On marketable air-pollution permits: The case for a system of pollution offsets

After examining the properties of several alternative forms of marketable permit systems for the control of air pollution, this paper proposes a system of pollution offsets as the most promising approach. Under the pollution-offset scheme, sources of emissions are free to trade emissions permits subject to the constraint of no violations of the predetermined air-quality standard at any receptor point. The paper shows that the pollution-offset system has the capacity to achieve the predetermined standards of air quality at the minimum aggregate abatement cost, while making comparatively modest demands both on the sources and on the administering agency.     

Frontal ambulacral and peribuccal areas of the spatangoid echinoid Echinocardium cordatum (Echinodermata): a functional entity in feeding mechanism

Echinocardium cordatum (Pennant, 1777) were collected in Normandy, France, in March and November 1985. The grooved frontal ambulacrum of the burrowing echinoid E. cordatum functions in transferring surface sediment from the apex to the mouth of the echinoid. Particles that fall down the burrow's chimney accumulate between the spines of the apical tuft and are taken over by specialized groove spines. Due to the slope of the groove and the type of floor spines it harbours, four successive regions can be recognized, namely the adapical region, the fasciolar region, the ambital region, and the adoral region. As a general rule aboral floor spines (i.e. club-shaped, golf-club-shaped, and isodiametric spines) function in gathering particles while propelling them mouthwards; they simultaneously embed particles in a mucous string. The oral floor spines (i.e. spatulated spines) function in hauling and guiding the mucous string towards the peribuccal area of the echinoid. Once facing the peribuccal area, particles are picked up by the peribuccal tube feet that either transfer them into the esophagus or scrape them out against the peribuccal spines. Spine-retained particles are either sucked up by the pumping action of the esophagus or fall to the burrow's floor where the tube feet may pick them up again. Together the apical tuft, the frontal groove, and the peribuccal area form an efficient food-collecting system that transfers trapped surface particles from the echinoid apex down to the mouth. Compared to that of most other spatangoids the frontal ambulacrum of E. cordatum is highly specialized. Such specialization is related to colonization of fine sediment, as is the occurrence of a chimney linking the burrow to the sediment surface. Actually the burrow's chimney is the only route for oxygen and food supply; it acts as a real ecological umbilical cord for spatangoids buried in fine sediment.     

Variable predation risk and the dynamic nature of mosquito antipredator responses to chemical alarm cues

Summary. Predation is a pervasive selective agent highly variable in space and time. Due to the costs associated with antipredator responses, prey would be at a selective advantage if they respond to predation threats with an intensitfy matching the threat posed by the predator. Many aquatic organisms have been shown to use chemical alarm cues present in the water to assess the level of risk in their environment. This includes mosquito larvae which show antipredator responses to conspecific alarm cues. In this study, we investigated the nature of the responses of larval mosquitoes Culex restuans to those cues. In our initial observations, we showed pond/population differences in the response intensity of C. restuans to alarm cues. In experiment 1, we showed that the response intensity to alarm cues could be increased by increasing the background level of risk in the mosquitoes’ environment (by adding salamander predators) and once turned on, the response intensity to alarm cues was likely maintained for the remainder of the mosquitoes’ aquatic life. In experiments 2 and 3, we investigated if the increase in response intensity to alarm cues was directly correlated with the level of background risk in the mosquitoes’ environment. When given increasing levels of background risk, mosquito larvae subsequently showed a graded response to conspecific alarm cues. This series of experiments demonstrates that the response intensity of larval mosquitoes to a standard concentration of alarm cues is not fixed, but rather dependent on the background level of risk in the environment. An understanding of the background level of risk is particularly important for comparing antipredator responses of prey between habitats.     

Locomotor kinematics and behaviour in the escape response of European sea bass, Dicentrarchus labrax L., exposed to hypoxia

To assess the effect of oxygen reduction on the escape response of sea bass, Dicentrarchus labrax, an integrative experimental approach was employed. The effect of hypoxia was tested on locomotor variables, i.e. cumulative distance (D), maximum swimming speed (V _max) and maximum acceleration (A _max). Behavioural variables, such as responsiveness (i.e. the proportion of individuals responding out of the total number of fish tested), response latency (i.e. the time interval between stimulus onset and the first detectable movement leading to the escape of the animal) and directionality (i.e. the proportion of escape responses in which the first detectable movement of the head was oriented away or towards the stimulus at its onset) were also considered. Four levels of oxygen were used: >85% (i.e. normoxia, the control treatment), 50, 20 and 10% of air saturation. Sea bass responsiveness decreased significantly at 10% of air saturation, while hypoxia did not have any effect on the response latency. At the onset of the escape response, the proportion of away/towards responses was random when oxygen was ≤50% of air saturation, suggesting an impairment of the left–right discrimination. Whatever the level of hypoxia, none of the locomotor variables (i.e. D, V _max and A _max) was significantly different from normoxia. Our study suggests that hypoxia may reduce sea bass elusiveness facing a predator by directly affecting its escape behaviour, possibly related to an impairment of the mechano-sensory performance and/or in the Mauthner cells involved in triggering the escape response.     

A Multimedia Chemical Fate Model with Time-Dependent Air-Water Transfer Rates

A multimedia model for the temporal evolution of the concentration of chemical species in a water basin and its bottom sediment layer has been tested with time-dependent air-water transfer rates varying with the meteorological conditions over the basin. The multimedia model uses the chemical fugacity approach in a system of two ordinary differential equations for the chemical species partition in the two mentioned media, with transfer through the sediment-water and the air-water interfaces. The air-water transfer rates are estimated by a micrometeorological preprocessor. A scenario in which known concentrations in air of a soluble pollutant (benzene) induce water and sediment pollution is tested on both synthetic (MonteCarlo-simulated) and real series of meteorological data. It is found that the use of time-dependent transfer coefficients affects not only the relaxation time, but also the long term concentration of the pollutant in water and sediment, that differs between 10 and 40% in the examined cases when compared with the same multimedia model using average constant transfer rates as usual. This is shown to be due to the statistical correlations between meteorological parameters and air pollutant concentrations, which stresses the advantages of a time-dependent estimation of the transfer coefficients. Correction terms are proposed to take into account the correlation effects when a constant parameters multimedia model is used.     

Interaction between Fe-cyanide complex and humic acids

The fate of cyanides in soil is strongly influenced by the formation of Fe cyanides, which can interact with organic and inorganic colloids and precipitate as stable compounds. Scarce information is available on the capacity of humic acids to interact with cyano-complexes and thus affect the leaching and prevent the risk of contamination of watertable. Here we show that interaction between humic acids (HAs) and ferricyanide complex led to a formation of ferricyanide-humo micelles, and that the interaction did not imply changes in the original structure of ferricyanide complex.     

Strong effects of various incidence and observation angles on spectrometric assessment of plumage colouration in birds

The assessment of plumage colouration has become a common procedure in many ornithological studies, especially after the discovery of differences between avian and human visual systems, namely the avian ability to perceive ultraviolet wavelengths. There are many techniques available for plumage colour assessment. Nevertheless, unidirectional reflectance spectrometry seems actually to be the method of choice and is used in most studies. The active avian visual communication skills, the physical characteristics of the plumage surface and the birds’ body shape prompted us to study plumage colouration with different angles of incidence and observation by bidirectional reflectance spectrometry. In this study, we explore the effect of different angles of incidence and observation, on a single plane of incidence, on the reflectance spectrometric assessment of five differently coloured body regions of the blue fronted Amazon parrot (Amazona aestiva). Measurements were made using a AVS-USB2000 spectrometer with a DH-2000 light source and two different reflection probes (bifurcated fibre optic probe and a specially designed fibre holder). The results of this study illustrate clear angle dependence of colour parameters in differently coloured non-iridescent plumage regions of the blue fronted Amazon parrot. Our results may have direct implications on the observed transmitted information of display and its associated predation risk (trade-off) in birds, but also in other animals. Moreover, the results show that unidirectional reflectance spectrometry alone may be a rather limited procedure to quantify and compare true colour of a complex surface such as birds’ plumage. Therefore, slight but behavioural important characteristics of plumage pattern may remain undiscovered with this method.     

Interpolation performance of a spatio-temporal model with spatially varying coefficients: application to PM<Subscript>10</Subscript> concentrations in Rio de Janeiro

In this work we present a Bayesian analysis in linear regression models with spatially varying coefficients for modeling and inference in spatio-temporal processes. This kind of model is particularly appealing in situations where the effect of one or more explanatory processes on the response present substantial spatial heterogeneity. We describe for this model how to make inference about the regression coefficients and response processes under two scenarios: when the explanatory processes are known throughout the study region, and when they are known only at the sampling locations. Using a simulation experiment we investigate how parameter inference and interpolation performance are affected by some features of the data and prior distribution that is used. The proposed methodology is used to model the dataset on PM₁₀ levels in the metropolitan region of Rio de Janeiro presented in Paez and Gamerman (2003).     

Search or relax: the case of bachelor wood bison

Summary Males of gregarious species of mammals often do not associate with female groups during the breeding season. Such males could leave groups either to search for new breeding opportunities, or to restore body condition before rejoining new female groups. To investigate these two competing hypotheses, we studied the chronology of male wood bison (Bison bison athabascae) associating with females, and their aggressive and sexual behaviour over two breeding seasons. With increasing age, males were more often solitary, were more involved in aggressive interactions, investigated the genitals of females more frequently, and tended females more often. Group size did not affect whether or not males joined or left groups. The presence of oestrous females in a group did not affect the number of bulls in that group, and did not affect the joining or leaving of males. Older, dominant males did not exclude younger ones from female groups. Males observed outside female groups spent relatively more time feeding and resting than bulls in groups. Changes in group composition experienced by a male often involved the joining or splitting of female groups, as opposed to actual transfer of males between groups. Our results suggest that males leave female groups in order to recover, not for the purpose of searching for new female groups. We argue that due to the fluidity of wood bison groups, it is possible for a male to encounter new females even when remaining in a female group. Correspondence to: P.E. Komers