| 1. |
- Persson, Anders, et al.
(författare)
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Effects of enrichment on simple aquatic food webs
- 2001
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 157:6, s. 654-669
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Tidskriftsartikel (refereegranskat)abstract
- Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.
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| 2. |
- Persson, Anders, et al.
(författare)
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Effects of enrichment on simple aquatic food webs
- 2001
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Ingår i: The American Naturalist. ; 157:6, s. 654-669
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Tidskriftsartikel (refereegranskat)abstract
- Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on
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| 7. |
- Persson, Henry, et al.
(författare)
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Modelling of foam spread on a burning liquid
- 2001
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Ingår i: Interflam 2001. International Interflam Conference. 9th proceedings. Vol. 1. September 17-19.. - : Interscience Communications Ltd.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Persson, Magnus, et al.
(författare)
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A new non-invasive ultrasonic method for simultaneous measurements of longitudinal and radial arterial wall movements: first in vivo trial.
- 2003
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Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961. ; 23:5, s. 247-251
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Tidskriftsartikel (refereegranskat)abstract
- During recent years, the radial movement of the arterial wall has been extensively studied, and measurements of the radial movement are now an important tool in cardiovascular research for characterizing the mechanical properties of the arterial wall. In contrast, the longitudinal movement of vessels has gained little or no attention as it has been presumed that this movement is negligible. With modern high-resolution ultrasound, it can, however, be seen that the intima-media complex of the arterial wall moves not only in the radial direction, but also in the longitudinal direction during pulse-wave propagation. This paper describes a new non-invasive ultrasonic method that is able to measure simultaneously two dimensionally arterial vessel wall movements. The method is demonstrated in a limited in vivo trial. Results from the in vivo trial show that, apart from the well-known radial movement, there is a distinct longitudinal movement in the human common carotid artery with, in this case, the intima-media complex moving substantially as compared with the region of the tunica adventitia. Two-dimensional evaluation of the vessel-wall movements, taking not only the radial movement, but also the longitudinal movement into account, may provide novel information of importance in the evaluation of vessel-wall function.
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| 9. |
- Persson, Magnus, et al.
(författare)
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Non-invasive measurement of arterial longitudinal movement
- 2002
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Ingår i: Proceedings of the IEEE Ultrasonics Symposium. - 1051-0117. ; 2, s. 1783-1786
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Konferensbidrag (refereegranskat)abstract
- In arterial vessel wall characterisation the longitudinal movements of vessels have gained little or no attention. It has been presumed that the arterial vessels move very little in the longitudinal direction. With modern high resolution ultrasound it can, however, be seen that arterial vessels move not only in the circumferential, but also in longitudinal direction. This paper describes a non-invasive, ultrasound based method which estimates the longitudinal and the circumferential movement, respectively. The method is demonstrated in a limited in vivo study of the common carotid artery. Results show that, apart from the well known circumferential movement, there is a distinct longitudinal movement.
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