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61.
Soil factors responsible for the inability of Visearía vulgaris to colonize or survive on calcareous soils in Scandinavia were studied using experiments with plant establishment from seeds and re-establishment of mature plants, in soils of naturally differing or artificially varied chemical properties. Limestone soil proved less suitable for re-establishment of mature plants, and establishment from seeds was not possible in this soil. The plants grown on limestone had a very low phosphorus content and displayed deficiency symptoms. Acid leptite soil and soil from the A-horizon of a dystric cambisol were suitable for plant establishment from seeds and re-establishment of adult individuals, respectively. However, growth increased significantly when pH-KCl was raised to 7.6 by adding CaC03. Establishment from seeds was successful in the Archaean and Ordovician limestone soils only when CaHP04 was added. The calcifuge behaviour of Visearía vulgaris is not due to negative effects of a high pH or a high Ca concentration in the soil. Inability to utilize the native phosphorus of such soils is the most evident explanation. 相似文献
62.
The objective of this study was to identify the causes of the limits of the geographical range of Hippocrepis comosa. Along a gradient from the northwestern distribution boundary towards the distribution centre in Germany, 46 field plots
were established where growth and microclimate were monitored simultaneously. In total, 11 vegetative and generative traits
and 7 microclimatic parameters were recorded over 7 time intervals during the vegetation period, together with 14 general
site parameters. Regression analyses were performed between all traits and environmental parameters in a certain interval.
At the beginning of the growing season the best positive correlation coefficients for vegetative growth were observed with
soil temperature. From the end of May to the middle of June, vegetative growth rates decreased and showed the best positive
correlation with soil water content. Despite credible relationships between vegetative growth and microclimate, their contribution
toward explaining the northern distribution boundary was found to be limited, because no correlation with the distance from
the distribution boundary was observed. The only growth parameter that showed both a positive correlation with distance from
the distribution boundary and a significant correlation with microclimate was the percentage of seed setting, which increased
towards the distribution centre and was correlated with air temperature. Further field observations on plots outside the actual
range of Hippocrepis comosa revealed no microclimatic reasons as to why the species was absent from these sites. This shows that the environmental parameters
are in no way deterministic for the range limit. The frost hardiness of Hippocrepis comosa was studied in additional laboratory experiments in which significant damage was not found above −18 °C for adult plants
and above −14 °C for seedlings, which is remarkably low and too low to be relevant for the northwestern distribution boundary.
Another field experiment revealed that seedling establishment exhibited a positive relationship to soil water content, which
became more favourable towards the range boundary. It is concluded that temperature, particularly air temperature, makes the
largest contribution to explaining the northern distribution boundary of Hippocrepis comosa in Germany and that mainly generative reproduction is affected.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
63.
Filipe Ribeiro Benigno Elvira Maria João Collares-Pereira Peter B. Moyle 《Biological invasions》2008,10(1):89-102
Freshwater ecosystems are seriously imperiled by the spread of non-native fishes thus establishing profiles of their life-history
characteristics is an emerging tool for developing conservation and management strategies. We did a first approach to determine
characteristics of successful and failed non-native fishes in a Mediterranean-climate area, the Iberian Peninsula, for three
stages of the invasion process: establishment, spread and integration. Using general linear models, we established which characteristics
are most important for success at each invasion stage. Prior invasion success was a good predictor for all the stages of the
invasion process. Biological variables relevant for more than one invasion stage were maximum adult size and size of native
range. Despite these common variables, all models produced a different set of variables important for a successful invasion,
demonstrating that successful invaders have a combination of biological traits that may favor success at all invasion stages.
However, some differences were found in relation to published studies on fish invasions in other Mediterranean-climate areas,
suggesting that characteristics of the recipient ecosystem are as relevant as the characteristics of the invading species. 相似文献
64.
We document the invasion of Chinook salmon (Oncorhynchus tshawytscha) to southern South America providing historical, current and future perspectives. We conducted field sampling, angler surveys,
and analyzed all written records, and found evidence of reproductive populations in more than ten Andean (and many more coastal)
watersheds draining mainly to the Pacific Ocean in Chile (39°–53° S), but also to the Atlantic Ocean in Argentina (50° S).
Invasion begun ∼25 years ago apparently from a few point sources of introduction by ocean ranching operations using spring-run
Chinook salmon originated from tributaries of the lower Columbia River, USA. The rapid spread suggests that Chinook salmon
were pre-adapted to their novel marine and freshwater environments because of similarities to equivalent North Pacific habitats,
and invasion may have been facilitated by low ecological resistance. Preliminary data suggest that populations express a latitudinal
gradient in juvenile migration life histories equivalent to that in their native range. Parallels to the only other establishment
of anadromous Chinook salmon outside their native range, New Zealand, suggests a predictable invasion rate. In South America,
the invasion is ongoing in southern areas, yet we deem unlikely colonization of rivers north of the range reached thus far.
This is the first anadromous salmon species to have invaded such a large range in South America, and it raises many evolutionary,
ecological, environmental and socioeconomic issues, with several discussed here.
相似文献
Cristián CorreaEmail: |
65.
大鼠脑神经干细胞系(RNSC-FMU 1)的建立和鉴定 总被引:1,自引:0,他引:1
采用无血清培养液分离和培养新生SD 大鼠脑的神经干细胞,以机械分散的方法传代,成功地建立了大鼠脑神经干细胞系(RSNC-FMU 1)。该细胞系可在体外长期传代,至今已在体外连续生长超过21个月(>100代),保持了神经干细胞的特性和正常的核型,经诱导可分化成为神经元、星形胶质细胞和少突胶质细胞,具有较旺盛的自新能力,倍增时间约为20h,并可冷冻保存,裸鼠体内移植证实其不具有成瘤性。该细胞系为神经干细胞研究提供了一个良好的工具。 相似文献
66.
《Journal of Asia》2022,25(1):101874
Virulence and invasion efficiency of the three entomopathogenic nematodes, Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae against the potato tuber moth (PTM), Phthorimaea operculella was evaluated. Also evaluated were the sex ratio of Steinernema spp. and host stages to determine if 1) the developmental stage of the host affects sex ratio of nematodes; 2) infective juveniles (IJs) concentration affects sex ratio in host developmental stages and 3) the establishment of IJs is affected by developmental stages of host. The PTM pre-pupa and pupa were exposed to IJs in filter substrate petri dish bioassays. By increasing the IJs concentrations, the number of established Steinernema spp. in both PTM stages increased and only decreased at the highest concentration. No reduction in established nematode numbers at the highest concentration was observed for H. bacteriophora. Sex ratio of S. carpocapsae in pre-pupa was affected by IJ concentration. PTM was more susceptible to Steinernema spp. than H. bacteriophora. Pre-pupa were more susceptible to S. feltiae but S. carpocapsae recorded as the most virulent EPN on pupa. Invasion efficiencies were similar for Steinernema and considerably higher than for H. bacteriophora. Despite a higher invasion efficiency of Steinernema into pupae, mortality was lower compared to pre-pupa No correlation was recorded between the invasion efficiencies of the EPNs and mortalities of PTM. The results showed that the invasion efficiency is not appropriate criterion to reflect the virulence of studied EPNs. Compared to H. bacteriophora both tested Steinernema spp. were good candidates for further studies as biocontrol agents of PTM. 相似文献
67.
68.
Introgression is a key process in conservation biology, genetic modification of (crop) species and in the evolutionary ecology of many species. Here we consider the case of introgression of insecticide resistance in the whitefly, Bemisia tabaci. B. tabaci is a species complex consisting of a range of biotypes, known to have a high degree of inter-biotype reproductive isolation. In areas where insecticide resistant and susceptible biotypes of B. tabaci coexist, introgression of the resistance gene will have considerable consequences for whitefly control. Using a stochastic branching process model we calculate the relative importance of life-history traits in determining the probability of introgression given that a hybridization event has occurred. We show that a fitness cost expressed through the average number of eggs laid, has the largest effect on the introgression probability as compared to fitness costs expressed through other life-history parameters. These results change when we consider a reproductive isolation mechanism, for which we show that the fitness cost expressed through the male survival and mating probability have the largest effect on the probability of introgression. 相似文献
69.
Md. Yeamin Hossain Zoarder Faruque Ahmed Jun Ohtomi Abu Hanif Md. Ibrahim Mohamed A. H. El-kady Bernerd Fulanda Susanta Kumar Chakraborty 《Environmental Biology of Fishes》2008,82(3):277-278
The Asian Silurid catfish Wallago attu is an endangered species. Populations are declining due to over-exploitation, pollution and environmental degradation. Law
enforcement to ban destructive fishing practices should be enhanced for the conservation of the populations. 相似文献
70.
Plant recruitment is limited by dispersal, if seeds cannot arrive at potential recruitment sites, and by establishment, due to a low availability of safe sites for recruitment. Seed-sowing experiments, scarcely applied along gradients of landscape alteration, are very useful to assess these limitations. Habitat loss and fragmentation may foster recruitment limitations by affecting all the processes from seed dispersal to seedling establishment. In this study, we perform a seed-sowing experiment to disentangle the importance of dispersal and establishment limitations in different stages of recruitment of the perennial herb Primula vulgaris in fragmented forests of the Cantabrian Range (Northwestern Spain). We evaluated the influence of ecological gradients resulting from habitat loss and fragmentation (modifications of habitat amount at the landscape and microhabitat scales, changes in the species’ population size, changes in seed predation and seedling herbivory) on seedling emergence, survival and early growth. We found strong evidence of dispersal limitation, as seedling emergence was very low in experimental replicates where no seeds were added. This limitation was independent of landscape alterations, as we found no relation with any of the ecological gradients studied. Establishment limitations at the germination phase were also unrelated to ecological gradients, probably because these limitations are more related to fine-scale environmental gradients. However, further monitoring revealed that seedling survival after summer and winter periods and seedling growth were conditioned by landscape alteration, as we found effects of habitat amount at the landscape and microhabitat scales, of presence of populations of P. vulgaris and of seedling herbivory. These effects were complex and sometimes opposite to what can be expected for adult plants, revealing the presence of different requirements between life stages. 相似文献