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Sökning: WFRF:(Hartvig Martin)

  • Resultat 1-10 av 17
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1.
  • Andersen, K. H., et al. (författare)
  • Damped trophic cascades driven by fishing in model marine ecosystems
  • 2010
  • Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : Royal Society Publishing. - 1471-2954. ; 277:1682, s. 795-802
  • 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)
  • How community ecology links natural mortality, growth, and production of fish populations
  • 2009
  • Ingår i: ICES Journal of Marine Science. - : Oxford University Press. - 1095-9289. ; 66:9, s. 1978-1984
  • 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)
  • Life-history constraints on the success of the many small eggs reproductive strategy
  • 2008
  • Ingår i: Theoretical Population Biology. - : Academic Press. - 1096-0325. ; 73:4, s. 490-497
  • 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.
  • Brose, Ulrich, et al. (författare)
  • Predicting the consequences of species lossusing size-structured biodiversity approaches
  • 2017
  • Ingår i: Biological Reviews. - : Wiley-Blackwell. - 1464-7931 .- 1469-185X. ; 92:2, s. 684-697
  • Forskningsöversikt (refereegranskat)abstract
    • Understanding the consequences of species loss in complex ecological communities is one of the great challenges in current biodiversity research. For a long time, this topic has been addressed by traditional biodiversity experiments. Most of these approaches treat species as trait-free, taxonomic units characterizing communities only by species number without accounting for species traits. However, extinctions do not occur at random as there is a clear correlation between extinction risk and species traits. In this review, we assume that large species will be most threatened by extinction and use novel allometric and size-spectrum concepts that include body mass as a primary species trait at the levels of populations and individuals, respectively, to re-assess three classic debates on the relationships between biodiversity and (i) food-web structural complexity, (ii) community dynamic stability, and (iii) ecosystem functioning. Contrasting current expectations, size-structured approaches suggest that the loss of large species, that typically exploit most resource species, may lead to future food webs that are less interwoven and more structured by chains of interactions and compartments. The disruption of natural body-mass distributions maintaining food-web stability may trigger avalanches of secondary extinctions and strong trophic cascades with expected knock-on effects on the functionality of the ecosystems. Therefore, we argue that it is crucial to take into account body size as a species trait when analysing the consequences of biodiversity loss for natural ecosystems. Applying size-structured approaches provides an integrative ecological concept that enables a better understanding of each species' unique role across communities and the causes and consequences of biodiversity loss.
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5.
  • Escudier, Bernard, et al. (författare)
  • Multidisciplinary management of metastatic renal cell carcinoma in the era of targeted therapies
  • 2012
  • Ingår i: Cancer Treatment Reviews. - : Elsevier. - 0305-7372 .- 1532-1967. ; 38:2, s. 127-132
  • Forskningsöversikt (refereegranskat)abstract
    • The use of targeted agents to treat metastatic renal cell carcinoma (mRCC) has significantly extended progression-free and overall survival but raises issues relating to the long-term delivery of care and the sustained monitoring of efficacy and toxicities, certain of which have not previously been experienced. In this paper, an expert group of medical oncologists, urologists and oncology nurses and pharmacists review and make informal recommendations on the multidisciplinary management of mRCC in the light of progress made and problems that have arisen. Decentralisation of care, with a shift in emphasis from large to small hospitals and possibly to the community, may offer advantages of cost and convenience. However, the major responsibility for care should continue to lie with clinicians (either medical oncologists or urologists) with extensive experience in mRCC, assisted by specialist nurses, and working in centres with facilities adequate to monitor efficacy and manage toxicities. That said, the extended survival of patients emphasises the importance of compliance and the long-term prevention, detection and management of side effects. Much of this will take place in the community. There is therefore a need for multidisciplinary working to extend beyond specialist centres to include general practitioners, community nurses and pharmacists. Although this paper focuses on mRCC, many of the considerations discussed are also relevant to the management of more common solid tumours in the era of targeted therapy.
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6.
  • Grand, Johannes, et al. (författare)
  • Mean arterial pressure during targeted temperature management and renal function after out-of-hospital cardiac arrest
  • 2019
  • Ingår i: Journal of Critical Care. - : Elsevier. - 0883-9441. ; 50, s. 234-241
  • 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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7.
  • Hartvig, Martin, et al. (författare)
  • Coexistence of structured populations with size-based prey selection.
  • 2013
  • Ingår i: Theoretical Population Biology. - : Academic Press. - 1096-0325. ; 89, s. 24-33
  • 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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8.
  • Hartvig, Martin (författare)
  • Food Web Ecology -- individual life-histories and ecological processes shape complex communities
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt)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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9.
  • Hartvig, Martin, et al. (författare)
  • Food web framework for size-structured populations.
  • 2011
  • Ingår i: Journal of Theoretical Biology. - : Academic Press. - 1095-8541. ; 272:1, s. 113-122
  • 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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  • Resultat 1-10 av 17
  • [1]2Nästa

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