Relationship between littoral grazers and metaphytic algae in five softwater lakes

The zoobenthos communities within the littoral zones of five low alkalinity, Ontario lakes were examined during summer 1987. Detached algal clouds or metaphyton, dominated by algae from the family Zygnemataceae, accumulated over the summer in three of these lakes. Previous researchers have hypothesized that diminished grazing pressure due to extirpation of acid sensitive herbivores might enhance the development of metaphytic algae at pHs less than 6. No overt consistent differences existed among the abundances of small (cladocerans, cyclopoids, ostracods, oligochaetes, dipterans) or medium (amphipods, gastropods, emphemeropterans, trichopterans) grazers in study lakes with or without metaphyton. Notable differences did exist, however, with respect to what we term large grazers. Crayfish, algivorous fish (mostly cyprinids), and to a lesser extent tadpoles, were absent or rare in the three lakes with metaphytic algae but abundant in those without. If a reduction in grazing pressure can be implicated as a factor in enhanced metaphyton development, our correlative results suggest that it is the large grazers, particularly crayfish, that are the most likely candidates.     

Principes généraux de déclenchement du plan blanc : place de la biologie

Le plateau technique hospitalier, qui inclut la chirurgie, l’obstétrique, la pédiatrie, l’anesthésie-réanimation, les explorations fonctionnelles et les disciplines interventionnelles, l’imagerie et la biologie, se doit d’être configuré dans une perspective d’accès aux soins de qualité 24 heures sur 24 pour la population du territoire qu’il dessert et pour répondre à l’accueil d’un grand nombre de victimes dans les êtablissements de santé, face à la survenue d’événements à caractère exceptionnel.     

Food web structure variability in the surface layer, at a fixed station influenced by the North Western Mediterranean Current

The structure of the planktonic community and the influence of mesozooplankton migration on the microbial food web were investigated during six diel studies from June 92 to June 93 in the surface waters of a station in the North-Western Mediterranean Sea. Each diel study consisted of sampling at 5 and 40 m every 3 h over 24 h. Most of the times diel cycles did not show any convincing diel patterns in any of the variables studied. Clear zooplankton migration was evident in only two diel studies.The ratio of heterotrophic/autotrophic biomasses varied from 0.68 to 3.0, with a strong dominance of the heterotrophic biomass under oligotrophic conditions. Differences in food web structure were probably related to the influences of coastal water and the North-Western Mediterranean Current. Thus we found that the planktonic food web variability relatable to hydrodynamic variability, to be greater than diel variability. However, very large differences in food web structure among dates were evident. For example proportion of Chl a found in the <10 µm fraction varied from 18 to 96%.     

Vertical foodweb structure of freshwater zooplankton assemblages estimated by stable nitrogen isotopes

Although theoretical foodweb models predict the presence of only three to four trophic categories, estimation of “potential” vertical foodweb structure from species lists and inferred feeding interactions suggest that as many as 7 trophic categories can occur in the pelagic foodwebs of North American glaciated lakes. A compilation of data on the nitrogen isotopic composition of zooplankton from 46 Canadian Shield lakes suggested the average existence of one “realized” trophic category in addition to that of filter-feeding, herbivorous cladocerans. When phytoplankton, planktivorous invertebrates, and plantivorous and piscivorous fish are included, the vertical foodweb structure in the pelagic zones of these lakes are greater than those hypothesized from some theoretical models.     

Empirical methodology for predicting changes in species range extension and richness associated with climate warming

Species richness and extent of geographical range for North American freshwater amphipods and crayfish are strongly correlated with mean annual absolute, or range of, temperature, respectively. Such spatially based relationships are shown to be useful for predicting the biological consequences arising through scenarios of temporal climate warming.     

Identical giemsa banding patterns of two macaca species: Macaca mulatta and M. fascicularis. A densitometric study.

Karyotypes of Macaca mulatta and M. fascicularis (2n equals 42) were compared using the Giemsa banding pattern technique. No differences between the chromosomes of both Macaca species were found with conventional staining methods. In the literature the occurrence of fertile hybrids is used as an argument in favor of conspecificity. The banding patterns were evaluated by comparison of their density distribution curves. Our data indicated no significant differences between the two Macaca species.     

Effect of endotoxin pretreatment on the pulmonary vascular response to hypoxia in O2-exposed lambs

We recently reported that endotoxin infusion before O2 exposure significantly reduced or delayed the onset of pulmonary edema formation and respiratory failure by reducing the oxidant stress of O2 exposure. Despite these beneficial effects of endotoxin treatment, lung microvascular permeability eventually increased, but postmortem lung water content was less than expected. Prolonged O2 breathing blunts or abolishes the pulmonary constrictor response to alveolar hypoxia in some species, and it is possible that the loss of this response could contribute further to edema formation. To determine whether the reduction in lung edema observed in endotoxin-treated, O2-exposed lambs was linked to the preservation of hypoxic pulmonary vasoconstriction (HPV), we measured pulmonary vascular resistance before and after 8 min of isocarbic hypoxia (inspired O2 fraction 0.12) during each day of O2 exposure. In six control lambs, the pressor response to hypoxia was abolished after 72 h in O2, and the lambs developed respiratory failure shortly thereafter. In six endotoxin-treated lambs, HPV was preserved for as long as 144 h of O2 exposure. In two control O2-exposed lambs in whom HPV was abolished, the infusion of either angiotensin or prostaglandin H2 analogue increased pulmonary vascular resistance by greater than 75%. We conclude that in lambs 1) hyperoxia abolishes the pulmonary vascular response to hypoxia, 2) endotoxin pretreatment reduces acute O2-induced lung injury and preserves the pulmonary constrictor response to hypoxia, and 3) the loss of HPV during O2 exposure may be the result of oxidant-mediated injury to the hypoxia response itself and not the result of diffuse damage to the vasoconstrictor effector mechanism.