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Selected AbstractsHabitat and food choice of Arctic charr in Linnévatn on Spitsbergen, Svalbard: the first year-round investigation in a High Arctic lakeECOLOGY OF FRESHWATER FISH, Issue 1 2007M.-A. Svenning Abstract,,, Habitat and diet of Arctic charr Salvelinus alpinus (L.) were studied by monthly sampling from late autumn to early summer in Linnévatn, Svalbard (78°3,N, 13°50,E). This is the first year-round study of a population of charr in the High Arctic, with samples being taken every 5,7 weeks. The ice cover lasted for more than 9 months, from mid-October to late July, with the greatest thickness in mid-May. Although most charr occupied the littoral zone during winter, the highest densities in April and October were found in the deeper areas (20 m) of the lake. The fish fed at all times of the year, but the number of stomachs with food and the stomach-filling indices were lowest during the darkest part of the season. The diet of smaller charr (<15 cm) varied strongly with season, showing a dominance of zooplankton in late autumn and chironomids in winter (larvae) and summer (pupae). The food choice was in accordance with the density of food items available. Larger fish (,15 cm) were mostly cannibalistic during the entire year. [source] A Relational Approach to Measuring Competition Among HospitalsHEALTH SERVICES RESEARCH, Issue 2 2002Min-Woong Sohn Objective. To present a new, relational approach to measuring competition in hospital markets and to compare this relational approach with alternative methods of measuring competition. Data Sources. The California Office of Statewide Health Planning and Development patient discharge abstracts and financial disclosure files for 1991. Study Design. Patient discharge abstracts for an entire year were used to derive patient flows, which were combined to calculate the extent of overlap in patient pools for each pair of hospitals. This produces a cross-sectional measure of market competition among hospitals. Principal Findings. The relational approach produces measures of competition between each and every pair of hospitals in the study sample, allowing us to examine a much more "local" as well as dyadic effect of competition. Preliminary analyses show the following: (1) Hospital markets are smaller than thought. (2) For-profit hospitals received considerably more competition from their neighbors than either nonprofit or government hospitals. (3) The size of a hospital does not matter in the amount of competition received, but the larger hospitals generated significantly more competition than smaller ones. Comparisons of this method to the other methods show considerable differences in identifying competitors, indicating that these methods are not as comparable as previously thought. Conclusion. The relational approach measures competition in a more detailed way and allows researchers to conduct more fine-grained analyses of market competition. This approach allows one to model market structure in a manner that goes far beyond the traditional categories of monopoly, oligopoly, and perfect competition. It also opens up an entirely new range of analytic possibilities in examining the effect of competition on hospital performance, price of medical care, changes in the market, technology acquisition, and many other phenomena in the health care field. [source] Phytoplankton and Epipelon Responses to Clear and Turbid Phases in a Seepage Lake (Buenos Aires, Argentina)INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2009María Adela Casco Abstract Annual changes in the algal density and concentrations of chlorophyll a, total phosphorus, and organic matter were analyzed in water and sediments at four sites characterized by the presence or absence of submerged and emergent macrophytes, during turbid- and clear-water conditions to determine the contribution of the algal components of the plankton and the epipelon and to identify the most typical species in each community. Three states were recognized: one turbid and two clear, with different submerged macrophyte cover. The peaks of phytoplankton and epipelon occurred in the turbid phase, whereas the highest proportion of true epipelic algae in sediments was reached in the second clear phase. The Oscillatoriaceae dominated during the turbid phase in the water and throughout the entire year within the sediments. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The link between migration, the reproductive cycle and condition of Sardinella aurita off Mauritania, north-west AfricaJOURNAL OF FISH BIOLOGY, Issue 5 2007R. Ter Hofstede The annual migration pattern of round sardinella Sardinella aurita up and down the north-western African coast between 12° N (Senegal) and 22° N (western Sahara) was shown to be associated with spawning activity and a distinct seasonality in fish condition, based on monthly sampling from commercial catches (2000,2003). Some S. aurita were found to spawn throughout the entire year, but a peak in spawning existed during the summer (June to September). The spawning cycle is apparent from seasonality in maturity stages, but is also demonstrated by the increase in gonad mass and fat content of the fish in springtime, the period preceding spawning. During the months after spawning, although feeding is maintained, the physical condition of the fish collapses, and fat content rapidly declines. [source] Interactive effects of increased temperature and CO2 on the growth of Quercus myrsinaefolia saplingsPLANT CELL & ENVIRONMENT, Issue 10 2001T. Usami Abstract The interactive effects of increased temperature and CO2 enrichment on the growth of 2-year-old saplings of Quercus myrsinaefolia, an evergreen broad-leaved oak, were studied throughout an entire year in the vicinity of their northernmost distribution. Saplings were grown under different conditions in two chambers: (1) a temperature gradient chamber at ambient temperature, 3 and 5 °C warmer conditions with an ambient CO2 concentration, and (2) in a CO2 temperature gradient chamber at 3 °C warmer conditions with 1·5 times the normal CO2 concentration, and 5 °C warmer conditions with doubled CO2 concentration. The 3 and 5 °C warmer conditions enhanced the relative growth rate during almost the entire year, producing 53 and 47% increases in annual biomass production, 27 and 44% enhancement of root growth during shoot dormancy and 3 and 5 week prolongation of the shoot growing period, respectively. However, a daily mean air temperature exceeding 30 °C under the 5 °C warmer condition caused a marked reduction in net assimilation rate (NAR) from July to September. The CO2 enrichment further enhanced the positive effects of warming in spring and the resulting increases in NAR almost completely compensated for the negative effect of warming during summer. From autumn to winter, attenuation of the effects of CO2 was compensated by the increased sink strength produced by the warming. The annual biomass production was more than doubled by the combination of temperature elevation and CO2 enrichment. [source] Moderate Seasonality in Testis Function of Domestic CatREPRODUCTION IN DOMESTIC ANIMALS, Issue 5 2007S Blottner Contents Adult male domestic cats are known to produce sperm throughout the year, although sexual activity is influenced by geographical location. In the northern hemisphere, feral domestic cats reproduce usually between January and July. Thus, seasonality in testicular activity might be suggested. The aim of the present study was to investigate gametogene and endocrine activity of cat testis throughout the entire year. Testes and epididymides (n = 10,12 per month) were collected after castration. Spermatogenesis was quantified by assessment of testicular sperm per testis and by flow cytometric analysis of the cells with different DNA content. Sperm from cauda epididymis were evaluated according to motility and morphological integrity. Testicular testosterone concentration was determined by enzyme immunoassay. Testis mass and sperm production varied moderately throughout the year. Significant seasonal variations were observed in the proportion of cells in the G2/M phase of cell cycle (p = 0.004) and the meiotic transformation (ratio of haploid : tetraploid cells; p = 0.021). Changes in testicular testosterone concentration were more pronounced and showed periods with high (spring) and significantly reduced testosterone levels (autumn). A marked seasonal alteration (p < 0.001) with a peak in March was assessed in the percentage of progressively motile sperm. The proportion of morphological intact sperm was also significantly higher in spring compared with winter time (p < 0.001). In conclusion, the study suggests moderate seasonal changes in quantity of sperm, more pronounced annual variation in hormone production and a distinct seasonal influence on functional sperm parameters in domestic cat. [source] | |||||||||||||