Weaving marine food webs from end to end under global change

Marine food web dynamics are determined by interactions within and between species and between species and their environment. Global change directly affects abiotic conditions and living organisms, impinging on all trophic levels in food webs. Different groups of marine researchers traditionally study different aspects of these changes. However, over medium to long time scales perturbations affecting food webs need to be considered across the full range from nutrients to top predators. Studies of end-to-end marine food webs not only span organism sizes and trophic levels, but should also help align multidisciplinary research to common goals and perspectives. Topics are described that bridge disciplinary gaps and are needed to develop new understanding of the reciprocal impacts of global change on marine food webs and ocean biogeochemistry. These include (1) the effects of nutrients on biomass and production, (2) the effects of varying element ratios on food web structure and food quality, (3) bulk flows of energy and material in food webs and their efficiencies of transfer, (4) the ecological effects of species richness and the roles of microbial organisms, (5) the role of feeding behaviour in food web dynamics and trophic controls, (6) the spatial dynamics of communities and links between different food webs, (7) the combined effects of body size and behaviour in determining dynamics of food webs, and (8) the extent to which the ability of marine organisms (and communities) to adapt will influence food web dynamics. An overriding issue that influences all topics concerns the time and space scales of ecosystem variability. Threads link different nodes of information among various topics, emphasizing the importance of tackling food web studies with a variety of modelling approaches and through a combination of field and experimental studies with a strong comparative approach.     

Priority Berthing For Congested Ports: rationale and a model

Adverse effects on a national economy of port congestion are identified. The rationale underlying a system of priority berthing for awaiting vessels is described and contrasted with the operational system of first‐come, first‐served. A system of priority berthing is capable of minimizing the generalized social cost of congestion and this is structured mathematically as a multi‐attribute, decision‐making problem. A worked example is outlined and a computer program described.     

Intercity rail services: A nested logit stated choice analysis of pricing options

There is a renewed interest in intercity and long-distance rail services in many countries, with both new high-speed rail services and improvements to conventional rail under review. The current study reports on an investigation using a stated choice experiment, of the demand for sleeper services between Sydney, Northern New South Wales (NSW) and Brisbane in Australia, a 12 to 14 hour trip, just after a decision by the NSW government to temporarily suspend sleeper services and introduce seating service only, pending an inquiry into the demand for such loss-making services under alternative price and service levels. A matrix of direct fare elasticities within the rail mode and between rail and competing modes are obtained for concession and non-concession travellers from a nested logit model. The empirical evidence extends our knowledge of the sensitivity of the long distance passenger market to a range of rails fares, distinguishing between classes of fares and levels of service.     

Regression modelling of the employment durations of UK seafaring officers in 1999

This paper presents the results of an econometric analysis of the duration of voyages undertaken by NUMAST deck and engineer officers in 1998-1999. Earlier papers examined the employment profile of the officers, and compared voyage patterns across organization type, company nationality, flag of registry, and ship type. Analysis of the various cross-tabulations of employment duration appeared to show that the key driver is ship type. Using regression analysis, it is shown that ship type does indeed have a significant influence on duration, as does ship size. Flag, organizational type and company type were all found to be statistically unimportant.     

Advanced emergency braking under split friction conditions and the influence of a destabilising steering wheel torque

The steering system in most heavy trucks is such that it causes a destabilising steering wheel torque when braking on split friction, that is, different friction levels on the two sides of the vehicle. Moreover, advanced emergency braking systems are now mandatory in most heavy trucks, making vehicle-induced split friction braking possible. This imposes higher demands on understanding how the destabilising steering wheel torque affects the driver, which is the focus here. Firstly, an experiment has been carried out involving 24 subjects all driving a truck where automatic split friction braking was emulated. Secondly, an existing driver–vehicle model has been adapted and implemented to improve understanding of the observed outcome. A common conclusion drawn, after analysing results, is that the destabilising steering wheel torque only has a small effect on the motion of the vehicle. The underlying reason is a relatively slow ramp up of the disturbance in comparison to the observed cognitive delay amongst subjects; also the magnitude is low and initially suppressed by passive driver properties.     

Effects of waste disposal on benthic faunal succession on the abyssal seafloor

Strategies to predict, and thus limit, potentially detrimental environmental impacts of abyssal disposal of wastes are severely limited by our lack of knowledge of deep-sea processes and lack of opportunity to directly study waste disposal in abyssal environments. Probable successional sequences following burial of benthic faunas by sewage sludge and dredged material on the abyssal seafloor are drawn by analogy with well-known processes in shallow-marine water. Scales of change and recovery of abyssal benthic faunas from episodic deposition of waste material are examined by extrapolation from what is currently known about turbidite sedimentary provinces, in particular, the Venezuela Abyssal Plain and the Great Meteor East area of the Madeira Abyssal Plain. Results suggest that initial benthic faunal recolonization would take place within years following episodic depositions of waste on the abyssal seafloor. Anoxic conditions or chemical inhibitory effects may delay initial benthic recolonization for hundreds of years. Establishment of equilibrium benthic faunal assemblages probably takes hundreds to potentially thousands of years. Potentially detrimental effects dictate that the surface areas of individual waste deposits should be minimized and the deposits should be isolated by capping with nontoxic materials or chemical barriers.     

Attitudinal and situational variables influencing urban mode choice: Some empirical findings

A mode choice decision structure incorporating traveler attitudes toward modes and situational constraints is investigated. The major hypothesis tested is that mode choice is determined primarily by situational constraints, such as auto ownership and income, secondly by the quality of alternative modes.The structure of the mode choice process is analyzed with respect to (1) applicability of certain choice criterion forms; (2) psychological weighting of modal attributes in the choice criterion; (3) strength of logit, probit, and discriminant functional forms; (4) the relative strength of socio-economic and attitudinal variables in predicting mode choice. An evaluation is made of 50 binary choice models fitted to a sample of 471 randomly drawn urban travelers. Results indicate that (1) the four choice criterion forms tested are all about equal in predictive strength; (2) psychological weighting has no effect on model strength, but does influence which modal attributes appear to determine choice; (3) the three functional forms tested are all about equal in strength; (4) situational factors account for 80–90% of variation explained by the models, attitudes toward modes 10–20%, thus confirming the primary hypothesis. Implications of these results for mode choice modeling and transit planning are discussed.This paper summarizes current research at the New York State Department of Transportation on the motivations and causes of travel behavior. Complete findings are available in Hartgen (1973).     

Structural models for the analysis of traveler attitude-behavior relationships

Traveler attitudes and behavior have been shown to correlate in numerous previous studies. However, the correlation by itself leaves open the nature of the interrelationships between traveler attitudes and behavior. For example, attitudes could either cause or be caused by behavior. In fact, both options are concurrently possible. Structural equations are applied to a set of data gathered from Los Angeles central business district workers to ascertain the direction and nature of interrelationships between attitudes and behavior with respect to frequency of taking the bus to work. A mutual dependence between attitudes and behavior is demonstrated in the context of this dataset and behavioral choice situation; behavior and attitudes concurrently cause each other. In addition, it is found that two attitudinal components, perceptions of and affect toward a mode, function differently with respect to travel behavior.