Some considerations of and perspectives in coastal ecology

Ecophysiological studies of plant species in wet saline habitats have been one-sided in the past, emphasizing sodium chloride only. More emphasis should be given to anaerobiosis, to mechanical factors, to the effects of a surplus of other nutrients in seawater and coastal ecosystems and their metabolic impact as well as to aspects of nutrient (re)allocation. Research should incorporate theoretical models on plant strategies maximizing yield, minimizing risk. At the population level, a new operational parameter for ecological optima and ecological stress is presented considering normal and skewed distributions of plant parameters in relation to growth and the concentration of mineral nutrients.Some considerations on the ecological effects of phenotypic plasticity and genetic variability are given by emphasizing the aspects of diaspores.Future investigations of coastal vegetation should consider the interaction of populations within plant communities, including the regulating effects of animals.Nomenclature of vascular plants follows H. Heukels & R. van der Meijden, 1983. Flora van Nederland, 20th ed. Wolters-Noordhoff, Groningen; that of plant communities V. Westhoff & A. J. den Held, 1969. Plantengemeenschappen in Nederland. Thieme & Cie, Zutphen.     

Embracing asymmetry in nature: How to account for skewness in ecological data

Asymmetric regression is an alternative to conventional linear regression that allows us to model the relationship between predictor variables and the response variable while accommodating skewness. Advantages of asymmetric regression include incorporating realistic ecological patterns observed in data, robustness to model misspecification and less sensitivity to outliers. Bayesian asymmetric regression relies on asymmetric distributions such as the asymmetric Laplace (ALD) or asymmetric normal (AND) in place of the normal distribution used in classic linear regression models. Asymmetric regression concepts can be used for process and parameter components of hierarchical Bayesian models and have a wide range of applications in data analyses. In particular, asymmetric regression allows us to fit more realistic statistical models to skewed data and pairs well with Bayesian inference. We first describe asymmetric regression using the ALD and AND. Second, we show how the ALD and AND can be used for Bayesian quantile and expectile regression for continuous response data. Third, we consider an extension to generalize Bayesian asymmetric regression to survey data consisting of counts of objects. Fourth, we describe a regression model using the ALD, and show that it can be applied to add needed flexibility, resulting in better predictive models compared to Poisson or negative binomial regression. We demonstrate concepts by analyzing a data set consisting of counts of Henslow’s sparrows following prescribed fire and provide annotated computer code to facilitate implementation. Our results suggest Bayesian asymmetric regression is an essential component of a scientist’s statistical toolbox.     

Circular distributions based on nonnegative trigonometric sums

A new family of distributions for circular random variables is proposed. It is based on nonnegative trigonometric sums and can be used to model data sets which present skewness and/or multimodality. In this family of distributions, the trigonometric moments are easily expressed in terms of the parameters of the distribution. The proposed family is applied to two data sets, one related with the directions taken by ants and the other with the directions taken by turtles, to compare their goodness of fit versus common distributions used in the literature.     

Graphical Method to Detect Departure from Normality with Special Application to Tukey's g and h Distributions

Given a sample, the problem of choosing one of a variety of theoretical distributions for data analysis has been a major concern to both theoretical and applied statisticians. On the basis of a graph drawn using a normal characterization, a method is given to detect departure from normality. Special mathematical study is presented for the proposed graphs. Tukey's g and h family of distributions are used as an alternate to normality.     

Confidence Limits on Heritability Under Non-normal Variations

Moment approximation for the non-normal sampling distribution of the ratio of mean squares in the balanced one-way Model II is found close to that of the Snedecor's F-distribution. The confidence limits for heritability of paternal half-sib correlations, derived employing F-distribution, are, in general, remarkably narrow for platykurtic and wide for leptokurtic sire effects than the normal limits. The effect of kurtosis of environmental deviations on these limits is of no consequence whereas the effect of skewness is invisible.     

Physiology of spontaneous [Ca2+]i oscillations in the isolated vasopressin and oxytocin neurones of the rat supraoptic nucleus

The magnocellular vasopressin (AVP) and oxytocin (OT) neurones exhibit specific electrophysiological behaviour, synthesise AVP and OT peptides and secrete them into the neurohypophysial system in response to various physiological stimulations. The activity of these neurones is regulated by the very same peptides released either somato-dendritically or when applied to supraoptic nucleus (SON) preparations in vitro. The AVP and OT, secreted somato-dendritically (i.e. in the SON proper) act through specific autoreceptors, induce distinct Ca²⁺ signals and regulate cellular events. Here, we demonstrate that about 70% of freshly isolated individual SON neurones from the adult non-transgenic or transgenic rats bearing AVP (AVP-eGFP) or OT (OT-mRFP1) markers, produce distinct spontaneous [Ca²⁺]_i oscillations. In the neurones identified (through specific fluorescence), about 80% of AVP neurones and about 60% of OT neurones exhibited these oscillations. Exposure to AVP triggered [Ca²⁺]_i oscillations in silent AVP neurones, or modified the oscillatory pattern in spontaneously active cells. Hyper- and hypo-osmotic stimuli (325 or 275 mOsmol/l) respectively intensified or inhibited spontaneous [Ca²⁺]_i dynamics. In rats dehydrated for 3 or 5 days almost 90% of neurones displayed spontaneous [Ca²⁺]_i oscillations. More than 80% of OT-mRFP1 neurones from 3 to 6-day-lactating rats were oscillatory vs. about 44% (OT-mRFP1 neurones) in virgins. Together, these results unveil for the first time that both AVP and OT neurones maintain, via Ca²⁺ signals, their remarkable intrinsic in vivo physiological properties in an isolated condition.     

Nonparametric statistical methods for cost-effectiveness analyses

Two measures often used in a cost-effectiveness analysis are the incremental cost-effectiveness ratio (ICER) and the net health benefit (NHB). Inferences on these two quantities are often hindered by highly skewed cost data. In this article, we derive the Edgeworth expansions for the studentized t-statistics for the two measures and show how they could be used to guide inferences. In particular, we use the expansions to study the theoretical performance of existing confidence intervals based on normal theory and to derive new confidence intervals for the ICER and the NHB. We conduct a simulation study to compare our new intervals with several existing methods. The methods evaluated include Taylor's interval, Fieller's interval, the bootstrap percentile interval, and the bootstrap bias-corrected acceleration interval. We found that our new intervals give good coverage accuracy and are narrower compared to the current recommended intervals.