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  • 1.
    Frossling, Jenny
    et al.
    SVA, Sweden Swedish University of Agriculture Science, Sweden .
    Ohlson, Anna
    SVA, Sweden Swedish University of Agriculture Science, Sweden .
    Bjorkman, Camilla
    Swedish University of Agriculture Science, Sweden .
    Håkansson, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Noremark, Maria
    SVA, Sweden .
    Application of network analysis parameters in risk-based surveillance - Examples based on cattle trade data and bovine infections in Sweden2012In: Preventive Veterinary Medicine, ISSN 0167-5877, E-ISSN 1873-1716, Vol. 105, no 3, p. 202-208Article in journal (Refereed)
    Abstract [en]

    Financial resources may limit the number of samples that can be collected and analysed in disease surveillance programmes. When the aim of surveillance is disease detection and identification of case herds, a risk-based approach can increase the sensitivity of the surveillance system. In this paper, the association between two network analysis measures, i.e. in-degree and ingoing infection chain, and signs of infection is investigated. It is shown that based on regression analysis of combined data from a recent cross-sectional study for endemic viral infections and network analysis of animal movements, a positive serological result for bovine coronavirus (BCV) and bovine respiratory syncytial virus (BRSV) is significantly associated with the purchase of animals. For BCV, this association was significant also when accounting for herd size and regional cattle density, but not for BRSV. Examples are given for different approaches to include cattle movement data in risk-based surveillance by selecting herds based on network analysis measures. Results show that compared to completely random sampling these approaches increase the number of detected positives, both for BCV and BRSV in our study population. It is concluded that network measures for the relevant time period based on updated databases of animal movements can provide a simple and straight forward tool for risk-based sampling.

  • 2.
    Håkansson, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Network analysis and optimization of animal transports2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is about animal transports and their effect on animal welfare. Transports are needed in today’s system of livestock farming. Long transports are stressful for animals and infectious diseases can spread via animal transports. With optimization methods transport times can be minimized, but there is a trade-off between short distances for the animals and short distances for the trucks. The risk of disease spread in the transport system and disease occurrence at farms can be studied with models and network analysis.

    The animal transport data and the quality of the data in the Swedish national database of cattle and pig transports are investigated in the thesis. The data is analyzed regarding number of transports, number of farms, seasonality, geographical properties, transport distances, network measures of individual farms and network measures of the system. The data can be used as input parameters in epidemic models.

    Cattle purchase reports are double reported and we found that there are incorrect and missing reports in the database. The quality is improving over the years i.e. 5% of cattle purchase reports were not correctly double reported in 2006, 3% in 2007 and 1% in 2008. In the reports of births and deaths of cattle we detected date preferences; more cattle births and deaths are reported on the 1st, 10th and 20th each month. This is because when we humans don’t remember the exact number we tend to pick nice numbers (like 1, 10 and 20). This implies that the correct date is not always reported.

    Network analysis and network measures are suggested as tools to estimate risk for disease spread in transport systems and risk of disease introduction to individual holdings. Network generation algorithms can be used together with epidemic models to test the ability of network measures to predict disease risks. I have developed, and improved, a network generation algorithm that generates a large variety of structures.

    In my thesis I also suggest a method, the good choice heuristic, for generating non-optimal routes. Today coordination of animal transports is neither optimal nor random. In epidemic simulations we need to model routes as close to the actual driven routes as possible and the good choice heuristic can model that. The heuristic is tuned by two parameters and creates coordination of routes from completely random to almost as good as the Clarke and Wright heuristic. I also used the method to make the rough estimate that transport distances for cattle can be reduced by 2-24% with route-coordination optimization of transports-to-slaughter.

    Different optimization methods can be used to minimize the transport times for animal-transports in Sweden. For transports-to-slaughter the strategic planning of “which animals to send where” is the first step to optimize. I investigated data from 2008 and found that with strategic planning, given the slaughterhouse capacity, transport distances can be decreased by about 25% for pigs and 40% for cattle. The slaughterhouse capacity and placement are limiting the possibility to minimize transport times for the animals. The transport distances could be decreased by 60% if all animals were sent to the closest slaughterhouse 2008. Small-scale and mobile slaughterhouses have small effect on total transport work (total transport distance for all the animals) but are important for the transport distances of the animals that travel the longest.

    List of papers
    1. Route planning reduces the costs of animal transportation: Animal welfare versus economics
    Open this publication in new window or tab >>Route planning reduces the costs of animal transportation: Animal welfare versus economics
    2007 (English)In: XIII International Congress in Animal Hygiene, June 17–21, 2007, Tartu, Estonia: Animal Health, Animal Welfare and Biosecurity, Volume 1 / [ed] A. Aaland, 2007, p. 1044-1048Conference paper, Published paper (Refereed)
    Abstract [en]

    Animals are more stressed on long transport routes with stops at many farms. The positions of farms and abattoirs are the basic properties that set the limits for route planning. Mobile abattoirs can reduce the cost of transportation and increase the welfare for the animals. The trade-offs between welfare and profit can be reduced by effective route planning. We have, by computer simulations, investigated how trade-offs differs between areas in Sweden and in general landscapes. The general results are applicable to any area and hence for animal transportation in general.

    Keywords
    Animal transport, route optimization, 1/f noise, DFT, cost, animal welfare
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-76358 (URN)978-9949-426-30-0 (ISBN)
    Conference
    International Congress in Animal Hygiene, June 17-21, Tartu, Estonia
    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-04-16Bibliographically approved
    2. Spatial and temporal investigations of reported movements, births and deaths of cattle and pigs in Sweden
    Open this publication in new window or tab >>Spatial and temporal investigations of reported movements, births and deaths of cattle and pigs in Sweden
    Show others...
    2009 (English)In: Acta Veterinaria Scandinavica, ISSN 1751-0147, E-ISSN 1751-0147, Vol. 51, no 37Article in journal (Refereed) Published
    Abstract [en]

    Background: Livestock movements can affect the spread and control of contagious diseases and new data recording systems enable analysis of these movements. The results can be used for contingency planning, modelling of disease spread and design of disease control programs. Methods: Data on the Swedish cattle and pig populations during the period July 2005 until June 2006 were obtained from databases held by the Swedish Board of Agriculture. Movements of cattle and pigs were investigated from geographical and temporal perspectives, births and deaths of cattle were investigated from a temporal perspective and the geographical distribution of holdings was also investigated. Results: Most movements of cattle and pigs were to holdings within 100 km, but movements up to 1200 km occurred. Consequently, the majority of movements occurred within the same county or to adjacent counties. Approximately 54% of the cattle holdings and 45% of the pig holdings did not purchase any live animals. Seasonal variations in births and deaths of cattle were identified, with peaks in spring. Cattle movements peaked in spring and autumn. The maximum number of holdings within a 3 km radius of one holding was 45 for cattle and 23 for pigs, with large variations among counties. Missing data and reporting bias ( digit preference) were detected in the data. Conclusion: The databases are valuable tools in contact tracing. However since movements can be reported up to a week after the event and some data are missing they cannot replace other methods in the acute phase of an outbreak. We identified long distance transports of cattle and pigs, and these findings support an implementation of a total standstill in the country in the case of an outbreak of foot-and-mouth disease. The databases contain valuable information and improvements in data quality would make them even more useful.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-51599 (URN)10.1186/1751-0147-51-37 (DOI)
    Note
    Original Publication: Maria Noremark, Nina Hakansson, Tom Lindström, Uno Wennergren and Susanna Sternberg Lewerin, Spatial and temporal investigations of reported movements, births and deaths of cattle and pigs in Sweden, 2009, ACTA VETERINARIA SCANDINAVICA, (51), 37. http://dx.doi.org/10.1186/1751-0147-51-37 Licensee: Acta Veterinaria Scandinavica / BioMed CentralAvailable from: 2009-11-09 Created: 2009-11-09 Last updated: 2017-12-12
    3. Network analysis of cattle and pig movements in Sweden: Measures relevant for disease control and risk based surveillance
    Open this publication in new window or tab >>Network analysis of cattle and pig movements in Sweden: Measures relevant for disease control and risk based surveillance
    Show others...
    2011 (English)In: PREVENTIVE VETERINARY MEDICINE, ISSN 0167-5877, Vol. 99, no 2-4, p. 78-90Article in journal (Refereed) Published
    Abstract [en]

    Registration of cattle and pig movements is mandatory in Sweden and all registered movements between farms in the years 2006-2008 were investigated using network analysis. The networks were analysed as monthly and yearly networks, separately per species and with the two species together. Measures that have been previously discussed in relation to outbreaks and disease control were calculated; moreover a measure of the ingoing infection chain was constructed. The ingoing infection chain captures ingoing contacts through other holdings, taking the temporal aspect and sequence of the movements into account. The distribution of the contacts among the holdings was skewed. Many farms had few or no contacts, while others had many, a pattern which has also been described from other countries. The cattle network and the combined network showed a recurring seasonal pattern, while this was not seen in the pig network. The in-degree was not equivalent to the ingoing infection chain; there were holdings with limited direct contacts, but a large number of indirect contacts. The ingoing infection chain could be a useful measure when setting up strategies for disease control and for risk based surveillance as it identifies holdings with many contacts through live animal movements and thus at potentially higher risk for introduction of contagious diseases.

    Place, publisher, year, edition, pages
    Elsevier Science B.V., Amsterdam., 2011
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-68337 (URN)10.1016/j.prevetmed.2010.12.009 (DOI)000290186100002 ()
    Available from: 2011-05-20 Created: 2011-05-20 Last updated: 2012-04-05
    4. Generating structure specific networks
    Open this publication in new window or tab >>Generating structure specific networks
    Show others...
    2010 (English)In: Advances in Complex Systems, ISSN 0219-5259, Vol. 13, no 2, p. 239-250Article in journal (Refereed) Published
    Abstract [en]

    Theoretical exploration of network structure significance requires a range of different networks for comparison. Here, we present a new method to construct networks in a spatial setting that uses spectral methods in combination with a probability distribution function. Nearly all previous algorithms for network construction have assumed randomized distribution of links or a distribution dependent on the degree of the nodes. We relax those assumptions. Our algorithm is capable of creating spectral networks along a gradient from random to highly clustered or diverse networks. Number of nodes and link density are specified from start and the structure is tuned by three parameters (gamma, sigma, kappa). The structure is measured by fragmentation, degree assortativity, clustering and group betweenness of the networks. The parameter gamma regulates the aggregation in the spatial node pattern and sigma and kappa regulates the probability of link forming.

    Keywords
    Network; spectral; assortativity; fragmentation; clustering; betweenness centralization; spatial network; network algorithm
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-58246 (URN)10.1142/S0219525910002517 (DOI)000279727100006 ()
    Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2017-12-12Bibliographically approved
    5. SpecNet: a spatial network algorithm that generates a wide range of specific structures
    Open this publication in new window or tab >>SpecNet: a spatial network algorithm that generates a wide range of specific structures
    2012 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 8Article in journal (Refereed) Published
    Abstract [en]

    Network measures are used to predict the behavior of different systems. To be able to investigate how various structures behave and interact we need a wide range of theoretical networks to explore. Both spatial and non-spatial methods exist for generating networks but they are limited in the ability of producing wide range of network structures. We extend an earlier version of a spatial spectral network algorithm to generate a large variety of networks across almost all the theoretical spectra of the following network measures: average clustering coefficient, degree assortativity, fragmentation index, and mean degree. We compare this extended spatial spectral network-generating algorithm with a non-spatial algorithm regarding their ability to create networks with different structures and network measures. The spatial spectral network-generating algorithm can generate networks over a much broader scale than the non-spatial and other known network algorithms. To exemplify the ability to regenerate real networks, we regenerate networks with structures similar to two real Swedish swine transport networks. Results show that the spatial algorithm is an appropriate model with correlation coefficients at 0.99. This novel algorithm can even create negative assortativity and managed to achieve assortativity values that spans over almost the entire theoretical range.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-76359 (URN)10.1371/journal.pone.0042679 (DOI)000307184700057 ()
    Note

    funding agencies|Swedish Civil Contingencies Agency (MSB)||Foreign Animal Disease Modeling program of the Science and Technology Directorate, Department of Homeland Security|ST-108-000017|

    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2017-12-07Bibliographically approved
    6. A strategic analysis of slaughterhouses and animal transportation in Sweden
    Open this publication in new window or tab >>A strategic analysis of slaughterhouses and animal transportation in Sweden
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The number of slaughterhouses in Sweden has decreased over time. Fewer slaughterhouses are expected to affect the transport time for animals and as a consequence animal welfare. We have analyzed the transportto- slaughter system, for pigs and cattle, using transport-data from 2008, geographical information for slaughterhouses and farms, and actual route distances between facilities. We made a strategic analysis of the existing slaughterhouses and tested the impact of numbers decreasing further.

    With strategic planning the potential reduction of transport distance is 25% for pigs and 40% for cattle. About 50% of the slaughterhouses in Sweden could be closed down with small effect on the total transport work. This implies that for the national total animal welfare which animals are sent where, is much more important than the number of slaughterhouses. However for the welfare (transport time and distance) of the animals in long transports number of slaughterhouses (regular or mobile) is important. Animal welfare weights of distances in the objective function decreases the amount of transports with long route times. We have investigated where in Sweden it would be beneficial to use mobile slaughterhouses. Animals are usually not sent to closest slaughterhouse; we show how slaughterhouse capacity must change if that transport strategy was applied.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-76360 (URN)
    Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-04-05Bibliographically approved
  • 3.
    Håkansson, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Flisberg, P.
    The Forestry Research Institute of Sweden, Uppsala, Sweden.
    Algers, B.
    Swedish University of Agricultural Sciences, Skara, Sweden.
    Rönnqvist, M.
    Norwegian School of Economics and Business Administration, Bergen, Norway.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    A strategic analysis of slaughterhouses and animal transportation in SwedenManuscript (preprint) (Other academic)
    Abstract [en]

    The number of slaughterhouses in Sweden has decreased over time. Fewer slaughterhouses are expected to affect the transport time for animals and as a consequence animal welfare. We have analyzed the transportto- slaughter system, for pigs and cattle, using transport-data from 2008, geographical information for slaughterhouses and farms, and actual route distances between facilities. We made a strategic analysis of the existing slaughterhouses and tested the impact of numbers decreasing further.

    With strategic planning the potential reduction of transport distance is 25% for pigs and 40% for cattle. About 50% of the slaughterhouses in Sweden could be closed down with small effect on the total transport work. This implies that for the national total animal welfare which animals are sent where, is much more important than the number of slaughterhouses. However for the welfare (transport time and distance) of the animals in long transports number of slaughterhouses (regular or mobile) is important. Animal welfare weights of distances in the objective function decreases the amount of transports with long route times. We have investigated where in Sweden it would be beneficial to use mobile slaughterhouses. Animals are usually not sent to closest slaughterhouse; we show how slaughterhouse capacity must change if that transport strategy was applied.

  • 4.
    Håkansson, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Henningsson, Markus
    Linköping University, Department of Management and Engineering, Industrial Marketing and Industrial Economics. Linköping University, The Institute of Technology.
    Rönnqvist, M.
    NHH, Bergen, Norway.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Route planning reduces the costs of animal transportation: Animal welfare versus economics2007In: XIII International Congress in Animal Hygiene, June 17–21, 2007, Tartu, Estonia: Animal Health, Animal Welfare and Biosecurity, Volume 1 / [ed] A. Aaland, 2007, p. 1044-1048Conference paper (Refereed)
    Abstract [en]

    Animals are more stressed on long transport routes with stops at many farms. The positions of farms and abattoirs are the basic properties that set the limits for route planning. Mobile abattoirs can reduce the cost of transportation and increase the welfare for the animals. The trade-offs between welfare and profit can be reduced by effective route planning. We have, by computer simulations, investigated how trade-offs differs between areas in Sweden and in general landscapes. The general results are applicable to any area and hence for animal transportation in general.

  • 5.
    Håkansson, Nina
    et al.
    Skovde University.
    Jonsson, A.
    Skovde University.
    Lennartsson, Jenny
    Skovde University.
    Lindström, Tom
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Generating structure specific networks2010In: Advances in Complex Systems, ISSN 0219-5259, Vol. 13, no 2, p. 239-250Article in journal (Refereed)
    Abstract [en]

    Theoretical exploration of network structure significance requires a range of different networks for comparison. Here, we present a new method to construct networks in a spatial setting that uses spectral methods in combination with a probability distribution function. Nearly all previous algorithms for network construction have assumed randomized distribution of links or a distribution dependent on the degree of the nodes. We relax those assumptions. Our algorithm is capable of creating spectral networks along a gradient from random to highly clustered or diverse networks. Number of nodes and link density are specified from start and the structure is tuned by three parameters (gamma, sigma, kappa). The structure is measured by fragmentation, degree assortativity, clustering and group betweenness of the networks. The parameter gamma regulates the aggregation in the spatial node pattern and sigma and kappa regulates the probability of link forming.

  • 6.
    Lennartsson, Jenny
    et al.
    Systems Biology Research Centre, Skövde University, Skövde, Sweden.
    Håkansson, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Jonsson, A.
    Systems Biology Research Centre, Skövde University, Skövde, Sweden.
    SpecNet: a spatial network algorithm that generates a wide range of specific structures2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 8Article in journal (Refereed)
    Abstract [en]

    Network measures are used to predict the behavior of different systems. To be able to investigate how various structures behave and interact we need a wide range of theoretical networks to explore. Both spatial and non-spatial methods exist for generating networks but they are limited in the ability of producing wide range of network structures. We extend an earlier version of a spatial spectral network algorithm to generate a large variety of networks across almost all the theoretical spectra of the following network measures: average clustering coefficient, degree assortativity, fragmentation index, and mean degree. We compare this extended spatial spectral network-generating algorithm with a non-spatial algorithm regarding their ability to create networks with different structures and network measures. The spatial spectral network-generating algorithm can generate networks over a much broader scale than the non-spatial and other known network algorithms. To exemplify the ability to regenerate real networks, we regenerate networks with structures similar to two real Swedish swine transport networks. Results show that the spatial algorithm is an appropriate model with correlation coefficients at 0.99. This novel algorithm can even create negative assortativity and managed to achieve assortativity values that spans over almost the entire theoretical range.

  • 7.
    Lennartsson, Jenny
    et al.
    Systems Biology Research Centre, Skövde University, Skövde, Sweden.
    Jonsson, Annie
    Systems Biology Research Centre, Skövde University, Skövde, Sweden.
    Håkansson, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Is a Sampled Network a Good Enough Descriptor? Missing Links and Appropriate Choice of RepresentationManuscript (preprint) (Other academic)
    Abstract [en]

    Missing links due to sampling difficulties can be a limitation in network analysis. Measurements and analysis of networks with insufficient data may make the actual properties indistinct and thus include too much uncertainty to lead to accurate inferences. In addition, in dynamical networks with low link degrees and high stochasticity one sample of the network structure during a finite time window may not be sufficient for general conclusions. Our interest here is to examine the possible consequences of analysis of networks with insufficient data. We studied how mean link degree in sampled networks affects predictions of the spread of disease. Networks with weighted links were used to run scenarios that assumed distance-dependent probabilities of disease transmission when applying general simulation methodology. These scenarios were compared with scenarios including randomly drawn probabilities of disease transmission. For both types of scenarios, we also tested two link-forming methods, one based on distance-dependence and the other on a random approach. Our findings imply that sampled networks must be improved by using statistical measures before attempting to estimate or predict the spread of disease. We conclude that, under the assumption of weighted links, predictions about the extent of an epidemic can be drawn only at mean degrees that are much higher than found in empirical studies. In reality, neither sampling procedures nor disease transmissions are completely dependent on distance. Our results show how this aspect enforces an even higher level of mean degree to be present in order to achieve reasonable predictions.

  • 8.
    Lindström, Tom
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Håkansson, Nina
    Skövde University.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    The shape of the spatial kernel and its implications for biological invasions in patchy environments2011In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 278, no 1711, p. 1564-1571Article in journal (Refereed)
    Abstract [en]

    Ecological and epidemiological invasions occur in a spatial context. In the study presented we tested how these processes relate to the distance dependence of spread or dispersal between spatial entities such as habitat patches or infective units. The distance dependence was described by a spatial kernel which can be characterized by its shape, quantified by kurtosis, and width, quantified by the kernel variance. We also introduced a method to analyze or generate non randomly distributed infective units or patches as point pattern landscapes. The method is based on Fourier transform and consists of two measures in the spectral representation; Continuity that relates to autocorrelation and Contrast that refers to difference in density of patches, or infective units, in different areas of the landscape. The method was also used to analyze some relevant empirical data where our results are expected to have implications for ecological or epidemiological studies. We analyzed distributions of large old trees (Quercus and Ulmus) as well as the distributions of farms (both cattle and pig) in Sweden. We tested the invasion speed in generated landscapes with different amount of Continuity and Contrast. The results showed that kurtosis, i.e. the kernel shape, was not important for predicting the invasion speed in randomly distributed patches or infective units. However, depending on the assumptions of dispersal, it may be highly important when the distribution of patches or infective units deviates from randomness, in particular when the Contrast is high. We conclude that speed of invasions and spread of diseases depends on its spatial context through the spatial kernel intertwined to the spatial structure. This implies high demands on the empirical data; it requires knowledge of both shape and width of the spatial kernel as well as spatial structure of patches or infective units.

  • 9.
    Lindström, Tom
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Håkansson, Nina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Westerberg, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Splitting the tail of the displacement kernel shows the unimportance of kurtosis2008In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 89, no 7, p. 1784-1790Article in journal (Refereed)
    Abstract [en]

    Animals disperse in space through different movement behaviors, resulting in different displacement distances. This is often described with a displacement kernel where the long-distance dispersers are within the tail of the kernel. A displacement with a large proportion of long-distance dispersers may have impact on different aspects of spatial ecology such as invasion speed, population persistence, and distribution. It is, however, unclear whether the kurtosis of the kernel plays a major role since a fatter tail also influences the variance of the kernel. We modeled displacement in landscapes with different amounts and configurations of habitats and handled kurtosis and variance separately to study how these affected population distribution and transition time. We conclude that kurtosis is not important for any of these aspects of spatial ecology. The variance of the kernel, on the other hand, was of great importance to both population distribution and transition time. We argue that separating variance and kurtosis can cast new light on the way in which long-distance dispersers are important in ecological processes. Consequences for empirical studies are discussed.

  • 10.
    Lögdberg, Frida
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Håkansson, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Lindström, Tom
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    The Importance of Distance-Dependent Synchrony of Coloured NoiseManuscript (preprint) (Other academic)
    Abstract [en]

    Local populations in patches close to each other would probably be influenced by similar environmental conditions. When increasing the distance between the patches the local population will experience less synchronized environments. Since, the degree of synchrony is important for the overall extinction risk it is probably likewise important to include distance dependence in environmental variation when studying environmental forcing on spatially subdivided populations. Thus, we will investigate the importance of including such distance dependent synchrony when studying coloured environmental variation applied to populations in explicit landscapes. We will introduce a method based on controlling the phases when generating 1/fnoise. The results showed large differences between fast or slow density regulation responses in populations. Extinction risk was several magnitudes larger when including distance dependent synchrony compared to randomly distributing environmental time series for overcompensatory dynamics. There was one exception; it is not necessary to include distance dependent synchrony for landscape with random patch distribution. For undercompensatory dynamics the effect from distant dependent synchrony was only apparent in the most aggregated patch  configurations.

  • 11.
    Noremark, Maria
    et al.
    Swedish University Agriculture Science.
    Hakansson, Nina
    University of Skövde.
    Lindström, Tom
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Sternberg Lewerin, Susanna
    SVA.
    Spatial and temporal investigations of reported movements, births and deaths of cattle and pigs in Sweden2009In: Acta Veterinaria Scandinavica, ISSN 1751-0147, E-ISSN 1751-0147, Vol. 51, no 37Article in journal (Refereed)
    Abstract [en]

    Background: Livestock movements can affect the spread and control of contagious diseases and new data recording systems enable analysis of these movements. The results can be used for contingency planning, modelling of disease spread and design of disease control programs. Methods: Data on the Swedish cattle and pig populations during the period July 2005 until June 2006 were obtained from databases held by the Swedish Board of Agriculture. Movements of cattle and pigs were investigated from geographical and temporal perspectives, births and deaths of cattle were investigated from a temporal perspective and the geographical distribution of holdings was also investigated. Results: Most movements of cattle and pigs were to holdings within 100 km, but movements up to 1200 km occurred. Consequently, the majority of movements occurred within the same county or to adjacent counties. Approximately 54% of the cattle holdings and 45% of the pig holdings did not purchase any live animals. Seasonal variations in births and deaths of cattle were identified, with peaks in spring. Cattle movements peaked in spring and autumn. The maximum number of holdings within a 3 km radius of one holding was 45 for cattle and 23 for pigs, with large variations among counties. Missing data and reporting bias ( digit preference) were detected in the data. Conclusion: The databases are valuable tools in contact tracing. However since movements can be reported up to a week after the event and some data are missing they cannot replace other methods in the acute phase of an outbreak. We identified long distance transports of cattle and pigs, and these findings support an implementation of a total standstill in the country in the case of an outbreak of foot-and-mouth disease. The databases contain valuable information and improvements in data quality would make them even more useful.

  • 12.
    Nöremark, Maria
    et al.
    SVA, National Veterinary Institute, Department of Disease Control and Epidemiology, Uppsala.
    Håkansson, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Sternberg Lewerin, Susanna
    SVA, SVA, National Veterinary Institute, Department of Disease Control and Epidemiology, Uppsala.
    Lindberg, Ann
    SVA, SVA, National Veterinary Institute, Department of Disease Control and Epidemiology, Uppsala.
    Jonsson, Annie
    Systems Biology Research Centre, Ecological Modelling, University of Skövde, Skövde.
    Network analysis of cattle and pig movements in Sweden: Measures relevant for disease control and risk based surveillance2011In: PREVENTIVE VETERINARY MEDICINE, ISSN 0167-5877, Vol. 99, no 2-4, p. 78-90Article in journal (Refereed)
    Abstract [en]

    Registration of cattle and pig movements is mandatory in Sweden and all registered movements between farms in the years 2006-2008 were investigated using network analysis. The networks were analysed as monthly and yearly networks, separately per species and with the two species together. Measures that have been previously discussed in relation to outbreaks and disease control were calculated; moreover a measure of the ingoing infection chain was constructed. The ingoing infection chain captures ingoing contacts through other holdings, taking the temporal aspect and sequence of the movements into account. The distribution of the contacts among the holdings was skewed. Many farms had few or no contacts, while others had many, a pattern which has also been described from other countries. The cattle network and the combined network showed a recurring seasonal pattern, while this was not seen in the pig network. The in-degree was not equivalent to the ingoing infection chain; there were holdings with limited direct contacts, but a large number of indirect contacts. The ingoing infection chain could be a useful measure when setting up strategies for disease control and for risk based surveillance as it identifies holdings with many contacts through live animal movements and thus at potentially higher risk for introduction of contagious diseases.

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