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Aberdeen, United Kingdom

Wallace J.M.,University of Aberdeen | Horgan G.W.,Biomathematics and Statistics Scotland | Bhattacharya S.,Dugald Baird Center for Research on Womens Health
Placenta | Year: 2012

Herein we report placental weight and efficiency in relation to maternal BMI and the risk of pregnancy complications in 55,105 pregnancies. Adjusted placental weight increased with increasing BMI through underweight, normal, overweight, obese and morbidly obese categories and accordingly underweight women were more likely to experience placental growth restriction [OR 1.69 (95% CI 1.46-1.95)], while placental hypertrophy was more common in overweight, obese and morbidly obese groups [OR 1.59 (95% CI 1.50-1.69), OR 1.97 (95% CI 1.81-2.15) and OR 2.34 (95% CI 2.08-2.63), respectively]. In contrast the ratio of fetal to placental weight (a proxy for placental efficiency) was lower (P < 0.001) in overweight, obese and morbidly obese than in both normal and underweight women which were equivalent. Relative to the middle tertile reference group (mean 622 g), placental weight in the lower tertile (mean 484 g) was associated with a higher risk of pre-eclampsia, induced labour, spontaneous preterm delivery, stillbirth and low birth weight (P < 0.001). Conversely placental weight in the upper tertile (mean 788 g) was associated with a higher risk of caesarean section, post-term delivery and high birth weight (P < 0.001). With respect to assumed placental efficiency a ratio in the lower tertile was associated with an increased risk of pre-eclampsia, induced labour, caesarean section and spontaneous preterm delivery (P < 0.001) and a ratio in both the lower and higher tertiles was associated with an increased risk of low birth weight (P < 0.001). Placental efficiency was not related to the risk of stillbirth or high birth weight. No interactions between maternal BMI and placental weight tertile were detected suggesting that both abnormal BMI and placental growth are independent risk factors for a range of pregnancy complications. © 2012 Elsevier Ltd. All rights reserved.

Sutherland C.,University of Aberdeen | Elston D.A.,Biomathematics and Statistics Scotland | Lambin X.,University of Aberdeen
Ecology | Year: 2012

Metapopulations function and persist through a combination of processes acting at a variety of spatial scales. Although the contributions of stage structure, spatially correlated processes, and the rescue effect to metapopulation dynamics have been investigated in isolation, there is no empirical demonstration of all of these processes shaping dynamics in a single system. Dispersal and settlement differ according to the life stage involved; therefore, stage-specific population size may outperform total population size when predicting colonization-extinction dynamics. Synchrony in patch dynamics can lead to accelerated metapopulation extinction, although empirical evidence of the interplay between correlated colonization events and correlated extinctions is lacking. Likewise, few empirical examples exist that provide compelling evidence of migration acting to reduce extinction risk (the rescue effect). We parameterized a hierarchy of metapopulation models to investigate these predictions using a seven-year study of a naturally occurring water vole (Arvicola amphibius) metapopulation. Specifically, we demonstrated the importance of local stage structure in predicting both colonization and extinction events using juvenile and adult population sizes, respectively. Using a novel approach for quantifying correlation in extinction events, we compared the scale of synchrony in colonization and extinction. Strikingly, the scale of dispersal acting to synchronize colonization was an order of magnitude larger than that of correlated extinctions (halving distance of the effect: 12.40 km and 0.89 km, respectively). Additionally, we found compelling evidence for the existence of a nontrivial rescue effect. Here we provide a novel empirical demonstration of a variety of metapopulation processes operating at multiple spatial scales, further emphasizing the need to consider stage structure and local synchrony in the dynamics of spatially dependent, stage-structured (meta) populations. © 2012 by the Ecological Society of America.

Beale C.M.,University of York | Baker N.E.,Tanzania Bird Atlas | Brewer M.J.,Biomathematics and Statistics Scotland | Lennon J.J.,Queens University of Belfast
Ecology Letters | Year: 2013

The extent to which climate change might diminish the efficacy of protected areas is one of the most pressing conservation questions. Many projections suggest that climate-driven species distribution shifts will leave protected areas impoverished and species inadequately protected while other evidence suggests that intact ecosystems within protected areas will be resilient to change. Here, we tackle this problem empirically. We show how recent changes in distribution of 139 Tanzanian savannah bird species are linked to climate change, protected area status and land degradation. We provide the first evidence of climate-driven range shifts for an African bird community. Our results suggest that the continued maintenance of existing protected areas is an appropriate conservation response to the challenge of climate and environmental change. © 2013 John Wiley & Sons Ltd/CNRS.

Wallace J.M.,University of Aberdeen | Bhattacharya S.,Dugald Baird Center for Research on Womens Health | Horgan G.W.,Biomathematics and Statistics Scotland
Placenta | Year: 2013

Introduction: The weight of the placenta is a crude but useful proxy for its function in vivo. Accordingly extremes of placental weight are associated with adverse pregnancy outcomes while even normal variations in placental size may impact lifelong health. Centile charts of placental weight for gestational age and gender are used to identify placental weight extremes but none report the effect of parity. Thus the objective was to produce gender and gestational age specific centile charts for placental weight in nulliparous and multiparous women. Methods: Data was extracted from the Aberdeen Maternity and Neonatal Databank for all women delivering singleton babies in Aberdeen city and district after 24 weeks gestation. Gestational age specific centile charts for placental weight by gender and parity grouping (n = 88,649 deliveries over a 30 year period) were constructed using the LMS method after exclusion of outliers (0.63% of deliveries meeting study inclusion criteria). Results: Tables and figures are presented for placental weight centiles according to gestational age, gender and parity grouping. Tables are additionally presented for the birth weight to placental weight ratio by gender. Placental weight and the fetal:placental weight ratio were higher in male versus female deliveries. Placental weight was greater in multiparous compared with nulliparous women. Discussion: We present strong evidence that both gender and parity grouping influence placental weight centiles. The differences at any given gestational age are small and the effects of parity are greater overall than those of gender. In contrast the birth weight to placental weight ratio differs by gender only. Conclusion: These UK population specific centile charts may be useful in studies investigating the role of the placenta in mediating pregnancy outcome and lifelong health. © 2012 Elsevier Ltd. All rights reserved.

Roberts A.M.I.,Biomathematics and Statistics Scotland
International Journal of Biometeorology | Year: 2012

Several methods exist for investigation of the relationship between records and weather data. These can be broadly classified into models that attempt to incorporate information about underlying biological processes, such as those based on the concept of thermal time, and linear regression methods. The latter are less driven by the biology but have the advantages of ease of use and flexibility. Regression can be used where there is no obvious mechanistic model or to suggest the form of a mechanistic or empirical model where there are several to choose from. Stepwise regression is commonly used in phenology. However, it requires aggregation of the weather records, resulting in loss of information. Penalised signal regression (PSR) was recently introduced to overcome this weakness. Here, we introduce a further method to the phenology context called fusion, which is a sparse version of PSR. In this paper, we compare the performance of these three regression methods based on simulations from two types of mechanistic models, the spring warming and sequential models. Given a suitable choice of temperature days as regression covariates, PSR and fusion performed better than stepwise regression for the spring warming model and PSR performed best for the sequential model. However, if a large number of redundant temperature days were included as covariates, the performance of PSR fell off whilst fusion was quite robust to this change. For this reason, it is best to use PSR and fusion methods in tandem, and to vary the number of covariates included. © 2011 ISB.

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