Habitats of the British amphibians (3): river valley marshes

An attempt to assess the distribution and abundance of the common British amphibians in low-lying river valley marshes in part of Sussex is reported. These areas contain large amounts of freshwater habitat, mainly in the form of drainage dykes which intersect otherwise continuous tracts of (predominantly) pasture land. Indigenous amphibians were, however, rare: Triturus vulgaris was well-spread across some of the areas examined but population densities were very low; Rana temporaria was very infrequent, and a single specimen of Triturus helveticus was seen. T. cristatus and Bufo bufo were not encountered at all. On the other hand, the introduced frog Rana ridibunda was common and widespread in one sector of the marshes. Possible explanations for these observations are discussed.     

Habitats of the British amphibians (2): suburban parks and gardens

An investigation was made into the use of park and garden ponds as breeding sites by amphibians in Sussex, England. Of the five common British species, three were widespread in the study area; in order of abundance (of records) these were: Rana temporaria > Triturus vulgaris > Bufo bufo. Although more or less randomly distributed with respect to each other, records of amphibians generally became scarce near the most intensively developed areas of town centres. Neither pond volume, age nor local geology seemed to exert significant effects on species distribution. Aquatic vegetation was also unimportant, but fish did prove to be a relevant factor: toads tended to be absent from ponds not containing fish, whereas newts demonstrated a slight preference for such pools. Neither pH nor ionic score correlated with the distribution of any of the three species individually, but large old ponds of high ionic scores were associated with a greater abundance of toads compared with frogs in situations where the two species occurred together. Surveys indicated that in the study area about 15% of gardens contained ponds and of these at least 50% were used as breeding sites by amphibians.     

Tropical alluvial forest fragmentation in the eastern lowlands of Colombia (1939–1997)

Alluvial forests are under high pressure from human activities because of their value as agricultural, wildlife, timber and recreational land. Despite this, spatial patterns of alluvial forest deforestation are not well known. We studied forest alterations in a 2800 ha alluvial ecosystem using aerial photographs. During the study period (1939–1997), forests with canopy heights greater than 15 m (high canopy mature forest; HCM forest) decreased by 70·4 per cent while forests with canopy heights less than 15 m (low canopy mature forest; LCM forest) forests decreased by 51 per cent, producing a highly fragmented landscape. Factors responsible for forest change included human activities and river dynamics. Although most of the deforestation was related to human disturbance, almost 27 per cent of forest losses were due to channel migration of the Meta River. HCM forests were the most affected land cover since they are easily accessed, viable for logging and occurred on fertile soils, which are valuable for agriculture. LCM forests were less affected since their soil fertilities and inundation regimes were unfavourable to human uses, and thus, less prone to anthropogenic disturbances. Copyright © 2006 John Wiley & Sons, Ltd.     

Infant mortality and soil type: a case study in south-central England (with discussion)

We have analysed the differences in infant mortality for 1981 to 1990 in areas of contrasting soil types in south-central England. The soils overlie rocks of varied lithology and hydrology, ranging from porous and permeable Chalk and limestones, to the generally wet and impermeable Oxford and Lower Jurassic Clays. The study area comprises 504 administrative wards, for each of which the soil has been classified as being predominantly‘Wet’, ‘ Intermediate’ or ‘Dry’, depending on the degree of seasonal or periodic waterlogging. The soil classes used are those mapped by the Soil Survey of England and Wales and relate closely to the underlying geology. We find proportionately more infant deaths on the‘Wet’ soils, and a gradation towards lower infant mortality rates on the drier soils. Overall, infant mortality on the‘Wet’ soils is 31·9 percent greater than on the‘Dry’ soils, for reasons that remain unexplained. This relation between infant mortality and soil moisture remains after the effect of social class has been removed.     

Soil fertility requirements of root chicory (Cichorium intybus var. sativum): a review

Abstract

Root chicory is mainly grown in Belgium and the Netherlands with production also elsewhere in Europe, India, and South Africa. The world’s crop is worth an estimated US$56.04 million. India and South Africa focus on supplying root chicory to the blend coffee industry. Only limited and variable information is available on the fertilizer requirements of root chicory. Most studies on nitrogen (N) report that chicory in cooler, temperate regions requires 40–75?kg?N/ha compared to 200?kg?N/ha in warmer areas. Recommended rates for phosphorus (P) range from 0 to 69?kg?P/ha. Poor responses to potassium (K) are reported with recommended rates from 0 to 190?kg?K/ha. Application rates for sulfur (S) of 10–30?kg?S/ha have been suggested. Suitable micronutrient requirements and soil acid saturation and pH values for root chicory have not been published. To establish crop norms a concerted effort is needed to quantify the fertilizer use of root chicory.     

利用内部信息的农用自动引导行走车的研究(第4报)——适应农业环境的控制系统

研究的行走控制系统由软、硬两部分组成,通过建立系统的控制模型,开发了利用非线性理论进行线性变换的直线行走控制方法和利用预测控制进行曲线行走控制的方法,通过实验确定了控制系统的参数;改造设计了行走车的行走与操向部分。实现了计算机的行走控制。     

Effect of the choice of food composition table on nutrient estimates: a comparison between the British and American (Chilean) tables

Objective: To determine the level of agreement between the American (Chilean) and British food composition tables in estimating intakes of macronutrients and antioxidants. DESIGN, SETTING AND SUBJECTS: Information based on a food-frequency questionnaire with emphasis on antioxidants was collected from 95 Chileans aged 24-28 years. Nutritional composition was analysed using the British table of food composition and the American table of food composition modified by Chilean food items. Mean differences and limits of agreement (LOAs) of estimated intake were assessed. RESULTS: Mean differences between the two tables of food composition ranged from 5.3% to 8.9% higher estimates when using the American (Chilean) table for macronutrients. For micronutrients, a bias towards a higher mean was observed for vitamin E, iron and magnesium when the American (Chilean) table was used, but the opposite was observed for vitamin A and selenium. The intra-class correlation coefficient (ICC) ranged from 0.86 (95% confidence interval (CI) 0.81-0.91) to 0.998 (95% CI 0.995-1.00), indicating high to excellent agreement. LOAs for macronutrients and vitamins A and C were satisfactory, as they were sufficiently narrow. There was more uncertainty for other micronutrients. CONCLUSION: The American table gives relative overestimates of macronutrients in comparison to the British table, but the relative biases for micronutrients are inconsistent. Estimates of agreement between the two food composition tables provide reassurance that results are interchangeable for the majority of nutrients.     

Intake and sources of phylloquinone (vitamin K(1)) in 4-year-old British children: comparison between 1950 and the 1990s

OBJECTIVES: To compare dietary intake and sources of phylloquinone (vitamin K1) in 4-year-old British children between 1950 and the 1990s, and report their variation by sociodemographic factors.Design: Nationally representative samples of 4-year-olds from the longitudinal Medical Research Council National Survey of Health and Development (NSHD) (1950) and the cross-sectional National Diet and Nutrition Surveys (NDNS, 1992/93 and 1997). SETTING: Great Britain. SUBJECTS: Subjects were 4599 children born on 3-9 March 1946 (NSHD) and 307 children in the 1990s (NDNS). RESULTS: Geometric mean dietary phylloquinone intake was significantly higher in 1950 (39 mug day(-1), 95% confidence interval (CI) 37, 40) compared with the 1990s (24 mug day(-1), 95% CI 22, 25) (P<0.001). This difference remained when intake was expressed per MJ energy intake and per kilogram body weight, and after accounting for sex, region and occupational social class of the family. In 1950, phylloquinone intake in Scotland was significantly lower than in the rest of Britain. By the 1990s these regional differences had disappeared. Food sources of phylloquinone intake changed significantly between 1950 and the 1990s, with fats and oils contributing more and vegetables less, although vegetables contributed most (60% and 48%, respectively) to phylloquinone intake in both surveys. CONCLUSIONS: Phylloquinone intakes of children have decreased significantly since 1950. With the suggested need for adequate phylloquinone intake for optimal development and maintenance of bone and the cardiovascular system, the substantially lower phylloquinone intakes reported in children of the 1990s, compared with 1950, may have implications for the health of these two systems in later adulthood.     

Cultivation and nitrogen requirements for drilled and broadcast winter barley on a surface water gley (Gleysol)

Direct drilling, seed broadcasting plus rotovation, rotovation plus drilling and shallow mouldboard ploughing plus drilling were examined as possible quick and cheap alternatives to conventional mouldboard ploughing. The experiment ran for four seasons during 1980–1984. In the first season nitrogen was top-dressed at a uniform rate slightly greater than recommended, but in the final three seasons, dressings were either at the recommended rate or at 40% greater than the recommended rate. The topsoil (0–300 mm depth) of the experimental site was a sandy clay loam containing 4% w/w easily oxidisable organic matter overlying a slowly permeable subsoil. The experimental site was situated in south-east Scotland.In the first season, the non-ploughing treatments yielded less than conventional ploughing treatments because wet weather prevented adequate chemical weed control. In the remaining three seasons direct-drilling and broadcasting plus rotovation yielded, on average, 6% more grain than the normal ploughed and rotovated plus drilled treatments. Total root lengths were least in the direct-drilled and broadcast treatments and plant populations were independent of treatment. In the broadcast and direct-drilled treatments, P and K and organic matter were concentrated in the surface layer as were most of the roots. Of the non-ploughing treatments, the direct-drilled soil was the most compact. The broadcast seedbed was the least compact because there was no traffic after the soil was cultivated to incorporate the seed. Direct-drilled soil was suspected to have the most stable structure because it contained most organic matter, particularly at the surface. Weed control, timing of operations and control of traffic were critical to the success of direct drilling. Since adverse weather conditions may prevent the attainment of such a high standard of management, the recommended minimum cultivation requirement is ploughing to > 150 mm depth. Increasing the nitrogen rate to 40% above that recommended gave an economically worthwhile 0.6 t ha⁻¹ increase in grain yield.     

Fire is a key element in the landscape-scale habitat requirements and global population status of a threatened bird: The Mallee Emu-wren (Stipiturus mallee)

The Mallee Emu-wren (Stipiturus mallee) is a threatened, narrow-range passerine endemic to south-eastern Australia. To inform future conservation measures for this poorly known species, we used ecological niche factor analysis, habitat suitability modelling and distance sampling to determine landscape-scale habitat requirements and estimate the population size. Using GIS software, we integrated digital layers of ecogeographic variables with; (1) presence-only observations to derive and validate a habitat suitability model using ecological niche factor analysis, and (2) distance sampling to determine population distribution and densities across vegetation types. We detected populations in only five of seven reserves which they had occupied in 2000. We estimate the global population size to be 16,821 individuals (range 8431-39, 104), 68% greater than the previously estimated 10,000 individuals, with a single large reserve containing the majority (∼92%) of the global population. The Mallee Emu-wren is a habitat specialist, primarily occurring in mallee-Triodia vegetation that has not been burnt for at least 15 years. The highest densities were in vegetation associations containing at least a 15% cover of Triodia, however, time since the habitat was last burnt was the overriding factor in determining densities. Large-scale wildfires are a pervasive threat to the global status of the Mallee Emu-wren, and the risk to remaining populations is exacerbated by the adverse impact of prolonged drought and the potential for altered fire regimes caused by global warming. Evaluation of the global population status, and the continued wildfire threat warranted recent reclassification of the Mallee Emu-wren from Vulnerable to Endangered according to IUCN Red List categories and criteria.     

Assessing quality of clearcut habitats for amphibians: Effects on abundances versus vital rates in the southern toad (Bufo terrestris)

Forest clearcutting is a form of habitat alteration that drastically alters the landscape and may contribute to declines in amphibian populations. Indeed, many studies have documented decreases in amphibian abundances and species richness in clearcuts. The development of effective conservation strategies to reduce the effects of timber harvesting has been hindered by lack of knowledge of the mechanisms underlying these changes in abundance. To better understand the potentially negative consequences of forest clearcutting, we used field enclosures in forested and clearcut habitats to examine changes in the survival and growth of juvenile southern toads (Bufo terrestris) over a two-month period. We also conducted a comparative monitoring study using drift fences and pitfall traps in forests and clearcuts to determine the effect of clearcutting on the abundance of juvenile southern toads. We found no significant effect of habitat on the number of juvenile southern toads captured in forests or clearcuts. In contrast, the average survival of toads in clearcut enclosures was significantly reduced compared to that of toads in forested enclosures (17 ± 5% versus 61 ± 3%). Toads surviving in clearcuts were also significantly smaller than those surviving in forested enclosures (27.9 ± 0.1 mm versus 30.3 ± 0.8 mm SVL). Our results highlight the difficulty in interpreting abundance patterns as a sole metric for habitat comparison. Because there is much interest in studying the effects of habitat alteration on amphibian populations, we recommend that future studies place more emphasis on determining changes in vital rates of populations following habitat alteration.     

The ecology of extinction: population fluctuation and decline in amphibians

Even among widespread species with high reproductive potentials and significant dispersal abilities, the probability of extinctions should be correlated both with population size variance and with the extent of population isolation. To address how variation in demographic characteristics and habitat requirements may reflect on the comparative risk of species decline, I examined 617 time series of population census data derived from 89 amphibian species using the normalized estimate of the realized rate of increase, ΔN, and its variance. Amphibians are demonstrably in general decline and exhibit a great range of dispersal abilities, demographic characteristics, and population sizes. I compared species according to life-history characteristics and habitat use. Among the populations examined, census declines outnumbered increases yet the average magnitudes for both declines and increases were not demonstrably different, substantiating findings of amphibian decline. This gives no support for the idea that amphibian population sizes are dictated by regimes featuring relatively rare years of high recruitment offset by intervening years of gradual decline such that declines may outnumber increases without negative effect. For any given population size, those populations living in large streams or in ponds had significantly higher variance than did populations of completely terrestrial or other stream-dwelling amphibians. This could not be related to life-history complexity as all the stream-breeding species examined have larvae and all of the wholly terrestrial species have direct development without a larval stage. Variance in ΔN was highest amongst the smallest populations in each comparison group. Estimated local extinction rates averaged 3.1% among pond-breeding frogs, 2.2% for pond-breeding salamanders, and negligible for both stream-breeding and terrestrial direct-developing species. Recoveries slightly exceeded extinctions among European pond-breeding frogs but not among North American pond-breeding frogs. Less common species had greater negative disparities between extinctions and recoveries. Species with highly fluctuating populations and high frequencies of local extinctions living in changeable environments, such pond- and torrent-breeding amphibians, may be especially susceptible to curtailment of dispersal and restriction of habitat.     

Nitrogen cycling in two Norway spruce (Picea abies) ecosystems and effects of a (NH4)2SO4 addition

Nitrogen cycling in two Norway spruce (Picea abies (L.) Karst.) ecosystems in the ARINUS experimental watershed areas Schluchsee and Villingen (Black Forest, SW Germany) and initial effects of a (NH₄)₂SO₄ treatment are discussed. Although N reserves in the soils are similar and atmospheric N input is the same low to moderate level characteristic for many forested areas in SW Germany, N export by both seepage and streamwater differs considerably. At Villingen, deposited N is almost totally retained in the ecosystem, whereas at Schluchsee N export is the order of the input. This is explained by differences in forest management history. The Villingen site had been subject to excessive biomass export (e.g., litter raking) leading to unfavorable microbial transformations in the soil. In contrast, as a ‘relic’ of the former beech stand, the Schluchsee site is characterized by high biological activity in the soil with vigorous nitrification despite low pH values. Accordingly, the two ecosystems responded differently to the additional N input (150 kg NH₄ ⁺ -N ha^?1 as (NH₄)₂SO₄). Nitrification starting immediately in the Schluchsee soils led to continued Al mobilization and leaching of basic cations and NO₃ ^?. The availability of Mg, already deficient before treatment, further decreased due to Mg leaching and marked N uptake by the stand. In contrast, most of the added N in Villingen was immobilized in the soil. Hence, uptake by the stand and leaching of NO₃ ^? and cations was correspondingly lower than at Schluchsee. The results emphasize the problems associated with the definition of generally applicable values for ‘critical loads’ of N deposition.     

Beaver (Castor canadensis) as a surrogate species for conserving anuran amphibians on boreal streams in Alberta, Canada

We explored the use of beaver (Castor canadensis) as a surrogate species for amphibian conservation on small (1st-4th-order) streams in the Boreal Foothills of west-central Alberta. Anuran call surveys indicated that beaver create breeding habitat for the boreal chorus frog (Pseudacris maculata), wood frog (Rana sylvatica) and western toad (Bufo boreas). No calling males of any species were recorded on unobstructed streams. Wood frog, the most abundant species, exhibited high rates of juvenile recruitment on beaver ponds. Pitfall traps captured more wood frogs on beaver ponds versus unobstructed streams, and most individuals (84%) were young-of-year. Abundance of young-of-year was strongly correlated with percent landscape occupied by beaver ponds indicating that anurans captured along streams originated in beaver ponds. Based on a novel combination of a digital elevation model and aerial photographs examined with GIS, statistical models showed that the probability of beaver pond occurrence on streams was positively associated with stream order and dependent on the interacting effects of distance to nearest forestry cutblock and availability of beaver foods (Populus spp.). We propose that the distribution and abundance of beaver ponds could be determined over large areas quickly and inexpensively by remote sensing and used to identify and monitor amphibian habitat, and possibly, populations. This work establishes the pre-eminence of beaver-created wetlands as amphibian habitat in the Boreal Foothills and that the incorporation of dam-building patterns into forest management strategies could aid amphibian conservation.     

Effects of habitat loss and fragmentation on amphibians: A review and prospectus

Habitat loss and fragmentation are among the largest threats to amphibian populations. However, most studies have not provided clear insights into their population-level implications. There is a critical need to investigate the mechanisms that underlie patterns of distribution and abundance. In order to understand the population- and species-level implications of habitat loss and fragmentation, it is necessary to move from site-specific inferences to assessments of how the influences of multiple factors interact across extensive landscapes to influence population size and population connectivity. The goal of this paper is to summarize the state of knowledge, identify information gaps and suggest research approaches to provide reliable knowledge and effective conservation of amphibians in landscapes experiencing habitat loss and fragmentation. Reliable inferences require attention to species-specific ecological characteristics and their interactions with environmental conditions at a range of spatial scales. Habitat connectivity appears to play a key role in regional viability of amphibian populations. In amphibians, population connectivity is predominantly effected through juvenile dispersal. The preponderance of evidence suggests that the short-term impact of habitat loss and fragmentation increases with dispersal ability. However, species with limited dispersal abilities are likely to be equally imperiled by habitat loss and fragmentation over longer time periods. Rigorous understanding of the effects of habitat loss and fragmentation on amphibians will require species-specific, multi-scale, mechanistic investigations, and will be benefit from integrating large empirical field studies with molecular genetics and simulation modeling. Molecular genetic methods are particularly suited to quantifying the influences of habitat structure across large spatial extents on gene flow and population connectivity. Conservation strategies would benefit by moving from generalizations to species and process specific recommendations and by moving from site-specific actions to implementing conservation plans at multiple scales across broad landscapes.     

Quantitative determination of NPK uptake requirements of taro (Colocasia esculenta (L.) Schott)

Taro yield in many parts of the world is stagnant mainly due to conventional blanket recommendation of fertilizers, lower nutrient use efficiency and imbalance in the use of nutrients. The Quantitative Evaluation of Fertility of Tropical Soils (QUEFTS) model was used for determining the region specific balanced NPK uptake requirements and recommendations for a target yield of taro. The constants for minimum and maximum accumulation (kg cormel kg^?1 nutrient) of N (33 and 177), P (212 and 606) and K (25 and 127) were derived as standard model parameters. The results showed that taro requires N, P and K accumulation of 12.97, 2.75 and 17.47?kg t^?1 of cormel yield, suggesting an average NPK ratio in the plant dry matter of about 4.7:1:6.4. The NPK fertilizer requirements for different potential yield situations were also calculated. The results need to be validated in major taro growing regions.     

Balance and immobilization of (15NH4)2SO4 in a soil after the addition of Didin as a nitrification inhibitor

Summary We studied the effect of a dicyandiamide-based nitrification inhibitor (Didin) on the kinetics of N transfer in soil. Incubation at various temperatures was carried out in the laboratory after adding ammonium sulfate labelled with ¹⁵N. Adding Didin increased the incorporation of mineral N in a form that could not be extracted by KCl. The temperature modified the incorporation kinetics, but after 1 year, no difference remained between the two treatments in which the inhibitor had been added, and in which the total N immobilized was 26% of the ¹⁵N added compared with 13% in the control treatment. Losses of ¹⁵N, measured by difference, were greater in the control treatment (approximately 14%) than in the treatments containing Didin (10%). The addition of a nitrification inhibitor did not lead to the development of denitrifying microflora, the losses being mainly attributable to volatilization of NH₃ encouraged by the high pH of the soil. The immobilized N was mainly found in the NH₄ ⁺ form, adsorbed at the beginning of the incubation and subsequently in the amino acids. It seemed that the Didin effect on microflora was indirect, arising from longer maintenance of the tracer in NH₄ ⁺ form. This hypothesis was borne out by computing the gross phenomena. The variation in results reported in the literature can therefore be attributed to modifications in immobilization kinetics.     

Delineation of terrestrial reserves for amphibians: post-breeding migrations of Italian crested newts (Triturus c. carnifex) at high altitude

Little is known about the terrestrial phase of high-altitude populations of European amphibians, in spite of potentially important implications for conservation and management. We followed 51 adult Italian crested newts (Triturus carnifex) that emigrated from an ephemeral lake (Lake Ameisensee, 1282 m a.s.l., Northern Calcareous Alps, Austria) with radio-tracking. Transmitters were inserted into each newt's stomach and we collected data until it did not relocate for more than 1 week or until the transmitter was regurgitated. Most newts migrated in a north-westerly direction towards an old growth spruce forest. Subterranean shelters, mostly 5-80 cm deep burrows of small mammals located 13-293 m from the lake, were reached in between 4 h and 7.8 days. Twenty percent of T. carnifex shared their refuges with other congeneric species. Females migrated significantly further (median distance 168 m) than males (median 53 m). We propose a terrestrial core reserve extending 100 m from the furthermost terrestrial refuges of newts found with radio-tracking linked with patches of old-growth forest. This terrestrial reserve is substantially larger than has been suggested as sufficient in the recent literature.     

中国农业工程学会的建立发展

中国农业工程学会于1979年11月正式成立。本文简要介绍该会成立前的历史回顾和近十年来的迅速发展经过。四十年代初期,我国致力于农业的有识之士发起成立中国农具学会;四十年代中期,我国留美学习农业工程专业的30多位学人,在大洋彼岸发起筹备中国农业工程师学会;七十年代后期,在有关部门的支持下,筹备成立了中国农业工程学会。十年来该会迅猛发展,目前已拥有23个地方学会、6个工作机构、11个专业学术委员会和2个事业机构,拥有全国会员5100名,其前途广阔,方兴未艾。