Effects of simulated current on the growth rate and nitrogen metabolism of Gracilaria tikvahiae (Rhodophyta)

In a series of multifactorial laboratory experiments, Gracilaria tikvahiae apical segments were grown in an apparatus in which they were exposed simultaneously to 3 simulated current speeds (7.5, 15, 22.5 cm s^-1) and a still control, and either 3 ammonium concentrations (<6, 37–39, and 119–136 M) under ample uniform light (ca 200 E m^-2 s^-1) or 3 light intensities (ca 35, 90, and 270 E m^-2 s^-1) with uniform surplus ammonium. Growth rates of apical segments were determined in each experiment as well as nitrogen and carbon composition of tissues and fluxes of NH₄, NO₃/NO₂, and PO₄ in media. In a supplementary series of field experiments, apical segments of G. tikvahiae weresimultaneously exposed to 2 different regimes of water motion in adjacent chambers at several sites characterized by widely different ammonium regimes. The application of simulated current significantly enhanced growth rates in all experiments which utilized recently collected plants. Generally, this enhancement was fully realized at 7.5 cm s^-1, with growth rates tending to plateau above that speed. Growth enhancement by simulated current was independent of ammonium concentration and was considerably reduced at the lowest light intensity. In experiments conducted with plants that had been maintained for several months in aquaria, simulated current failed to enhance growth rates. This suggested that growth responses were at least partly a function of prior conditioning. Growth rates were a direct function of light intensity and an inverse function of ammonium concentration, indicating ammonium inhibition at the higher applied concentrations. Simulated current slightly enhanced rates of ammonium uptake but this did not consistently result in reduced C:N ratios, suggesting that the growth-stimulating effect of relative water motion was attributable to factors other than N uptake. There was evidence of luxury consumption of ammonium. In field experiments, growth rates were not significantly related to exposure to water motion.     

Sampling pure fetal blood in twin pregnancies by fetoscopy using a single uterine puncture

A technique for sampling pure fetal blood in twin pregnancies using a single uterine entry with a fetoscope is described. The fetoscope was inserted into one sac and after blood had been obtained from that, twin, the fetus in the other sac was sampled by trans-septal passage of the blood-sampling needle. This was done in six out of seven patients, the first in the series having two separate insertions of the fetoscope, one into each sac. Pure fetal blood was taken from all 14 fetuses, either from the placental insertion of the umbilical cord or the umbilicus, and the volume of the samples ranged from 200 μl to 1200 μl. In six patients the fetuses were at risk of β-thalassaemia and in one of haemophilia A. Some observations are made relating zygosity to the ultrasonic and fetoscopic appearance of the septum between the sacs.     

Improving the contingent valuation method: A psychological perspective

Results of research on the social psychology of human decision making that offer direction for improving the contingent valuation method are reviewed. The paper focuses on the findings of that literature related to (1) limitations of human information processing and judgment-making abilities, (2) the influence of elicitation stimuli and expectations, and (3) quality of decision making in the face of too much or too little stress. Within the context of this literature, specific research directions are recommended that can improve the validity and reliability of the results of contingent valuation studies. More multidisciplinary studies are encouraged.     

MEASURING ECONOMIC LOSSES FROM GROUND WATER CONTAMINATION: AN INVESTIGATION OF HOUSEHOLD AVOIDANCE COSTS1

ABSTRACT: Economic losses from ground water contamination were estimated in a central Pennsylvania community. The averting expenditures method was applied via a mail survey of households in which water contained the unregulated volatile organic chemical, perchloroethylene (PCE). Expenditures were estimated at $148,900 (1987 dollars) over the six-month contamination period or approximately $252 per household annually. These costs underestimate the lower bound measure of welfare losses to households from ground water contamination. An upper bound measure of welfare losses was estimated at $383 per household annually. These estimates do not represent the full economic losses resulting from ground water contamination since the study did not address municipal-level and business avoidance costs and losses from actual health effects, increased fear and anxiety, ecological damages, and nonuser ground water benefits. The results expand the existing empirical base of information about municipal-level responses and economic losses from ground water contamination to include household-level impacts. The findings indicate that households undertake substantial averting actions in response to ground water contamination and that such actions can have significant economic consequences. The extent and magnitude of avoidance costs documented suggests that policy-makers should give greater attention to this category of economic losses.     

Sex differences in the ontogeny of social behavior in pikas: possible relationships to dispersal and territoriality

Summary A laboratory study on the ontogeny of social behavior in pikas (Ochotona princeps), an alpine lagomorph, was conducted to determine the role of early relationships between adult females and young and among siblings in the development of territorial and dispersal behaviors. Sex differences during development were examined because field studies have reported greater dispersal distances in young females than young males. At birth, females were significantly heavier than males. There were no sex differences in nursing frequency until after the 2nd week of age, when males initiated more nursing attempts than females. By the end of the weaning period (weeks 5 and 6), adult females became non-interactive with young, but aggression of young toward littermates and the mother increased until the eighth week. At this time, young males outweighed their sibling females. Young were dominant over their mothers by the age of 5 weeks, and young males were dominant over their sibling females.Sex differences were observed in aggression, scent-marking, exploratory activity, and submissive vocalizations, with higher rates in young males, except for submissive vocalizations, which were higher in females (Table 2). Vocalizations and scent-marking behavior increased over time, and were positively correlated with interaction rates.These data support the hypothesis that female young disperse farther than male young largely as the result of unsuccessful competition with male siblings for available territories close to the birthplance. A dispersal strategy for pkkas is proposed.