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991.
Hydrodynamic forces are an important determinant of subtidal community structure, particularly when they limit the distribution
and foraging ability of mobile consumers. We examined the effect of wave action on the rate of movement and destructive grazing
of a kelp bed by the green sea urchin (Strongylocentrotus droebachiensis) under field conditions. We measured density and rate of advance at fixed intervals along ∼100 m of a grazing front over
1 year, and quantified individual movement rates in the barrens 5–10 m behind the urchin front using a time-lapse videography.
Seasonal variation in the mean rate of advance of the front (range: 0–4 m month−1) was explained by changes in urchin density at the front (120–360 individuals m−2), which in turn varied inversely with significant wave height (0.5–2 m). Water temperature (0.8–17.6°C) had no effect on
the rate of advance or on urchin density (aggregation) at the front, except when temperature exceeded 17°C. Movement of individual
urchins also was affected by wave action: we observed a significant decrease in speed and displacement of urchins with increasing
significant wave height. Wave action had no effect on the proportion of urchins moving or the degree of linearity of their
movements. We propose that the decrease in urchin density at the front associated with increased wave action, results from
de-aggregation, which reduces the risk of dislodgement, combined with a reduction in urchin movement in barrens, which supplies
new urchins to the front. 相似文献
992.
Tov Elperin Nathan Kleeorin Michael A. Liberman Victor S. L’vov Igor Rogachevskii 《Environmental Fluid Mechanics》2007,7(2):173-193
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. 相似文献
993.
Frédéric Mineur Mark P. Johnson Christine A. Maggs Herre Stegenga 《Marine Biology》2007,151(4):1299-1307
Hull fouling is thought to have been the vector of introduction for many algal species. We studied ships arriving at a Mediterranean
harbour to clarify the present role of commercial cargo shipping in algal introductions. A total of 31 macroalgal taxa were
identified from 22 sampled hulls. The majority of records (58%) were of species with a known cosmopolitan geographical distribution.
Due to a prevalence of cosmopolitan species and a high turnover of fouling communities, species composition of assemblages
did not appear to be influenced by the area of origin, length of ship or age of coating. In the light of the present results,
hull fouling on standard trading commercial vessels does not seem to pose a significant risk for new macroalgal species introductions.
However, a high proportion of non-cosmopolitan species found on a ship with non-toxic coating may modify this assessment,
especially in the light of the increasing use of such coatings and the potential future changes in shipping routes. 相似文献
994.
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. 相似文献
995.
In order to assess diet composition and niche breadth of this species, we analysed the stomach content of 182 specimens collected
monthly along the eastern coast of Sicily (Central Mediterranean Sea). Overall, 50 prey taxa belonging to five major groups
(algae, gastropods, crustaceans, polychaetes, fishes) were identified in 102 full stomachs. Benthic or epibenthic crustaceans,
such as decapods, amphipods and isopods were the most important prey, whereas algae, gastropods, polychaetes and fishes were
only occasionally ingested. In terms of composition by species, the diet of Scorpaena maderensis was characterized by a variety of rare or unimportant prey, which was consumed by few individuals only, although sometimes
in large amount. As a result, S. maderensis can be considered a generalized and opportunistic feeder. The feeding intensity followed roughly a seasonal trend, with a
minimum food intake in summer. The individual fish size was the most important factor affecting diet. According to the observed
ontogenetic shift, small-sized individuals fed primarily on small crustaceans (i.e. amphipods and isopods), whereas large-sized
specimens consumed preferably bigger and more vagile prey, such as walking and swimming decapods. No significant differences
in diet were observed in relation to sex of predator and sampling season. 相似文献
996.
Gail L. Patricelli Marc S. Dantzker Jack W. Bradbury 《Behavioral ecology and sociobiology》2007,61(7):1099-1110
Studies of animal acoustic communication have found that the frequency and temporal structure of acoustic signals can be shaped
by selection for efficient communication. The directionality of acoustic radiation may also be adapted for communication,
but we know relatively little about how directionality varies with signal function, sender morphology, and the environment
in which the sound is transmitted. We tested the hypothesis that the directionality of a vocalization is adapted to its function
in communication. This hypothesis predicts that vocalizations that are directed to multiple conspecifics (e.g., advertisements
and alarms) will be relatively omnidirectional because this will maximize the number of neighbors and mates that receive the
signal, and that vocalizations directed to particular individuals will be relatively directional because this will maximize
detection of the signal by the targeted receiver and minimize eavesdropping. To test these predictions, we measured the directionality
and amplitude of red-winged blackbird (Agelaius pheoniceus) vocalizations in the field by recording vocalizations simultaneously on eight calibrated microphones encircling the bird.
We found significant variation in directionality among vocalizations. Supporting our predictions, we found that the most omnidirectional
vocalizations were those used to alert conspecifics to danger, and the most directional vocalizations are those used during
courtship and solicitation of copulation, when the costs of eavesdropping are likely to be high. These results suggest that
the directionality of red-winged blackbird vocalizations is shaped by selection for effective communication. This study is
the first to provide statistical support for the hypothesis that directionality is related to the function of a signal in
communication. 相似文献
997.
Mangrove forests and seagrass beds frequently occur as adjacent habitats in the temperate waters of southeastern Australia.
At low tide when fish cannot occupy mangroves they might utilise adjacent habitats, including seagrass. We first sampled small
fish from seagrass beds close to and far from mangroves in the Pittwater estuary, NSW, Australia. Seagrass beds close to mangroves
had a greater density of fish species than beds far from mangroves (close: mean 16.0 species net−1, SE 1.0; far: 13.2, 1.3; P < 0.05). In particular, juvenile fish were in greater densities near to than far from mangroves (close: 5.3, 0.4; far: 3.1,
0.4; P < 0.05). We then sampled the mangrove forests during the high tide and seagrass beds during the low tide, in beds along a
continuum of distances from mangroves. Multivariate analysis showed that fish assemblages differed with distance from mangroves,
and the differences were attributed to the composition of the fish assemblage (i.e. presence/absence of fish species), not
the abundances of individual species. In particular, fish that utilise mangrove forests at high tide were found in greater
species densities and species richness in seagrass nearer to mangroves. A negative relationship was found between the density
of mangrove-utilising fish species and the distance of the bed from mangroves (R
2 = 0.37, P < 0.05). This confirms the important connectivity between mangroves and seagrass for fish in temperate Australian waters. 相似文献
998.
A single population of short-beaked common dolphins (Delphinus delphis Linnaeus) occurs in the western North Atlantic from Florida to Newfoundland. Dolphins killed in a swordfish driftnet fishery
between 1989 and 1998 provided samples for the present study. These were combined with additional observations from carcasses
collected from stranding programs. Samples were examined from 74 female and 161 male short-beaked common dolphins. A highly
significant male bias in the sex ratio of both the bycatch and stranding samples suggests that sex-based habitat partitioning
or school segregation occurs in this population. Age was estimated from decalcified thin sections of teeth and testis and
ovarian samples were examined both macro- and microscopically. Analyses showed that reproduction was both seasonal and synchronized.
Females reached sexual maturation at approximately age eight; males matured at 9.5 years. Conception occurred during July
and August (mean day 24 July). Gestation was estimated to last just under a year, so most females gave birth during July and
August (mean day 15 July). Annual pregnancy rate was estimated to be between 25 and 33%. Males undergo a fivefold seasonal
increase in testes mass and a twofold increase in seminiferous tubule diameter. Peak sperm production potential was observed
in July. At the end of the breeding season testis size and activity decreased after August. Male dolphins in this population
are hypothesized to engage in some form of sperm competition. 相似文献
999.
Haihui Wang Bogdan Z. Dlugogorski Eric M. Kennedy 《Journal of Loss Prevention in the Process Industries》1998,11(6):373-381
A mathematical model is presented to describe steady-state mass transfer and oxidation processes in coal at low temperatures in a fixed-bed flow reactor. The model incorporates the effects of partial pressure of oxygen, temperature and coal particle size, and accounts for the rate of coal oxidation and the composition of oxygenated products at high pressures. This is an important development since previous models did not include the effect of pressure in their formulation. It is found that, when the partial pressure of oxygen increases the rate of oxygen consumption increases accordingly. However, the influence of partial pressure of oxygen on the rate of oxidation is less pronounced when the pressure surpasses 1 MPa. In addition the model predicts that, for a constant partial pressure of oxygen, higher rates of oxygen consumption occur at lower total pressures. The same trends are also found for the concentration of oxygenated products at the reactor outlet. It is suggested that, the variation of partial pressure of oxygen leads to different concentration levels of oxygen at the surface and within the pores of coal particles, substantially affecting the rate of oxidation. 相似文献
1000.
IntroductionPolycyclicaromatichydrocarbons (PAHs)arewidespreadenvironmentalpollutantsintheatmosphere.Theyaregeneratedinthecombustion .Themajorsourcesidentifiedincludefossilfuels,vehiculartraffic,industrialprocesses,smokinganddomesticheating (Peltonen ,1995) .T… 相似文献