Influences of sex,sex composition of brood and hatching order on mass growth in common terns<Emphasis Type="Italic"> Sterna hirundo</Emphasis>

We studied sex-dependent mass growth of chicks of the monomorphic common tern Sterna hirundo which fledged at a colony site in Wilhelmshaven, Germany, between 1997 and 1999. Brood size, brood mates' sex and hatching order (a-, b- and c-chicks) were known for many individuals, which were sexed by molecular techniques. Daily growth rates and age of fledging were independent of sex. However, in all years male chicks reached higher peak mass and fledged up to 5.2% heavier than female chicks. Broods with at least two fledglings showed that besides sex, brood size interacting with sex composition affected chick mass. In mixed broods, brothers had higher peak and pre-fledging mass than sisters they were reared with. Especially in the combination a-daughter and b-son the brothers were heavier. Lowest mass was found in broods with three nest mates of the same sex. A detailed study of 24 three-fledgling broods showed that male c-chicks were heavier than their siblings. The results reveal an advantage for chicks in mixed broods, especially for sons, and more especially if the son was a c-chick. Higher mass and possibly dominance of sons in c-position might be related to higher maternal androgen levels, which are known to increase with each egg laid. The results suggest that even in a monomorphic species, sons might be more expensive to rear, and are discussed with respect to sibling competition, parental effort, survival of sons, as well as to fitness benefits favoring parents producing sons.     

Population dynamics and growth of juveniles of the velvet swimming crab Necora puber (Decapoda: Portunidae)

Recruitment variability plays a critical role in determining local population densities of benthic organisms, but extreme vulnerability at the onset of juvenile life is a trait that is largely responsible for population survivorship trends. The aim of the present study was to determine the role of juvenile recruitment in the population structure of Necora puber. Juveniles of N. puber were collected from the lower intertidal of rocky shores of Plymouth Sound (southwest coast of the UK) and monthly size–frequency distribution were used to determine the dynamics and the growth of the population. The parameters of the von Bertalanffy growth function were estimated (K=0.281 year⁻¹; t ₀=0.043; C=0.103; and t _s=0.268) assuming a L _∞=105 mm. Growth was markedly seasonal and present results indicated a slower juvenile growth rate than described previously for N. puber. The recruitment period was extensive and was two times higher in 2001 than in 2000 at the start of the 1+ year, but levelled off at the end of the 1+ year class on three of the four shores studied. Instantaneous mortality as high as 5.1 year⁻¹(99.4% year⁻¹) was observed during the higher recruitment year. Early juvenile mortality appears to be density dependent and a demographic bottleneck appears to limit the number of juveniles on some shores.     

Clustering of aerosols in atmospheric turbulent flow

A mechanism of formation of small-scale inhomogeneities in spatial distributions of aerosols and droplets associated with clustering instability in the atmospheric turbulent flow is discussed. The particle clustering is a consequence of a spontaneous breakdown of their homogeneous space distribution due to the clustering instability, and is caused by a combined effect of the particle inertia and a finite correlation time of the turbulent velocity field. In this paper a theoretical approach proposed in Elperin et al. (2002) Phys Rev E 66:036302 is further developed and applied to investigate the mechanisms of formation of small-scale aerosol inhomogeneities in the atmospheric turbulent flow. The theory of the particle clustering instability is extended to the case when the particle Stokes time is larger than the Kolmogorov time scale, but is much smaller than the correlation time at the integral scale of turbulence. We determined the criterion of the clustering instability for the Stokes number larger than 1. We discussed applications of the analyzed effects to the dynamics of aerosols and droplets in the atmospheric turbulent flow.     

The effect of ambient temperature on forager sound production and thoracic temperature in the stingless bee, <Emphasis Type="Italic">Melipona panamica</Emphasis>

Foragers of the stingless bees genus Melipona may produce intranidal sounds that are correlated with food location and quality. In this study, we provide the first detailed analysis of pulsed sounds produced by Melipona panamica foragers while feeding on a carbohydrate food source. We trained foragers to a 2.5-M sucrose feeder under normal, ambient temperature (23–33°C) and lower temperature (11–25°C) conditions. We recorded forager sounds under both conditions and tested the effect of temperature of the thorax, feeder plate, and air on sound temporal characteristics. Forager energetic expenditure and the number of pulses per visit were significantly higher in the cold condition than in the normal condition. Foragers spent a longer time at the feeder under the cold condition than during the normal condition. Interpulse durations were significantly shorter in the cold condition than in the normal condition and became progressively and significantly shorter at the end of each performance. Thus, pulse production increased before departure. Foragers increased their thoracic temperatures above ambient at all experimental air temperatures. Under chilled conditions, foragers had a significantly greater difference between thorax temperature and ambient air temperature than under normal conditions. Foragers must achieve a minimum flight muscle temperature before take-off, and thus forager sounds may be linked to muscle warm-up.     

Juvenile–adult associations in sea urchins ( Strongylocentrotus franciscanus and S. droebachiensis ): protection from predation and hydrodynamics in S. franciscanus

Juvenile red sea urchins, Strongylocentrotus franciscanus, aggregate under adult conspecifics, whereas sympatric juvenile green sea urchins, Strongylocentrotus droebachiensis, are typically more solitary and dispersed. Neither the potential advantage of juvenile sheltering nor the differences in post-settlement behavior between the two species has been demonstrated experimentally, but may be related to protection from predators and/or hydrodynamics. In predation experiments, juvenile vulnerability differed in the two species as the seastar Pycnopodia helianthoides consistently chose juvenile S. franciscanus over S. droebachiensis (100% vs. 0%). When associated with adults, juvenile mortality decreased dramatically in S. franciscanus (90% alone vs. 5% with adults), but very little in S. droebachiensis (85% vs. 75%). Not surprisingly, juvenile behavioral responses in the two species reflect this difference in vulnerability. Juvenile S. franciscanus sheltered under adults when predation risk was high, but not when risk was low (44% vs. 13%), whereas sheltering in S. droebachiensis was infrequent and not related to predation risk (7% for high risk versus 5% for low risk). From a hydrodynamic perspective, the presence of an adult led to the creation of a hydrodynamic refuge for juveniles, where average water velocities were reduced by > 60% around the adult urchin. Again, striking differences in sheltering rate were apparent in S. franciscanus (52% vs. 13% for high flow and low flow, respectively), but not S. droebachiensis (5% for high flow versus 4% for low flow). Sheltering behavior was also species-specific as juveniles did not shelter at high rates under adults of the opposite species (≤ 16%). A field survey confirmed these finding in that juvenile S. franciscanus abundance was associated with both adults and water motion (R ² = 0.80, P = 0.008, best-subsets regression). These results suggest that sheltering confers juvenile S. franciscanus with a degree of protection from predators and water motion, and that species-specific differences in this post-settlement behavior may be related to the differences in the protection afforded by adults.     

Sex difference in signature whistle production of free-ranging bottlenose dolphins,Tursiops truncates

Signature whistles of 42 free-ranging bottle-nose dophin calves were compared to those of their mothers. Humans judged their similarity by inspection of spectrograms. There was a sex difference in the tendency of calves to produce whistles similar to or different from those of their mothers; most female calves produced whistles that were different from those of their mothers, whereas male calves were more likely to produce whistles that were similar to those of their mothers. Because matrilineally related females associate together and use signature whistles to establish and/or maintain contact with their calves, there may be a selective pressure for females to produce whistles that are distinct from those of their mothers. There may be fewer constraints governing whistle development in males, with the result that some males produce whistles similar to those of their mothers and others do not.     

A qualitative characterization of the competitive nonrenewable resource extracting firm

Using variational differential equations, a systematic qualitative analysis is carried out for the competitive nonrenewable resource extracting firm. The parameters of interest are the output price, variable input price, discount rate, lease length, initial resource stock, and various tax rates. The effects of changes in these parameters on the entire optimal time paths of the current shadow value of the stock, the resource stock, and the extraction rate are characterized in the perturbed phase plane.     

The Surface Roughness of a Rubber Soling Material Determines the Coefficient of Friction on Water-Lubricated Surfaces

For more than a decade, evidence has been accumulating that points to the fact that the microscopic roughness of the footwear soling surface is a major determinant of slip-resistance on lubricated surfaces, but conclusive experimental proof has been lacking. This article describes an experiment in which five pairs of shoes were soled with the same rubber compound. Four of the pairs were abraded by different grades of grit to produce a range of roughness values. The coefficient of friction (CoF) of the five solings was then measured repeatedly by the walking traction method on wet surfaces including glazed wall tiles, vinyl asbestos coated with the wax floor polish, and both sides of a sheet of float glass. The Kruskal-Wallis statistical test proved beyond doubt that the soling roughness is a major factor in determining the CoF of this rubber soling material; p < 10⁻⁵. Nearly all of the grip was due to surface roughness of the soling material on these atypically smooth floors, although the surface roughness of the floors also had a significant effect on CoF; p < 0.003. Float glass is shown to be a promising reference floor material for the measurement of CoF of footwear; there was no statistical difference between results for the two sides of the glass sheet. Float glass could be used in the development of a standard CoF test method because new sheets of glass from the same manufacturer are identical and extremely smooth. The specification of CoF values for solings/floors combinations in lubricated conditions is of little value unless associated with roughness measurements and knowledge of how wear will affect the surface roughness of the sole. This article reports the first evidence that any specification of flooring by measuring CoF based on dry surfaces could lead to an increase in the number of injuries caused by slipping on the wet surfaces. Published by Elsevier Science Ltd     

Does Decentralization Matter in Environmental Management?

/ Questionnaires from 39 state National Pollutant Discharge Elimination System (NPDES) agencies were analyzed using principal component analysis and multiple regression. Decentralized programs scored better in a fundamental indicator of efficiency (lower percentage of expired permits) and in the key effectiveness measure of unit-cost compliance achieved. In no case did centralized states score significantly better than decentralized ones. These results indicated support for the theory that superior local knowledge is the key mechanism. Case studies of five states suggested internal program adjustments may cause outcomes to converge towards efficiency and effectiveness, perhaps explaining the large number of variables showing no difference between centralized programs and decentralized ones.KEY WORDS: NPDES; Compliance; Decentralization; Outcome; Efficiency; Unit-cost analysis     

ANALYSIS OF NITROGEN MANAGEMENT STRATEGIES USING EPIC1

ABSTRACT: This paper illustrates a method of using a hydrologic/water quality model to analyze alternative management practices and recommend best management practices (BMPs) to reduce nitrate-nitrogen (NO₃^--N) leaching losses. The study area for this research is Tipton, an agriculturally intensive area in southwest Oklahoma. We used Erosion Productivity Impact Calculator (EPIC), a field-scale hydrologic/water quality model, to analyze alternative agricultural management practices. The model was first validated using observed data from a cotton demonstration experiment conducted in the Tipton area. Following that, EPIC was used to simulate fertilizer response curves for cotton and wheat crops under irrigated and dryland conditions. From the fertilizer response functions (N-uptake and N-leaching), we established an optimum fertilizer application rate for each crop. Individual crop performances were then simulated at optimum fertilizer application rates and crop rotations for the Tipton area, which were selected based on three criteria: (a) minimum amount of NO₃^--N leached, (b) minimum concentration of NO₃^--N leached, and (c) maximum utilization of NO₃^--M. Further we illustrate that by considering residual N from alfalfa as a credit to the following crop and crediting NO₃^--N present in the irrigation water, it is possible to reduce further NO₃^--N loss without affecting crop yield.