bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecosystem monitoring in the development of sustainable fisheries in Lake Tanganyika
Authors: Mölsä H. , Sarvala J. , Badende S. , Chitamwebwa D. , Kanyaru R. , Mulimbwa M. , Mwape L.
Published: October 2002

Ecological, socio-economical, and institutional elements were combined when the Lake Tanganyika Framework Fisheries Management Plan was designed as the outcome of the FAO/Finland Lake Tanganyika Research Project in 1992–1999. The scientific synthesis provided a physical and limnological reference for understanding the biological productivity of the Lake Tanganyika pelagic ecosystem. Socio-economic surveys and community referenda were conducted to introduce and evaluate the proposed management measures amongst fishers, fish processors, and traders. During the transitional period prior to the implementation phase of the Fisheries Management Plan, an ecosystem approach in its simplest form is being utilized in monitoring the lake and fishery. Key parameters in meteorology and water movements are followed to assess the physical forces affecting upwelling, vertical mixing, and flow regimes of the pelagic ecosystem. Basic limnology, zooplankton community, and fish biology are studied to complement the time series of earlier project data. The long-term monitoring helps to identify which changes are caused by, for example, global climate change, and which ones may be owing to the fishery or other human activities. Some correlation occurs between the seasonal development of catch per unit effort of Stolothrissa tanganicae and copepod biomass. Sound data collection, timely conclusions, and appropriate reporting are essential for the decision-making in regard to management measures and applying the precautionary approach of FAO Code of Conduct for Responsible Fisheries. Strong personnel commitment and close links to the local fishery community are needed to supply the local development attempts with valuable scientific advice. In Tanganyika the institutional sustainability is required to harmonise legal arrangements and establish regional organization. The project results show the lake fisheries are best managed for the whole lake rather than separately by each country.
Pelagic food web as the basis of fisheries in Lake Tanganyika: A bioenergetic modeling analysis
Authors: Sarvala Jouko , Tarvainen Marjo , Salonen Kalevi , Mölsä Hannu
Published: October 2002

Fisheries in Lake Tanganyika, East Africa, are mainly based on two predominantly planktivorous clupeids (Stolothrissa tanganicae and Limnothrissa miodon) and a centropomid predator (Lates stappersi), caught with lift nets, purse seines, and beach seines by traditional, artisanal, and industrial fishers. The biological basis and sustainability of the present fisheries were assessed in a comprehensive project “Research for the Management of the Fisheries on Lake Tanganyika” in 1992–1998. Production in the whole lake was estimated for the entire pelagic food chain leading to the commercially important fish species. Preliminary calculations based on a constant production efficiency suggested that while the crustacean zooplankton production was sufficient to maintain the estimated planktivorous fish production, the food requirements of piscivorous fish exceeded the production of potential prey.

Here, the food consumption by pelagic fish was estimated with a bioenergetic model using actual diet data for different size classes. In order to reveal potential differences in the food web sustaining the fisheries, separate calculations were made for different parts of the lake, which harbor different fish community compositions and size structures. According to the bioenergetic calculations, the food requirements of the planktivorous fish were a reasonable fraction (25–38%) of the zooplankton production. In contrast, very high predation pressure was indicated on shrimps (73–104%), and especially on prey fish (>100%), suggesting that the total biomass of the prey planktivores had been underestimated, or that the predatory fish biomass was overestimated.

Annual catch of Stolothrissa tanganicae was 18–35% of estimated production in individual countries and 25% in the whole lake. For Limnothrissa miodon , the corresponding ratio was moderately low (19–22%) in Tanzania and Zambia, but high (55–61%) in Democratic Republic of Congo and Burundi; in the whole lake, the exploitation rate was 30%. For Lates stappersi , the catch/production ratios were very high (76–112%) in all parts of the lake, and even the lakewide average exploitation rate was as high as 94%. These figures suggest that the present clupeid fishery is on a sustainable basis, while the Lates populations are clearly overexploited.
Monitoring, assessing, and managing fish stocks in Lake Malawi/Nyassa: Current approaches and future possibilities
Authors: Darwall W. R. T. , Allison E. H.
Published: October 2002

Approaches to the provision of advice on fishery management are changing from reliance on single species stock assessments to multi-species, multi-gear, and ecosystem approaches. Many of these new approaches may, however, be too expensive to apply to small-scale fisheries in developing countries. The fish stocks of Lake Malawi/Nyassa are currently managed by restrictions on fishing gears, fishing areas, and fishing times. Catch statistics and an annual frame survey of fishing effort provide input data for stock assessment studies that are used to derive these recommendations. This management approach is ineffective with several important fish stocks in decline, reports of local species extinctions, and changes in community structure as a result of the disappearance of larger, more valuable species. Failure to enforce management regulations results partly from an imbalance of economic and human resource allocation between the collection of monitoring data, timely analysis of that data, production of workable recommendations, and enforcement of these recommendations. We recommend redressing the imbalance through a reduction in the scale of catch surveys so that resources can be redirected towards data processing, timely provision of advice, management actions, and enforcement. A number of further modifications are recommended to improve and better match the levels of precision of catch and effort data. The implications of current moves away from “state-led” management to “community-based” management are discussed briefly.
The relationship between organic matter, invertebrates, and bacteria in the sediments of Lake Malawi
Authors: Buat Patrick , Ramlal Patricia S. , Guildford Stephanie J.
Published: October 2002

In the surface sediments below the oxic-anoxic interface in meromictic Lake Malawi, there is little or no evidence of biological activity. As the water depth increases, even in sediments within the oxic zone microbial activity, as measured by 14C leucine incorporation, decreases; the benthic invertebrates decrease in biomass and diversity; and the amount of detrital material remaining in the sediments increases from <1% at 10 m to >14% at 125 m. This relationship with depth could be owing to several factors. At shallower depths, there is terrestrial material available for bacteria to use, as well as detrital material derived from autochthonous production. This detrital material can be degraded in the sediments by the benthic invertebrates, which release dissolved organic carbon and smaller particles through excretion that bacteria can use. As the water depth increases, the bacteria in the water column are able to degrade much of the planktonic debris, leaving the more refractory carbon particles to settle to the sediment. It appears that when there are enough benthic invertebrates, there is still substantial bacterial activity. As the depth increases, the benthic invertebrates disappear and, although there is still detrital carbon available, the bacteria appear unable to utilize it. We suggest that the benthic invertebrates are essential to the processing of detrital carbon and a shift in the degree of anoxia within the lake could seriously alter the cycling of carbon.
Sustainable management of the African Great Lakes: Science for development?
Authors: Allison Edward H.
Published: October 2002

The African Great Lakes have recently been the subject of several major scientific studies. Many of these studies were undertaken within projects aiming to support management programs to conserve the environment and ensure sustainable resource use. This article argues that such projects could be enhanced by more careful attention to “process” issues. In particular, the article highlights that to have positive management impact, such projects need a clear understanding of what is implied by “sustainable management,” careful attention to participatory research and decision-making processes, and critical analysis of widely-held assumptions about the causes of, and potential solutions to, environmental change in Africa. This shift in emphasis from scientific project outputs (what you do) to the process of linking science to policy and management (the way that you do it) could ensure the management decisions made are based on sound science, but also account for issues of equity, livelihood security, and empowerment. This should ensure that science and development agendas are engaged more constructively in efforts towards sustainable management.
Soft sediment as a constraint on the spread of the zebra mussel in western Lake Erie: Processes and impacts
Authors: Coakley John P. , Rasul N. , Ioannou S. E. , Brown G. R.
Published: October 2002

The zebra mussel (Dreissena), inadvertently introduced to the Great Lakes in 1986, has since expanded to cover most of the shallow-water, hard substrates in Lakes Erie and Ontario. Colony densities exceed 300,000 per m2 in some bedrock areas of western Lake Erie. The objective of this study was to investigate the spread of zebra mussel onto soft sediment areas of the western basin of Lake Erie and to identify natural controls on the large-scale colonization of such sediments. Combined side scan sonar, underwater video imagery, and direct diver observation showed three modes of viable zebra mussel colonies in soft substrates: 1) attachment to zebra mussel shell debris deposited in linear troughs (stripes); 2) attachment to shells built up over hard substrates intermittently covered by soft sediments (footballs); and 3) as isolated clumps (druses) attached to dropstones, unionid clams, or their shells. Their spatial distribution suggests that zebra mussel expansion onto soft sediments is supplied primarily by nearby hard substrate areas. Zebra mussel populations living on soft sediment have the normal size distribution as those found on hard surfaces, often with a bimodal or trimodal character, representing cohorts of different ages. At the sites studied, there was a large proportion of dead shells, suggesting colonization over an extended period, as well as a relatively high mortality rate due to burial by periodic catastrophic sedimentation after storms. This vulnerability and the need to be near to source areas make it unlikely that the zebra mussel (D. polymorpha) will continue to expand into areas of soft sediment remote from hard substrate areas. The impact of the zebra mussel colonies on important textural properties of the substrate was not dramatic, but median grain diameter was significantly finer, organic carbon significantly higher, and sediment consistency more clayey below zebra mussel mats. Metal content was generally higher in the samples below zebra mussel mats, but the differences were statistically significant only in the case of iron and maganese. However, the sediment concentrations of metals at all sites were much greater than those at the remote Mid-basin site that was barren of zebra mussels, suggesting an overall metal enrichment near zebra mussel colonies.
Planktonic ciliates of the North American Great Lakes: Lakes Superior, Huron, Erie, and Ontario
Authors: Munawar Mohiuddin , Lynn Denis H.
Published: October 2002

Lakewide information about the planktonic ciliates of the North American Great Lakes has been lacking. Previously published data are limited spatially and temporally and based on few samples. This article focuses on ciliates sampled in lakewide longitudinal surveys conducted by Fisheries and Oceans Canada in four of the Great Lakes. Extensive sampling (n = 442) was conducted at stations distributed across Lakes Superior, Huron, Erie, and Ontario in various years from 1979–2000. The study focuses on abundance, biomass, and size spectrum. Our data demonstrate that ciliates contribute significantly to the planktonic communities of the Great Lakes. Mean abundance ranged from <1.0 to >14,000 l−1. Mean biomass ranged from <1.0 to >680 mg m-3. The mean abundance and biomass values are comparable to those reported earlier by other investigators from Great Lakes and other temperate lakes. Abundance and biomass differences, between the upper and lower Great Lakes, decreased from the 1980s compared to 1990s sampling when four- to ten-fold and two-fold decreases were recorded for the lower and upper Great Lakes, respectively. The six most common genera in these samples were Askenasia, Halteria, Balanion, Strobilidium, Strombidium, and Urotricha.

The ciliate community was dominated by cells <30 μm equivalent spherical diameter. Pre- and post-zebra mussel size spectra of ciliates were compared for Lakes Erie and Ontario. The mean equivalent spherical diameter was significantly greater in Lake Erie in the post years compared to pre-mussel period. On the other hand, in Lake Ontario the mean diameter was significantly greater in the pre-mussel period than the post. It is likely that shifts in these distributions may be due to shifts in the relative abundance of the prey species of the ciliates. Among other factors, zebra mussels may be indirectly influencing the size-frequency distribution of the ciliate community.
Statistical trend analysis and classification of Lake Erie with size-fractionated primary production changes
Authors: El-Shaarawi A. H. , Munawar M.
Published: October 2002

The article uses exploratory and change-point methods to investigate changes in the level and spatial pattern of size-fractionated primary productivity in Lake Erie during the summers of 1992 and 1996. In July 1992 and 1996 primary productivity measurements were made at 44 and 34 sampling stations, respectively, and separated into three size classes (<2 μm, 2 to 20 μm, >20 μm). Spatially, the overall productivity increased gradually from east to west, with the medium size class showing the highest rate of increase. The 1996 productivity was higher than that of the 1992 in almost all size classes. The 1996 level appears to be nearly proportional to the 1992 level for the medium and larger size classes. For the small size class, the increase occurs only in the western region of the Lake. These findings were supported graphically and by statistical modelling. Using geographical coordinates of sampling locations as explanatory variables, change-point analysis is used to separate the lake into regions such that each region has its own regression regime. The findings indicate that the characteristics of the east basin extend beyond its traditional physical boundaries and into the central basin. This analysis provides a more accurate characterization of the lake than the traditional practice of assuming that lake is divided into three homogeneous basins. Here the lake is divided into regions where the concentration within each region is allowed to vary but according to its own regression model.
CUTTING CARBON EMISSIONS AT A PROFIT (PART I): OPPORTUNITIES FOR THE UNITED STATES
Authors: Krause Florentin , DeCanio Stephen J. , Hoerner J. Andrew , Baer Paul
Published: October 2002

This article identifies and corrects shortcomings in recent modeling studies on the economics of reducing greenhouse gas emissions in the United States. The major assessments of the Kyoto Protocol—by the U.S. Energy Information Administration, the Clinton White House Council of Economic Advisers, the U.S. Department of Energy Interlaboratory Working Group, and the Stanford Energy Modeling Forum—are found to be seriously incomplete. Each study omits one or several of four major cost‐reducing policy options, resulting in cost estimates that are far too pessimistic.

In the present study, these shortcomings are overcome through the integrated evaluation of all major cost‐cutting policy options within a coherent least‐cost framework. Three domestic policies—a national carbon cap and permit trading program, productivity‐enhancing market reforms and technology programs, and recycling of permit auction revenues into economically advantageous tax cuts—are combined with international emissions allowance trading.

This analysis shows that an integrated least‐cost strategy for mitigating U.S. greenhouse gas emissions would produce an annual net output gain of roughly 0.4% of GDP in 2010 and about 0.9% of GDP in 2020. On a cumulative net present value basis, the United States would gain $250 billion by 2010 and $600 billion by 2020. International flexibility mechanisms (including emissions trading) are of only secondary significance in realizing these productivity, output, and welfare gains.
INCREASING STREAMFLOW TO SUSTAIN SALMON AND OTHER NATIVE FISH IN THE PACIFIC NORTHWEST
Authors: Jaeger William K. , Mikesell Raymond
Published: October 2002

According to biologists, increasing streamflows is among the measures necessary to protect salmon and other native fish in the Pacific Northwest. Yet our understanding of the costs and most cost‐effective approaches is hampered by lack of comparative experience. This article attempts to address both of these issues. The analysis finds that the costs of streamflow augmentation may be modest, between $1 and $10 per capita per year for the region. Apart from largE‐scale actions on the Snake and Columbia Rivers, we find that streamflow augmentation will require decentralized approaches, and their cost‐effective implementation will require localized scientific information, constant monitoring, and hands‐on management to acquire water through purchases, leases, and contingent contracts when and where appropriate.
A PORTFOLIO OF THREATS TO AMERICAN AGRICULTURE
Authors: Blank Steven C.
Published: October 2002

This article outlines some of the biggest economic issues threatening the long‐term survival of American farming and ranching. In general, the threats are derived from the intersection of global and local scales of decision making. International economic development, personal finance decisions, and political, social, and environmental issues are all part of the portfolio of threats. At the top of the list of threats is the bottom line. Profit margins are being squeezed, causing producers to diversify out of agriculture to earn sufficient returns to enable them to remain in agriculture as long as possible. American policy is expected to allow agriculture to continue shrinking because (1) the sector is losing its comparative advantage, and (2) it may become a deadweight loss to the economy.
MEASURING THE EFFECT OF SEXUAL ORIENTATION ON INCOME: EVIDENCE OF DISCRIMINATION?
Authors: Berg Nathan , Lien Donald
Published: October 2002

The effect of nonheterosexuality on individual income is estimated using 1991–1996 General Social Survey data. Other researchers have concluded that homosexuals earn less than similarly qualified workers, in contrast to the popular perception that homosexuals are more affluent than nonhomosexuals. Using improved statistical techniques, this article finds noticeable earnings effects that go in opposite directions across genders. Nonheterosexual men earn 22% less than heterosexual men, and nonheterosexual women earn 30% more than heterosexual women. These findings, viewed together with previous empirical work on this topic, help narrow the field of theories that can explain the sexual‐orientation earnings gaps present in the data.
EFFECTS OF HEAVY DRINKING IN COLLEGE ON STUDY EFFORT, GRADE POINT AVERAGE, AND MAJOR CHOICE
Authors: Wolaver Amy M.
Published: October 2002

This article measures the effects of college drinking on study hours, grade point average (GPA), and major choice using simultaneous equation models and data from the 1993 College Alcohol Study. Binging and intoxication decrease GPA directly and indirectly by reducing study hours. Greater frequency of drinking increases the effect on study hours but not the total effect on GPA. College drinking increases the probability of choosing a business major but decreases the probability of choosing engineering. Simulations show that the effects of heavy drinking on GPA and major choice reduce future weekly earnings by between 0.3 and 9.8%.
DO HMOS ENCOURAGE PREVENTION? AN ANALYSIS OF ALTERNATIVE HEALTH CARE PLANS
Authors: Miceli Thomas J. , Heffley Dennis
Published: October 2002

We examine consumers' choice of preventive care and providers' choice of capacity (which affects the transaction costs of consuming health care) under alternative health care financing plans. We show that consumers choose Pareto‐optimal prevention and providers choose optimal capacity under a pure feE‐for‐service (FFS) plan and under a mixed plan that includes an up‐front fee and a fee for service. Under a pure prepaid plan, however, consumers may over‐ or underconsume prevention. In the former case, capacity restrictions under such a plan (e.g., long office waits, limited options) may be interpreted as a second‐best response to overconsumption. We also find that the dollar costs of health care are higher under the prepaid plan. These conclusions cast doubt on some of the presumed advantages of HMOs.
THE IMPACT OF CASINO GAMBLING ON PERSONAL BANKRUPTCY FILING RATES
Authors: Barron John M. , Staten Michael E. , Wilshusen Stephanie M.
Published: October 2002

Personal bankruptcies soared in the United States between 1994 and 1998. One activity that can precipitate personal financial crises and that has also experienced dramatic growth is commercial gambling, especially casino gambling. This article builds a simple model of bankruptcy choice and empirically tests the model using unique county‐level data on debt, income, household age, population density, and casino gambling as well as state measures of employment and marital stability, health insurance coverage, and garnishment restrictions. The authors find that the proximity of casino gambling appears to be associated with higher bankruptcy rates, but that the local impact is far more pronounced than the influence of casino gambling on the national filing rate. To quantify the magnitude of the impact, the analysis predicts over a 5% decline in 1998 filing rates for counties surrounding a casino, and a 1% decline in the nationwide filing rate if one were to eliminate casino gambling. Consequently, although casino gambling exerts important local effects, nationwide the incidence and growth of casino gambling does not explain much of the rise in bankruptcies during the past decade.
DID THE NEW ECONOMY VANQUISH THE REGIONAL BUSINESS CYCLE?
Authors: Partridge Mark D. , Rickman Dan S.
Published: October 2002

The record economic expansion of the 1990s has led many to speculate that the United States is experiencing a New Economy. Along with the belief that strong growth could continue without accelerating inflation, there has been speculation that regional disparities in economic performance are disappearing in the New Economy. The historical patterns of state labor market performance are compared with recent trends to assess whether the 1990s represent a departure from the past. The conclusion is that regional disparities continue to exist. If anything, many of the historical patterns are stronger today than in the 1970s and 1980s.
THE PATH OF TECHNOLOGY DIFFUSION: WHICH NEIGHBORS TO LEARN FROM?
Authors: Zhang Xiaobo , Fan Shenggen , Cai Ximing
Published: October 2002

This study uses a panel data set of 25 years over 280 districts in rural India and applies a geographic information systems (GIS) program to investigate the regional neighborhood effect on the rate of diffusion of new technologies. The results show that in the technology diffusion process, the early successful adopters have a larger effect on neighboring adopters than do the early unsuccessful adopters. Hence, use of the aggregate or the simple average of adoption rate among neighborhoods as a proxy for the neighborhood effect, a common practice in the learning literature, may be inappropriate. We also find that education and irrigation play important roles in facilitating technology diffusion.
ENDOGENOUS PROTECTION IN A TRADE LIBERALIZING ECONOMY: THE CASE OF SOUTH AFRICA
Authors: Holden Merle , Casale Daniela
Published: October 2002

This article aims to establish the changes that occurred in the institutional structures governing trade policy in South Africa during the period 1990–1998. It also examines the forces that influenced the application of tariff policy by the major tariff‐setting bodies by applying various theories of endogenous protection to their decisions. Using firm‐level data on applications made to the Board on Tariffs and Trade, the study finds that when estimating a probit model, employment considerations rather than capital invested influenced the board's decisions to grant protection. In addition, the board is found to have granted protection even in the face of tariff lines having been bound under the Uruguay Round. The article argues that this should not be interpreted as a reversal of the trade liberalization but rather as an attempt by the board to cushion firms from the acceleration in the tariff rationalization process that occurred after the GATT offer. Finally, it is suggested that the board's response to changes in import penetration ratios between industries that were considered organized provides prima facie evidence of the superior lobbying ability of such industries.
Design strategies of sea urchin teeth: structure, composition and micromechanical relations to function
Authors: Wang R. Z. , Addadi L. , Weiner S.
Published: October 2002

The teeth of sea urchins comprise a variety of different structural entities, all of which are composed of magnesium–bearing calcite together with a small amount of organic material. The teeth are worn down continuously, but in such a way that they remain sharp and functional. Here we describe aspects of the structural, compositional and micromechanical properties of the teeth ofParacentrotus lividususing scanning electron microscopy, infrared spectrometry, atomic absorption, X–ray diffraction and microindentation. The S–shaped single crystalline calcitic fibres are one of the main structural elements of the tooth. They extend from the stone part to the keel. The diameter of the fibres increases gradually from less than 1 micrometre at the stone tip to about 20 micrometres at the keel end, while their MgCO3contents decrease from about 13 mol per cent to about 4.5 mol %. Each fibre is coated by a thin organic sheath, and surrounded by polycrystalline calcitic discs containing as much as 35 mol % MgCO3. This structure constitutes a unique kind of gradient fibre–reinforced ceramic matrix composite, whose microhardness and toughness decrease gradually from the stone part to the keel. Primary plates are also important structural elements of the tooth. Each primary plate has a very unusual sandwich–like structure with a calcitic envelope surrounding a thin apparently amorphous CaCO3layer. This central layer, together with the primary plate/disc interface, improves the toughness of this zone by stopping and blunting cracks. The self–sharpening function of the teeth is believed to result from the combination of the geometrical shape of the main structural elements and their spatial arrangement, the interfacial strength between structural elements, and the hardness gradient extending from the working stone part to the surrounding zones. The sea urchin tooth structure possesses an array of interesting functional design features, some of which may possibly be applicable to materials science.
Subfossil mammalian tracks (Flandrian) in the Severn Estuary, S. W. Britain: mechanics of formation, preservation and distribution
Authors: Allen J. R. L.
Published: October 2002

Mammalian tracks and trackways are widely preserved at all stratigraphical levels in the Flandrian sediments of tidal mudflat and marsh origins which formed over the last 8000–9000 years on the marginal wetlands of the inner Bristol Channel and Severn Estuary. The fauna recorded in this way, however, is less diverse than that known from the few, small assemblages of skeletal remains, including some from archaeological sites, so far assessed. Missing or rarely represented in terms of tracks are the smaller of the large mammals. Humans are represented by tracks throughout the Flandrian deposits. In the earlier Flandrian, they were accompanied by deer and aurochs which gave way, in the later Flandrian, to domesticated cattle and sheep/goat; there are sporadic indications of the presence of horse. Wolf/dog, represented by just two records, is the only smaller large mammal so far recorded as a track.

The tracks were made, modified, and eventually preserved under a wide variety of sedimentological conditions on the margins of the estuary. Those environmental conditions constrained the quality of the anatomical evidence preserved in the tracks but can be inferred from the character of the tracks. Field experiments suggest that the moisture content of the sediment at the time was crucial to the general nature of the tracks. The mudflat–marsh silts which received the tracks varied from semi–liquid to firm, depending on tidal and seasonal factors and on the elevation of the sedimentary surface relative to the tidal frame. Some tracks were made in marsh peats which offered little resistance. Deep tracks preserving little detail were produced in weak sediments of high moisture content; tracks formed in strong, firm muds retained full anatomical detail. Referring to mechanical theory, and to a series of laboratory experiments using plasticine, the act of making a track is shown to be similar in character and effect to the indentation of an ideal elastic–plastic material by a punch. The punch represents the descending limb of the animal, the face of the punch the sole of the animal's foot, and the elastic–plastic material the sediment which is pierced and deformed by the downward action of the limb. The character of the experimental tracks, and the range and relative size of the deformation structures they include, is qualitatively similar to what is recorded from the field. Many of the tracks recorded from the field were variously modified in a changeable and dynamic environment before final burial and preservation.
Correlated evolution and independent contrasts
Authors: Price Trevor
Published: October 2002

The use of the independent contrast method in comparative tests is studied. It is assumed that: (i) the traits under investigation are subject to natural selection; (ii) closely related species are similar because they share many characteristics of their niche, inherited from a common ancestor; and (iii) the current adaptive significance of the traits is the focus of investigation. The main objection to the use of species values in this case is that third variables which are shared by closely related species confound the relationship between the focal traits. In this paper, I argue that third variables are largely not controlled by the contrast methods, which are designed to estimate correlated evolution. To the extent that third variables also show correlated evolution, the true relationship among the traits of interest will remain obscured. Although the independent contrast method does not resolve the influence of third traits it does, in principle, provide a greater resolution than the use of the species mean values. However, its validity depends on the applicability of an evolutionary model which has a substantial stochastic component. To illustrate the consequences of relaxing this assumption I consider an alternative model on an adaptive radiation, where species come to fill a fixed niche space. Under this model, the expected value for the contrast correlation differs from that for the species correlation. The two correlations differ because contrasts reflect the historical pattern of diversification among species, whereas the species values describe the present–day relationships among the species. If the latter is of interest, I suggest that assessing significance based on the species correlations can be justified, providing that attention is paid to the role of potentially confounding third traits. Often, differences between contrast and species correlations may be biologically informative, reflecting changes in correlations between traits as an adaptive radiation proceeds; contrasts may be particularly useful as a means of investigating past history, rather than current utility of traits.
Cerebral oxygenation and haemodynamics in the foetus and newborn infant
Authors: Wyatt John S.
Published: October 2002

Quantitative techniques have been derived for the measurement of global cerebral blood flow, cerebral blood volume, its reponse to changing arterial carbon dioxide tension and mixed cerebral venous saturation in the human newborn undergoing intensive care. Normal ranges have been established and significant disturbances of cerebral oxygenation and perfusion have been demonstrated in a variety of pathological conditions. Recently, absolute cerebral deoxyhaemoglobin concentration has been obtained in the newborn using second differential spectroscopy. When combined with the measurement of total cerebral haemoglobin concentration, the mean saturation of cerebral blood (SmcO2) may be obtained, allowing global cerebral oxygenation to be determined continuously in the intensive care unit.

Marked changes in the concentrations of cerebral oxy– and deoxyhaemoglobin have been observed in foetuses undergoing labour. Measurements of SmcO2from the foetal brain prior to delivery have shown the unexpected close correlation with acid–base status at birth Although movement artefact remains a theoretical risk during uterine contractions, preliminary measurements of optical path length by intensity–modulated spectroscopy have demonstrated only small fluctuations. In future the clinical application of time, phase and spatially resolved spectroscopy is likely to improve both the quantitative accuracy and the regional specificity of physiological measurements in the foetal and neonatal brain.
Managing water resources for crop production
Authors: Wallace J. S. , Batchelor C. H.
Published: October 2002

Increasing crop production to meet the food requirements of the world's growing population will put great pressure on global water resources. Given that the vast freshwater resources that are available in the world are far from fully exploited,
globally
there should be sufficient water for future agricultural requirements. However, there are large areas where low water supply and high human demand may lead to
regional
shortages of water for future food production. In these arid and semi–arid areas, where water is a major constraint on production, improving water resource management is crucial if Malthusian disasters are to be avoided. There is considerable scope for improvement, since in both dryland and irrigated agriculture only about one–third of the available water (as rainfall, surface, or groundwater) is used to grow useful plants. This paper illustrates a range of techniques that could lead to increased crop production by improving agricultural water use efficiency. This may be achieved by increasing the total amount of water available to plants or by increasing the efficiency with which that water is used to produce biomass. Although the crash from the Malthusian precipice may ultimately be inevitable if population growth is not addressed, the time taken to reach the edge of the precipice could be lengthened by more efficient use of existing water resources.
Mutuality and solidarity: assessing risks and sharing losses
Authors: Wilkie David
Published: October 2002

Mutuality is the principle of private, commercial insurance; individuals enter the pool for sharing losses, and pay according to the best estimate of the risk they bring with them. Solidarity is the sharing of losses with payment according to some other scheme; this is the principle of state social insurance; essential features of solidarity are comprehensiveness and compulsion. Private insurance is subject to the
uberrima fides
principle, or utmost good faith; each side declares all it knows about the risk. The Disability Discrimination Act requires insurers to justify disability discrimination on the basis of relevant information, actuarial, statisical or medical, on which it is reasonable to rely. it could be very damaging to private insurance to abandon
uberrima fides
. However, although some genetic information is clearly useful to underwriters, other information may be so general as to be of little use. The way in which mortality rates are assessed is also explained.
Genetic diversity and disease susceptibility
Authors: Bodmer Walter F.
Published: October 2002

The range of genetic diversity within human populations is enormous. Genetic susceptibility to common chronic disease is a significant part of this genetic diversity, which also includes a variety of rare, clear–cut, inherited diseases. Modern DNA–based genomic analysis can now routinely lead to the identification of genes involved in disease susceptibility, provides the basis for genetic counselling in affected families, and can be used more widely for a genetically targeted approach to disease prevention. This naturally raises problems concerning the use of information not just in an individulal's decisions, but also for employment, and health and life insurance.
Representing geometrical knowledge
Authors: Anderson James A. D. W.
Published: October 2002

This paper introduces perspex algebra which is being developed as a common representation of geometrical knowledge. A perspex can currently be interpreted in one of four ways. First, the algebraic perspex is a generalization of matrices, it provides the most general representation for all of the interpretations of a perspex. The algebraic perspex can be used to describe arbitrary sets of coordinates. The remaining three interpretations of the perspex are all related to square matrices and operate in a Euclidean model of projective space–time, called perspex space. Perspex space differs from the usual Euclidean model of projective space in that it contains the point at nullity. It is argued that the point at nullity is necessary for a consistent account of perspective in top–down vision. Second, the geometric perspex is a simplex in perspex space. It can be used as a primitive building block for shapes, or as a way of recording landmarks on shapes. Third, the transformational perspex describes linear transformations in perspex space that provide the affine and perspective transformations in space–time. It can be used to match a prototype shape to an image, even in so called ‘accidental’ views where the depth of an object disappears from view, or an object stays in the same place across time. Fourth, the parametric perspex describes the geometric and transformational perspexes in terms of parameters that are related to everyday English descriptions. The parametric perspex can be used to obtain both continuous and categorical perception of objects. The paper ends with a discussion of issues related to using a perspex to describe logic.
Preface to Immune effector mechanisms in parasitic infections, a Discussion held at The Royal Society on the 19 and 20 February 1997.
Authors: Liew F. Y. , Vickerman K.
Published: October 2002

Preface to the published proceedings of Immune effector mechanisms in parasitic infections, a Discussion held at The Royal Society on the 19 and 20 February 1997, organized and edited by F. Y. Liew and K. Vickerman.
Antigenic variation inGiardia lambliaand the host's immune response
Authors: Nash Theodore E.
Published: October 2002

Giardia lamblia, a protozoan parasite of the small intestine of humans and other animals, undergoes surface antigenic variation. The antigens involved belong to a family of variant–specific surface proteins (VSPs), which are unique, cysteine–rich zinc finger proteins. The patterns of infection in humans and animals fail to show the expected cyclical waves of increasing and decreasing numbers of parasites expressing unique VSPs. Nevertheless, changes in VSP expression occur within the populationin vivoowing to selection of VSPs by both immune and non–immune mechanisms. After inoculation of a singleG. lambliaclone (able to persist in in the absence of immune pressure) expressing one VSP (greater than 90 per cent) into mice or humans, the original VSP continues to be expressed until 2 weeks post inoculation (p.i.), when many other VSPs gradually replace it. Selection by immune–mediated processes is suggested because switching occurs at the same time that humoral responses are first detected. In most mouse strains, switching also occurs at about two weeks. Almost all trophozoites are eliminated at three weeks (p.i.), but a barely detectable infection persists over months. In neonatal mice, apparent self–cure is delayed until the sixth or seventh week. Antigenic switching does not occur in adult or neonatal SCID mice, but does occur in neonatal nude mice, thus implicating B–cell–mediated mechanisms in immune switching. Not all VSPs are expressed to the same degreein vivo. Some VSPs appear to be preferentially selected whereas others are eliminated on a non–immune basis. In infections in which immunity does not play a role, such as in SCID mice, and during the first week of infection in immunocompetent mice or gerbils, persisting VSPs are preferentially expressed and maintained whereas non–persisting VSPs are replaced within the first week of infection. The purpose of antigenic variation may be presentation of a wide assortment of VSPs to hosts, increasing the chance of a successful initial infection or reinfection. Immune selection of variants comes into play following biological selection.
Parietal and hippocampal contribution to topokinetic and topographic memory
Authors: Berthoz Alain
Published: October 2002

This paper reviews the involvement of the parietal cortex and the hippocampus in three kinds of spatial memory tasks which all require a memory of a previously experienced movement in space. The first task compared, by means of positron emission tomography (PET) scan techniques, the production, in darkness, of self–paced saccades (SAC) with the reproduction, in darkness, of a previously learned sequence of saccades to visual targets (SEQ). The results show that a bilateral increase of activity was seen in the depth of the intraparietal sulcus and the medial superior parietal cortex (superior parietal gyrus and precuneus) together with the frontal sulcus but only in the SEQ task, which involved memory of the previously seen targets and possibly also motor memory.

The second task is the vestibular memory contingent task, which requires that the subject makes, in darkness, a saccade to the remembered position of a visual target after a passively imposed whole–body rotation. Deficits in this task, which involves ‘vestibular memory’, were found predominantly in patients with focal vascular lesions in the parieto–insular (vestibular) cortex, the supplementary motor area–supplementary eye field area, and the prefrontal cortex.

The third task requires mental navigation from the memory of a previously learned route in a real environment (the city of Orsay in France). A PET scan study has revealed that when subjects were asked to remember visual landmarks there was a bilateral activation of the middle hippocampal regions, left inferior temporal gyrus, left hippocampal regions, precentral gyrus and posterior cingulate gyrus. If the subjects were asked to remember the route, and their movements along this route, bilateral activation of the dorsolateral cortex, posterior hippocampal areas, posterior cingulate gyrus, supplementary motor areas, right middle hippocampal areas, left precuneus, middle occipital gyrus, fusiform gyrus and lateral premotor area was found. Subtraction between the two conditions reduced the activated areas to the left hippocampus, precuneus and insula.

These data suggest that the hippocampus and parietal cortex are both involved in the dynamic aspects of spatial memory, for which the name ’topokinetic memory’ is proposed. These dynamic aspects could both overlap and be different from those involved in the cartographic and static aspects of ‘topographic’ memory.
Hippocampal involvement in human topographical memory⋮evidence from functional imaging
Authors: Maguire Eleanor A.
Published: October 2002

Functional brain imaging in humans is beginning to reveal a network of brain regions that subserve topographical learning: the medial parietal lobe, the posterior cingulate gyrus, occipitotemporal areas, the parahippocampal gyrus and the right hippocampus. These findings illuminate the patient lesion literature where all of these brain regions have been implicated at one time or another in cases of topographical disorientation. Once topographical information is acquired, the neuroanatomy that supports its use from either episodic or semantic memory is similar to that activated during encoding. The specific contributions of extrahippocampal regions within the topographical memory system are being revealed, such as the role of the right parahippocampal gyrus in object–in–place encoding. The right hippocampus is clearly involved in processing spatial layouts over long as well as short time–courses, and participates in both the encoding and the retrieval of topographical memory. The ventromedial orbitofrontal cortex is recruited when information in the topographical memory system is not sufficient to produce direct navigation to a goal place.