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Showing papers by "Government of Canada published in 1990"


Journal ArticleDOI
01 Jun 1990-Ecology
TL;DR: The results suggest that the mechanisms underlying the tropic cascade are complex and that predators affect phytoplankton by altering nutrient recycling rates as well as zooplankon grazing rates.
Abstract: Two predators of zooplankton, fish (yellow perch) and larval insects (Chaoborus), were manipulated within in situ mesocosms to assess their indirect effects on phytoplankton. The two predators caused similar reductions in zooplankton size and biomass, and as a consequence, zooplankton grazing rates on phytoplankton. However, phytoplankton increased relative to predator—free controls only in enclosures with fish and not in enclosures with Chaoborus, suggesting that fish have effects on phytoplankton independent of their effects on zooplankton grazing rates. Estimation of phosphorus excretion rates of zooplankton and fish suggests that fish render P more available to phytoplankton in two ways: (1) by directly excreting and egesting P, and (2) by increasing rates of P excretion by the zooplankton community. The latter effect resulted because small zooplankton have higher biomass—specific excretion rates than large zooplankton. The importance of nutrient regeneration is further supported by the response of phytoplankton community structure. Phytoplankton taxa exhibiting enhanced biomass in the presence of fish were those with high P requirements, including green and blue—green algae and dinoflagellates; other phytoplankton groups did not respond to manipulations. These results suggest that the mechanisms underlying the tropic cascade are complex and that predators affect phytoplankton by altering nutrient recycling rates as well as zooplankton grazing rates.

228 citations


Journal ArticleDOI
TL;DR: A Strategy for Tourism and Sustainable Developments as mentioned in this paper is a strategy for tourism and sustainable development in the developing world, which is based on the concept of sustainable development of sustainable tourism.
Abstract: (1990). A Strategy for Tourism and Sustainable Developments. World Leisure & Recreation: Vol. 32, No. 3, pp. 12-18.

86 citations


Journal ArticleDOI
TL;DR: In this paper, the accumulation of and hepatic monooxygenase induction by 2,3,4,7,8-pentachlorodibenzofuran (PnCDF) were studied in juvenile rainbow trout (Onchorhynchus mykiss) by feeding treated food for 31 d followed by a 180 d depuration period.
Abstract: Accumulation of and hepatic monooxygenase induction by 2,3,4,7,8-pentachlorodibenzofuran (PnCDF) were studied in juvenile rainbow trout (Onchorhynchus mykiss) by feeding treated food for 31 d followed by a 180 d depuration period. Efficiency of assimilation was 44 and 41% at exposure concentrations of 9.0 and 0.82 ng g−1 PnCDF, respectively. Depuration of PnCDF followed first-order kinetics with half-lives (based on toluene extraction of 14C-radiolabel corrected for growth dilution) of 61 and 69 d at the low and high exposure concentrations, respectively. Monooxygenase enzyme induction measured by ethoxyresorufin-O-deethylase (EROD) activity in individual trout livers was 84- and four-fold higher after 31 d of exposure to 9.0 and 0.82 ng g−1, respectively, than in livers of unexposed fish. Sustained EROD activity at the high treatment concentrations was observed during the 180 d depuration phase. Ethoxyresorufin-O-deethylase activity declined at approximately half the rate of elimination of PnCDF. No significant differences between growth rates of treated and control fish were found.

57 citations


Journal ArticleDOI
TL;DR: A total of 3999 Trichoptera adults, represented by 8 families, 17 genera and 33 species was collected in emergence traps in 1983 and 1984 from five stations on the Ochre River, Manitoba (50° 04′ N, 99° 48′ W) as mentioned in this paper.
Abstract: A total of 3999 Trichoptera adults, represented by 8 families, 17 genera and 33 species was collected in emergence traps in 1983 and 1984 from five stations on the Ochre River, Manitoba (50° 04′ N, 99° 48′ W). Species composition for the two years was comparable, but as the result of a summer spate in 1984, abundance was only 40% of that in 1983. Species diversity by station was negatively correlated with substrate instability of the reach, whereas density per trap was negatively correlated with substrate instability and local factors such as sedimentation in some reaches following peak discharges. Analysis of historical peak discharge records indicated that relatively infrequent mid-summer spates had a detrimental effect on subsequent emergence of the Trichoptera fauna. The combination of spates and unstable stream bed substrate resulting from land use practices in the drainage basin have resulted in an impoverished caddisfly fauna in the Ochre River in comparison with other rivers in Manitoba.

51 citations


Journal ArticleDOI
TL;DR: In this paper, a general formula empirically derived for partitioning rainwater into throughfall and stemflow is described, which is suitable for calculating without rain data on an event basis, the weekly or monthly quantity of throughfall or stemflow reaching the ground under different stands.

45 citations


Journal ArticleDOI
TL;DR: The results indicate that most amino acids stimulate at least three different receptors, and only the linear multiple receptor model predicted these results.

37 citations


Journal ArticleDOI
TL;DR: The integrated olfactory nerve activity (integrated NTR) in response to stimulation by various amino acids was investigated in Arctic char during cross-adaptation using a linear multiple receptor model fitting.

33 citations


Journal ArticleDOI
TL;DR: The results showed that annuli were laid down on pike cleithra and pelvic fin rays and OTC-induced mortality was statistically insignificant.
Abstract: . Oxytetracycline (OTC) was intraperitoneally injected into pike, Esox lucius L., to determine the validity of ages derived from cleithra and pelvic fin rays, to determine the rate of OTC incorporation into calcified structures, to decermine suitable marking dosages and to assess OTC-induced mortality. The results showed that annuli were laid down on pike cleithra and pelvic fin rays. OTC was incorporated into most calcified structures as early as 6 h after injection and all structures were marked within 24 h. A dosage range of 25–50 mg OTC/kg fish was appropriate for marking pike. OTC-induced mortality was statistically insignificant.

30 citations


Journal ArticleDOI
TL;DR: Discriminant analysis, based on nine morphological characters, was used to successfully classify body scales of the three species, and the importance of M. duerrschmidtiae as a bioindicator in future lake monitoring and paleolimnological inference studies is discussed.
Abstract: A new species, Mallomonas duerrschmidtiae, with characteristics common to both Mallomonas crassisquama (Asmund) Fott and Mallomonas pseudocoronata Prescott, is described from acidic lakes low in specific conductance and total phosphorus concentration. Characteristics of scales, bristles and spines serve to separate the three taxa. The length and area of scales of M. duerrschmidtiae are significantly larger than those of M. crassisquama but smaller than those of M. pseudocoronata. Although the anterior submarginal ribs of scales of M. duerrschmidtiae may become extended to form short wings, the scales lack the large forward projecting anterior wings characteristic of scales of M. pseudocoronata. Features of the dome and junction between the arms of the V-rib and anterior submarginal ribs also serve to distinguish between the three species. Cells of M. duerrschmidtiae also possess long, smooth and thick spines on their posterior scales and lack helmet bristles. M. duerrschmidtiae has different maxima along pH, temperature, specific conductance, total phosphorus and seasonal gradients than either M. crassisquama or M. pseudocoronata. Discriminant analysis, based on nine morphological characters, was used to successfully classify body scales of the three species. The importance of M. duerrschmidtiae as a bioindicator in future lake monitoring and paleolimnological inference studies is discussed.

28 citations


Journal ArticleDOI
James Haley1
TL;DR: The authors compared three different types of theoretical explanations of sticky wages: implicit contracts, efficiency wage models and insider/outsider models, and reconsiders Keynes' rationale for sticky wages, which focuses on relative wage issues.
Abstract: . The paper compares three different types of theoretical explanation of ‘sticky’wages. They are implicit contracts, efficiency wage models and insider/outsider models. It then reconsiders Keynes’rationale for sticky wages, which focuses on relative wage issues. Finally, the paper considers possible directions for future research.

21 citations


Journal ArticleDOI
TL;DR: Skeletal muscle is the largest T3 tissue pool and seems highly responsive to altered physiologic state.
Abstract: Tissue T3 (3,5,3'-triiodo-L-thyronine) concentrations were measured in rainbow trout, Salmo gairdneri, after digestion by Pronase or collagenase and extraction with ethanolic ammonia (99:1, v/v) followed by 2N NH4OH and chloroform. Recoveries of [(125)I]T3 administered in vivo or in vitro were high and consistent and there was close parallelism between sample dilutions and the radioimmunoassay curve, but recoveries of unlabeled T3 administered in vitro were low and variable. Alternatively, trout were brought to isotopic equilibrium by [(125)I]T3 infusion for 96 h, the extracted [(125)I]T3 determined by gel filtration and the tissue T3 content calculated from the specific activity of plasma [(125)I]T3. By the latter method, tissue T3 concentrations were: intestine (4.2 ng/g), kidney (2.5), liver (2.8), stomach (1.5), heart (1.0), muscle (0.7), gill (0.6) and skin (0.3). Muscle (67% of body weight) comprised the largest tissue T3 pool (82% of all tissues examined). Seven days exposure of trout to water acidified with H2SO4 (pH 4.8) or acidified water containing aluminum (21.6 mM), decreased tissue T3 content generally and particularly in muscle (14% of controls). In conclusion, skeletal muscle is the largest T3 tissue pool and seems highly responsive to altered physiologic state.

Journal ArticleDOI
TL;DR: It is suggested that the differences in the morphogenesis and structure of the secondary palates of various vertebrates may reflect environmentally enforced adaptation, resulting in different programming of cells.
Abstract: The oral cavity of embryos and larvae of the teleost Onchorhynchus kisutch was examined. Tissues were obtained at different ages prior to and after hatching and processed for transmission and scanning electron microscopy. A bilaterally symmetrical bulge developed from the superolateral aspect of the oral cavity and projected toward its floor, along the sides of the tongue. The bulge extended from behind the primary palate to a position midway below the eye, anterior to the gill arches, and it is suggested to be the homologue of the secondary palate of higher vertebrates. Ultrastructurally, the epithelium differentiated as the stratified squamous type and it contained mucous cells. However, the features of programmed cell death seen during palatogenesis in mammals were absent in fish. The fish palate mesenchyme, unlike that of higher vertebrates, was chondrified. Also in contrast to higher vertebrates, alterations were seen in the fish palatal basement membrane. A transient appearance of adepidermal granules in the lamina lucida region was followed by organization of collagen fibrils, first into an orthogonal pattern and then into a herring-bone arrangement, in the lamina reticularis region. There was no further advancement in the morphogenesis of fish palate. It is suggested that the differences in the morphogenesis and structure of the secondary palates of various vertebrates may reflect environmentally enforced adaptation, resulting in different programming of cells.