High-resolution microwave images of saturn

An analysis of high-resolution microwave images of Saturn and Saturn's individual rings is presented. Radio interferometric observations of Saturn taken at the Very Large Array in New Mexico at wavelengths of 2 and 6 centimeters reveal interesting new features in both the atmosphere and rings. The resulting maps show an increase in brightness temperature of about 3 K from equator to pole at both wavelengths, while the 6-centimeter map shows a bright band at northern mid-latitudes. The data are consistent with a radiative transfer model of the atmosphere that constrains the well-mixed, fully saturated, NH(3) mixing ratio to be 1.2 x 10(-4) in a region just below the NH(3) clouds, while the observed bright band indicates a 25 percent relative decrease of NH(3) in northern mid-latitudes. Brightness temperatures for the classical rings are presented. Ring brightness shows a variation with azimuth and is linearly polarized at an average value of about 5 percent. The variations in ring polarization suggest that at least 20 percent of the ring brightness is the result of a single scattering process.     

Chaotic Dynamics in an Insect Population

A nonlinear demographic model was used to predict the population dynamics of the flour beetle Tribolium under laboratory conditions and to establish the experimental protocol that would reveal chaotic behavior. With the adult mortality rate experimentally set high, the dynamics of animal abundance changed from equilibrium to quasiperiodic cycles to chaos as adult-stage recruitment rates were experimentally manipulated. These transitions in dynamics corresponded to those predicted by the mathematical model. Phase-space graphs of the data together with the deterministic model attractors provide convincing evidence of transitions to chaos.     

Stocked rainbow trout (Oncorhynchus mykiss) affect space use by Warpaint Shiners (Luxilus coccogenis)

Due to widespread stocking, Rainbow Trout (Oncorhynchus mykiss Walbaum) are perhaps the most widely distributed invasive species in the world. Nonetheless, little is known about the effects of stocked Rainbow Trout on native non‐game species. We conducted experiments in an artificial stream to assess the effects of hatchery Rainbow Trout on home range and behaviour of Warpaint Shiners (Luxilus coccogenis Cope), a common minnow frequently found in stocked Southern Appalachian streams. We used the LoCoH algorithm to generate polygons describing the home ranges used by Warpaint Shiners. When a stocked trout was present Warpaint Shiners: (a) increased home range size by 57%, (b) were displaced into higher velocity mesohabitats, and (c) reduced mean overlap between the home ranges of individual warpaint shiners. Rainbow Trout did not significantly affect the edge/area ratio of Warpaint Shiner home ranges. Warpaint Shiner density (two and five fish treatments) did not significantly affect any response variable. Displacement from preferred microhabitats and increases in home range size likely result in increased energy expenditure and exposure to potential predators (i.e., decreased individual fitness) of Warpaint Shiners when stocked trout are present.     

Effects of within-patch habitat structure and variation on fish assemblage characteristics in the Bernecei stream, Hungary

Abstract –  Over a 3-year period we examined variability in physical habitat structure and species richness, abundance and assemblage composition of fishes in 13 habitat patches in the Bernecei stream, Hungary. Principal component analysis of habitat structure data from patches elucidated a riffle-run-pool habitat gradient across patches. Temporal habitat variability increased significantly from riffle to pool patches. Fish assemblage characteristics displayed relatively continuous change over the habitat gradient and were relatively stable within patches. Assemblage structure properties (e.g., species richness) displayed different responses to the habitat gradient and to within-patch habitat variability. In general, pool patches had more diverse assemblages and greater within-patch assemblage variability than riffle patches. However, within-patch dynamics were largely determined by the population dynamics of a habitat generalist (i.e., minnow). Broad scale environmental variability (i.e., a catastrophic 100-year flood) also appeared to affect within-patch fish assemblage characteristics. Our results demonstrate that fish assemblage structure is influenced by physical variability (i.e., both floods and spatio-temporal habitat variability) within the Bernecei stream.     

Use of Leicester's “rheological model for mechano-sorptive deflections of beams”

Summary The model for mechano-sorptive deformation proposed by Leicester is used to predict stress relaxation of wood drying under constraint from apparent creep of drying wood under constant load. The predictions are compared with measurements on four pairs of beams, one beam in each pair being tested under constant load, the other at constant deflection. Agreement was sufficiently close to demonstrate the value of the model.     

Turbidity, velocity and interspecific interactions affect foraging behaviour of rosyside dace (Clinostomus funduloides) and yellowfin shiners (Notropis lutippinis)

Abstract –  Fish diversity is strongly affected by habitat degradation (e.g., increased turbidity) and invasive species. We examined the effects of turbidity, velocity, length, dominance and intra- and interspecific competition on focal point depth, movement rate, dominance and aggression rate in native rosyside dace ( Clinostomus funduloides ) and invasive yellowfin shiners ( Notropis lutipinnis ) in a southern Appalachian stream (NC, USA). We compared results for intra- and interspecific groups of fishes at two densities (two and four fishes), three turbidity levels (10, 20 and 30 nephelometric turbidity units), and two velocities (12, 18 cm·s⁻¹). Dominance was significantly correlated with length in intraspecific groups of both species, and dominant fish held more profitable foraging positions about 75% of the time. Yellowfin shiners were dominant more often than rosyside dace in interspecific trials. Akaike's Information Criterion indicated that models containing turbidity, velocity, species and intraspecific competition, explained the greatest amount of information in focal point depth data. By contrast, movement and aggression rates were best explained by models based on dominance and velocity. Finally, aggression rate was best explained by models containing fish length and turbidity. These results indicate that habitat degradation, intra- and interspecific interactions influence the foraging behaviour and future success of these species in the Little Tennessee River drainage.     

Microhabitat use by fish in the lower Rio Matarraña, Spain, 1984–1987

We quantified microhabitat use in Barbus graellsii, Cyprinus carpio, Chrondostoma toxostoma, Esox lucius, Gobio gobio and Leuciscus cephalus during 1984–1987 in the lower Rio Matarraña, Spain. Fluctuations in numerical abundances of assemblage members increased during 1986–1987. These increased fluctuations were due to decreases in the abundances of Ch. toxostoma, E. lucius and G. gobio during the latter 2 years of our study. Only C. carpio increased slightly in abundance during this period. An analysis of microhabitat availability data indicated that 16 seasonal samples could be assigned to 1 of 6 groups ranging from: seasons with zero velocities, shallower depths and an algal/debris substratum to those with high velocities and depths and a substratum composed of algae/debris, rubble and gravel. Most seasonal changes in the substratum were attributable to conditions inhospitable to the growth of benthic algae (i. e., high velocities or low oxygen levels) rather than to actual changes in the underlying lithospheric substratum. Principle component analyses indicated that most species were overrepresented in deeper microhabitats with depositional substrata. Ch. toxostoma, however, tended to occur over rubble substrata in both shallow and deep microhabitats. Most seasonal changes in microhabitat use were produced by seasonal variations in microhabitat availability. However, all species except E. lucius exhibited seasonal variations in microhabitat use that typically involved velocity, depth and substratum composition. Although smaller specimens of most species were found closer to the substratum in 1984–1985, they tended to occupy shallow areas in 1986–1987. Canonical analyses of discriminants and univariate data demonstrated that the distance from the substratum was the best predictor of interspecific differences in microhabitat use. Species could be arrayed along a vertical gradient with L. cephalus and Ch. toxostoma occupying mid-water column positions, B. graellsii and C. carpio occurring in lower-water column microhabitats and E. lucius and G. gobio strongly associated with the substratum. Changes in interspecific microhabitat use were not correlated with changes in species abundances, and hence, interspecific competition did not appear to strongly influence microhabitat use during our study.