hh.sePublications
Change search
Refine search result
1234 151 - 187 of 187
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 151.
    Verikas, Antanas
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), CAISR - Center for Applied Intelligent Systems Research.
    Bacauskiene, Marija
    Department of Applied Electronics, Kaunas University of Technology, Studentu 50, LT-3031, Kaunas, Lithuania.
    Malmqvist, Kerstin
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Selecting salient features for classification committees2003In: Artificial Neural Networks and Neural Information Processing — ICANN/ICONIP 2003 / [ed] Kaynak, O Alpaydin, E Oja, E Xu, L, Heidelberg: Springer Berlin/Heidelberg, 2003, Vol. 2714, p. 35-42Conference paper (Refereed)
    Abstract [en]

    We present a neural network based approach for identifying salient features for classification in neural network committees. Our approach involves neural network training with an augmented cross-entropy error function. The augmented error function forces the neural network to keep low derivatives of the transfer functions of neurons of the network when learning a classification task. Feature selection is based on two criteria, namely the reaction of the cross-validation data set classification error due to the removal of the individual features and the diversity of neural networks comprising the committee. The algorithm developed removed a large number of features from the original data sets without reducing the classification accuracy of the committees. By contrast, the accuracy of the committees utilizing the reduced feature sets was higher than those exploiting all the original features. © Springer-Verlag Berlin Heidelberg 2003.

  • 152.
    Verikas, Antanas
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), CAISR - Center for Applied Intelligent Systems Research.
    Lipnickas, Arunas
    Kaunas University of Technology, Department of Applied Electronics, Studentu 50, 3031, Kaunas, Lithuania.
    Malmqvist, Kerstin
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Selecting neural networks for making a committee decision2002In: ARTIFICIAL NEURAL NETWORKS - ICANN 2002 / [ed] Dorronsoro, J R, Berlin: Springer Berlin/Heidelberg, 2002, Vol. 2415, p. 420-425Conference paper (Refereed)
    Abstract [en]

    To improve recognition results, decisions of multiple neural networks can be aggregated into a committee decision. In contrast to the ordinary approach of utilizing all neural networks available to make a committee decision, we propose creating adaptive committees, which are specific for each input data point. A prediction network is used to identify classification neural networks to be fused for making a committee decision about a given input data point. The jth output value of the prediction network expresses the expectation level that the jth classification neural network will make a correct decision about the class label of a given input data point. The effectiveness of the approach is demonstrated on two artificial and three real data sets.

  • 153.
    Vretare Strand, Viveka
    et al.
    Limnology, Department of Ecology, Lund University, Sweden.
    Weisner, Stefan E.B.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Interactive effects of pressurized ventilation, water depth and substrate conditions on Phragmites australis2002In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 131, no 4, p. 490-497Article in journal (Refereed)
    Abstract [en]

    Pressurized ventilation acts to increase the oxygen supply to roots and rhizomes in some species of emergent plants. In a greenhouse experiment, we investigated how pressurized ventilation affected growth, biomass allocation and mineral content of Phragmites australis in two water depths (15 cm or 75 cm) and two substrates (organic sediment or sand). Through perforating each stem above the water surface, pressurized ventilation was inhibited without affecting oxygen diffusion. In controls, 10-20% of the stems were perforated to make certain that lack of efflux sites would not limit pressurized ventilation. Plants with inhibited pressurized ventilation had lower oxygen concentrations in their stem bases than control plants. Growth was lower in plants with inhibited pressurized ventilation compared to controls except when plants grew in a combination of sand and shallow water. In plants grown in an organic sediment, but not in those grown in sand, inhibition of pressurized ventilation resulted in decreased biomass allocation to soil roots but increased allocation to aquatic roots. Stem perforation affected the tissue concentrations of nitrogen, phosphorus, magnesium, manganese and aluminium but not of calcium or iron. We suggest that the lower growth in plants with inhibited pressurized ventilation was caused by decreased mineral uptake, which may have resulted from the decreased proportional allocation to soil root weight, from decreased mineral availability or from impaired root function. In plants grown in sand in shallow water, diffusion seemed to cover the oxygen demand, as pressurized ventilation did not affect growth.

  • 154.
    Vretare, Viveka
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Influence of pressurized ventilation on performance of an emergent macrophyte (Phragmites australis)2000In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 88, no 6, p. 978-987Article in journal (Refereed)
    Abstract [en]

    1 Pressurized ventilation, which increases gas exchange between aerial and submerged plant parts, has been found in various emergent macrophyte species. We investigated the potential for this mechanism to affect growth, morphology and biomass allocation in Phragmites australis in glasshouse experiments. 2 Inhibition of pressurized ventilation by perforation of stems above the water surface resulted in decreased oxygen concentrations in stem bases and rhizomes. Perforation caused little mechanical damage. 3 Allometric methods were used to evaluate treatment effects on biomass allocation and morphology. 4 Inhibition of pressurized ventilation resulted in decreased allocation to belowground weight and decreased rhizome penetration into the substrate in two of three experiments. Treatment also decreased growth rate, rhizome length and number of rhizomes when substrate had a high organic content. In the third experiment, growth clearly decreased in deep water, although inhibition of pressurized ventilation did not affect growth, biomass allocation or morphology at either of the water depths tested. 5 Decreased allocation to below-ground parts and decreased rhizome lengths may be adaptations to allow the oxygen concentration in roots and rhizomes to be maintained above a critical level when the oxygen supply is low. 6 Pressurized ventilation may improve the performance of P. australis but only under certain conditions (e.g. not when growth rate is low or the substrate has a high redox potential).

  • 155.
    Vretare, Viveka
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Strand, John A.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Graneli, Wilhelm
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Phenotypic plasticity in Phragmites australis as a functional response to water depth2001In: Aquatic Botany, ISSN 0304-3770, E-ISSN 1879-1522, Vol. 69, no 2-4, p. 127-145Article in journal (Refereed)
    Abstract [en]

    We have performed investigations to see if the emergent macrophyte Phragmites australia (Cav.) Trin. ex Steud. exhibits phenotypic plasticity as a response to water depth and if such responses in biomass allocation pattern and morphology are functional responses, improving the performance of the plant. In greenhouse experiments plants were grown in deep or shallow water to evaluate plastic responses. Allometric methods were used to handle effects caused by size differences between treatments. To evaluate if phenotypic responses to water depth are functional, the relative growth rate (RGR) of plants acclimatised to shallow or deep water, respectively, were compared in deep water, and the growth of plants in fluctuating and constant water level were compared. When grown in deep (70 or 75 cm), compared to shallow (20 or 5 cm) water, plants allocated proportionally less to below-ground weight, made proportionally fewer but taller stems, and had rhizomes that were situated more superficially in the substrate. Plants acclimatised to shallow water had lower RGR than plants acclimatised to deep water, when they were grown in deep water, and plants in constant water depth (40 cm) grew faster than plants in fluctuating water depth (15/65 cm). In an additional field study, the rhizomes were situated superficially in the sediment in deep, compared to shallow water. We have shown that P. australis acclimatises to deep water with phenotypic plasticity through allocating more resources to stem weight, and also by producing fewer but taller stems, which will act to maintain a positive carbon balance and an effective gas exchange between aerial and below-ground parts. Furthermore, the decreased proportional allocation to below-ground parts probably results in decreased nutrient absorption, decreased anchorage in the sediment and decreased carbohydrate reserves. Thus, in deep water, plants have an increased risk of becoming uprooted and experience decreased growth and dispersal rates. (C) 2001 Elsevier Science B.V. All rights reserved.

  • 156.
    Vårdal, Hege
    et al.
    Department of Systematic Zoology, Evolutionary Biology Centre, Uppsala University, Sweden.
    Sahlén, Göran
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Ronquist, Fredrik
    Department of Systematic Zoology, Evolutionary Biology Centre, Uppsala University, Sweden.
    Morphology and evolution of the cynipoid egg (Hymenoptera)2003In: Zoological Journal of the Linnean Society, ISSN 0024-4082, E-ISSN 1096-3642, Vol. 139, no 2, p. 247-260Article in journal (Refereed)
    Abstract [en]

    We describe gross egg morphology and provide the first data on eggshell ultrastructure in cynipoids (Hymenoptera) based on species representing three distinctly different life histories: internal parasitoids of endopterygote larvae, gall inducers and phytophagous inquilines (guests in galls). We then use existing phylogenetic hypotheses to identify putative changes in egg structure associated with evolutionary life-history transitions. We find four major structural changes associated with the shift from parasitoids laying their eggs inside a host larva to gall inducers laying their eggs in or on plants: (1) from a narrow and gradually tapering gross form to a distinct division into a stout body and a long and thin stalk; (2) from a thin to a thick eggshell; (3) from a flexible to a rigid endochorion; and (4) from crystal bundles with shifting orientation in the exochorion to layers of parallel crystal rods. By contrast, we find no major changes in egg structure associated with the transition from gall inducers to inquilines. Comparison between pre- and post-oviposition eggs of one gall inducer and one inquiline suggests that mechanical stress during the passage through the egg canal gives rise to numerous tiny stress fractures in the boundary separating the exo- and endochorion. In one of the gall inducers, Diplolepis rosae, that end of the egg, which is inserted into the plant, has a specialized and apparently porous shell that may permit chemical exchange between the embryo and the plant. Other structures that could facilitate chemical communication with the host plant through the eggshell were, however, not observed in the eggs of gall inhabitants.

  • 157.
    Vårhammar, Annelie
    Halmstad University, School of Business, Engineering and Science.
    Is there canine distemper virus in the Antarctic seal populations?2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The highly contagious canine distemper virus (CDV) has caused many so called epizootics, i.e. widespread transmissions of severe diseases in animal populations. Antibodies to CDV have been found several times in the northern hemisphere, but only once in the 1980’s in the phocid seal populations on the remote continent of Antarctica. This raises the question of whether the virus is enzootic or if it has been eliminated from the seal populations, which brings forth this study with serological testing on recently sampled seals. In this study, samples of 49 crabeater seals (Lobodon carcinophagus), 49 Weddell seals (Leptonychotes weddellii) and 14 Ross seals (Ommatophoca rossii) from two separate expeditions with the Swedish icebreaker Oden in year 2008/2009 and 2010/2011 were tested for antibodies to CDV using enzyme-linked immunosorbent assay (ELISA). The ELISA was repeated three times on the same samples but unexpectedly showed inconsistent results. Statistical analysis revealed that there were significant differences in titre values between the three trials in all three species. The results must therefore be considered unreliable for the purpose of estimating antibody prevalence and should be discarded. The inconsistency could be explained by the ELISA kit being designed for dogs. Thus, the present study is valuable as a pilot study and shows that ELISA tests on seals developed for dogs should be treated with caution and that the samples need to be re-tested with other methods, preferably by using a virus neutralization test. The present study reviews the preceding literature concerning the prevalence of antibodies against CDV in the Antarctic seals, and also displays how the results of a future re-testing can be used to assess the susceptibility of a future outbreak of CDV in the seals of Antarctica.

  • 158.
    Waara, Sylvia
    et al.
    Department of Physiological Botany, University of Uppsala, Uppsala, Sweden.
    Pijnacker, Laas P.
    Rijksuniversiteit Groningen, Department of Genetics, Groningen, Netherlands.
    Ferwerda, Margriet A.
    Rijksuniversiteit Groningen, Department of Genetics, Groningen, Netherlands.
    Wallin, Anita
    Uppsala Universitet, Department of Physiological Botany, Uppsala, Sweden.
    Eriksson, Tage
    Uppsala Universitet, Department of Physiological Botany, Uppsala, Sweden.
    A cytogenetic and phenotypic characterization of somatic hybrid plants obtained after fusion of two different dihaploid clones of potato (Solatium tuberosum L.)1992In: Theoretical and Applied Genetics, ISSN 0040-5752, E-ISSN 1432-2242, Vol. 85, no 4, p. 470-479Article in journal (Refereed)
    Abstract [en]

    Somatic hybrid plants of various ploidy levels obtained after chemical fusion between two dihaploid clones of potato Solanum tuberosum L. have been analysed by cytological, morphological and molecular methods. The hybrid nature of tetraploid and hexaploid plants and the genome dosage in hexaploid hybrids were confirmed by Giemsa C-banding. Tetraploid and hexaploid hybrids showed numerical as well as structural chromosome mutations. The latter occurred mainly in the nuclear organizing chromosome. The tetraploid hybrids were more vigorous than the dihaploid parents as demonstrated by an increase in height, enlargement of leaves, increase in the number of internodes, restored potential for flowering and increased tuber yield. The grouping of tetraploid somatic hybrids into various classes on the basis of leaf morphology revealed that plants with a full chromosome complement were more uniform than aneuploids. Many hexaploid somatic hybrids were also more vigorous than the dihaploidparents and could be grouped into two different classes on the basis of floral colour and tuber characteristics, the differences being due to their different dosage of parental genomes. Most of the tetraploid somatic hybrids showed pollen development halted at the tetrad stage as one of the parental clones contained a S. Stoloniferum cytoplasm. However, one tetraploid plant produced pollen grains with high viability. The chloroplast genome in the hybrid plants was determined by RFLP analysis. All of the hybrids had a cpDNA pattern identical to one parent, which contained either S. Tuberosum or S. Stoloniferum cpDNA. A slight preference for S. Tuberosum plastids were observed in hybrid plants. No correlation between pollen development and plastid type could be detected. © 1992 Springer-Verlag.

  • 159.
    Waara, Sylvia
    et al.
    Department of Physiological Botany, Uppsala University, Uppsala, Sweden.
    Wallin, Anita
    Department of Physiological Botany, Uppsala University, Uppsala, Sweden.
    Eriksson, Tage
    Department of Physiological Botany, Uppsala University, Uppsala, Sweden.
    Production and analysis of intraspecific somatic hybrids of potato (Solanum tuberosum L.)1991In: Plant Science, ISSN 0168-9452, Vol. 75, no 1, p. 107-115Article in journal (Refereed)
    Abstract [en]

    Photoplasts of two dihaploid lines of potato were fused to produce a large number of intraspecific somatic hybrid plants among which plants of the expected tetraploid level might be found. Fusion frequencies up to 12% (mean 7%) were observed using a revised polyethylene glycol fusion protocol. Fusion products were identified by the dual fluorescence emission from the chloroplasts in mesophyll protoplasts (red) and from the fluorescein diacetate stain in light and norflurazon bleached protoplasts (yellow-green). Hybrid cells were isolated 2–3 days after fusion and cultured at a cell density of 2000 cells/ml. From a total of 1363 isolated putative hybrid cells, 258 divided to form calli. Plants were regenerated from 166 of these. Isozyme analysis confirmed the hybrid nature in 57 of 58 analysed plants. Ploidy was determined in 51 plants; 12% were tetraploid, 41% hexaploid, 12% octoploid and 35% were mixoploid. Expression of isocitrate dehydrogenase isozymes indicated that the majority of the hexaploid hybrids contained 2 genomes of the bleached parent and one genome of the mesophyll parent. This study shows that tetraploid somatic hybrid potato plants can be obtained by the fusion and selection method presented.

  • 160.
    Wagenhoff, Annika
    et al.
    Cawthron Institute, Nelson, New Zealand.
    Liess, Antonia
    Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden .
    Thresholds in ecosystem structural and functionalresponses to agricultural stressors can informlimit setting in streams2017In: Freshwater Science, ISSN 2161-9549, E-ISSN 2161-9565, Vol. 36, no 1, p. 178-194Article in journal (Refereed)
    Abstract [en]

    Setting numeric in-stream objectives (limits, criteria) to inform limits on catchment loads for major land-use stressors is a promising policy instrument to prevent ecosystem degradation. Management objectives can be informed by thresholds identified from stressor–response shapes of ecological indicators based on field survey data. Use of multiple structural and functional indicators and different organism groups provides multiple lines of evidence to make objectives more robust. We measured a suite of ecological indicators during a regional field survey in New Zealand. We built flexible boosted regression tree (BRT) models with a predictor set consisting of nutrient, sediment, and environmental variables and investigated the fitted functions for different types of thresholds across each stressor gradient. Congruence of impact initiation (II) thresholds for N among macroinvertebrate metrics and 2 periphyton indicators provided multiple lines of evidence for ecosystem change with small increases in N concentrations above background levels. Impact cessation (IC) on macroinvertebrate metrics at total N = ~0.5 mg/L (below N concentrations that saturate important ecosystem processes) highlighted sensitivity of macroinvertebrate communities to eutrophication. We found few stressor–response relationships for sediment. We suggest use of sediment-specific macroinvertebrate metrics and a reliable measure of deposited fine sediment in the future. Few indicators responded to phosphorus (P) concentration. Limited information for setting P objectives highlights the need to develop alternative indicators of P loading. Statistical analysis based on single-stressor inferential threshold models suggested that these models carry high risk of identifying spurious thresholds and are less suitable for setting management objectives. II and IC thresholds of multiple ecological indicators can be used to set robust objectives aimed at different levels of protection of ecosystem health.

  • 161.
    Wagner, Wolfgang
    et al.
    Institut für Pädagogie und Psychologie, Johannes-Kepler-University, Linz, Austria.
    Kronberger, Nicole
    Department of Social and Economic Psychology, University of Linz, Linz, Austria.
    Allum, Nick
    Methodology Institute, London School of Economics and Political Science, London, United Kingdom.
    De Cheveigné, Suzanne
    Laboratoire Communication et Politique, Centre National de la Recherche Scientifique (CNRS), Paris, France.
    Diego, Carmen
    Department of Sociology, ISCTE, University of Lisabon, Lisabon, Portugal.
    Gaskell, George
    Methodology Institute, London School of Economics, London, United Kingdom.
    Heinben, Marcus
    Centre of Technology Assessment in Baden-Württemberg, Stuttgart, Germany.
    Midden, Cees J. H.
    Department of Technology Management, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Ødegaard, Marianne
    Centre for Technology and Culture, University of Oslo, Oslo, Norway.
    Öhman, Susanna
    Mid Sweden University, Östersund, Sweden.
    Rizzo, Bianca
    Department of Communication, University of Siena, Siena, Italy.
    Rusanen, Timo
    Department of Social Sciences, University of Kuopio, Kuopio, Finland.
    Stathopoulou, Angeliki
    Department of Qualitative Research, Metron Analysis S.A., Athens, Greece.
    Pandora's genes — images of genes and nature2002In: Biotechnology: The making of a global controversy / [ed] Martin W. Bauer, George Gaskell, Cambridge: Cambridge University Press, 2002, 1, p. 244-278Chapter in book (Other academic)
  • 162.
    Wahlbäck, Kalle
    Halmstad University, School of Business, Engineering and Science.
    General factors that regulate survival among ectotherms at northern latitudes: a study of sand lizard, Lacerta agilis, habitat in southern Sweden2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Open sand habitats in Sweden has been declining for the past century and this is mirrored by the increasing fragmentation and attenuation of species bound to these habitats. Many threatened species coexist in the same habitats as sand lizards, habitats best described as warm sites with a long continuity. Often with a sand-based substrate and a mosaic landscape of heather Calluna vulgaris, herbs, and patches of grass. Generally, areas with open sand are one of the keys for species bound to these habitats considering many of the species use south-facing sand slopes as nesting sites since it holds a warmer microhabitat that is beneficial for incubation of eggs and thus is essential for the whole lifecycle. This study investigates four current sand lizard (Lacerta agilis) localities in the county of Skåne and compares them to four empty localities in Southern Halland with similar character. The data collected from the study sites were analyzed to see if there were any significant differences between the populated and empty localities and thus could give information if key structures in the habitat are missing. The result from the analysis clearly shows that both the study sites Vapnö and Långenäsudden have the key structures that are essential for the sand lizard and could be considered as suitable habitats for potential new sand lizard populations. Information about both recreational pressure and predator abundance in these study sites would be an essential step in the final evaluation of the adequacy of the habitat as a whole.

    Download full text (pdf)
    fulltext
  • 163.
    Ware, Jessica L.
    et al.
    Rutgers University, Newark, NJ, USA.
    Karlsson, Maria
    Lund University, Lund, Sweden.
    Sahlén, Göran
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Koch, Kamilla
    Johannes Gutenberg Universität Mainz, Mainz, Germany.
    Evolution of reproductive strategies in libellulid dragonflies (Odonata: Anisoptera)2012In: Organisms Diversity & Evolution, ISSN 1439-6092, E-ISSN 1618-1077, Vol. 12, no 3, p. 313-323Article in journal (Refereed)
    Abstract [en]

    In Libellulidae, oocyte production has been assumed to be continuous, with periods of egg-laying interspersed with periods of resting/eating; however, recent work suggests that two types of oocyte production are common: either (a) continuous or (b) step-wise. These are mirrored in the arrangement of the ovarioles in the ovaries. Likewise, two types of mate-guarding behavior have been observed in Libellulidae: (1) non–contact guarding and (2) tandem guarding in which the male either hovers above the female or is physically attached to her during oviposition. Using molecular (mitochondrial and nuclear) data we explored the evolution of female reproductive traits, focusing on ovariole morphology, as well as guarding behavior, in Libellulidae. Continuous egg production appears to have evolved more than once, as have tandem and non-contact guarding. We discuss how the evolution of different ovariole types and guarding behavior may have been influenced by habitat instability, dispersal and crowded oviposition sites; thus, migratory behavior or habitat availability may have been the driving force of ovariole evolution.

  • 164.
    Weisner, Stefan
    Limnology, Departmeni of Ecology, University of Lund, Sweden.
    The relation between wave exposure and distribution of emergent vegetation in a eutrophic lake1987In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 18, no 3, p. 537-544Article in journal (Refereed)
    Abstract [en]

    Maximum water depth penetration and changes in horizontal distribution during 39yr of the emergent vegetation in Lake Krankesjon, S Sweden, were investigated. The capacity of the emergent vegetation to penetrate into deeper water areas was higher at wave exposed than at sheltered sites. Differences in biomass and biomass allocation of the dominant species, Phragmites australis, between an exposed and a sheltered site suggest that horizontal expansion towards deeper water at sheltered sites is limited by unfavourable substrate conditions.

  • 165.
    Weisner, Stefan E. B.
    et al.
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS), Environmental Science, Wetland Research Centre.
    Strand, John A.
    Rural economy and agricultural society, Lilla Böslid, Eldsberga.
    Ecology and management of plants in aquatic ecosystems2002In: Handbook of ecological restoration: Vol. 1, Principles of restoration / [ed] Martin R. Perrow, Anthony J. Davy, Cambridge: Cambridge University Press , 2002, p. 242-256Chapter in book (Refereed)
    Abstract [en]

    The central role of macrophytes for the functioning of aquatic systems means that the most effective way to manage these systems is often through vegetation management. For this we need to understand the mechanisms regulating vegetation distribution. Submerged macrophyte distribution is mainly related to water depth, water transparency and epiphytic growth. The distribution of emergent vegetation can largely be predicted from water depth and substrate characteristics. Also, in both submerged and emergent macrophytes, the effects on the vegetation of grazing can be dramatic. Management should aim at providing environmental conditions favouring the desired ecosystem state, rather than methods directly aimed at the vegetation. For example, the best method for promoting establishment of emergent vegetation is often lowering of the water level. To establish submerged vegetation, water transparency can be increased through biomanipulation (the removal of zooplanktivorous fish leading to increased zooplankton grazing pressure on phytoplankton). Changes in water depth and introduction of grazers are often effective measures to control growth of aquatic weeds.

  • 166.
    Weisner, Stefan E.B.
    Limnology, Lund University, Lund, Sweden .
    Effects of an organic sediment on performance of young Phragmites australis clones at different water depth treatments1996In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 330, no 3, p. 189-194Article in journal (Refereed)
    Abstract [en]

    Performance of young Phragmites australis plants was examined after 7 weeks on an artificial nutrient-enriched inorganic substrate and on the same substrate to which an organic sediment from a eutrophic lake was added, at three different water depth treatments. Growth decreased, and proportional allocation of biomass to roots increased, with the addition of sediment. These differences were significant in shallow and deep water, but not at a medium depth. Concentrations of phosphorus and nitrogen in plant biomass decreased, and concentration of iron increased, with addition of sediment. The effects of sediment addition may have resulted from a decreased availability of nutrients in the substrate or from an impaired root functioning. Nutrient exhaustion in the substrate, due to a fast plant growth, can explain the relatively strong effects in shallow water. Deep water, on the other hand, probably restricted oxygen transport to the roots, resulting in an impaired root functioning in the low-redox sediment environment. The results show that, especially in relatively deep water, growth of undisturbed plants of P. australis may be inhibited by eutrophication of sediments, probably because of an impaired root functioning in sediments containing reduced toxic compounds (e.g. ferrous iron).

  • 167.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Factors affecting the internal oxygen supply of Phragmites australis (Cav.) Trin. ex Steudel in situ1988In: Aquatic Botany, ISSN 0304-3770, E-ISSN 1879-1522, Vol. 31, no 3-4, p. 329-335Article in journal (Refereed)
    Abstract [en]

    Oxygen concentration in basal stems of Phragmites australis (Cav.) Trin. ex Steudel was measured in situ, in monospecific stands. The mean O2 concentration in basal stems, and mean shoot length above water, decreased in deeper water. Oxygen concentration in basal stems was correlated to shoot length above water at a given water depth, and the mean O2 concentration in basal stems of shoots with similar length above water decreased in deeper water. The results suggest that O2 transport from shoots to below-ground parts is restricted in deep water by: (1) small shoot length above water; (2) long O2 transport distance. No influence of substrate redox potential on O2concentration in basal stems was found. © Copyright 1988 Elsevier B.V.

  • 168.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Long-term competitive displacement of Typha latifolia by Typha angustifolia in a eutrophic lake1993In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 94, no 3, p. 451-456Article in journal (Refereed)
    Abstract [en]

    This study follows the outcome of long-term competition between a broad-leaved and a narrow-leaved Typha species, T. latifolia and T. angustifolia respectively, in a eutrophic lake. The lake was bordered by a zone of T. latifolia, at one location interrupted by a T. angustifolia stand. Distributional changes of the T. angustifolia stand and the adjacent zone of T. latifolia were measured on aerial photographs (less-than-or-equal-to 13 years) and along ground-level transects (6 years). A second stand of T. angustifolia was established with transplanted ramets within a formerly homogeneous zone of T. latifolia, and displacement between the two species was measured along ground-level transects after 6 years. Differences between the species in shoot performance were investigated to help explain the relative competitive abilities of the two Typha species. T. angustifolia expanded at the expense of T. latifolia at all water depths where both species occurred, except in very shallow water. Expansion rates suggest that T. angustifolia was not affected by the presence of T. latifolia in water depths exceeding 0.25 m. The Typha species were significantly negatively associated according to rank correlations of shoot densities, and changes of shoot densities, along the transects. These results suggest that T. angustifolia is competitively superior to T. latifolia, contradicting earlier studies. The higher competitive ability of T. angustifolia is consistent with its having taller shoots and a higher standing crop in early summer. Further, shoot height distributions indicated a closer integration of shoot emergence during spring in T. angustifolia than in T. latifolia. A high leaf area/shoot weight ratio suggest that T. latifolia may instead be relatively fast-growing, achieving competitive superiority over narrower-leaved Typha species during a transient period after simultaneous seedling establishment.

  • 169.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Within-lake patterns in depth penetration of emergent vegetation1991In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 26, no 1, p. 133-142Article in journal (Refereed)
    Abstract [en]

    1. Within-lake relations of wave exposure (WE), and substratum softness (cone penetration depth; CPD) and organic content (loss on ignition; LOI), to water depth penetration of the emergent vegetation (DPE) was investigated in seven eutrophic lakes in southern Sweden, ranging in area from 1 to 46 km2. 2. There was a positive relationship between WE and DPE within lakes. This relationship, however, only occurred for sites with relatively soft substrata, for which CPD and LOI were negatively related to both WE and DPE. 3. Analysis of aerial photographs revealed that expansion of the emergent vegetation towards open water, or recession from open water, was not related to wave exposure or water depth, except in one lake where expansion mainly occurred at high exposures. 4. For relatively static vegetation on soft substrata, regressions with CPD0.5 explained 62-88% of the within-lake variation of DPE. These regressions did not differ among lakes. Expanding and recessing vegetation were significantly dislocated towards shallower and deeper water, respectively, than predicted from the regression models for static vegetation. 5. Phragmites australis dominated at the lakeward edge of the emergent vegetation, followed in frequency by Typha angustifolia. More broad-leaved species were generally restricted to shallow water and very soft substrata. 6. The results suggest that changes in the distribution of emergent vegetation in moderately wave exposed eutrophic lakes can be predicted largely from substratum character and water depth.

  • 170.
    Weisner, Stefan E.B.
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Ekstam, Börje
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Influence of germination time on juvenile performance of Phragmites australis on temporarily exposed bottoms – implications for the colonization of lake beds1993In: Aquatic Botany, ISSN 0304-3770, E-ISSN 1879-1522, Vol. 45, no 2-3, p. 107-118Article in journal (Refereed)
    Abstract [en]

    Three cohorts of seedlings of Phragmites australis (Cav.) Trin ex Steud., germinated in May, June and July, were allowed to grow in shallow water (depth 5 cm or less) in southern Sweden. In the autumn, size parameters were measured on the plants. In the second year, the water level was raised to 0.8 m and emergence of shoots, plant survival and size parameters were recorded. The mean plant weight by the end of the first year differed markedly between cohorts. Rhizome biomass showed a relationship of 700:70:1 between the May, June and July cohorts. In the second year, rate of emergence above the water surface, and maximum height of plants that did not reach the water surface, was positively related to the size (mass) the plants had achieved after the first year. Only plants that emerged above the water surface survived the second summer, resulting in survival rates for the May, June and July cohorts of 90%, 68% and 0%, respectively. The rhizome weight of the smallest survivors had decreased after the second summer compared with values after the first summer. Hence, they were not capable of ‘reloading’ their rhizomes during the second year. In a temperate climate, the size of juvenile plants after the first year, which is strongly dependent on early germination on exposed bottoms (i.e. bottoms without standing water), determines their water depth tolerance during the second year. The timing and duration of exposure, as well as the subsequent depth of re-flooding, are all of fundamental importance for successful ‘lakeward’ seedling expansion of P. australis.

  • 171.
    Weisner, Stefan E.B.
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Eriksson, Peder G.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Granéli, Wilhelm
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Leonardson, Lars
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Influence of Macrophytes on Nitrate Removal in Wetlands1994In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 23, no 6, p. 363-366Article in journal (Refereed)
    Abstract [en]

    Efficient nitrate removal from wetlands depends on denitrification. Macrophytes support denitrification by supplying organic carbon. Organic carbon available to denitrifying bacteria is released from plant litter and from living macrophytes. Macrophytes offer attachment surfaces for epiphytes, also producing organic matter, and for denitrifying bacteria. Emergent macrophytes are generally more productive than submerged macrophytes, but submerged macrophytes have more epiphytes and offer a larger attachment area in the water column for denitrifying bacteria. Emergent and submerged vegetation differ in their seasonal patterns of release of organic carbon. We conclude that a mixture of emergent and submerged macrophytes may be beneficial for nitrogen removal in wetlands with a surface-flow of nitrate-rich water. The influence of vegetation on wetland hydraulics must also be considered. A wetland design with deeper parts favoring submerged macrophytes alternating, along the water flow, with shallower parts covered by emergent macrophytes, may promote denitrification processes and distribution of water flow.

  • 172.
    Weisner, Stefan E.B.
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Graneli, Wilhelm
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Influence of substrate conditions on the growth of Phragmites australis after a reduction in oxygen transport to below-ground parts1989In: Aquatic Botany, ISSN 0304-3770, E-ISSN 1879-1522, Vol. 35, no 1, p. 71-80Article in journal (Refereed)
  • 173.
    Weisner, Stefan E.B.
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Graneli, Wilhelm
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Ekstam, Börje
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Influence of submergence on growth of seedlings of Scirpus lacustris and Phragmites australis1993In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 29, no 3, p. 371-375Article in journal (Refereed)
    Abstract [en]

    1. Seeds of Scirpus lacustris and Phragmites australis were germinated in early June, and twenty-four seedlings of each species were subsequently exposed to submerged conditions (eight seedlings at each of the water depths 0.2, 0.4 and 0.8 m), in outdoor 500-l tanks in southern Sweden. Weight and shoot length of the plants were measured in September. 2. The Phragmites seedlings did not show any significant growth when submerged. The Scirpus seedlings, however, developed submerged leaves and exhibited considerable submerged growth. One Scirpus plant, in shallow water (0.2 m), had developed an aerial shoot by September. Shoot length of the remaining (submerged) Scirpus plants was positively related to plant weight within water depth treatments, and was higher, in relation to plant weight, in deeper water. Mean weight in September of the submerged Scirpus plants decreased with increased water depth. 3. In south Swedish lakes with a lowered water table, Scirpus often occupies large areas on the lakeward side of the reed belt, which is generally dominated by Phragmites. The differences between the two species, in performance of submerged seedlings, suggest that this zonation may be created through successful submerged seedling establishment of Scirpus on the lakeward side of Phragmites.

  • 174.
    Weisner, Stefan E.B.
    et al.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Miao, Shi Li
    Everglades Department, South Florida Water Management District, West Palm Beach, USA .
    Use of morphological variability in Cladium jamaicense and Typha domingensis to understand vegetation changes in an Everglades marsh2004In: Aquatic Botany, ISSN 0304-3770, E-ISSN 1879-1522, Vol. 78, no 4, p. 319-335Article in journal (Refereed)
    Abstract [en]

    The northern Florida Everglades have experienced an expansion of cattail (Typha domingensis) and a decrease of sawgrass (Cladium jamaicense) communities. In this study, spatial and temporal within-species variability in plant performance were used to explore the mechanisms causing the distributional changes of cattail and sawgrass. Biomass, shoot density, plant weight, shoot height, and biomass allocation to different plant components (leaves, shoot bases, roots and rhizomes), were sampled in cattail and sawgrass stands along a nutrient gradient within water conservation area 2A during two sequential years with different water level conditions. The shoot height–leaf weight relationships were analysed with allometric methods. Sawgrass exhibited responses to nutrient limitation that resembled functional responses to deep water, indicating that impact of deep water was stronger when plant growth was limited by nutrient deficiency. In cattail, responses along the nutrient gradient were less pronounced. Plant responses along the nutrient gradient differed between years. This was most evident in sawgrass, showing that this species was more affected by water depth than cattail. Responses in sawgrass suggested that this species had to sacrifice important plant functions in deep water at low-nutrient sites. The results in this study emphasise that, to preserve and restore sawgrass communities, lower water levels are required. For cattail, a combination of low phosphorus availability and disturbances (such as extended droughts and outbreaks of herbivores) is needed to stop the ongoing expansion. Management of these ecosystems must consider the relative roles of water level, nutrient enrichment, and disturbances, for vegetation development.

  • 175.
    Weisner, Stefan E.B.
    et al.
    Limnology, Lund University, Lund, Sweden .
    Strand, John A.
    Limnology, Lund University, Lund, Sweden .
    Sandsten, Håkan
    Limnology, Lund University, Lund, Sweden .
    Mechanisms regulating abundance of submerged vegetation in shallow eutrophic lakes1997In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 109, no 4, p. 592-599Article in journal (Refereed)
    Abstract [en]

    Shallow eutrophic lakes tend to be either in a turbid state dominated by phytoplankton or in a clear-water state dominated by submerged macrovegetation. Recent studies suggest that the low water turbidity in the clear-water state is maintained through direct and in-direct effects of the submerged vegetation. This study examined what mechanisms may cause a recession of the submerged vegetation in the clear-water state, and thereby a switch to the turbid state. The spatial distribution of submerged vegetation biomass was investigated in two shallow eutrophic lakes in the clear-water state in southern Sweden. Biomass of submerged vegetation was positively correlated with water depth and wave exposure, which also were mutually correlated, suggesting that mechanisms hampering submerged vegetation were strongest at shallow and/or sheltered locations. The growth of Myriophyllum spicatum, planted in the same substrate and at the same water depth, was compared between sheltered and wave exposed sites in two lakes. After 6 weeks the plants were significantly smaller at the sheltered sites, where periphyton production was about 5 times higher than at the exposed sites. Exclosure experiments were conducted to evaluate the effects of waterfowl grazing on macrophyte biomass. Potamogeton pectinatus growth was decreased by grazing, whereas M. spicatum was not affected. The effects were greater at a sheltered than at a wave-exposed site, and also negatively related to distance from the reed belt. These results suggest that competition from epiphytes and waterfowl grazing hamper the development of submerged vegetation at sheltered and/or shallow locations. An increased strength of these mechanisms may cause a recession of submerged vegetation in shallow eutrophic lakes in the clear-water state and thereby a switch to the turbid state.

  • 176.
    Weisner, Stefan
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Strand, John A.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Rhizome architecture in Phragmites australis in relation to water depth: Implications for within-plant oxygen transport distances1996In: Folia Geobotanica, ISSN 1211-9520, E-ISSN 1874-9348, Vol. 31, no 1, p. 91-97Article in journal (Refereed)
    Abstract [en]

    Phragmites australis (CAV.) TRlN. ex STEUD. is a perennial plant, largely relying on its rhizomes for resource storage, spreading and anchorage in the substrate. Vertical distribution and length of horizontal rhizomes of Phragmites australis were investigated at the reed bed edge in a lake in southern Sweden. In deep water, horizontal rhizomes were relatively short and superficially situated in the substrate. It is hypothesised that this is an adaptation to water depth by keeping O-2-transport distances through shoots and rhizomes as short as possible. In shallow water, P. australis rhizomes generally penetrated deeply into the substrate, probably improving anchorage and nutrient uptake possibilities. Further, horizontal rhizomes were longer in shallow water, which may increase the rate of vegetative spread. Because of these changes in rhizome architecture, "critical within-plant oxygen transport distances" did not change with water depth. This indicates that P. australis maximises the extension of its rhizomes in relation to spatial differences in water depth. This may limit the ability of P. australis to tolerate sudden temporal increases in water depth or eutrophication.

  • 177.
    Weisner, Stefan
    et al.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Tonderski, Karin
    Linköpings Universitet.
    Biomassa kan produceras och näring återvinnas: Ett framtidsperspektiv2002In: Våtmarksboken: Skapande och nyttjande av värdefulla våtmarker / [ed] Karin Tonderski , Stefan Weisner, Jan Landin, Hans Oscarsson, Göteborg: Vattenstrategiska forskningsprogrammet (VASTRA) , 2002, p. 123-134Chapter in book (Refereed)
  • 178.
    Wertz, Ingrid
    et al.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Weisner, Stefan E.B.
    Limnology, Department of Ecology, Lund University, Lund, Sweden.
    Potamogeton pectinatus and Myriophyllum spicatum response to sediments from a calcareous, shallow, eutrophic lake1997In: Journal of freshwater ecology, ISSN 0270-5060, E-ISSN 2156-6941, Vol. 12, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    The effect of sediment composition on the growth of Potamogeton pectinatus and Myriophyllum spicatum was evaluated by a greenhouse experiment in which segments of both species were grown on 37 sediments, which ranged from highly flocculent to sandy, collected from the calcareous, shallow eutrophic Lake Krankesjon. The two species responded similarly to the 37 sediment types; there was a strong correlation between the find biomass of M. spicatum and the find biomass of P. pectinatus for a given sediment type. Our results indicated that in these sediments, organic matter and density were not effective predictors of macrophyte growth. Root:shoot ratios of both P. pectinatus and M. spicatum were inversely related to the final biomass, and phosphorus and nitrogen concentrations of M. spicatum shoots were inversely related to root:shoot ratios. This suggests that plants were responding to sediment infertility by allocating proportionately more growth to root formation. Tissue analysis indicated that M. spicatum growth was phosphorus limited on some sediments, and this may have been a result of reduced phosphorus availability due to binding with calcium.

  • 179.
    Wikenros, Camilla
    et al.
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, Sweden.
    Aronsson, Malin
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, Sweden.
    Liberg, Olof
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, Sweden.
    Jarnemo, Anders
    Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
    Hansson, Jessica
    Halmstad University.
    Wallgren, Märtha
    3 Forestry Research Institute of Sweden, Uppsala Science Park, SE-751 83, Uppsala, Sweden.
    Sand, Håkan
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, Sweden.
    Bergström, Råger
    3 Forestry Research Institute of Sweden, Uppsala Science Park, SE-751 83, Uppsala, Sweden.
    Fear or food - Abundance of red fox in relation to occurrence of lynx and Wolf2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, no 1, article id 9059Article in journal (Refereed)
    Abstract [en]

    Apex predators may affect mesopredators through intraguild predation and/or supply of carrion from their prey, causing a trade-off between avoidance and attractiveness. We used wildlife triangle snow-tracking data to investigate the abundance of red fox (Vulpes vulpes) in relation to lynx (Lynx lynx) and wolf (Canis lupus) occurrence as well as land composition and vole (Microtus spp.) density. Data from the Swedish wolf-monitoring system and VHF/GPS-collared wolves were used to study the effect of wolf pack size and time since wolf territory establishment on fox abundance. Bottom-up processes were more influential than top-down effects as the proportion of arable land was the key indicator of fox abundance at the landscape level. At this spatial scale, there was no effect of wolf abundance on fox abundance, whereas lynx abundance had a positive effect. In contrast, at the wolf territory level there was a negative effect of wolves on fox abundance when including detailed information of pack size and time since territory establishment, whereas there was no effect of lynx abundance. This study shows that different apex predator species may affect mesopredator abundance in different ways and that the results may be dependent on the spatiotemporal scale and resolution of the data. © 2017 The Author(s).

  • 180.
    Wikenros, Camilla
    et al.
    Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Sciences, Riddarhyttan, Sweden; Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland.
    Jarnemo, Anders
    Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
    Frisén, Marielle
    Halmstad University.
    Kuijper, Dries P. J.
    Mammal Research Institute, Polish Academy of Sciences, Waszkiewicza 1, Białowieża, Poland.
    Schmidt, Krzysztof
    Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland.
    Mesopredator behavioral response to olfactory signals of an apex predator2017In: Journal of ethology, ISSN 0289-0771, E-ISSN 1439-5444, Vol. 35, no 2, p. 161-168Article in journal (Refereed)
    Abstract [en]

    Olfactory signals constitute an important mechanism in interspecific interactions, but little is known regarding their role in communication between predator species. We analyzed the behavioral responses of a mesopredator, the red fox (Vulpes vulpes), to an olfactory cue (scat) of an apex predator, the lynx (Lynx lynx) in BiałowieÅŒa Primeval Forest, Poland, using video camera traps. Red fox visited sites with scats more often than expected and the duration of their visits was longer at scat sites than at control sites (no scat added). Vigilant behavior, sniffing and scent marking (including over-marking) occurred more often at scat sites compared to control sites, where foxes mainly passed by. Vigilance was most pronounced during the first days of the recordings. Red fox behavior was also influenced by foxes previously visiting scat sites. They sniffed and scent marked (multiple over-marking) more frequently when the lynx scat had been over-marked previously by red fox. Fox visits to lynx scats may be seen as a trade-off between obtaining information on a potential food source (prey killed by lynx) and the potential risk of predation by an apex predator. © 2017, The Author(s).

  • 181.
    Wittwer, Torben
    et al.
    Department of Earth and Ecosystem Sciences, Lund University.
    Sahlén, Göran
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Suhling, Frank
    Institut für Geoökologie, Technische Universität Braunschweig, Braunschweig, Germany.
    Does one community shape the other?: Dragonflies and fish in Swedish lakes2010In: Insect Conservation and Diversity, ISSN 1752-458x, Vol. 3, no 2, p. 124-133Article in journal (Refereed)
    Abstract [en]

    1. Freshwater communities are often structured by predation. In permanent lentic freshwater habitats dragonfly larvae aremajor predators which, in return, suffer predation by fish. Antipredator traits vary between the dragonfly species, and the dragonfly communities are therefore shaped by the presence of fish. But fish communities vary, and as different fish species affect dragonflies in different ways, the species composition of the fish community may affect the composition of the dragonfly community.

    2. We sampled dragonfly larvae in 24 lakes with a known fish stock in south-western Sweden, and explored the impact of fish as well as vegetation structure on dragonfly communities by means of multivariate analyses.

    3. We found that the presence of four fish species affected the community structure of dragonflies. The impact strength depended mainly on the abundance of Perca fluviatilis, with which most dragonfly species were negatively correlated. Many dragonfly species were also positively correlated with the occurrence of at least one fish species, which may reflect similar habitat requirements or imply indirect positive effects of these fish species.

    4. Of the 24 recorded dragonfly species, four did not occur in lakes dominated by P. fluviatilis, whereas only one species was lacking in lakes dominated by Rutilus rutilus. The dragonfly species diversity was higher in R. rutilus lakes than in P. fluviatilis lakes.

    5. Our results suggest that the fish species composition is a major determinant of the dragonfly community, which in turn will influence the lower trophic levels.

     

     

  • 182.
    Woin, Per
    et al.
    Department of Ecology, Chemical Ecology and Ecotoxicology, Lund University, Lund, Sweden.
    Wendt-Rasch, Lina
    Department of Ecology, Chemical Ecology and Ecotoxicology, Lund University, Lund, Sweden.
    Pirzadeh, P.
    Department of Ecology, Chemical Ecology and Ecotoxicology, Lund University, Lund, Sweden.
    Effects of metsulfuron methyl and cypermethrin exposure on freshwater model ecosystems2003In: Aquatic Toxicology, ISSN 0166-445X, E-ISSN 1879-1514, Vol. 63, no 3, p. 243-256Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate the short-term (2 weeks) effects of the herbicide metsulfuron methyl alone and in combination with the insecticide cypermethrin in freshwater enclosures (80 l). We used a factorial design with four levels of herbicide (0, 1, 5, 20 mg/l) and two levels of insecticide (0 and 0.05 mg/l). The root growth of the macrophyte species Elodea canadensis and Myriophyllum spicatum decreased following exposure to the lowest concentration of metsulfuron methyl tested. Metsulfuron methyl exposure resulted in a decreased pH in the aquatic enclosure at the lowest concentration tested, which is most likely a further indication of decreased macrophyte primary production. The biomass of periphytic algae growing on the leaves of M. spicatum increased in the enclosures exposed to metsulfuron methyl. The species composition of the periphytic algae differed significantly from the controls in the enclosures exposed to 20 mg/l of the herbicide. The increased biomass of periphytic algae on the leaves of the macrophytes is probably an indirect effect of the herbicide exposure. The exposure to metsulfuron methyl possibly induced a leakage of nutrients from the macrophyte leaves, which promoted an increased algal growth. The exposure to metsulfuron methyl did not alter the biomass or the species composition of the phytoplankton community. The zooplankton communities in the enclosures were dominated by rotifers, which were not affected by the exposure to cypermethrin. However, a cypermethrin exposure of 0.05 mg/l initially decreased the abundance of copepod nauplii. Ten days after exposure, the abundance of nauplii was significantly higher in the insecticide-exposed enclosures compared with the non-exposed enclosures. This might be an indication of a sub-lethal stress response, which either increased the number of offspring produced or induced an increased hatching of copepod resting stages. No combined effects of the herbicide and insecticide exposure, either direct or indirect, were observed in the enclosure study. Significant effects on the macrophytes were observed following exposure to 1 mg metsulfuron methyl per litre in the enclosure study. Furthermore, a single species laboratory assay indicated that the shoot elongation of E. canadensis decreased following exposure to ]/0.1 mg metsulfuron methyl per litre. These concentrations are well within the range of expected environmental concentrations, thus this study shows that aquatic ecosystems, in particular those which are macrophyte- dominated, may be affected by metsulfuron methyl at concentrations that may well occur in water bodies adjacent to agricultural land.

  • 183.
    You, Liwen
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Computational prediction models for proteolytic cleavage and epitope identification2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The biological functions of proteins depend on their physical interactions with other molecules, such as proteins and peptides. Therefore, modeling the protein-ligand interactions is important for understanding protein functions in different biological processes. We have focused on the cleavage specificities of HIV-1 protease, HCV NS3 protease and caspases on short oligopeptides or in native proteins; the binding affinity of MHC molecules with short oligopeptides and identification of T cell epitopes. we expect that our findings on HIV-1 protease, HCV NS3 protease and caspases generalize to other proteases. In this thesis, we have performed analysis on these interactions from different perspectives - we have extended and collected new substrate data sets; used and compared different prediction methods (e.g. linear support vector machines, neural networks, OSRE method, rough set theory and Gaussian processes) to understand the underlying interaction problems; suggested new methods (i.e. a hierarchical method and Gaussian processes with test reject method) to improve predictions; and extracted cleavage rules for protease cleavage specificities. From our studies, we have extended oligopeptide substrate data sets and collected native protein substrates for HIV-1 protease, and a new oligopeptide substrate data set for HCV protease. We have shown that all current HIV-1 protease oligopeptide substratde data sets and our HCV data set are linearly separable; for HIV-1 protease, size and hydrophobicity are two important physicochemical properties in the recognition of short oligopeptide substrates to the protease; and linear support vector mahine is the state-of-the-art for this protease cleavage prediction problem. Our hierarchical method combining protein secondary structure information and experimental short oligopeptide cleavage information an improve the prediction of HIV-1 protease cleavage sites in native proteins. Our rule extraction method provides simple an accurate cleavage rules with high fidelity for HIV-1 and HCV proteases. For MHC molecules, we showed that high binding affinities are not necessarily correlated to immunogenicity on HLA-restricted peptides. Our test reject method combined with Gaussian processes can simplify experimental design by reducing false positives for detecting potential epitopes in large pathogen genomes.

  • 184.
    You, Liwen
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Detection of cleavage sites for HIV-1 protease in native proteins2006In: Proceedings of LSS Computational Systems Bioinformatics Conference: Computational Systems Bioinformatics Conference (vol. 5), Imperial College Press, 2006, p. 249-256Conference paper (Refereed)
    Abstract [en]

    Predicting novel cleavage sites for HIV-1 protease in non-viral proteins is a difficult task because of the scarcity of previous cleavage data on proteins in a native state. We introduce a three-level hierarchical classifier which combines information from experimentally verified short oligopeptides, secondary structure and solvent accessibility information from prediction servers to predict potential cleavage sites in non-viral proteins. The best classifier using secondary structure information on the second level classification of the hierarchical classifier is the one using logistic regression. By using this level of classification, the false positive ratio was reduced by more than half compared to the first level classifier using only the oligopeptide cleavage information. The method can be applied on other protease specificity problems too, to combine information from oligopeptides and structure from native proteins.

    Download full text (pdf)
    fulltext
  • 185.
    Zsoldos, Andreas
    Halmstad University, School of Business, Engineering and Science.
    Study on biomass in semiaquatic insects (Odonata) over a 20-year period in central, Sweden.2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This study is about how biomass of dragonflies insects have changed over the past 20-years in a forested area of central Sweden. This was done by analysing previously collected Odonata larvae stored in ethanol where sampling effort corrects the weight per locality. The results display a small but significant biomass increase over past decades, going against the recently observed trend of biomass decline in insects. However, this biomass gain was not even between the families, the ones that increased the most was Aesnidae and Libelluidae.  The reasons for the observed increase are discussed, some possible suggestions are less disturbance in their environments and their ability to adapt due to their long evolution giving them a phenotypical advantage.

    Download full text (pdf)
    fulltext
  • 186.
    Åhlén Mulio, Sandra
    Halmstad University, School of Business, Engineering and Science.
    Auchenorrhyncha community composition inrestored wetlands of different age in Southwest of Sweden:: Can different communities or species be used as indicators for naturalness?2015Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [sv]

    Våtmarker är hotade ekosystem som är artrika och tillhandahåller viktiga ekosystemtjänster. Man började restaurera våtmarker i Sverige som åtgärd inom jordbruket för minskad avrinning av närsalter, men senare även ur bevarandebiologiskt perspektiv. Främst riktades insatserna mot fåglar och däggdjur, men numera även många insekter.

    Insekter används alltmer som indikatorer för olika ändamål och Auchenorrhyncha (stritar) utgör en sådan grupp som börjat få alltmer uppmärksamhet. Då de livnär sig på växtsaft, förekommer i stort sett överallt där vaskulära växter har sin utbredning och ofta har specifika krav på både habitat och födoväxter, uppfyller de därmed många av kraven som ställs på en indikatorart. Stritar valdes därför för att se om de kan nyttjas som indikatorer på restaurerade våtmarkers grad av “naturalness”.

    Håvning och uppsamling med modifierad lövblås användes för att samla stritarna. Analyser över artfördelningen I landskapet visade signifikanta resultat på en icke slumpartad fördelning av arterna över de olika insamlingslokalerna och indikatorarter kunde väljas varefter ett modifierat index användes för att uppskatta arternas kvalité. Statistiska analysmetoder applicerades på insamlade variabler, men utan signifikans. Jaccards coeffcient of community användes för att verifera effektiviteten av insamlingen och det visade sig att jag i snitt samlat 1/3 av de arter som finns i landskapet. Ett fåtal arter uppfyllde kraven och i kombination med ett index över naturalness kunde 4 slutgiltiga arter väljas som indikatorarter. Auchenorrhyncha kan användas som indikatorer på naturalness i restaurerade våtmarker men då resultatet av denna studie inte var övertygande i sig själv bör man i framtida studier kombinera indexmetoderna med andra analyser och taxa för en helhetsbild när det gäller bedömning av naturalness i restaurerade våtmarker. Nya fynd av stritar för Halland och en rödlistad art hittades också i och med detta arbete och kan ses som ett bidrag till en uppdaterad förekomstbild i det svenska landskapet.

  • 187.
    Åsedahl, Linnea
    et al.
    Halmstad University, School of Business, Engineering and Science.
    Lindmark, Alexandra
    Halmstad University, School of Business, Engineering and Science.
    Identifiering av riskzoner för större vilt inom Halmstad kommuns vägnät2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    An increased infrastructure is one of today’s biggest reasons for the fragmentation ofhabitats, making it harder for wildlife to move without risks when crossing roads. To see inwhich extent larger mammals crosses roads greenways were identified in the urban parts ofHalmstad municipality, after which a study was made on the presence of wildlife duringwinter 2015/2016. Ten areas were chosen along road 600 (Tylösandsvägen), road 610(Kustvägen), trunk road 15, trunk road 25 and trunk road 26 where inventories were carriedout for a period of seven days distributed over a period of two months. Wildlife abundanceof moose, roe deer, fallow deer, red deer, hare, wild boar, badger, red fox, wolf and lynxwere investigated by identification of track stamps in order to find out if any of the tenplaces constitutes a danger zone for wildlife-vehicle accidents and if there are anydifferences in wildlife abundance close to and further from the road as well as in woodlandand open land. The result of the study along with wildlife accident statistics show that someof the investigated areas form danger zones for larger animals; two adjacent areas alongtrunk road 26 and one area along trunk road 15. There were no significant difference inwildlife abundance on different distances from the road which means that wildlife followsthe greenways and do not see the road as an obstacle, thus more likely to crossover. Therewere also no significant difference in wildlife abundance in woodland and open land,meaning wildlife-vehicle accidents are not more likely to occur in one type of land over theother.

    Download full text (pdf)
    fulltext
1234 151 - 187 of 187
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf