The importance of demographic niches to tree diversity   总被引：1，自引：0，他引：1  

Condit R  Ashton P  Bunyavejchewin S  Dattaraja HS  Davies S  Esufali S  Ewango C  Foster R  Gunatilleke IA  Gunatilleke CV  Hall P  Harms KE  Hart T  Hernandez C  Hubbell S  Itoh A  Kiratiprayoon S  Lafrankie J  de Lao SL  Makana JR  Noor MN  Kassim AR  Russo S  Sukumar R  Samper C  Suresh HS  Tan S  Thomas S  Valencia R  Vallejo M  Villa G  Zillio T 《Science (New York, N.Y.)》2006,313(5783):98-101

Most ecological hypotheses about species coexistence hinge on species differences, but quantifying trait differences across species in diverse communities is often unfeasible. We examined the variation of demographic traits using a global tropical forest data set covering 4500 species in 10 large-scale tree inventories. With a hierarchical Bayesian approach, we quantified the distribution of mortality and growth rates of all tree species at each site. This allowed us to test the prediction that demographic differences facilitate species richness, as suggested by the theory that a tradeoff between high growth and high survival allows species to coexist. Contrary to the prediction, the most diverse forests had the least demographic variation. Although demographic differences may foster coexistence, they do not explain any of the 16-fold variation in tree species richness observed across the tropics.  相似文献   

Observations on Babesiosoma mariae (Apicomplexa: Dactylosomatidae) from the Okavango Delta,Botswana     

Smit NJ  Van As JG  Davies AJ 《Folia parasitologica》2003,50(1):85-86

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Can State Tax Policy Increase Economic Activity and Reduce Inequality?          下载免费PDF全文

Harvey Cutler  Martin Shields  Stephen Davies 《Growth and change》2018,49(1):142-164

Previous research shows that when changes in national commodity and income tax rates affect labor supply decisions differently, relative rates can be altered to increase welfare. In the U.S., 40 states impose both a sales and income tax; however, the reliance varies widely. This paper uses a computable general equilibrium model to examine tax policy changes in Colorado. The findings suggest that the revenue neutral changes to income and sales tax rates can affect both the level of economic activity and the distribution of income. When labor force participation is highly sensitive to income tax rate changes—which this paper suggests is the case—progressive changes to Colorado's tax policy changes can both reduce inequality and increase output and employment.  相似文献   

Nicotinic acid supplementation of diets for the African catfish, Clarias gariepinus (Burchell)     

P C Morris  R T M Baker  S J Davies 《Aquaculture Research》1998,29(11):791-799

Semi-purified diets containing 39% crude protein and 5% lipid were used to identify the qualitative requirement of African cattish, Clarias gariepinus (Burchell), for niacin and to characterize the pathologies associated with a deficiency of this vitamin. After 48 days of feeding, C. gariepinus supplied with the unsupplemented diet had developed severe deficiency symptoms and were subsequently withdrawn from the growth study. Niacin deficiency was characterized by feed refusal, listlessness, weight loss, poor feed utilization and high mortality. The skin overlaying the lateral line of the deficient fish became haemorrhagic and this clinical sign was accompanied by severe anaemia. After 126 days of feeding, fish fed diets containing 17.0 mg niacin kg^?1 had also developed a dermopathy. but without anaemia or high mortality. The feeding of diets containing less than 33.1 mg niacin kg^?1 resulted in suboptimal feed efficiency and poor protein utilisation. Allometric analysis of proximate composition indicated that carcass moisture, protein and ash were influenced by fish size, and not by dietary niacin content. However, significantly more lipid per unit of weight gain was deposited in the carcasses of fish fed the unsupplemented diet than in fish fed diets containing 17.0mgkg^?1. The indicators used in the present study could not be applied to accurately determine a value for niacin requirement. However, until a more accurate assessment is performed, it is recommended that diets for C. gariepinus contain not less than 33.1 mg nicotinic acid kg^?1 feed.  相似文献   

Processing of astaxanthin‐rich Haematococcus cells for dietary inclusion and optimal pigmentation in Rainbow trout,Oncorhynchus mykiss L.          下载免费PDF全文

A.J. Young  J. Pritchard  D. White  S. Davies 《Aquaculture Nutrition》2017,23(6):1304-1311

A range of physical cell disruption techniques have been evaluated to aid the processing of astaxanthin‐rich haematocysts of Haematococcus pluvialis for inclusion in salmonid feeds. Cell disruption by a scalable pressure treatment system was shown to be effective in breaking open the haematocysts without altering the content or isomeric composition of carotenoids in the algal cells. Storage of disrupted cells was optimal at ?20°C in the dark under nitrogen. Disrupted cells were spray‐dried, incorporated into commercial diets and fed to rainbow trout (Oncorhynchus mykiss L.). A marketable level of pigmentation in fish muscle was achieved after 10‐week dietary supplementation. The geometric and optimal isomer composition of the astaxanthin deposited in the muscle was nearly identical to that seen in Haematococcus. Changes were observed in the chirality of the astaxanthin deposited in the skin in comparison with that isolated from both the white muscle and the alga.  相似文献   

Making agricultural landscapes more sustainable for freshwater biodiversity: a case study from southern England     

Bella Davies  Jeremy Biggs  Penny Williams  Stewart Thompson 《水产资源保护:海洋与淡水生态系统》2009,19(4):439-447

• 1. Agriculture is known to have a range of deleterious impacts on freshwater habitats and biota and many countries have introduced measures to attempt to mitigate these impacts through agri‐environment initiatives. Despite the protection they provide, water bodies (any discrete body of surface fresh water) in farmland landscapes commonly remain impaired by agriculture. In some areas of the UK there have been calls to halt farming completely, indicating that the measures offered for the widespread protection of aquatic systems, particularly the use of buffer strips, may not be extensive enough to provide sufficient protection for freshwater biota.
• 2. This study investigated whether existing agri‐environment measures for the widespread protection of aquatic habitats could be better deployed to provide a higher level of protection for the aquatic macrophytes and macroinvertebrates of a study area in southern England.
• 3. Reserve selection procedures were used to reallocate the area of land that could be remunerated under the Environmental Stewardship scheme as buffer strips bordering water bodies, so that a higher level of protection was provided for both the richness and rarity of aquatic species in the study area.
• 4. Almost 395 ha were available for reallocation in the reserve selection process, which was found to provide a satisfactory level of protection for up to 90% of the surveyed species.
• 5. The results showed that the agri‐environment scheme in England has a great deal of potential to provide more effective protection for the aquatic biodiversity of agricultural landscapes if measures are targeted.

Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Survey of mussel (Mytilus) species at Scottish shellfish farms     

Patricia Joana Dias  Aurelien Dordor  David Tulett  Stuart Piertney  Ian M Davies  & Michael Snow 《Aquaculture Research》2009,40(15):1715-1722

Mytilus trossulus and its hybrids with the native species Mytilus edulis and also Mytilus galloprovincialis have been recently detected in both farmed and natural populations of mussels in Scotland, adding complexity to the known M. edulis × M. galloprovincialis hybrid zone in Europe. Mytilus trossulus was first found in Scotland at aquaculture sites, where it was associated with significant losses in production and reductions in profitability. Mytilus trossulus and its hybrids have been identified at higher frequencies in farm stock than in natural intertidal populations, raising concerns about the potential wider impact of M. trossulus genotypes at mussel aquaculture sites in Scotland. The present study clarifies the composition of Mytilus species in cultivation at Scottish mussel aquaculture farms, by screening samples from 41 mussel aquaculture sites using a high-throughput real-time PCR methodology. Mytilus edulis alleles were detected at all sites. Mytilus galloprovincialis alleles were detected from samples collected at 39 sites, and M. trossulus alleles were found at five sites. Overall, M. trossulus genotypes were restricted in their geographical distribution. It is suggested that, in order to support the sustainability of the Scottish shellfish cultivation industry, the economic impact arising from the presence of M. trossulus could be limited through good management practice.  相似文献   

Plant response to evapotranspiration and soil water sensor irrigation scheduling methods for papaya production in south Florida     

Kati W. Migliaccio  Bruce Schaffer  Frederick S. Davies 《Agricultural Water Management》2010,97(10):1452-1460

An irrigation study was conducted to determine the effects of implementing different irrigation practices on growth and yields of papaya plants in south Florida. Treatments included using automated switching tensiometers based on soil water status, irrigation based on ET calculated from historic weather data and a set schedule irrigation regime. The study consisted of two trials (2006-2007 and 2008-2009). Water volumes applied, plant height and diameter, leaf gas exchange, leaf petiole nutrient levels, fruit yields and fruit total soluble solids were measured throughout the study. For both trials, significantly more water was applied in the set schedule irrigation treatment than in all other treatments; historic ET and soil water based treatments received only about 31-36% of the water applied in the set schedule irrigation. Trunk diameter and plant height per unit water volume applied values for the set schedule treatment were significantly lower than those from all other treatments during both trials. The set schedule treatment in both trials also had the lowest crop production water use efficiency (CP-WUE); CP-WUE values among all other treatments were generally not significantly different from each other. Soil water and historic ET-based irrigation methods were identified as more sustainable practices compared to set schedule irrigation due to the lower water volumes applied while maintaining plant nutrient content, growth, photosynthetic rates, and fruit yields for this production system.  相似文献   

Patenting life? The opportunities for protecting molecular biological inventions in Europe     

Jonathan M. Davies 《Pest management science》1998,52(4):403-404

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Dietary supplementation of autolysed yeast enhances growth,liver functionality and intestinal morphology in African catfish     

Ayodeji A. Adeoye  Sam O. Obasa  Femi J. Fawole  Alex H. L. Wan  Simon J. Davies 《Aquaculture Nutrition》2020,26(3):772-780

A feeding trial was conducted to evaluate the potential of dietary supplementation of autolysed brewer's yeast (AY) on African catfish. The catfish (22.5 ± 1.15 g/fish, 20 fish 33 L/tank) were fed with either of diets (390 g/kg crude protein, 140 g/kg lipid) supplemented with 0, 3, 6 or 10 g/kg AY (n = 3). After 49 days of feeding, the final body weight and metabolic growth rate of the catfish fed 3 g/kg AY (3‐AY) diet were higher than those fed the control diet (p < .05). The lowest level (p < .05) of alanine transaminase was detected in the blood of the catfish fed 3‐AY diet. The mid‐intestinal histology of the catfish revealed no significant difference (p > .05) in intestinal perimeter ratio. However, an elevated (p < .05) abundance of goblet cells and intraepithelial leucocytes were found in the intestine of catfish fed 3, 6 and 10 g/kg AY diets, with the highest level of abundance recorded in the mid‐intestine of the catfish fed 3‐AY diet. The results suggest that dietary 3 g/kg autolysed brewer's yeast supplementation improves growth performance of African catfish without deleterious effect on liver functionality and gut morphology.  相似文献