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- Persson, L., et al.
(författare)
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TROPHIC INTERACTIONS IN TEMPERATE LAKE ECOSYSTEMS - A TEST OF FOOD-CHAIN THEORY
- 1992
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Ingår i: American Naturalist. ; 140:1, s. 59-84
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Tidskriftsartikel (refereegranskat)abstract
- In a comparative study covering 11 temperate lake ecosystems of low to intermediate productivity, we tested the predictions of the food chain model developed by L. Oksanen et al. The pelagic habitat of the most unproductive lakes lacked secondary carnivores (piscivores), whereas secondary carnivores inhabited the more productive lakes in agreement with the assumption that food chain length is limited by the productivity of the system. The observed relationships between planktivores (primary carnivores), zooplankton (herbivores), and phytoplankton (primary producers) were in agreement with the predictions of the Oksanen et al. model for three- and four-trophic-link systems. Piscivore relationships were significant only when the biomass of piscivorous perch only was used as the independent variable (piscivorous perch amounted to greater-than-or-equal-to 97% of total piscivore biomass in five out of six four-link systems). The results suggest that gross patterns of food web dynamics in temperate lakes may be collapsed into food chain dynamics. However, as the higher trophic levels of most lakes were dominated by the same two species, an alternative hypothesis is that the simplicity of the food webs studied allowed food chain dynamics to approximate food web dynamics. The food chain model tested gave accurate predictions of trophic-level relationships within the rather narrow productivity range studied. However, previous data suggest that, due to size-structured interactions, secondary carnivores (piscivores) play a minor role in highly productive systems, a circumstance that may explain the postulated increase in mortality rate of zooplankton with increasing productivity. The observed increase in number of trophic levels with productivity does not necessarily imply a causal relationship between productivity and food chain length, as lake productivity is also correlated with structural complexity (in the form of submerged vegetation and an oxygenated hypolimnion). Habitat heterogeneity may thus influence food chain length, and in general it is likely that food chain length will depend on more than one environmental variable.
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- Andréasson, S, et al.
(författare)
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Medical laboratory technologists' perception of professional self. A study of Swedish MLTs employed in clinical chemistry
- 1992
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Ingår i: Scandinavian Journal of Caring Sciences. - 0283-9318 .- 1471-6712. ; 6:2, s. 67-74
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Tidskriftsartikel (refereegranskat)abstract
- The subjective perception of professional self was studied for a sample of Medical Laboratory Technologists (MLTs) employed in Clinical Chemistry in Sweden. The sample (N = 488) consisted of a randomized tenth of members of their trade union. A mailed questionnaire with 21 items concerning self-description compared with peers in a seven-point Likert type scale was completed by 332 (68%). There was no significant overall difference concerning the four principal types of workplace: Clinical Chemistry, Blood Serology, Primary Care and Clinical Chemistry/Blood Serology. The main difference was found between those in managerial posts (N = 72) and the other MLTs (N = 260). Factor analysis showed three principal components, labelled Professionalism, Work Ethic, and Empathy, but also a different composition of variables of the components for the manager group compared with the non-manager group.
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| 5. |
- Larsson, Per, et al.
(författare)
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Factors determining the uptake of persistent pollutants in an eel population (Anguilla anguilla L.) of a eutrophic lake
- 1991
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Ingår i: Environmental Pollution. - 0269-7491 .- 1873-6424. ; 69:1, s. 39-50
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of persistent pollutants in an eel population from a eutrophic lake of southern Scandinavia was examined. The origin of PCBs, DDT, DDE and lindane found in the fish was most likely the atmosphere. The most important factors for uptake of the chlorinated hydrocarbons was age (exposure time), growth rate and fat content. The life cycle of the eel is unique with a stage in freshwater when energy reserves (fat stored in muscular tissue) and lipophilic pollutants are accumulated. This stage is followed by a long migration to the spawning areas in the Sargasso Sea when pollutants are released from the fat deposits. These two stages followed by a once-in-a-lifetime spawning behaviour, makes the eel especially vulnerable to persistent pollutants. The effects of persistent pollutants combined with the eel's unusual life cycle may explain the decline in the eel population in northern Europe in recent decades.
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