as a whole, and this readiness generally decreased with increasing diaspore size. Smaller Arionid slugs (58 mm body length; mean) mostly fed on the elaiosome but also swallowed small diaspores and therefore not only act as elaiosome consumers, a nutrient rich appendage on myrmecochorous diaspores, but may also disperse seeds. Large Arionid slugs (>100 mm body length) swallowed diaspores of all sizes. Diaspores swallowed by gastropods were defecated without damage. Within-species variability in body size also affect seed dispersal potential, as larger individuals of the red slug (Arion rufus) swallowed more diaspores of wood anemone (Anemone nemorosa) than smaller ones.Conclusions and Significance
Our results help to generalize the finding that gastropods consume and potentially disperse seeds of myrmecochores. The dispersal potential of gastropods is strongly influenced by diaspore size in relation to gastropod size. 相似文献9.
Effects of plant diversity, plant productivity and habitat parameters on arthropod abundance in montane European grasslands 总被引:4,自引:0,他引:4
Jrg Perner Carla Wytrykush Ansgar Kahmen Nina Buchmann Ilka Egerer Sylvia Creutzburg Nidal Odat Volker Audorff Wolfgang W. Weisser 《Ecography》2005,28(4):429-442
Arthropod abundance has been hypothesized to be correlated with plant diversity but the results of previous studies have been equivocal. In contrast, plant productivity, vegetation structure, abiotic site conditions, and the physical disturbance of habitats, are factors that interact with plant diversity, and that have been shown to influence arthropod abundance. We studied the combined effect of plant species diversity, productivity and site characteristics on arthropod abundance in 71 managed grasslands in central Germany using multivariate statistics. For each site we determined plant species cover, plant community biomass (productivity), macro- and micronutrients in the soil, and characterized the location of sites with respect to orographic parameters as well as the current and historic management regimes. Arthropods were sampled using a suction sampler and classified a priori into functional groups (FGs). We found that arthropod abundance was not correlated with plant species richness, effective diversity or Camargo's evenness, even when influences of environmental variables were taken into account. In contrast, plant community composition was highly correlated with arthropod abundances. Plant community productivity influenced arthropod abundance but explained only a small proportion of the variance. The abundances of the different arthropod FGs were influenced differentially by agricultural management, soil characteristics, vegetation structure and by interactions between different FGs of arthropods. Herbivores, carnivores and detritivores reacted differently to variation in environmental variables in a manner consistent with their feeding mode. Our results show that in natural grassland systems arthropod abundance is not a simple function of plant species richness, and they emphasize the important role of plant community composition for the abundance patterns of the arthropod assemblages. 相似文献
10.
Ingo Schöning Erik Grüneberg Carlos A. Sierra Dominik Hessenmöller Marion Schrumpf Wolfgang W. Weisser Ernst-Detlef Schulze 《Plant and Soil》2013,370(1-2):625-639