Constraints on group size in primates and carnivores: population density and day-range as assays of exploitation competition

Summary We hypothesise that foraging group size (FGS) and population group size (PGS) in primates and carnivores are related to quantifiable variables indexing the intensity of exploitative competition. Group size is predicted to increase with both food density and travel capabilities, as estimated by the constraint-free day-range (DR_s), i.e. the day-range of a solitary individual uninfluenced by competition from conspecifics. We test this exploitation competition hypothesis among primates and carnivores, using data on populations, species and genera. Food density was indexed by population density. Where DR_s could be estimated by regression it was found to be correlated with observed day-range (DR_m). DR_s was therefore indexed by DR_m in all species. Population density and DR_m were associated with each other, but in a multiple regression each variable contributed independently to explaining variation in group size. PGS was predicted better than FGS, but regressions involving either measure of group size were significant in all analyses. The multiple regression analyses were validated by the method of linear contrasts, which accounts for possible lack of independence among taxa. We conclude that species differences in group size are influenced by both food density and DR_s. This suggests that variation in the intensity of exploitation competition is partly responsible for differences in group size.Correspondence to: R.W. Wrangham     

Locomotory behaviour and swimming performance of the Norway lobster,Nephrops norvegicus,in the presence of an acoustic tag

Observations have been made on the locomotory behaviour and swimming performances of the Norway lobster, Nephrops norvegicus (L.), fitted with an acoustic transmitter ventrally under the cephalothorax. The walking behaviour of adult males (44 mm carapace length) appeared to be unaffected, but the tag caused significant reductions in certain measures of tail-flip swimming performance such as swimming speed and endurance. Flume-tank experiments in low water currents suggested that the transmitter would increase hydrodynamic drag during swimming by 9 to 32%, depending on lobster size. Given the weight and dimensions of the acoustic transmitters currently available, it is considered advisable to confine acoustic tracking studies to relatively large N. norvegicus.Correspondence to: C. J. Chapman     

Population dynamics of Mytilicola intestinalis in Mytilus edulis in south west England

The population dynamics of Mytilicola intestinalis Steuer in mussels (Mytilus edulis L.) from the River Lynher, Cornwall, England, have been studied over 3 years. By transplanting uninfested mussels from the River Erme, South Devon, into the Lynher mussel bed, the study was extended to the growth and development of new infestations under natural conditions. Female Mytilicola intestinalis are shown to breed twice, and two generations of parasites coexist for most of the year, with recruitment taking place in summer and autumn. One generation contributes its first brood to the autumn recruits before overwintering and contributing its second brood to the following summer's recruits. The other generation overwinters as juvenile and immature stages to contribute its two broods successively to the summer and autumn recruits. Environmental temperatures are believed to control the rates of development at all stages rather than acting as triggers in the onset or cessation of breeding at specific times. There is no evidence to support the contention that heavily infested mussels are killed, and parasite mortality is shown to be density-independent.     

Transport of particulate matter in natural waters — modelling and in situ-measurements

The significant processes controlling the fate of particulates are convection an dispersion on one hand, and sedimentation on the other hand. Due to inteparticulated reactions, larger aggregates can be formed from smaller units thus changing the sedimentation characteristics. These phenomena are summarized in a mathematical model whereby hydrodynamic effects as well as the control mechanisms of the dissolved phase are included. A relationship was derived on the basis of energy considerations leading to the formulation of a critical sedimentation velocity of the suspensa, which determines the transport capacity of the flowing system. The sedimentation term is calculated from the above discussed transport capacity, hydro-dynamic parameters and suspending media properties. Aggregation effects are taken into account as an increase of sedimentation velocities of the particles. The equations are solved in a particular computational routine such that the horizontal distribution of suspended solids in a natural system can be describe as function of the above discussed phenomena. The model was tested with in situ-measurements. It was found that the observed processes are described satisfactorily by this model.     

An examination of health data following two major earthquakes in Russia

Thus the hazards to health observed from these two earthquakes can be summarised as follows: (a) massive immediate damage, the main victims being women and children; (b) the seriously injured suffer mainly from fractures (17%), head injuries (15-30%) and soft tissue conusions with haemhorrage; (c) a change in the physical features of a country which unfavourably affect the environment; (d) some time after the earthquake the appearance of communicable disease; (e) increases in cases of cardiovascular disease neuroses and psychoses.     

Intertemporal and intergenerational pareto efficiency: A comment

In a recent issue of this Journal, Sandler and Smith developed an analysis from which they concluded that discounting is Pareto inefficient in an intertemporal context. This comment questions the validity of that conclusion and demonstrates the essential role played by the discount rate in achieving intertemporal Pareto efficiency within a market economy.