| 1. |
- Andersen, K. H., et al.
(författare)
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Damped trophic cascades driven by fishing in model marine ecosystems
- 2010
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 277:1682, s. 795-802
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Tidskriftsartikel (refereegranskat)abstract
- The largest perturbation on upper trophic levels of many marine ecosystems stems from fishing. The reaction of the ecosystem goes beyond the trophic levels directly targeted by the fishery. This reaction has been described either as a change in slope of the overall size spectrum or as a trophic cascade triggered by the removal of top predators. Here we use a novel size- and trait-based model to explore how marine ecosystems might react to perturbations from different types of fishing pressure. The model explicitly resolves the whole life history of fish, from larvae to adults. The results show that fishing does not change the overall slope of the size spectrum, but depletes the largest individuals and induces trophic cascades. A trophic cascade can propagate both up and down in trophic levels driven by a combination of changes in predation mortality and food limitation. The cascade is damped as it comes further away from the perturbed trophic level. Fishing on several trophic levels leads to a disappearance of the signature of the trophic cascade. Differences in fishing patterns among ecosystems might influence whether a trophic cascade is observed.
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| 2. |
- Andersen, K. H., et al.
(författare)
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How community ecology links natural mortality, growth, and production of fish populations
- 2009
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1095-9289 .- 1054-3139. ; 66:9, s. 1978-1984
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Tidskriftsartikel (refereegranskat)abstract
- Andersen, K. H., Farnsworth, K. D., Pedersen, M., Gislason, H., and Beyer, J. E. 2009. How community ecology links natural mortality, growth, and production of fish populations. - ICES Journal of Marine Science, 66: 1978-1984.
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| 3. |
- Andersen, K H, et al.
(författare)
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Life-history constraints on the success of the many small eggs reproductive strategy
- 2008
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 1096-0325 .- 0040-5809. ; 73:4, s. 490-497
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Tidskriftsartikel (refereegranskat)abstract
- The reproductive strategy of most fishes is to produce a large number of tiny eggs, leading to a huge difference between egg size and asymptotic body size. The viability of this strategy is examined by calculating the life-time reproductive success R-0 as a function of the asymptotic body size. A simple criterion for the optimality of producing small eggs is found, depending on the rate of predation relative to the specific rate of consumption. Secondly it is shown that the success of the reproductive strategy is increasing with asymptotic body size. Finally the existence of both upper and lower limits on the allowed asymptotic sizes is demonstrated. A metabolic upper limit to asymptotic body size for all higher animals is derived.
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| 4. |
- Grand, Johannes, et al.
(författare)
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Mean arterial pressure during targeted temperature management and renal function after out-of-hospital cardiac arrest
- 2019
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Ingår i: Journal of Critical Care. - : Elsevier BV. - 0883-9441. ; 50, s. 234-241
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: This study investigates the association between mean arterial pressure (MAP) and renal function after out-of-hospital cardiac arrest (OHCA). Materials and methods: Post-hoc analysis of 851 comatose OHCA-patients surviving >48 h included in the targeted temperature management (TTM)-trial. Results: Patients were stratified by mean MAP during TTM in the following groups; <70 mmHg (22%), 70–80 mmHg (43%), and > 80 mmHg (35%). Median (interquartile range) eGFR (ml/min/1.73 m2) 48 h after OHCA was inversely associated with MAP-group (70 (47–102), 84 (56–113), 94 (61–124), p <.001, for the <70-group, 70–80-group and > 80-group respectively). After adjusting for potential confounders, in a mixed model including eGFR after 1, 2 and 3 days this association remained significant (pgroup_adjusted = 0.0002). Higher mean MAP was independently associated with lower odds of renal replacement therapy (odds ratioadjusted = 0.77 [95% confidence interval, 0.65–0.91] per 5 mmHg increase; p =.002]). Conclusions: Low mean MAP during TTM was independently associated with decreased renal function and need of renal replacement therapy in a large cohort of comatose OHCA-patients. Increasing MAP above the recommended 65 mmHg could potentially be renal-protective. This hypothesis should be investigated in prospective trials.
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| 5. |
- Hartvig, Martin, et al.
(författare)
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Coexistence of structured populations with size-based prey selection.
- 2013
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 1096-0325 .- 0040-5809. ; 89, s. 24-33
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Tidskriftsartikel (refereegranskat)abstract
- Species with a large adult-offspring size ratio and a preferred predator-prey mass ratio undergo ontogenetic trophic niche shift(s) throughout life. Trophic interactions between such species vary throughout life, resulting in different species-level interaction motifs depending on the maximum adult sizes and population size distributions. We explore the assembly and potential for coexistence of small communities where all species experience ontogenetic trophic niche shifts. The life-history of each species is described by a physiologically structured model and species identity is characterised by the trait: size at maturation. We show that a single species can exist in two different states: a 'resource driven state' and a 'cannibalistic state' with a large scope for emergent Allee effects and bistable states. Two species can coexist in two different configurations: in a 'competitive coexistence' state when the ratio between sizes at maturation of the two species is less than a predator-prey mass ratio and the resource level is low to intermediate, or in a 'trophic ladder' state if the ratio of sizes at maturation is larger than the predator-prey mass ratio at all resource levels. While there is a large scope for coexistence of two species, the scope for coexistence of three species is limited and we conclude that further trait differentiation is required for coexistence of more species-rich size-structured communities.
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| 6. |
- Hartvig, Martin
(författare)
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Food Web Ecology -- individual life-histories and ecological processes shape complex communities
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis sets out a food web framework for size-structured populations. The framework enables an ecological approach to food web modelling as the individual life-history from birth, through maturation, and ultimately death is explicitly resolved with the use of bioenergetics based on individual body size. Each population resolves size-structure through a size-spectrum containing the individual abundance as a continuous function of body size. Individuals select prey items of a suitable size, which can be popularised as "big ones eat smaller ones". This allows individuals to change diet throughout life (life-history omnivory). In the framework individual food consumption leads to growth in body size and allocation to reproduction, which drives the population dynamics as opposed to instantaneous population increase in unstructured food web models. Paper I introduces the framework and shows how a simple realistic parametrisation is possible when a trait-based species characterisation is used. An analytical approximation of the food web framework is derived, and validated through comparison with dynamic simulations. Paper II extends the dynamic framework by also considering space, and demonstrates how large food webs can be formed through sequential community assembly. The resulting communities resemble the topology of natural food webs as well as complying with empirical data on diversity and biomass distributions -- demonstrating that individual-level food encounter and prey-selection from the rule "big ones eat smaller ones" lead to complex and realistic food webs. Paper III uses the analytical solution of the framework to show the conditions under which the many-small-eggs strategy of the fishes is a viable strategy. Paper IV utilises the trait-based species description to show that coexisting species pairs involved in intraguild predation exist for all resource levels. The model thus explains empirically observed coexistence at high resource levels contrary to contemporary theoretical models. Paper V demonstrates how harvesting initiates a trophic cascade that may propagate both downwards and upwards in trophic levels, and that the harvesting pattern may influence whether or not trophic cascades are empirically detected. In Paper VI the analytical solution is used to provide a theoretical understanding of empirically observed relationships between natural mortality, growth, and production rates.
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| 7. |
- Hartvig, Martin, et al.
(författare)
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Food web framework for size-structured populations.
- 2011
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 1095-8541 .- 0022-5193. ; 272:1, s. 113-122
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Tidskriftsartikel (refereegranskat)abstract
- We synthesise traditional unstructured food webs, allometric body size scaling, trait-based modelling, and physiologically structured modelling to provide a novel and ecologically relevant tool for size-structured food webs. The framework allows food web models to include ontogenetic growth and life-history omnivory at the individual level by resolving the population structure of each species as a size-spectrum. Each species is characterised by the trait 'size at maturation', and all model parameters are made species independent through scaling with individual body size and size at maturation. Parameter values are determined from cross-species analysis of fish communities as life-history omnivory is widespread in aquatic systems, but may be reparameterised for other systems. An ensemble of food webs is generated and the resulting communities are analysed at four levels of organisation: community level, species level, trait level, and individual level. The model may be solved analytically by assuming that the community spectrum follows a power law. The analytical solution provides a baseline expectation of the results of complex food web simulations, and agrees well with the predictions of the full model on (1) biomass distribution as a function of individual size, (2) biomass distribution as a function of size at maturation, and (3) relation between predator-prey mass ratio of preferred and eaten food. The full model additionally predicts the diversity distribution as a function of size at maturation.
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| 8. |
- Rall, Bjoern C., et al.
(författare)
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Universal temperature and body-mass scaling of feeding rates
- 2012
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Ingår i: Philosophical Transactions of the Royal Society B: Biological Sciences. - : The Royal Society. - 1471-2970 .- 0962-8436. ; 367:1605, s. 2923-2934
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of feeding rates is the basis to understand interaction strength and subsequently the stability of ecosystems and biodiversity. Feeding rates, as all biological rates, depend on consumer and resource body masses and environmental temperature. Despite five decades of research on functional responses as quantitative models of feeding rates, a unifying framework of how they scale with body masses and temperature is still lacking. This is perplexing, considering that the strength of functional responses (i.e. interaction strengths) is crucially important for the stability of simple consumer-resource systems and the persistence, sustainability and biodiversity of complex communities. Here, we present the largest currently available database on functional response parameters and their scaling with body mass and temperature. Moreover, these data are integrated across ecosystems and metabolic types of species. Surprisingly, we found general temperature dependencies that differed from the Arrhenius terms predicted by metabolic models. Additionally, the body-mass-scaling relationships were more complex than expected and differed across ecosystems and metabolic types. At local scales (taxonomically narrow groups of consumer-resource pairs), we found hump-shaped deviations from the temperature and body-mass-scaling relationships. Despite the complexity of our results, these body-mass-and temperature-scaling models remain useful as a mechanistic basis for predicting the consequences of warming for interaction strengths, population dynamics and network stability across communities differing in their size structure.
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| 9. |
- van Deurs, Mikael, et al.
(författare)
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Critical threshold size for overwintering sandeels (Ammodytes marinus)
- 2011
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 158:12, s. 2755-2764
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Tidskriftsartikel (refereegranskat)abstract
- Several ecologically and commercially important fish species spend the winter in a state of minimum feeding activity and at lower risk of predation. To enable this overwintering behaviour, energetic reserves are generated prior to winter to support winter metabolism. Maintenance metabolism in fish scales with body size and increases with temperature, and the two factors together determine a critical threshold size for passive overwintering below which the organism is unlikely to survive without feeding. This is because the energetic cost of metabolism exceeds maximum energy reserves. In the present study, we estimated the energetic cost of overwintering from a bioenergetic model. The model was parameterised using respirometry-based measurements of standard metabolic rate in buried A. tobianus (a close relative to A. marinus) at temperatures from 5.3 to 18.3 degrees C and validated with two independent long-term overwintering experiments. Maximum attainable energy reserves were estimated from published data on A. marinus in the North Sea. The critical threshold size in terms of length (L(th)) for A. marinus in the North Sea was estimated to be 9.5 cm. We then investigated two general predictions: (1) Fish smaller than L(th) display winter feeding activity, and (2) size at maturation of iteroparous species is larger than L(th) to ensure sufficient energy reserves to accommodate both the metabolic cost of passive overwintering and reproductive investments. Both predictions were found to be consistent with data on size at maturation and total body energy in December and February.
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| 10. |
- Winther-Jensen, Matilde, et al.
(författare)
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Comorbidity burden is not associated with higher mortality after out-of-hospital cardiac arrest*
- 2016
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Ingår i: Scandinavian Cardiovascular Journal. - : Informa UK Limited. - 1401-7431 .- 1651-2006. ; 50:5-6, s. 305-310
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Tidskriftsartikel (refereegranskat)abstract
- Objectives. We investigated whether comorbidity burden of comatose survivors of out-of-hospital cardiac arrest (OHCA) affects outcome and if comorbidity modifies the effect of target temperature management (TTM) on final outcome. Design. The TTM trial randomized 939 patients to 24 h of TTM at either 33 or 36 °C with no difference regarding mortality and neurological outcome. This post-hoc study of the TTM-trial formed a modified comorbidity index (mCI), based on available comorbidities from the Charlson comorbidity index (CCI). Results. Bystander cardiopulmonary resuscitation (CPR) decreased with higher comorbidity group, p = 0.01. Comorbidity groups were univariately associated with higher mortality compared to mCI0 (HRmCI1: 1.55, CI: 1.25–1.93, p mCI2: 2.01, CI: 1.55–2.62, p mCI ≥ 3: 2.16, CI: 1.57–2.97, p C11: 1.17, CI: 0.92–1.48, p = 0.21, HRmCI2: 1.28, CI: 0.96–1.71, p = 0.10, HRmCI ≥ 3: 1.37, CI: 0.97–1.95, p = 0.08). There was no interaction between comorbidity burden and level of TTM on outcome, p = 0.61. Conclusion. Comorbidity burden was associated with higher mortality following OHCA, but when adjusting for confounders, the influence was no longer significant. The association between mCI and mortality was not modified by TTM. Comorbidity burden is associated with lower rates of bystander cardiopulmonary resuscitation after OHCA.
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