29 results on '"Hoyle, Andrew"'
Search Results
2. Multi-objective evolutionary design of antibiotic treatments
- Author
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Ochoa, Gabriela, Christie, Lee A., Brownlee, Alexander E., and Hoyle, Andrew
- Published
- 2020
- Full Text
- View/download PDF
3. Studies in adaptive dynamics
- Author
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Hoyle, Andrew Steven
- Subjects
515.39 - Published
- 2005
4. When and why direct transmission models can be used for environmentally persistent pathogens
- Author
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Benson, Lee, primary, Davidson, Ross S., additional, Green, Darren M., additional, Hoyle, Andrew, additional, Hutchings, Mike R., additional, and Marion, Glenn, additional
- Published
- 2021
- Full Text
- View/download PDF
5. Impact Of Menstrual Cycle On Body Composition Measures And Resting Metabolism
- Author
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Gould, Lacey, primary, Cabre, Hannah, additional, Brewer, Gabrielle, additional, Blue, Malia, additional, Hirsch, Katie, additional, Gordon, Amanda, additional, Hoyle, Andrew, additional, and Smith-Ryan, Abbie, additional
- Published
- 2021
- Full Text
- View/download PDF
6. Effect Of Acute Feeding On Bioelectrical Impedance Vector Analysis Calculated Phase Angle In Healthy Subjects
- Author
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Hoyle, Andrew T., primary, Gould, Lacey M., additional, Cabre, Hannah E., additional, Gordon, Amanda N., additional, and Smith-Ryan, Abbie E., additional
- Published
- 2021
- Full Text
- View/download PDF
7. Relationship Between Maximal Fat Oxidation And Ventilatory Threshold In Endurance Trained Males
- Author
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Saylor (Cabre), Hannah E., primary, Greenwalt, Casey E., additional, Gould, Lacey M., additional, Gordon, Amanda N., additional, Hoyle, Andrew T., additional, and Smith-Ryan, Abbie E., additional
- Published
- 2021
- Full Text
- View/download PDF
8. Body Composition Of NCAA Division I Football Players Pre And Post COVID-19 Quarantine
- Author
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Gordon, Amanda N., primary, Blue, Malia N.M, additional, Cabre, Hannah E., additional, Gould, Lacey M., additional, Hirsch, Katie R., additional, Hoyle, Andrew T., additional, and Smith-Ryan, Abbie, additional
- Published
- 2021
- Full Text
- View/download PDF
9. Effects of Whey and Pea Protein Supplementation on Post-Eccentric Exercise Muscle Damage: A Randomized Trial
- Author
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Nieman, David C., primary, Zwetsloot, Kevin A., additional, Simonson, Andrew J., additional, Hoyle, Andrew T., additional, Wang, Xintang, additional, Nelson, Heather K., additional, Lefranc-Millot, Catherine, additional, and Guérin-Deremaux, Laetitia, additional
- Published
- 2020
- Full Text
- View/download PDF
10. Correction: Predicting the Potential for Natural Recovery of Atlantic Salmon (Salmo salar L.) Populations following the Introduction of Gyrodactylus salaris Malmberg, 1957 (Monogenea)
- Author
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Denholm, Scott J., Hoyle, Andrew S., Shinn, Andrew P., Paladini, Giuseppe, Taylor, Nick G. H., and Norman, Rachel A.
- Subjects
Conservation of Natural Resources ,Models, Statistical ,Multidisciplinary ,Platyhelminths ,Salmo salar ,lcsh:R ,Correction ,Animals ,lcsh:Medicine ,lcsh:Q ,lcsh:Science ,Host-Parasite Interactions - Abstract
Gyrodactylus salaris (Monogenea, Platyhelminthes) is a notifiable freshwater pathogen responsible for causing catastrophic damage to wild Atlantic salmon stocks, most notably in Norway. In some strains of Baltic salmon (e.g., from the river Neva) however, the impact is greatly reduced due to some form of innate resistance that regulates parasite numbers, resulting in fewer host mortalities. Gyrodactylus salaris is known from 17 European states; its status in a further 35 states remains unknown; the UK, the Republic of Ireland and certain watersheds in Finland are free of the parasite. Thus, the parasite poses a serious threat if it emerges in Atlantic salmon rearing regions throughout Europe. At present, infections are generally controlled via extreme measures such as the treatment of entire river catchments with the biocide rotenone, in order to remove all hosts, before restocking with the original genetic stock. The use of rotenone in this way in EU countries is unlikely as it would be in contravention of the Water Framework Directive. Not only are such treatments economically and environmentally costly, they also eradicate the potential for any host/parasite evolutionary process to occur. Based on previous studies, UK salmon stocks have been shown to be highly susceptible to infection, analogous to Norwegian stocks. The present study investigates the impact of a G. salaris outbreak within a naïve salmon population in order to determine long-term consequences of infection and the likelihood of coexistence. Simulation of the salmon/ G. salaris system was carried out via a deterministic mathematical modelling approach to examine the dynamics of host-pathogen interactions. Results indicated that in order for highly susceptible Atlantic strains to evolve a resistance, both a moderate-strong deceleratingly costly trade-off on birth rate and a lower overall cost of the immune response are required. The present study provides insights into the potential long term impact of G. salaris if introduced into G. salaris-free territories and suggests that in the absence of external controls salmon populations are likely to recover to high densities nearing 90% of that observed pre-infection.
- Published
- 2017
11. Highly efficient lubrication
- Author
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Hoyle, Andrew
- Subjects
Industrial equipment and supplies industry -- Product information ,Business ,Business, international ,Construction and materials industries ,AS-i (Lubricant) -- Usage - Published
- 2007
12. Predicting the Potential for Natural Recovery of Atlantic Salmon (Salmo salar L.) Populations following the Introduction of Gyrodactylus salaris Malmberg, 1957 (Monogenea)
- Author
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Denholm, Scott J., primary, Hoyle, Andrew S., additional, Shinn, Andrew P., additional, Paladini, Giuseppe, additional, Taylor, Nick G. H., additional, and Norman, Rachel A., additional
- Published
- 2016
- Full Text
- View/download PDF
13. Reproductive Trade-Offs May Moderate the Impact of Gyrodactylus salaris in Warmer Climates
- Author
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Denholm, Scott J, Norman, Rachel, Hoyle, Andrew, Shinn, Andrew, and Taylor, Nicholas G H
- Abstract
Gyrodactylus salaris is a notifiable freshwater ectoparasite of salmonids. Its primary host is Atlantic salmon (Salmo salar), upon which infections can cause death, and have led to massive declines in salmon numbers in Norway, where the parasite is widespread. Different strains of S. salar vary in their susceptibility, with Atlantic strains (such as those found in Norway) exhibiting no resistance to the parasite, and Baltic strains demonstrating an innate resistance sufficient to regulate parasite numbers on the host causing it to either die out or persist at a low level. In this study, Leslie matrix and compartmental models were used to generate data that demonstrated the population growth of G. salaris on an individual host is dependent on the total number of offspring per parasite, its longevity and the timing of its births. The data demonstrated that the key factor determining the rate of G. salaris population growth is the time at which the parasite first gives birth, with rapid birth rate giving rise to large population size. Furthermore, it was shown that though the parasite can give birth up to four times, only two births are required for the population to persist as long as the first birth occurs before a parasite is three days old. As temperature is known to influence the timing of the parasite's first birth, greater impact may be predicted if introduced to countries with warmer climates than Norway, such as the UK and Ireland which are currently recognised to be free of G. salaris. However, the outputs from the models developed in this study suggest that temperature induced trade-offs between the total number of offspring the parasite gives birth to and the first birth timing may prevent increased population growth rates over those observed in Norway.
- Published
- 2013
14. Evolutionary behaviour, trade-offs and cyclic and chaotic population dynamics
- Author
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Hoyle, Andrew, Bowers, Roger, and White, Andrew
- Subjects
Trade-offs ,Logistic equation ,Chaos ,Evolutionary branching ,Adaptive dynamics - Abstract
Many studies of the evolution of life-history traits assume that the underlying population dynamical attractor is stable point equilibrium. However, evolutionary outcomes can change significantly in different circumstances. We present an analysis based on adaptive dynamics of a discrete-time demographic model involving a trade-off whose shape is also an important determinant of evolutionary behaviour. We derive an explicit expression for the fitness in the cyclic region and consequently present an adaptive dynamic analysis which is algebraic.We do this fully in the region of 2-cycles and (using a symbolic package) almost fully for 4-cycles. Simulations illustrate and verify our results.With equilibrium population dynamics, trade-offs with accelerating costs produce a continuously stable strategy (CSS) whereas trade-offs with decelerating costs produce a non-ES repellor. The transition to 2-cycles produces a discontinuous change: the appearance of an intermediate region in which branching points occur. The size of this region decreases as we move through the region of 2-cycles. There is a further discontinuous fall in the size of the branching region during the transition to 4-cycles. We extend our results numerically and with simulations to higher-period cycles and chaos. Simulations show that chaotic population dynamics can evolve from equilibrium and vice-versa.
- Published
- 2011
15. Sexually antagonistic co-evolution: a model and an empirical test
- Author
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Hoyle, Andrew and Gilburn, Andre
- Subjects
seaweed fly ,resistance trait ,Coelopa ursine ,sexual conflict ,pre-mating struggle ,coelopidae ,persistence trait ,sexual size dimorphism - Abstract
Models reveal that sexually antagonistic co-evolution exaggerates female resistance and male persistence traits. Here we adapt an established model by including directional sexual selection acting against persistence. We find similar equilibria to previous models showing that sexually antagonistic co-evolution can be limited by counteracting sexual, as well as, natural selection. We tested the model using empirical data for the seaweed fly, Coelopa ursina, in which body size acts as a persistence and a resistance trait. Our model can generate continuous co-evolutionary cycles and stable equilibria, however, all simulations using empirically derived parameter estimates reach stable equilibria. Thus, stable equilibria might be more common in nature than continuous co-evolutionary cycles, suggesting that sexual conflict is unlikely to promote speciation. The model predicts male biased sexual size dimorphism for C. ursina, comparable with empirically observed values. Male persistence is shown to be more sensitive than female resistance to changes in model parameters.
- Published
- 2010
16. Exclusion of generalist pathogens in multihost communities
- Author
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Greenman, Jonathan and Hoyle, Andrew
- Subjects
species coexistence ,apparent competition ,transmission ,biological control ,persistence ,infectious diseases ,populations ,invasion threshold ,Multihost SIS model ,tuberculosis ,frequency dependence ,cattle ,badgers ,impact ,competition ,force of infection - Abstract
Knowing how to control a pathogen that infects more than one host species is of increasing importance because the incidence of such infections grows with continuing environmental change. Of concern are infections transmitted from wildlife to humans or livestock. To determine which options are available to control a pathogen in these circumstances, we analyze the pathogen invasion matrix for the multihost susceptible-infected-susceptible model. We highlight the importance of both community structure and the column sum or row sum index, an indicator of both force of infection and community stability. We derive a set of guidelines for constructing culling strategies and suggest a hybrid strategy that has the advantages of both the bottom-up and the top-down approaches, which we study in some detail. The analysis holds for an arbitrary number of host species, enabling the analysis of large-scale ecological systems and systems with spatial dimensions. We test the robustness of our methods by making two changes in the structure of the underlying dynamic model, adding direct competition and introducing frequency-dependent infection transmission. In particular, we show that the introduction of an additional host can eliminate the pathogen rather than eliminate the resident host. The discussion is illustrated with a reference to bovine tuberculosis.
- Published
- 2008
17. The influence of trade-off shape on evolutionary behaviour in classical ecological scenarios
- Author
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Hoyle, Andrew, Bowers, Roger, White, Andrew, and Boots, Michael
- Subjects
shapes ,trade-offs ,frequency dependence ,evolution ,TIPs - Abstract
Trade-off shapes are crucial to evolutionary outcomes. However, due to different ecological feedbacks their implications may depend not only on the trade-off being considered but also the ecological scenario. Here, we apply a novel geometric technique, trade-off and invasion plots (TIPs), to examine in detail how the shape of trade-off relationships affect evolutionary outcomes under a range of classic ecological scenarios including Lotka-Volterra type and host-parasite interactions. We choose models of increasing complexity in order to gain an insight into the features of ecological systems that determine the evolutionary outcomes. In particular we focus on when evolutionary attractors, repellors and branching points occur and how this depends on whether the costs are accelerating (benefits become 'increasingly' costly), decelerating (benefits become 'decreasingly' costly) or constant. In all cases strongly accelerating costs lead to attractors while strongly decelerating ones lead to repellors, but with weaker relationships, this no longer holds. For some systems weakly accelerating costs may lead to repellors and decelerating costs may lead to attractors. In many scenarios it is weakly decelerating costs that lead to branching points, but weakly accelerating and linear costs may also lead to disruptive selection in particular ecological scenarios. Using our models we suggest a classification of ecological interactions, based on three distinct criteria, that can produce one of four fundamental TIPs which allow for different evolutionary behaviour. This provides a baseline theory which may inform the prediction of evolutionary outcomes in similar yet unexplored ecological scenarios. In addition we discuss the implications of our results to a number of specific life-history trade-offs in the classic ecological scenarios represented by our models.
- Published
- 2008
18. Reproductive Trade-Offs May Moderate the Impact of Gyrodactylus salaris in Warmer Climates
- Author
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Denholm, Scott J., primary, Norman, Rachel A., additional, Hoyle, Andrew S., additional, Shinn, Andrew P., additional, and Taylor, Nick G. H., additional
- Published
- 2013
- Full Text
- View/download PDF
19. PEPAʼd Oysters: Converting Dynamic Energy Budget Models to Bio-PEPA, Illustrated by a Pacific Oyster Case Study
- Author
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Scott, Erin, primary, Hoyle, Andrew, additional, and Shankland, Carron, additional
- Published
- 2013
- Full Text
- View/download PDF
20. A basic guide to patient safety (3)
- Author
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Hoyle, Andrew, primary
- Published
- 2006
- Full Text
- View/download PDF
21. A basic guide to patient safety (2): Risk analysis
- Author
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Hoyle, Andrew, primary
- Published
- 2005
- Full Text
- View/download PDF
22. A prescription for disaster?
- Author
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Hoyle, Andrew, primary
- Published
- 2005
- Full Text
- View/download PDF
23. Reproductive Trade-Offs May Moderate the Impact of Gyrodactylus salaris in Warmer Climates.
- Author
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Denholm, Scott J., Norman, Rachel A., Hoyle, Andrew S., Shinn, Andrew P., and Taylor, Nick G. H.
- Subjects
CLIMATE change ,ECTOPARASITES ,FRESHWATER ecology ,SALMONIDAE ,ATLANTIC salmon ,DISEASE susceptibility - Abstract
Gyrodactylus salaris is a notifiable freshwater ectoparasite of salmonids. Its primary host is Atlantic salmon (Salmo salar), upon which infections can cause death, and have led to massive declines in salmon numbers in Norway, where the parasite is widespread. Different strains of S. salar vary in their susceptibility, with Atlantic strains (such as those found in Norway) exhibiting no resistance to the parasite, and Baltic strains demonstrating an innate resistance sufficient to regulate parasite numbers on the host causing it to either die out or persist at a low level. In this study, Leslie matrix and compartmental models were used to generate data that demonstrated the population growth of G. salaris on an individual host is dependent on the total number of offspring per parasite, its longevity and the timing of its births. The data demonstrated that the key factor determining the rate of G. salaris population growth is the time at which the parasite first gives birth, with rapid birth rate giving rise to large population size. Furthermore, it was shown that though the parasite can give birth up to four times, only two births are required for the population to persist as long as the first birth occurs before a parasite is three days old. As temperature is known to influence the timing of the parasite's first birth, greater impact may be predicted if introduced to countries with warmer climates than Norway, such as the UK and Ireland which are currently recognised to be free of G. salaris. However, the outputs from the models developed in this study suggest that temperature induced trade-offs between the total number of offspring the parasite gives birth to and the first birth timing may prevent increased population growth rates over those observed in Norway. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
24. Optimising antibiotic treatments using evolutionary algorithms
- Author
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Goranova, Mila, Ochoa, Gabriela, and Hoyle, Andrew
- Subjects
Antibiotics ,Antibiotics--Health aspects ,Drug resistance in microorganisms ,Algorithms ,Stochastic models ,Mathematical models - Abstract
Antimicrobial resistance is one of the biggest threats to global health, food security, and development. Antibiotic overuse and misuse are the main drivers for the emergence of resistance. Studies in the medical sphere have indicated that shortened antibiotic treatments can be as effective as standard fixed-dose ones and have shown that an initial higher dose followed by a lower maintenance dose are more beneficial to patients with critical illnesses. It is crucial to optimise the use of existing antibiotics in order to improve medical outcomes, decrease toxicity and reduce the emergence of resistance. We formulate the design of antibiotic dosing regimens as a continuous optimisation problem and use several evolutionary algorithms as the search technique. Regimens are represented as vectors of real numbers encoding daily doses, which can vary across the treatment duration. A stochastic mathematical model of bacterial infections with tuneable resistance levels is used to evaluate the effectiveness of evolved regimens. The main objective is to minimise the treatment failure rate, subject to a constraint on the maximum total antibiotic used. We consider simulations with different levels of bacterial resistance; two ways of administering the drug (orally and intravenously); as well as coinfections with two strains of bacteria. The approach produced effective dosing regimens, with an average improvement in lowering the failure rate 30%, when compared with standard fixed-daily-dose regimens with the same total amount of antibiotic. A general pattern of an optimised treatment is found, where if 2x is the standard daily dose then the optimised treatment follows the 3x mg, followed by several 2x mg with a last dose of x mg. A noise handling technique is used to minimise the runtime of the experiments while maintaining the quality of treatments. The results of this work indicate that clinical studies confirming the effectiveness of this approach could be highly beneficial to future of antibiotic treatments.
- Published
- 2022
25. The fight against antimicrobial resistance : optimising antibiotic usage to treat bacterial infections
- Author
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Paterson, Iona K., Hoyle, Andrew, and Ochoa, Gabriela
- Subjects
615.3 ,Antimicrobial ,Resistance ,Mathematical Modelling ,Antibiotics ,Drug resistance, Bacterial ,Infectious diseases ,Epidemiology ,Mathematical modelling--theory and applications - Abstract
Antibiotic resistance is one of the major health concerns of the 21st century. Antibiotics are essential for the health and well-being of both humans and animals. However, the increase in antibiotic resistant bacteria poses a threat to the continued use of antibiotics to successfully treat bacterial infections. Current research within hospital settings has focused on the use of multi-antibiotic approaches in a variety of treatment patterns. Yet there is limited knowledge on the optimal use of single antibiotic treatments. With the spread of resistance linked to the overuse and misuse of antibiotics, optimal treatment regimens aim to maximise the success of eradicating an infection while minimising the amount of antibiotic required. This thesis therefore aimed to combine mathematical modelling with a genetic algorithm approach to identify optimal dosage regimens for the use of a single antibiotic. A mathematical model was developed to predict the dynamics of bacterial populations within an infection. A susceptible only infection was initially considered before being extended to include a resistant population. These models were incorporated into a genetic algorithm and used to search for dosage regimens which maximise bacterial eradication and minimise antibiotic use. Taking a theoretical approach, it was found that administering an antibiotic with a high initial dose followed by lowering doses is the optimal treatment regimen. A case study of a Vibrio anguillarum infection within Galleria mellonella larvae was used to parameterise the one strain bacterial model to a biologically realistic system. The results are consistent with those from the theoretical parameter sets. A tapered treatment regimen maximises the success of eradicating the bacterial infection while minimising the amount of antibiotic required. Laboratory experiments were performed which provided credibility to the results found. Finally, the assumption of fixed time intervals between doses was relaxed and the genetic algorithm used to identify both the dose and time intervals of optimal treatment regimens. Varying either the doses or the time intervals separately produced no significant difference in the success of eradicating an infection. When combined, the results showed that significantly better regimens could be identified. These regimens further increased bacterial eradication while using less antibiotic to do so. More work is required to identify a general treatment pattern when both variables are optimised due to the high variability in solutions. However, a shift away from conventional constant dose treatment regimens is required to prolong the future effectiveness of antibiotics.
- Published
- 2019
26. Process algebra with layers : a language for multi-scale integration modelling
- Author
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Scott, Erin G., Shankland, Carron, and Hoyle, Andrew
- Subjects
004 ,multi-scale models ,process algebra ,computational modelling ,integrated scales ,Multiscale modeling ,Algebra - Abstract
Multi-scale modelling and analysis is becoming increasingly important and relevant. Analysis of the emergent properties from the interactions between scales of multi-scale systems is important to aid in solutions. There is no universally adopted theoretical/computational framework or language for the construction of multi-scale models. Most modelling approaches are specific to the problem that they are addressing and use a hybrid combination of modelling languages to model specific scales. This thesis addresses if process algebra can offer a unique opportunity in the definition and analysis of multi-scale models. In this thesis the generic Process Algebra with Layers (PAL) is defined: a language for multi-scale integration modelling. This work highlights the potential of process algebra to model multi-scale systems. PAL was designed based on features and challenges found from modelling a multi-scale system in an existing process algebra. The unique features of PAL are the layers: Population and Organism. The novel language modularises the spatial scales of the system into layers, therefore, modularising the detail of each scale. An Organism can represent a molecule, organelle, cell, tissue, organ or any organism. An Organism is described by internal species. An internal species, dependent on the scale of the Organism, can also represent a molecule, organelle, cell, tissue, organ or any organism. Populations hold specific types of Organism, for example, life stages, cell phases, infectious states and many more. The Population and Organism layers are integrated through mirrored actions. This novel language allows the clear definition of scales and interactions within and between these scales in one model. PAL can be applied to define a variety of multi-scale systems. PAL has been applied to two unrelated multi-scale system case studies to highlight the advantages of the generic novel language. Firstly the effects of ocean acidification on the life stages of the Pacific oyster. Secondly the effects of DNA damage from cancer treatment on the length of a cell cycle and cell population growth.
- Published
- 2016
27. Mathematical modelling of population and disease control in patchy environments
- Author
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Lintott, Rachel A., Hoyle, Andrew S., and Norman, Rachel A.
- Subjects
511 ,mathematical ecology ,population dynamics ,mathematical modelling ,patchy habitats ,disease control ,harvesting ,optimal control ,Mathematical modelling theory and applications ,Disease Management - Abstract
Natural populations may be managed by humans for a number of reasons, with mathematical modelling playing an increasing role in the planning of such management and control strategies. In an increasingly heterogeneous, or `patchy' landscape, the interactions between distinct groups of individuals must be taken into account to predict meaningful management strategies. Invasive control strategies, involving reduction of populations, such as harvesting or culling have been shown to cause a level of disturbance, or spatial perturbation, to these groups, a factor which is largely ignored in the modelling literature. In this thesis, we present a series of deterministic, differential equation models which are used to investigate the impact of this disturbance in response to control. We address this impact in two scenarios. Firstly, in terms of a harvested population, where extinction must be prevented whilst maximising the yield obtained. Secondly, we address the impact of disturbance in an epidemic model, where the aim of the control strategy is to eradicate an endemic pathogen, or to prevent the invasion of a pathogen into a susceptible population. The movement of individuals between patches is modelled as both a constant rate, and a function which is increasing with population density. Finally, we discuss the 'optimal' control strategy in this context. We find that, whilst a population harvested from a coupled system is able to produce an inflated yield, this coupling can also cause the population to be more resistant to higher harvesting efforts, increasing the effort required to drive the population to extinction. Spatial perturbation raises this extinction threshold further still, providing a survival mechanism not only for the individuals that avoid being killed, but for the population as a whole. With regards to the eradication of disease, we show that disturbance may either raise or lower the pathogen exclusion threshold depending on the particular characteristics of the pathogen. In certain cases, we have shown that spatial perturbation may force a population to be susceptible to an infectious invasion where its natural carrying capacity would prevent this.
- Published
- 2014
28. Mathematical models for the control of Argulus foliaceus in UK stillwater trout fisheries
- Author
-
McPherson, Nicola J., Norman, Rachel, Taylor, Nicholas G. H., Hoyle, Andrew, and Bron, James
- Subjects
639 ,Argulus foliaceus ,macroparasite ,mathematical model ,A. foliaceus ,O. mykiss ,Rainbow trout ,Parasite ,Emamectin benzoate ,ODE ,Ordinary differential equations ,Trout fisheries Great Britain ,Arguloida - Abstract
Species of Argulus are macro-, ecto-parasites known to infect a wide variety of fish, but in the UK mainly cause problems in rainbow (Oncorhynchus mykiss) and brown trout (Salmo trutta). Argulus foliaceus is estimated to have caused problems in over 25% of stillwater trout fisheries in the UK. While A. foliaceus does not usually cause high levels of mortality, the parasite affects fish welfare, and also makes fish harder to catch due to morbidity and reduced appetite. This can cause severe economic problems for the fishery, resulting in reduced angler attendance due to poor capture rates and the reduced aesthetic appearance of fish; in the worst-case scenario this can result in the closure of the fishery. Current methods of control include chemical treatment with chemotherapeutant emamectin benzoate (Slice), physical intervention with egg-laying boards which are removed periodically and cleaned in order to reduce the number of parasites hatching into the environment, and the complete draining and liming of the lake to remove all free-living and egg stages of the parasite. While these treatments have all been shown to reduce parasite numbers, none are known to have resulted in permament eradication of the parasite. There is evidence to suggest that A. foliaceus will eventually develop resistance to Slice - the only currently available chemical treatment against the infection - and egg-laying boards and the draining and liming of the lake are both time- and labour-intensive. Previous studies have shown that slow fish turnover is a risk factor with respect to A. foliaceus infections, and with a wide variety of stocking practices occurring in the UK one of the first aims of this project was to determine their impact on the host-parasite dynamics. Mathematical models provide a cost-effective way of examining the impact of such practices, and after a literature review (chapter one), in chapter two a three-compartment mathematical model was adapted for use in the A. foliaceus-trout system. Four generalised stocking methods were then incorporated and analysed, and a minimum threshold host density was found to be necessary to sustain the parasite. Including a function which reduced the capture rate as the parasite burden increased allowed the parasite to survive at a lower host density, as susceptible fish were removed from the water at a slower rate, and attached parasites also remained in the water for longer. This resulted in hysteresis in the model, as the invasion threshold for the parasite remained the same, but once established the parasite became harder to eradicate, requiring significant reductions in the host density. In chapter three the model was further developed in order to improve its biological real- ism. Several features were added and these included: natural host mortalities, a separate compartment for the parasite egg population, and parasite survival after the natural or parasite-induced mortality of its host. In chapter four seasonality was added by incorporating temperature-dependent egg-laying rates and an over-wintering period during which the parasite was unable to reproduce. The model was then fit to the available data, and estimates for the rate of parasite-induced host mortalities and the parasite’s rate of attachment to a host were found. In chapter five we returned to stocking methods, this time looking at the frequency and timing of stocking events and the impact of imposing a rod limit (whereby anglers are only permitted to capture four fish per visit); it was concluded that while current guidelines suggest that very frequent trickle stocking is recommended when dealing with Argulus spp. infections, monthly stocking does not appear to worsen the infection, and if the fish capture rate is high then less-frequent stocking may also be permissable - particularly if stocking occurs towards the end of the year when the parasite is no longer active. This practice may, however, be detrimental to the fishery due to low fish densities in the summer months. In chapter six treatment with Slice was included in the model, and it was demonstrated that with constant treatment, and in the absence of reservoir hosts and a withdrawal period from the drug prior to stocking treated fish into the fishery, the parasite was eradicated. Under current veterinary cascade guidelines, however, trout are required to undergo a withdrawal period of 500 degree days prior to being made available for human consumption. When this was included in the model the drug still decreased parasite abundance, but did not eradicate it - this is in agreement with results reported by communications with fishery managers currently treating fish with Slice. A reduction in the withdrawal period of 25% was shown to further decrease parasite abundance, but still did not result in parasite extinction. As constant treatment with Slice is not advisable due to the potential for resistance build-up, we then sought to find time at which to apply a single treatment of Slice, and found that this was in August when the temperature was highest and the parasite was reproducing and attaching to hosts quickly. Egg-laying boards were also incorporated into the model and similarly to findings by Fenton et al. [11] the success of this treatment was mostly dependent on the proportion of eggs being laid on the boards (as opposed to natural substrates). In contrast with the A. coregoni system, however, the boards would have to be cleaned and replaced more frequently that once per year, as several cohorts of A. foliaceus emerge during a single year.
- Published
- 2013
29. Mathematical models for investigating the long-term impact of Gyrodactylus salaris infections on Atlantic salmon populations
- Author
-
Denholm, Scott J., Norman, Rachel, Shinn, Andrew, Hoyle, Andrew, and Taylor, Nicholas G. H.
- Subjects
597 ,Mathematical modelling ,Gyrodactylus salaris ,Atlantic salmon ,multiple strains ,parasite ,pathogen ,Epidemiology Mathematical models ,Fishes Diseases ,Host-parasite relationship - Abstract
Gyrodactylus salaris Malmberg, 1957, is a notifiable freshwater ecto-parasite that infects both wild and farmed populations of Atlantic salmon (Salmo salar, L.). It has caused catastrophic damage to wild salmon stocks in Norway since its accidental introduction in 1975, reducing salmon density in some rivers by 98% over a period of five years. It is estimated that G. salaris has cost the Norwegian salmon industry more than 500 million EUR. Currently the UK has G. salaris free status under EU law, however, it is believed that if G. salaris emerged in the UK the impact would be similar to that witnessed in Norway. The aim of this thesis is to develop mathematical models that describe the salmon-G. salaris system in order to gain a greater understanding of the possible long-term impact the parasite may have on wild populations of Atlantic salmon in G. salaris-free territories such as the UK. Mathematical models, including deterministic, Leslie matrix and individual based models, were used to investigate the impact of G. salaris on Atlantic salmon at the individual and population level. It is known that the Atlantic strain of Atlantic salmon, examples of which occur naturally in Norway and the UK, does not have any resistance to G. salaris infections and the parasite population is able to quickly grow to epidemic levels. In contrast, the Baltic strain of Atlantic salmon, examples of which occur naturally in Sweden and Russia, exhibits some form of resistance and the parasite is unable to persist. Thus, baseline models were extended to include immunity to infection, a trade-off on salmon reproductive rate, and finally, to consider interactions between populations of G. salaris and multiple strains of salmon exhibiting varying levels of immunity from fully susceptible to resistant. The models proposed predict that in the absence of host resistance or an immune response infections by G. salaris will result in an epidemic followed by the extinction of the salmon host population. Models also predict that if salmon are able to increase their resistance to G. salaris infections through mutations, salmon population recovery after the epidemic is indeed possible within 10-15 years post introduction with low level parasite coexistence. Finally, models also highlight areas where additional information is needed in order to improve predictions and enable the estimation of important parameter values. Model predictions will ultimately be used to assist in future contingency planning against G. salaris outbreaks in the UK and possibly as a basis for future models describing other fish/ecto-parasite systems.
- Published
- 2013
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