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  • 1.
    Hof, Anouschka R
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Roland
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nilsson, Christer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    The usefulness of elevation as a predictor variable in species distribution modelling2012Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 246, s. 86-90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Species distribution models (SDMs) are increasingly used to forecast impacts of climate change on species geographic distributions, but the reliability of predictions is scrutinized. The main limitation of SDMs lies in their assumption that species' ranges are determined mostly by climate, which is arguable. For instance, biotic interactions, habitat and elevation may affect species ranges. The inclusion of habitat-related variables as predictors in SDMs is generally accepted, but there is no consensus regarding the inclusion of elevation. A review of randomly chosen literature revealed that elevation is used as a predictor variable by just over half of the papers studied with no apparent trends as to why, except that papers predicting mammal species distributions for large regions included elevation more often than not, and that papers that predicted mammal ranges for small regions tended to exclude elevation. In addition, we compared the performance of SDMs with and without elevation as a predictor variable for the distribution of north European mammals and plants and found that the difference between their performances is statistically significant for mammals, slightly favouring exclusion of elevation. No differences were found for plants.

    (C) 2012 Elsevier B.V. All rights reserved.

  • 2.
    Lindh, Magnus
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Zhang, Lai
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Falster, Daniel
    Franklin, Oskar
    Brännström, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Plant diversity and drought: The role of deep roots2014Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 290, s. 85-93Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Extreme temperatures and droughts in the wake of climate change potentially threaten plant diversity. A strategy that plants use to improve survival during seasonal drought is to establish deep roots, aptly named tap roots for their ability to tap into groundwater. Little is known, however, about the role of deep roots in maintaining plant diversity. Here, we extend an established model of plants canopies by Iwasa et al. (1985), in which plants of different heights compete for light, to allow strategic investments in an optional tap root. We investigate how emerging diversity varies with water table depth, soil water gradient and drought-induced mortality rate. Having a tap root enables plants to reach deep water, thus reducing mortality, but also carries a construction cost, thus inducing a tradeoff. We find (1) that tap roots maintain plant diversity under increasing drought mortality, (2) that tap roots evolve when ground water is accessible at low to intermediate depths, (3) no viable strategies at high drought mortality and deep water table, and (4) Red Queen evolutionary dynamics in mixed communities with and without tap root.

  • 3.
    Lundström, Niklas L. P.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Zhang, Hong
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik. Department of Financial Mathematics, Jiangsu University, Zhenjiang, Jiangsu 212013, PR China.
    Brännström, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik. Evolution and Ecology Program, International Institute for Applied Systems Analysis, 2361 Laxenburg, Austria.
    Pareto-efficient biological pest control enable high efficacy at small costs2017Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 364, s. 89-97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Biological pest control is increasingly used in agriculture as an alternative to traditional chemical pest control. In many cases, this involves a one-off or periodic release of naturally occurring and/or genetically modified enemies such as predators, parasitoids, or pathogens. As the interaction between these enemies and the pest is complex and the production of natural enemies potentially expensive, it is not surprising that both the efficacy and economic viability of biological pest control are debated. Here, we investigate the performance of very simple control strategies. In particular, we show how Pareto-efficient one-off or periodic release strategies, that optimally trade off between efficacy and economic viability, can be devised and used to enable high efficacy at small economic costs. We demonstrate our method on a pest–pathogen–crop model with a tunable immigration rate of pests. By analyzing this model, we demonstrate that simple Pareto-efficient one-off and periodic release strategies are efficacious and simultaneously have profits that are close to the theoretical maximum obtained by strategies optimizing only the profit. When the immigration rate of pests is low to intermediate, one-off control strategies are sufficient, and when the immigration of pests is high, periodic release strategies are preferable. The methods presented here can be extended to more complex scenarios and be used to identify promising biological pest control strategies in many circumstances.

  • 4.
    Manusch, C
    et al.
    ETH, Dept Environm Syst Sci, Inst Terr Ecosyst, CH-8092 Zurich, Switzerland.
    Bugmann, H
    ETH, Dept Environm Syst Sci, Inst Terr Ecosyst, CH-8092 Zurich, Switzerland.
    Heiri, C
    Swiss Fed Inst Forest Snow & Landscape Res, CH-8903 Birmensdorf, Switzerland.
    Wolf, A
    ETH, Dept Environm Syst Sci, Inst Terr Ecosyst, CH-8092 Zurich, Switzerland.
    Tree mortality in dynamic vegetation models - A key feature for accurately simulating forest properties2012Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 243, s. 101-111Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic vegetation models are important tools in ecological research, but not all processes of vegetation dynamics are captured adequately. Tree mortality is often modeled as a function of growth efficiency and maximum age. However, empirical studies have shown for different species that slow-growing trees may become older than fast-growing trees, implying a correlation of mortality with growth rate and size rather than age. We used the ecosystem model LPJ-GUESS to compare the standard age-dependent mortality with two size-dependent mortality approaches. We found that all mortality approaches, when calibrated, yield a realistic pattern of growing stock and Plant Functional Type (PFT) distribution at five study sites in Switzerland. However, only the size-dependent approaches match a third pattern, i.e. the observed negative relationship between growth rate and longevity. As a consequence, trees are simulated to get older at higher than at lower altitudes/latitudes. In contrast, maximum tree ages do not change along these climatic gradients when the standard age-dependent mortality is used. As tree age and size determine forest structure, our more realistic mortality assumptions improved forest biomass estimation, but indicate a potential decline of carbon storage under climate change. We conclude that tree mortality should be modeled as a function of size rather than age. (C) 2012 Elsevier B.V. All rights reserved.

  • 5.
    Nanos, Nikos
    et al.
    Technical University of Madrid, Spain.
    Larson, Kajsa
    Umeå universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Milleron, Matias
    Technical University of Madrid, Spain.
    Sjöstedt de Luna, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Inverse modeling for effective dispersal: Do we need tree size to estimate fecundity?2010Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 221, nr 20, s. 2415-2424Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The estimation of the dispersal kernel for the seedling and sapling stages of the recruitment process was made possible through the application of inverse modeling to dispersal data. This method uses the spatial coordinates of adult trees and the counts of seedlings (or saplings) in small quadrats to estimate the dispersal kernel. The unknown number of recruits produced by an adult tree (the fecundity) is estimated – simultaneously with the dispersal kernel – via an allometric linear model relating the unknown quantity with a (easily) measured characteristic of the adult tree (usually the basal area). However, the allometric relation between tree size and reproductive success in the sapling (or seedling) stage may not be strong enough when numerous, well-documented, post-dispersal processes (such as safe-site limitation for recruitment) cause large post-dispersal seedling mortality, which is usually unrelated to the size of the tree that dispersed them. In this paper we hypothesize that when tree size and reproductive success in the seedling/sapling stage are not well correlated then the use of allometry in inverse modeling is counter-productive and may lead to poor model fits. For these special cases we suggest using a new model for effective dispersal that we term the unrestricted fecundity (UF) model that, contrary to allometric models, makes no assumptions on the fecundities; instead they are allowed to vary freely from one tree to another and even to be zero for trees that are reproductively inactive. Based on this model, we examine the hypothesis that when tree size and reproductive success are weakly correlated and the fecundities are estimated independently of tree size the goodness-of-fit and the ecological meaning of dispersal models (in the seedling or sapling stage) may be enhanced. Parameters of the UF model are estimated through the EM algorithm and their standard errors are approximated via the observed information matrix. We fit the UF model to a dataset from an expanding European beech population of central Spain as well as to a set of simulated dispersal data were the correlation between reproductive success and tree size was moderate. In comparisons with a simple allometric model, the UF model fitted the data better and the parameter estimates were less biased. We suggest using this new approach for modeling dispersal in the seedling and sapling stages when tree size (or other adult-specific covariates) is not deemed to be in strong relation to the reproductive success of adults. Models that use covariates for modeling the fecundity of adults should be preferred when reproductive success and tree size guard a strong relationship.

  • 6.
    Portalier, Sebastien M. J.
    et al.
    Department of Biology, McGill University.
    Cherif, Mehdi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Zhang, Lai
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Fussmann, Gregor F.
    Department of Biology, McGill University.
    Loreau, Michel
    Centre for Biodiversity Theory and Modelling, Station d’Ecologie Expérimentale du CNRS.
    Size-related effects of physical factors on phytoplankton communities2016Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 323, s. 41-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phytoplankton communities are influenced by light availability. Therefore, one factor promoting phytoplankton species persistence is their ability to stay within the euphotic zone. This ability is determined by the interplay between species mass, buoyancy and dispersion, which are driven by physical factors. In this study, we investigate how these physical factors and light-use efficiency, all correlated with cell size, influence species persistence. Our model shows, first, that species can persist only within a size-dependent range of turbulence strength. The minimal level of turbulence required for persistence increases drastically with cell size, while all species reach similar maximal levels of turbulence. Second, the maximal water column depth allowing persistence is also size-dependent: large cells show a maximal depth at both low and high turbulence strength, while small cells show this pattern only at high turbulence strength. This study emphasizes the importance of the physical medium in ecosystems and its interplay with cell size for phytoplankton dynamics and bloom condition.

  • 7.
    Wolf, Annett
    Forest Ecology, Institute of Terrestrial Ecosystems, Department of Environmental Science, ETH Zurich, Universitätsstrasse 16, CH-8092 Zurich, Switzerland.
    Estimating the potential impact of vegetation on the water cycle requires accurate soil water parameter estimation2011Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 222, nr 15, s. 2595-2605Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well known that vegetation dynamics at the catchment scale depends on the prevailing weather and soil moisture conditions. Soil moisture, however, is not equally distributed in space due to differences in topography, weather patterns, soil properties and the type and amount of vegetation cover. To elucidate the complex interaction between vegetation and soil moisture, the dynamic vegetation model LPJ-GUESS (Smith et al., 2001), which provides estimations of vegetation dynamics, but does not consider lateral water fluxes was coupled with the hydrological TOPMODEL (cf. Beven, 2001) in order to be able to evaluate the importance of these lateral fluxes. The new model LG-TM was calibrated and validated in two climatically different mountain catchments. The estimations of runoff were good, when monthly and weekly time scales were considered, although the low flow periods at winter time were somewhat underestimated. The uncertainty in the climate induced change vegetation carbon storage caused by the uncertainty in soil parameters was up to 3–5 kg C m−2 (depending on elevation and catchment), compared to the total change in vegetation carbon storage of 5–9 kg C m−2. Therefore accurate estimates of the parameters influencing the water holding capacity of the soil, for example depth and porosity, are necessary when estimating future changes in vegetation carbon storage. Similarly, changes in plant transpiration due to climatic changes could be almost double as high (88 mm m−2) in the not calibrated model compared to the new model version (ca 50 mm m−2 transpiration change). The uncertainties in these soil properties were found to be more important than the lateral water exchange between grid cells, even in steep topography at least for the temporal and spatial resolution used here.

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