On size and growth in freshwater fish

Patterns of growth and size achieved in freshwater fish are examined with relation to the issues of indeterminate and determinate growth and asymptotic growth. Various authors suggest minimum, average and maximum sizes attained by fish, variously pointing to very small gobies and very large sharks, with most fish being about 150 mm long. Growth in fish is distinctive in that typically it continues throughout life, even though it becomes slower with increasing age and the onset of sexual maturity. Growth rates and size achieved by fish are highly flexible and subject to both genetic and environmental controls, so that size reached may vary with environmental variables such as water temperatures and food availability (both food abundance and prey types and sizes). Frequency distributions of 5 disparate freshwater fish faunas (Papua-New Guinea 267 species and tropical; North America 709 species and subtropical to Arctic; Australia 176 species and tropical to temperate; New Zealand and Great Britain 27 and 39 species and both warm to cool temperate) closely resemble distributions generated by the theoretical model of Hutchinson & MacArthur, and also data on diverse faunas. Frequency distributions in these faunas are closely similar, with a majority of species being small. This similarity would seem to suggest a general explanation. However, examination of the freshwater fish fauna of North America suggests that, rather than showing a predominance of large fish in the Arctic, the fauna has more large fish towards the tropics, though the proportion of large fish there is lower owing to the proliferation of small species in the tropics and a paucity of them towards the Arctic. Analysis shows a shift in the size composition of the fauna with latitude and shows that the general pattern for the whole of North America consists of a composite series of rather different patterns. This suggests that there is probably no meaningful general explanation of the overall patterns seen in these diverse and disparate faunas and that the similarity in overall size distributions between freshwater fish faunas of North America, New Guinea, Australia and New Zealand are of little ecological or evolutionary significance. The generality of Cope's rule is questionable, especially for fish, in which dwarfing and/or evolution towards smaller size are seen to be common phenomena.     

Error propagation associated with benefits transfer-based mapping of ecosystem services

An increasing number of studies are taking the important first step in global efforts to conserve key ecosystem services by mapping their spatial distributions. However, a lack of primary data for most services in most places has largely forced such mapping exercises to be based on proxies. The common way of producing these proxies is through benefits transfer-based mapping, in which estimates of the values of services are obtained from a small region for particular land cover types, and then extrapolated to a larger area for these same types. However, the errors that may result from such extrapolations are poorly understood. Here, we separate the generalization errors associated with benefits transfer mapping into three constituent components - uniformity, sampling, and regionalization error - and evaluate their effects using primary data for four ecosystem services in England. Variation in ecosystem services within a particular land cover type (uniformity error) alone led to a poor fit to primary data for most services; sampling effects (sampling error) and extrapolating from a small region to a larger area (regionalization error) led to substantial, but highly variable, additional reductions in the fit to primary data. We also show that combining multiple ecosystem services into a single layer is likely to be even more problematic as it contains the errors in each of the constituent layers. These errors are sufficiently large to undermine decisions that might be based on such extrapolated maps. Greatly improved mapping of the actual distributions of ecosystem services is therefore needed to achieve the goal of conserving these vital assets.     

Consequences of feasible future agricultural land‐use change on soil organic carbon stocks and greenhouse gas emissions in Great Britain

The aim of this study was to assess the consequences of feasible land‐use change in Great Britain on GHG emissions mainly through the gain or loss of soil organic carbon. We use estimates of per‐area changes in soil organic carbon (SOC) stocks and in greenhouse gas (GHG) emissions, coupled with Great Britain (GB) county‐level scenarios of land‐use change based on historical land‐use patterns or feasible futures to estimate the impact of potential land‐use change between agricultural land‐uses. We consider transitions between cropland, temporary grassland (<5 yr under grass), permanent grass (>5 yr under grass) and forest. We show that reversion to historical land‐use patterns as present in 1930 could result in GHG emission reductions of up to ca. 11 Mt CO₂‐eq./yr (relative to a 2004 baseline), because of an increased permanent grassland area. By contrast, cultivation of 20% of the current (2004) permanent grassland area for crop production could result in GHG emission increases of up to ca. 14 Mt CO₂‐eq./yr. We conclude that whilst change between agricultural land‐uses (transitions between permanent and temporary grassland and cropland) in GB is likely to be a limited option for GHG mitigation, external factors such as agricultural product commodity markets could influence future land‐use. Such agricultural land‐use change in GB could have significant impacts on Land‐use, Land‐Use Change and Forestry (LULUCF) emissions, with relatively small changes in land‐use (e.g. 5% plough out of grassland to cropland, or reversion of cropland to the grassland cover in Nitrate Vulnerable Zones of 1998) having an impact on GHG emissions of a similar order of magnitude as the current United Kingdom LULUCF sink. In terms of total UK GHG emissions, however, even the most extreme feasible land‐use change scenarios account for ca. 2% of current national GHG emissions.     

英国农业科技人员管理的特点及其启示简

英国作为一个稳定、发达的资本主义国家,依靠其雄厚的工业技术基础和较完善的农业科研、教育和管理体系的支撑,已经成为世界农业科技强国。英国农业在注重以市场需求为导向,坚持科学研究与农业生产紧密结合,重视科技创新成果转化,加强职业技能培训,突出实践操作能力,运用第三方评价模式提高评价结果的公信度等方面,具有很多成功的经验和先进的特点。分析和研究英国农业科技人员管理的特点,对促进中国农业发展具有一定的启示和借鉴意义。     

Patterns of rarity in the native British flora

We have combined published data on ecology and conservation status with phylogenetic information for all native British angiosperms. We use this information to explore patterns of threat with regard to taxonomy, ecology and life history.Threat status is significantly clumped among orders. However among genera, we identify only Limonium (sea lavenders) and Sorbus (whitebeams) as containing more threatened species than expected under a hypergeometric model, and we discuss the artefactual reasons for this finding. We present a table of Britain's 10 most threatened families according to this statistic.Threat status is also strongly clumped across habitat types using two published schemes. In an analysis excluding artificially influential genera, we identify the `arable and horticultural', `montane', `inland rock', and `supra-littoral sediment' habitats as containing more threatened species than would be expected under a hypergeometric model and discuss these results.Finally, we use phylogenetically independent contrasts to show that threat status is correlated with small size, low fecundity, and insect rather than wind pollination for the native British flora.     

简要回顾英国的景观设计

英国是一个具有悠久造园传统的国家,同时也是对现代景观设计产生很大影响的国家,尤其是英国的风景式造园,即自然主义的风景园林,对欧洲乃至世界都产生了很大影响,因此,对英国景观设计的历史进行梳理和回顾,学习其景观设计的思想和手法,有着重要的意义。     

Relationship between distributions of threatened plants and protected areas in Britain

The establishment and maintenance of a system of protected areas is central to regional and global strategies for the conservation of biodiversity. The current global trend towards human population growth and widespread environmental degradation means that such areas are becoming increasingly isolated in fragmented habitat islands. In regions in which this process is well advanced a high proportion of species are thus predicted to have become restricted to protected areas. Here using uniquely detailed datasets for Britain, a region with close to the global level of percentage coverage by statutory protected areas, we determine the extent of restriction of Red List vascular plant species of conservation concern to these areas. On the basis of currently known distributions, overall our results strongly support the importance of a dual conservation strategy in Britain, in which protected areas are maintained with particular reference to those biodiversity features (such as many threatened plant species) that are highly dependent on them, and in which components of the wider landscape are also managed in such a way as to promote the abundance and distribution of such features with particular reference to those which are unlikely to persist in protected areas alone.     

The use of ground vegetation and humus type as indicators of soil nutrient regime for an ecological site classification of British forests

In many countries ground vegetation and humus type are used as indicators of forest soil quality, especially nutrient regime. This paper reports the development of such methods for use in British forests, within a new Ecological Site Classification combining climate, soil moisture regime and soil nutrient regime.

To develop a field assessment method for soil nutrient regime, a study was made of soil chemistry, humus type and ground vegetation in British forests. Sites were selected in both mature plantations and semi-natural woodlands. Soil and humus profiles were described and the soil was sampled volumetrically for later chemical analysis. Vascular ground vegetation was recorded in quadrats by species cover fraction, and classified according to the existing British National Vegetation Classification. Soils were analyzed for a number of chemical variables. Vegetation data were treated by application of the species indicator values for soil reaction (R) and soil nitrogen (N), as proposed by Ellenberg [Vegetation Ecology of Central Europe, 4th Edition. Cambridge University Press, Cambridge]. Site mean indicator values mR and mN (weighted by species cover fraction) were then calculated. Multivariate statistical analysis techniques were applied to both the soil chemical and the vegetation sample data.

Soil nutrient regime was shown to be a composite gradient of several soil chemical variables, of which the pH value and the availability of mineral (especially nitrate) nitrogen, and of calcium, were of particular importance. The species composition of the ground vegetation was related to position on this soil nutrient gradient. The vegetation: soil nutrient correlation using the site mean Ellenberg values was satisfactory (r=0.89), but was improved by using indicator values generated from within the present data. The occurrence of the major humus types (mor, moder and mull) is broadly related to soil nutrient regime defined in this way. Both ground vegetation and humus type can therefore be used as soil nutrient indicators in British forests.

A division of the soil nutrient gradient into five classes (Very Poor, Poor, Medium, Rich and Very Rich) is proposed. Future sampling work may lead to the definition of an additional class of soils with carbonate nutrient regimes. The Ecological Site Classification will provide forest managers in Great Britain with an improved basis for the selection of tree species for planting, and the adoption of silvicultural methods best suited to the site.     

Study on the pathogenicity of ostertagiosis due to Ostertagia circumcincta in sheep,in Iraq

The response of Awassi sheep to Ostertagia circumcincta, the most prevalent ovine strongylid species in Iraq, was studied.A dose of 100000 larvae of O. circumcincta (Iraqi strain) induced moderate clinical symptoms of ostertagiosis. These symptoms were correlated with elevated pH of the abomasal fluid and increased plasma pepsinogen levels. There was no evidence of larval inhibition since the majority of the fourth stage larvae (L₄) continued their development. No appreciable loss of worm population was observed and most of the parasites survived and exhibited a prolific egg-laying potential six moths after initial infection. Assessments of the pathophysiological changes were performed and correlated with parasitological and clinical observations.The Awassi breed of sheep, the most prevalent in the Arab Middle East, seems to be more susceptible to ostertagiosis than other breeds and there was no spontaneous self-cure in this breed.