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Sökning: WFRF:(Jonsson Tomas)

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11.
  • Jonsson, Tomas, et al. (författare)
  • Predictive power of food web models based on body size decreases with trophic complexity
  • 2018
  • Ingår i: Ecology Letters. - : Wiley-Blackwell Publishing Inc.. - 1461-023X .- 1461-0248. ; 21:5, s. 702-712
  • Tidskriftsartikel (refereegranskat)abstract
    • Food web models parameterised using body size show promise to predict trophic interaction strengths (IS) and abundance dynamics. However, this remains to be rigorously tested in food webs beyond simple trophic modules, where indirect and intraguild interactions could be important and driven by traits other than body size. We systematically varied predator body size, guild composition and richness in microcosm insect webs and compared experimental outcomes with predictions of IS from models with allometrically scaled parameters. Body size was a strong predictor of IS in simple modules (r(2)=0.92), but with increasing complexity the predictive power decreased, with model IS being consistently overestimated. We quantify the strength of observed trophic interaction modifications, partition this into density-mediated vs. behaviour-mediated indirect effects and show that model shortcomings in predicting IS is related to the size of behaviour-mediated effects. Our findings encourage development of dynamical food web models explicitly including and exploring indirect mechanisms.
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12.
  • Jonsson, Tomas, et al. (författare)
  • Trophic interactions affect the population dynamics and risk of extinction of basal species in food webs
  • 2010
  • Ingår i: Ecological Complexity. - : Elsevier. - 1476-945X .- 1476-9840. ; 7:1, s. 60-68
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper addresses effects of trophic complexity on basal species, in a Lotka–Volterra model with stochasticity. We use simple food web modules, with three trophic levels, and expose every species to random environmental stochasticity and analyze (1) the effect of the position of strong trophic interactions on temporal fluctuations in basal species’ abundances and (2) the relationship between fluctuation patterns and extinction risk. First, the numerical simulations showed that basal species do not simply track the environment, i.e. species dynamics do not simply mirror the characteristics of the applied environmental stochasticity. Second, the extinction risk of species was related to the fluctuation patterns of the species.More specifically, we show (i) that despite being forced by random stochasticity without temporal autocorrelation (i.e. white noise), there is significant temporal autocorrelation in the time series of all basal species’ abundances (i.e. the spectra of basal species are red-shifted), (ii) the degree of temporal autocorrelation in basal species time series is affected by food web structure and (iii) the degree of temporal autocorrelation tend to be correlated to the extinction risks of basal species.Our results emphasize the role of food web structure and species interactions in modifying the response of species to environmental variability. To shed some light on the mechanisms we compare the observed pattern in abundances of basal species with analytically predicted patterns and show that the change in the predicted pattern due to the addition of strong trophic interactions is correlated to the extinction risk of the basal species. We conclude that much remain to be understood about the mechanisms behind the interaction among environmental variability, species interactions, population dynamics and vulnerability before we quantitatively can predict, for example, effects of climate change on species and ecological communities. Here, however, we point out a new possible approach for identifying species that are vulnerable to environmental stochasticity by checking the degree of temporal autocorrelation in the time series of species. Increased autocorrelation in population fluctuations can be an indication of increased extinction risk.
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13.
  • Karlsson, Patrik, et al. (författare)
  • Food web structure and interaction strength pave the way for vulnerability to extinction
  • 2007
  • Ingår i: Journal of Theoretical Biology. - : Elsevier. - 0022-5193 .- 1095-8541. ; 249:1, s. 77-92
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper focuses on how food web structure and interactions among species affects the vulnerability, due to environmental variability, to extinction of species at different positions in model food webs. Vulnerability is here not measured by a traditional extinction threshold but is instead inspired by the IUCN criteria for endangered species: an observed rapid decline in population abundance. Using model webs influenced by stochasticity with zero autocorrelation, we investigate the ecological determinants of species vulnerability, i.e. the trophic interactions between species and food web structure and how these interact with the risk of sudden drops in abundance of species. We find that (i) producers fulfil the criterion of vulnerable species more frequently than other species, (ii) food web structure is related to vulnerability, and (iii) the vulnerability of species is greater when involved in a strong trophic interaction than when not. We note that our result on the relationship between extinction risk and trophic position of species contradict previous suggestions and argue that the main reason for the discrepancy probably is due to the fact that we study the vulnerability to environmental stochasticity and not extinction risk due to overexploitation, habitat destruction or interactions with introduced species. Thus, we suggest that the vulnerability of species to environmental stochasticity may be differently related to trophic position than the vulnerability of species to other factors.Earlier research on species extinctions has looked for intrinsic traits of species that correlate with increased vulnerability to extinction. However, to fully understand the extinction process we must also consider that species interactions may affect vulnerability and that not all extinctions are the result of long, gradual reductions in species abundances. Under environmental stochasticity (which importance frequently is assumed to increase as a result of climate change) and direct and indirect interactions with other species some extinctions may occur rapidly and apparently unexpectedly. To identify the first declines of population abundances that may escalate and lead to extinctions as early as possible, we need to recognize which species are at greatest risk of entering such dangerous routes and under what circumstances. This new perspective may contribute to our understanding of the processes leading to extinction of populations and eventually species. This is especially urgent in the light of the current biodiversity crisis where a large fraction of the world's biodiversity is threatened.
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14.
  • Laubmeier, A. N., et al. (författare)
  • From theory to experimental design : Quantifying a trait-based theory of predator-prey dynamics
  • 2018
  • Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 13:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Successfully applying theoretical models to natural communities and predicting ecosystem behavior under changing conditions is the backbone of predictive ecology. However, the experiments required to test these models are dictated by practical constraints, and models are often opportunistically validated against data for which they were never intended. Alternatively, we can inform and improve experimental design by an in-depth pre-experimental analysis of the model, generating experiments better targeted at testing the validity of a theory. Here, we describe this process for a specific experiment. Starting from food web ecological theory, we formulate a model and design an experiment to optimally test the validity of the theory, supplementing traditional design considerations with model analysis. The experiment itself will be run and described in a separate paper. The theory we test is that trophic population dynamics are dictated by species traits, and we study this in a community of terrestrial arthropods. We depart from the Allometric Trophic Network (ATN) model and hypothesize that including habitat use, in addition to body mass, is necessary to better model trophic interactions. We therefore formulate new terms which account for micro-habitat use as well as intra-and interspecific interference in the ATN model. We design an experiment and an effective sampling regime to test this model and the underlying assumptions about the traits dominating trophic interactions. We arrive at a detailed sampling protocol to maximize information content in the empirical data obtained from the experiment and, relying on theoretical analysis of the proposed model, explore potential shortcomings of our design. Consequently, since this is a "pre-experimental" exercise aimed at improving the links between hypothesis formulation, model construction, experimental design and data collection, we hasten to publish our findings before analyzing data from the actual experiment, thus setting the stage for strong inference.
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15.
  • Lövdén, Martin, et al. (författare)
  • The dimensionality of between-person differences in white matter microstructure in old age
  • 2013
  • Ingår i: Human Brain Mapping. - : Wiley. - 1065-9471 .- 1097-0193. ; 34:6, s. 1386-1398
  • Tidskriftsartikel (refereegranskat)abstract
    • Between-person differences in white matter microstructure may partly generalize across the brain and partly play out differently for distinct tracts. We used diffusion-tensor imaging and structural equation modeling to investigate this issue in a sample of 260 adults aged 60–87 years. Mean fractional anisotropy and mean diffusivity of seven white matter tracts in each hemisphere were quantified. Results showed good fit of a model positing that individual differences in white matter microstructure are structured according to tracts. A general factor, although accounting for variance in the measures, did not adequately represent the individual differences. This indicates the presence of a substantial amount of tract-specific individual differences in white matter microstructure. In addition, individual differences are to a varying degree shared between tracts, indicating that general factors also affect white matter microstructure. Age-related differences in white matter microstructure were present for all tracts. Correlations among tract factors did not generally increase as a function of age, suggesting that aging is not a process with homogenous effects on white matter microstructure across the brain. These findings highlight the need for future research to examine whether relations between white matter microstructure and diverse outcomes are specific or general. Hum Brain Mapp, 2012. © 2012 Wiley Periodicals, Inc.
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16.
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17.
  • Roos, Henrik, et al. (författare)
  • Identification of patches with high ecological importance of broadleaved forests and open lands with valuable trees in Valle : Using a biodiversity capacity landscape metric, combining area and connectivity, to examining management options
  • 2021
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • This study is a complement to previous studies of regional action plans of green infrastructure in Valle (County Administrative Board 2016; County Administrative Board 2019). The aim was to identify the relative importance of biotope patches of broadleaved forest and open lands with valuable trees, respectively, in Valle for the maintenance and enhancement of biodiversity. A testversion of the method Biotope Biodiversity Capacity Indicator (BBCI) was applied on the two biotopes of broadleaved forest and open lands with valuable trees in Valle. BBCI was developed within the project “Landscape biodiversity capacity: a tool for measuring, monitoring and managing” financed by the Swedish Environmental Protection Agency, Miljövårdsanslaget (2019-2021).The results of the BBCI-analysis identified hotspots areas for the two studied biotopes in Valle, that is, areas with important patches for the sustainability of BBCI. For broadleaved forest, the northern part of Valle stands out as highly importantand for open lands with valuable trees the south-southwest parts of Valle stands out as the most important area. In this study, effects on BBCI from restauration of broadleaved forests to open land with valuable trees was evaluated. Calculations of BBCI shows encouraging results of an increased capacity for biodiversity of the biotope with open lands with valuable trees but not a significant decrease in biodiversity capacity of broadleaved forest, despite the area losses and fragmentation caused from the restauration. Both biotopes have BBCI values above one, showing that they are sustainable within a 100 year period. The result can be used as support to management plans of nature reserves in a landscape setting and as recommendations or advice to private land owners. Moreover, the study was produced within the work of BIOGOV, where regional action plans for nature, tourisms, culture and small enterprises were under development.
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18.
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19.
  • Roubinet, Eve, et al. (författare)
  • High Redundancy as well as Complementary Prey Choice Characterize Generalist Predator Food Webs in Agroecosystems
  • 2018
  • Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
  • Tidskriftsartikel (refereegranskat)abstract
    • Food web structure influences ecosystem functioning and the strength and stability of associated ecosystem services. With their broad diet, generalist predators represent key nodes in the structure of many food webs and they contribute substantially to ecosystem services such as biological pest control. However, until recently it has been difficult to empirically assess food web structure with generalist predators. We utilized DNA-based molecular gut-content analyses to assess the prey use of a set of generalist invertebrate predator species common in temperate agricultural fields. We investigated the degree of specialization of predator-prey food webs at two key stages of the cropping season and analysed the link temperature of different trophic links, to identify non-random predation. We found a low level of specialization in our food webs, and identified warm and cool links which may result from active prey choice or avoidance. We also found a within-season variation in interaction strength between predators and aphid pests which differed among predator species. Our results show a high time-specific functional redundancy of the predator community, but also suggest temporally complementary prey choice due to within-season succession of some predator species.
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20.
  • Thorgeirsson, Thorgeir E, et al. (författare)
  • A variant associated with nicotine dependence, lung cancer and peripheral arterial disease
  • 2008
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 452:7187, s. 9-638
  • Tidskriftsartikel (refereegranskat)abstract
    • Smoking is a leading cause of preventable death, causing about 5 million premature deaths worldwide each year(1,2). Evidence for genetic influence on smoking behaviour and nicotine dependence (ND)(3-8) has prompted a search for susceptibility genes. Furthermore, assessing the impact of sequence variants on smoking-related diseases is important to public health(9,10). Smoking is the major risk factor for lung cancer (LC)(11-14) and is one of the main risk factors for peripheral arterial disease (PAD)(15-17). Here we identify a common variant in the nicotinic acetylcholine receptor gene cluster on chromosome 15q24 with an effect on smoking quantity, ND and the risk of two smoking- related diseases in populations of European descent. The variant has an effect on the number of cigarettes smoked per day in our sample of smokers. The same variant was associated with ND in a previous genomewide association study that used low- quantity smokers as controls(18,19), and with a similar approach we observe a highly significant association with ND. A comparison of cases of LC and PAD with population controls each showed that the variant confers risk of LC and PAD. The findings provide a case study of a gene - environment interaction(20), highlighting the role of nicotine addiction in the pathology of other serious diseases.
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