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T Oksanen

Publications and source records attributed to T Oksanen.

6 recordsLinked to original sources
PubMed2000

Are lemmings prey or predators?

Large oscillations in the populations of Norwegian lemmings have mystified both professional ecologists and lay public. Ecologists suspect that these oscillations are driven by a trophic mechanism: either an interaction between lemmings and their food supply, or an interaction between lemmings and their predators. If lemming cycles are indeed driven by a trophic interaction, can we tell whether lemmings act as the resource ('prey') or the consumer ('predator')? In trophic interaction models, peaks of resource density generally have a blunt, rounded shape, whereas peaks of consumer density are sharp and angular. Here we have applied several statistical tests to three lemming datasets and contrasted them with comparable data for cyclic voles. We find that vole peaks are blunt, consistent with their cycles being driven by the interaction with predators. In contrast, the shape of lemming peaks is consistent with the hypothesis that lemmings are functional predators, that is, their cycles are driven by their interaction with food plants. Our findings suggest that a single mechanism, such as interaction between rodents and predators, is unlikely to provide the 'universal' explanation of all cyclic rodent dynamics.

Animals↗
PubMed2000

Treatment of recycled kraft pulps with Trichoderma reesei hemicellulases and cellulases.

Effects of recycling ECF-bleached softwood kraft pulp on pulp properties were evaluated in the laboratory. The tensile strength, fiber flexibility and WRV lost during drying of the pulp were recovered by refining between the cycles which, however, resulted in deteriorated drainage properties. The recycled pulps were treated with purified Trichoderma reesei cellulases and hemicellulases and the changes in fiber properties due to enzymatic treatments were characterized. The endoglucanases (EG I and EG II) significantly improved pulp drainage already at low dosage levels, and EG II was found to be more effective at a given level of carbohydrate solubilization. Combining hemicellulases with the endoglucanase treatments increased the positive effects of the endoglucanases on pulp drainage. However, as a result of the endoglucanase treatments a slight loss in strength was observed. Combining mannanase with endoglucanase treatments appeared to increase this negative effect, whereas the impact of xylanase was not significant. Although the drainage properties of the pulps could be improved by selected enzymes, the water retention capacity of the dried hornified fibers could not be recovered by any of the enzymes tested.

Biotechnology↗
PubMed1996

Hypopigmented skin alterations resembling tuberous sclerosis in normal skin.

The significance of hypopigmented skin findings as manifestations of the gene for tuberous sclerosis (TS) in near relatives of TS patients is a difficult problem. We therefore studied the number and kind of whitish skin alterations found in 100 medical students and 100 school children. Ninety three percent of the former and 79% of the latter had some whitish lesions, many of them scars. Twenty percent of the adults and 12% of the children had roundish or oval macules larger than 10 mm in diameter, not known to be scars. In clinical practice with TS patients, our attention has been drawn to whitish raised masses or streaks in their first degree relatives. These were also found in study subjects so the significance of such lesions remains unclear. The role of Wood's light turned out to be questionable, far from pathognomonic for TS; 25% of all the whitish findings and 53% of the hypopigmented macules larger than 10 mm in diameter showed distinct or brilliant fluorescence under Wood's light.

Adult↗
PubMed1990

Prevention of travellers' diarrhoea by Lactobacillus GG.

A placebo-controlled double-blind study was conducted on the efficacy of Lactobacillus GG in preventing travellers' diarrhoea. Altogether 820 persons travelling on holiday to southern Turkey to two destinations were randomized into two groups receiving either Lactobacillus GG or placebo in identical sachets. On the return flight each participant completed a questionnaire indicating the incidence of diarrhoea and related symptoms during the trip. Of the original group 756 (92%) subjects completed the study acceptably. The overall incidence of diarrhoea was 43.8% (331 cases). The total incidence of diarrhoea in the placebo group was 46.5% and in the Lactobacillus GG 41.0% indicating an overall protection of 11.8%. Protection rates varied between two different destinations with the maximum protection rate reported as 39.5%. Among older age groups there was significantly less diarrhoea when compared to younger travellers. Lactobacillus GG appeared to be effective in reducing the occurrence of travellers' diarrhoea in one of the two destinations with no side effects.

Adolescent↗