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721.
Michael?J.?W.?StokesburyEmail author Chris?Harvey-Clark Jeffrey?Gallant Barbara?A.?Block Ransom?A.?Myers 《Marine Biology》2005,148(1):159-165
Three Greenland sharks (Somniosus microcephalus) were tagged with electronic tags, in Baie St. Pancrace, St. Lawrence Estuary, Quebec, Canada. One shark was tagged on 23 July 2004, with an acoustic telemetry tag. Two sharks were each tagged with a pop-up satellite archival tag (PSAT) on 27 August 2004. Two of the sharks remained in or close to the bay, one for 47 days and the other for at least 66 days. The third shark left the bay immediately after tagging on 27 August 2004. This shark entered the main channel of the St. Lawrence Estuary, and had moved 114.9 km upstream by 1 November 2004 when the tag reported to ARGOS satellites. The tags provided a total of 179 days of data on the movement and environmental preferences of Greenland sharks in the St. Lawrence Estuary. Sharks that reported depth and ambient water temperature data from the bay showed significant diel differences in depth preferences and corresponding ambient temperatures. The sharks remained near the bottom of the water column during the day and displayed increased vertical movements at night. The shark that resided in the main channel did not show this pattern, but generally remained at depths between 325 and 352 m. Sharks in the bay experienced water temperatures that ranged from −1.1 to 8.6°C at depths from 0 to 67 m. In the main channel the shark experienced temperatures that ranged from 1.0 to 5.4°C at depths from 132 to 352 m. This is the first report of numerous Greenland sharks inhabiting shallow near shore bays during summer and autumn. 相似文献
722.
The Kelvin–Helmholtz (KH) instability is traditionally viewed as an initial-value problem, wherein wave perturbations of a
two-layer shear flow grow over time into billows and eventually generate vertical mixing. Yet, the instability can also be
viewed as a boundary-value problem. In such a framework, there exists an upstream condition where a lighter fluid flows over
a denser fluid, wave perturbations grow downstream to eventually overturn some distance away from the point of origin. As
the reverse of the traditional problem, this flow is periodic in time and exhibits instability in space. A natural application
is the mixing of a warmer river emptying into a colder lake or reservoir, or the salt-wedge estuary. This study of the KH
instability from the perspective of a boundary-value problem is divided into two parts. Firstly, the instability theory is
conducted with a real frequency and complex horizontal wavenumber, and the main result is that the critical wavelength at
the instability threshold is longer in the boundary-value than in the initial-value situation. Secondly, mass, momentum and
energy budgets are performed between the upstream, unmixed state on one side, and the downstream, mixed state on the other,
to determine under which condition mixing is energetically possible. Cases with a rigid lid and free surface are treated separately.
And, although the algebra is somewhat complicated, both end results are identical to the criterion for complete mixing in
the initial-value problem. 相似文献
723.
Valuation of climate-change effects on Mediterranean shrublands. 总被引:1,自引:0,他引:1
Pere Riera Josep Pe?uelas Verónica Farreras Marc Estiarte 《Ecological applications》2007,17(1):91-100
In general, the socioeconomic analysis of natural systems does not enter into the realms of natural science. This paper, however, estimates the human-welfare effects of possible physicochemical and biological impacts of climate change on Mediterranean shrublands over the coming 50 years. The contingent choice method was applied to elicit the trade-offs in perceived values for three climate-sensitive attributes of shrubland (plant cover, fire risk, and soil erosion) and for the costs of programs designed to mitigate changes. Soil erosion was found to be the attribute of shrubland that most concerned the population, followed by fire risk and then plant cover. An increase of 1% in the shrubland area affected by erosion was estimated to cost each person on average 2.9 euros per year in terms of lost welfare, a figure that is equivalent in terms of perceptions of social welfare to an increase of 0.24% in the shrub area burned annually and a decrease of 3.19% in the area of plant cover. These trade-off values may help ecologists, policy makers, and land managers to take social preferences into account. 相似文献
724.
Fabrice?HelfensteinEmail author Richard?H.?Wagner Etienne?Danchin 《Behavioral ecology and sociobiology》2003,54(4):370-376
Socially monogamous partners suffer conflicting interests concerning various aspects of reproduction such as parental care, copulation and fertilization. Female black-legged kittiwakes commonly eject their mates' sperm immediately following copulations. Because sperm ejection reduces male sperm competitiveness and paternity assurance, males and females have conflicting interests as regards sperm ejection. Males whose mates ejected their sperm at least once remained longer on their mates' backs after the last insemination which apparently prevented the females from ejecting sperm. These results suggest that compelling females to retain their sperm may be a previously unidentified tactic employed by males to assure their paternity. Females tried to prevent their mates from witnessing sperm ejection by ejecting sperm after their mates departed from the nest. Females were more likely to eject sperm when they terminated the copulations by unbalancing the male. The conflict over sperm ejection was related to the ability of the females to end the copulations which covaried with the body mass of their mates. These findings suggest that conflicts in monogamous pairs also exist over the disposition of sperm.Communicated by C.R. Brown 相似文献
725.
Brian?D.?WisendenEmail author Mike?S.?Pollock Robyn?J.?Tremaine Jeff?M.?Webb Monique?E.?Wismer Douglas?P.?Chivers 《Behavioral ecology and sociobiology》2003,54(5):485-490
Chemical and visual sources of information are used by aquatic prey during risk assessment. Here, we test the behavioral response of littoral prey fish to combinations of chemical alarm cues (skin extract) and the visual presence of a fish shoal. We scented minnow traps with either alarm cues or water (control) placed inside the trap, a jar that contained either a fish shoal or nothing (control), and recorded the number and species of fish captured. We predicted that chemical alarm cues would reduce the number of fish captured and that a fish shoal would increase the number of fish captured. The predicted effect of chemical and visual cues combined depended on the nature of the interaction. We found that the lowest catch rate was for the combination of alarm cue + no shoal, but the highest catch rate occurred for the combination of alarm cue + shoal. Fish shoal + water had the second highest catch rate and no shoal + water had the second lowest catch rate. We conclude that chemical alarm cues induce area avoidance in the absence of a shoal, but a strong behavioral proclivity to increase shoal cohesion in the presence of a shoal. The presence of a shoal in the traps induced alarmed fish to shoal with them and thus, enter the traps. This occurred even though traps were the source of the alarm cue.Communicated by A. Mathis 相似文献
726.
Woodlands of the Mediterranean speciesJuniperus oxycedrus ssp.macrocarpa (maritime juniper) are both vulnerable and ecologically important. Their ecology and biological status along the SW coast
of Spain are not well known; this, the first major study of these juniper populations is a basis for future research and restoration
policies. These communities are subject to harsh conditions, the plant composition being controlled by several factors at
different scales. On a large scale, climate and soil texture play an important role in controlling the soil water availability
to plants, and in separating xerophytic from mesic communities. On a small scale, coastal physiography, and substrate composition
are related to differences in the floristic composition. Coastal plantations modify environmental conditions, such as sand
mobility and salt spray deposition, inducing important changes in plant communities. The population of maritime juniper on
this coast was estimated in ca. 25 000 individuals, of which 93.6% are concentrated in three locations. Large proportions
of young individuals were found in extensive and protected populations. Howerver, adult individuals dominated the smaller
populations located under pine plantations. This limitation of recruitment may be imposed by several factors. A male biased
ratio was detected on the southern coast of Cádiz, which I hypothesize is due to the lower cost of pollen production in a
stressful habitat. Preservation of suitable habitats, the recovery of abandoned pine plantations, and the connection between
juniper populations, seem to be important requisites for the conservation of maritime juniper in the southwestern coast of
Spain. 相似文献
727.
This study evaluated variations in heavy metal contamination of stream waters and groundwaters affected by an abandoned lead–zinc mine, where a rockfill dam for water storage will be built 11 km downstream. For these purposes, a total of 10 rounds of stream and groundwater samplings and subsequent chemical analyses were performed during 2002–2003. Results of an exploratory investigation of stream waters in 2000 indicated substantial contamination with heavy metals including zinc (Zn), iron (Fe) and arsenic (As) for at least 6 km downstream from the mine. Stream waters near the mine showed metal contamination as high as arsenic (As) 8,923 μg L−1, copper (Cu) 616 μg L−1, cadmium (Cd) 223 μg L−1 and lead (Pb) 10,590 μg L−1, which greatly exceeded the Korean stream water guidelines. Remediation focused on the mine tailing piles largely improved the stream water qualities. However, there have still been quality problems for the waters containing relatively high concentrations of As (6–174 μg L−1), Cd (1–46 μg L−1) and Pb (2–26 μg L−1). Rainfall infiltration into the mine tailing piles resulted in an increase of heavy metals in the stream waters due to direct discharge of waste effluent, while dilution of the contaminated stream waters improved the water quality due to mixing with metal free rain waters. Levels of As, Cu and chromium (Cr) largely decreased after heavy rain but that of Pb was rather elevated. The stream waters were characterized by high concentrations of calcium (Ca) and sulfate (SO4), which were derived from dissolution and leaching of carbonate and sulfide minerals. It was observed that the proportions of Ca and SO4 increased while those of bicarbonate (HCO3) and sodium and potassium (Na+K) decreased after a light rainfall event. Most interestingly, the reverse was generally detected for the groundwaters. The zinc, being the metal mined, was the most dominant heavy metal in the groundwaters (1758–10,550 μg L−1) near the mine, which far exceeded the Korean standard of 1000 μg L−1 for drinking water. The decreases in the heavy metals contents in the groundwaters associated with reduced rainfall were quite different from the increases observed for the stream waters, which is not clearly understood at this time and warrants further investigation. 相似文献
728.
Critical swimming speeds of late-stage coral reef fish larvae: variation within species,among species and between locations 总被引:3,自引:0,他引:3
Rebecca?FisherEmail author Jeffrey?M.?Leis Domine?L.?Clark Shaun?K.?Wilson 《Marine Biology》2005,147(5):1201-1212
The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators,
obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns
of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean.
Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition
factor of these same larvae. Among species U-crit ranged from 5.5 cm s−1 to 100.8 cm s−1 (mean=37.3 cm s−1), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species
should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming
ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations
were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters
may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families
at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly
slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests
that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat
use following settlement. 相似文献
729.
Rapha?l?JeansonEmail author Jean-Louis?Deneubourg Anne?Grimal Guy?Theraulaz 《Behavioral ecology and sociobiology》2004,55(4):388-394
Insect societies are often confronted with choices among several options such as food sources of different richness or potential nest sites with different qualities. The mechanisms by which a colony as a whole evaluates these situations and takes the appropriate decision are of crucial importance for its survival. Here we studied how collective decisions arise from individual behaviors when a group of workers of the ant Messor barbarus is given a choice between two aggregation sites. Two hundred ants were introduced into an arena and given a choice between two tubes connected to the arena. The tubes had different physical properties: dry and transparent (termed as dry), humid and transparent (termed as humid), or dry and dark (termed as dark). After 30 min, most ants were found to be aggregated in a humid tube when paired with a dry tube, or in a dark tube when paired with a humid one. When two humid tubes were in competition, ants aggregate more in one of the sites. The choice of ants was consistent throughout experiments. An analysis of individual behaviors shows that the probability of an ant recruiting and the intensity of its trail-laying behavior strongly depend on the quality of the tubes. Our study suggests that the selection of an aggregation site does not require that individual ants directly compare sites, but rather relies on the synergy between amplification processes involving recruitment by chemical trails, and a modulation of the individual resting time in a site as a function of its population.Communicated by L. Sundström 相似文献
730.
Elina?PortjanskajaEmail author Marina?Krichevskaya Sergei?Preis Juha?Kallas 《Environmental Chemistry Letters》2004,2(3):123-127
The photocatalytic oxidation of humic substances in aqueous solutions and natural waters with TiO2 attached to buoyant, hollow glass micro-spheres was studied. A maximum oxidation efficiency of 3.6 mg W–1 h–1 was achieved in neutral or alkaline media at a plane surface concentration of the catalyst attached to the micro-spheres of 25 g m–2. Proceeding by different mechanisms in acidic and alkaline media, the photocatalytic oxidation efficiency did not benefit from an excessive presence of hydroxyl radical promoters, hydrogen peroxide and alkali. 相似文献