Biomathematics and Statistics

Aberdeen, United Kingdom

Biomathematics and Statistics

Aberdeen, United Kingdom

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Cornulier T.,University of Aberdeen | Yoccoz N.G.,University of Tromsø | Bretagnolle V.,CNRS Chizé Center for Biological Studies | Brommer J.E.,University of Helsinki | And 21 more authors.
Science | Year: 2013

Suggestions of collapse in small herbivore cycles since the 1980s have raised concerns about the loss of essential ecosystem functions. Whether such phenomena are general and result from extrinsic environmental changes or from intrinsic process stochasticity is currently unknown. Using a large compilation of time series of vole abundances, we demonstrate consistent cycle amplitude dampening associated with a reduction in winter population growth, although regulatory processes responsible for cyclicity have not been lost. The underlying syndrome of change throughout Europe and grass-eating vole species suggests a common climatic driver. Increasing intervals of low-amplitude small herbivore population fluctuations are expected in the future, and these may have cascading impacts on trophic webs across ecosystems.


Buckland S.T.,University of St. Andrews | Baillie S.R.,British Trust for Ornithology | Dick J.M.,UK Center for Ecology and Hydrology | Elston D.A.,Biomathematics and Statistics | And 6 more authors.
Environmental and Ecological Statistics | Year: 2012

We consider quantification of biodiversity in the context of targets set by the Convention on Biological Diversity. Implicit in such targets is a requirement to monitor biodiversity at a regional level. Few monitoring schemes are designed with these targets in mind. Monitored sites are typically not selected to be representative of a wider region, and measures of biodiversity are often biased by a failure to account for varying detectability among species and across time. Precision is often not adequately quantified. We review methods for quantifying the biodiversity of regions, consider issues that should be addressed in designing and evaluating a regional monitoring scheme, and offer a practical guide to what types of survey are appropriate for addressing different objectives for biodiversity monitoring. © 2012 Springer Science+Business Media, LLC.


Rhind S.M.,Macaulay Institute | Kyle C.E.,Macaulay Institute | MacKie C.,Macaulay Institute | McDonald L.,Macaulay Institute | And 10 more authors.
Journal of Environmental Monitoring | Year: 2010

Liver concentrations of selected pollutant classes were determined in groups of sheep fetuses and their dams, at 55 (Experiment 1) and 110 (Experiment 2) days of gestation (term = 145 d) following exposure, throughout their breeding lives and after mating, to pasture treated with either inorganic fertiliser (control, CC) or with sewage sludge (treated, TT). In a unique study designed to separate the respective contributions of environmental sources and mobilised tissue to the available EDC burden, in additional groups of animals, pollutant burdens at 110 days gestation were assessed following exposure to the respective treatments, either throughout their breeding lives until mating, but not thereafter (TC), or only between mating and slaughter (CT) (Experiment 3). With very few exceptions, maternal and fetal liver concentrations of diethylhexyl phthalate (DEHP) and selected polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDE) and polycyclic aromatic hydrocarbons (PAHs) were not significantly affected by sludge exposure in any group. In some cases, maternal and fetal tissue EDC concentrations were different but the differences were not consistent, and maternal and fetal concentrations of none of the classes of chemical were significantly correlated. It was not possible to identify a single chemical, or class of chemical, that may be responsible for previously observed physiological effects of exposure to sludge-treated pastures. It is concluded that exposure of sheep to pastures fertilised with sewage sludge was not associated with increased liver concentrations of EDCs, irrespective of the stage of development at which they were measured and of maternal tissue mobilisation and EDC release during gestation. Thus, retrospective measurements of EDC tissue burdens could not be used to accurately assess earlier fetal EDC insults. © 2010 The Royal Society of Chemistry.


Theobald C.,Biomathematics and Statistics | Theobald C.,University of Edinburgh | Chatterjee A.,University of West Georgia | Horgan G.,Biomathematics and Statistics | Horgan G.,University of Aberdeen
Food and Chemical Toxicology | Year: 2012

Many dietary consumption variables show strong positive skewness or large proportions of zeros. Attempts to normalize such data using transformations such as powers and logarithms can be unsuccessful: this results in poor estimates of their probability distributions, and hence of the proportions of the population whose consumption is beyond recommended limits. As an alternative to such transformations, the use of finite mixtures of standard distributions offers flexible modeling of data having skewed or multi-modal distributions, such as data on dietary consumption. In many dietary studies, individuals are asked to report their consumptions on several days. The use of finite-mixture models for such repeated data requires generalization to take account of the resulting hierarchical structure in the data. We first consider how finite mixture models might be extended to data with repeated records, and then apply a Bayesian version of one such extension to data on the consumption of retinol (Vitamin A) by British adults over 7 consecutive days. We also illustrate how factors such as sex and age may be included in the model. The mixture-model approach is found to provide better estimates than alternative methods of the probability distributions of daily consumptions and of maximum consumption over 7. days. © 2011 Elsevier Ltd.


Rhind S.M.,Macaulay Institute | Kyle C.E.,Macaulay Institute | MacKie C.,Macaulay Institute | Yates K.,Macaulay Institute | Duff E.I.,Biomathematics and Statistics
Environmental Pollution | Year: 2011

Muscle tissue was collected from ewes and lambs derived from farms throughout Scotland and sample concentrations of five endocrine disrupting compound groups were determined. Farms of origin were categorised according to geographic region. There were few statistically-significant differences with region or distance from cities. However, the magnitude of the difference between the highest and lowest mean values in ewe muscle from different regions exceeded 30% for 13 of the 15 compounds that were consistently detected in muscle, with animals derived from the industrialised region having the highest mean values for 11 of the 13 compounds. A less marked trend was apparent in the lamb muscle (8 of 13 highest were in the industrialised region). The physiological effects of such small differences in exposure to mixtures of pollutants remain to be determined. © 2010 Elsevier Ltd. All rights reserved.


Ballingall K.T.,Moredun Research Institute | Rocchi M.S.,Moredun Research Institute | McKeever D.J.,Royal Veterinary College | Wright F.,Biomathematics and Statistics
PLoS ONE | Year: 2010

Highly polymorphic genes with central roles in lymphocyte mediated immune surveillance are grouped together in the major histocompatibility complex (MHC) in higher vertebrates. Generally, across vertebrate species the class II MHC DRA gene is highly conserved with only limited allelic variation. Here however, we provide evidence of trans-species polymorphism at the DRA locus in domestic sheep (Ovis aries). We describe variation at the Ovar-DRA locus that is far in excess of anything described in other vertebrate species. The divergent DRA allele (Ovar-DRA*0201) differs from the sheep reference sequences by 20 nucleotides, 12 of which appear non-synonymous. Furthermore, DRA*0201 is paired with an equally divergent DRB1 allele (Ovar-DRB1*0901), which is consistent with an independent evolutionary history for the DR sub-region within this MHC haplotype. No recombination was observed between the divergent DRA and B genes in a range of breeds and typical levels of MHC class II DR protein expression were detected at the surface of leukocyte populations obtained from animals homozygous for the DRA*0201, DRB1*0901 haplotype. Bayesian phylogenetic analysis groups Ovar-DRA*0201 with DRA sequences derived from species within the Oryx and Alcelaphus genera rather than clustering with other ovine and caprine DRA alleles. Tests for Darwinian selection identified 10 positively selected sites on the branch leading to Ovar-DRA*0201, three of which are predicted to be associated with the binding of peptide antigen. As the Ovis, Oryx and Alcelaphus genera have not shared a common ancestor for over 30 million years, the DRA*0201 and DRB1*0901 allelic pair is likely to be of ancient origin and present in the founding population from which all contemporary domestic sheep breeds are derived. The conservation of the integrity of this unusual DR allelic pair suggests some selective advantage which is likely to be associated with the presentation of pathogen antigen to T-cells and the induction of protective immunity. © 2010 Ballingall et al.

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