Sex ratio manipulation in response to maternal condition in pigeons: evidence for pre-ovulatory follicle selection

A number of recent reports have documented offspring sex ratio biases in birds. However, to date the potential mechanisms that have been put forward to explain the proximate basis for these deviations are entirely speculative. Using a captive population of domestic pigeons (Columba livia domestica), I tested the hypothesis that mothers in relatively poor physical condition should overproduce daughters by manipulating maternal body condition around the time of egg laying by continuous egg removal and differing feeding regimes. During treatment, females were fed a controlled quantity of food. This, combined with the high energetic costs of repeated egg production caused a significant reduction in maternal body weight. In contrast, during control when food was available ad libitum, maternal body weight did not decline, despite repeated egg production. No significant deviation from parity was evident in the sex ratio of either the first or second eggs during control, whereas during treatment a significant female bias was evident in not only the first egg, but also in the second egg. The absence of single-egg clutches, the rarity of infertile eggs and the lack of laying delays between eggs strongly suggests that the mechanism of sex ratio adjustment in pigeons occurs prior to ovulation. The highly skewed sex-distribution within the two-egg clutches and the unexpectedly large amount of variation in the yolk weight of eggs produced during treatment (but not control) are consistent with the expectations of pre-ovulatory selective resorption of wrong sex ovarian follicles.     

Power-law behaviour and parametric models for the size-distribution of forest fires

This paper examines the distribution of areas burned in forest fires. Empirical size distributions, derived from extensive fire records, for six regions in North America are presented. While they show some commonalities, it appears that a simple power-law distribution of sizes, as has been suggested by some authors, is too simple to describe the distributions over their full range. A stochastic model for the spread and extinguishment of fires is used to examine conditions for power-law behaviour and deviations from it. The concept of the extinguishment growth rate ratio (EGRR) is developed. A null model with constant EGRR leads to a power-law distribution, but this does not appear to hold empirically for the data sets examined. Some alternative parametric forms for the size distribution are presented, with a four-parameter ‘competing hazards’ model providing the overall best fit.     

High-ranking females bias their investment in favour of male calves in captive Ammotragus lervia

Calf suckling behaviour is a valid measure of maternal investment in the Saharan arrui, Ammotragus lervia sahariensis, since this variable is strongly correlated with the inter-birth interval. High-ranking females allocate their resources preferentially towards their sons, as the average suckling rate is significantly higher in male calves than in female calves during their 1st month of life, when maternal investment reaches the highest values of the whole lactation period. However, average suckling-bout duration shows no sex differences. Some maternal behaviours, such as sniffing and licking, are strongly correlated with suckling events. Only during the calves’ 1st week is the mother responsible for maintaining proximity; but from the following week on the calves are mainly responsible for maintaining it. In addition, when the calves are 1 month old, high-ranking females tend to maintain a stronger link with their male calves. Female calves spend more time with their mothers than male calves during their 1st month of life, if the mother’s rank is lower than 60%; otherwise, the opposite occurs, male calves being close to their mothers for longer, even from their 1st week of life. Finally, the higher the maternal rank the higher the proportion of male calves delivered. Received: 18 April 1995/Accepted after revision: 11 February 1996     

长江口柱状沉积物中有机质C/N比的研究

对长江口四个站位沉积物中有机质的C／N比在垂向上的分布进行了研究，在影响沉积物中有机质C／N比的环境因素中，上覆水体的水深、盐度、密度以及浊度对其有一定的影响．在研究沉积物中有机质C／N比的分布及其影响因素的基础上，进一步估算了陆源输入和海洋自生有机碳在这四个站位沉积物有机碳中所占的比例，结果表明，海洋自生组分占沉积物总有机碳的比例分别为：53．57％(8号站位)、20．34％(11号站位)，12．28％(17号站位)和32．73％(26号站位)．     

山一村山地生态系统结构功能和系统调控

本文对山－村山地生态系统的结构和功能、能量产投比、生物量等进行实地调查和研究。结果表明，通过多年生态建设，山地生态系统已显示较好的经济、环境和社会效益。     

荔枝花雄蕊和雌蕊发育过程中碳氮化合物的动态变化

比较分析了荔枝花性决定中碳氮化合物的动态变化。结果发现：C/N较大有利于雄蕊分化,反之则有利于雌蕊分化;氨基酸含量较高有利于雌蕊分化,雄蕊的氨基酸含量仅为雌蕊的一半。脯氨酸与花粉育性存在着密切相关关系。另外,探讨了雌蕊或雄蕊败育的生理意义,在长期的进化中,败育的雌蕊或雄蕊“废物”重新被利用,为同一花中迅速发育的雌蕊或雄蕊提供能量和物质的需求,表5参13。     

西太平洋海域海水和雨水的化学特征

本工作测定了西太平洋海域中海水、海水悬浮物和海面上雨水的元素组成和浓度。通过富集因子的计算,探讨海面上雨水中微量元素的富集程度及其来源,讨论了海面上气溶胶粒子大小与洗出因子的关系,结果表明不同质量粒径大小的微量元素在公海上具有相似的洗出因子。     

松嫩平原西部不同土地覆被水盐动态对比研究

通过对6种土地覆被2003年6～10月水盐时空动态进行分析，对比不同土地覆被水盐动态变化差异，结果发现：采样期内，不同土地覆被(碱斑地除外)0-120cm剖面含水量均出现明显峰值，大豆地和羊草草地在7月底出现峰值，玉米地和向日葵地在8月初，退化草地则在8月底才达到，比羊草草地滞后了一个月。除羊草草地外，其他土地覆被剖面含水量变化呈W型，只是波动幅度各不相同。采样期内，羊草草地剖面含水量的相对变率最大，为74％，其他依次为退化草地、大豆地、向日葵地、玉米地，碱斑地最低，仅为6．4％。相对于农田土地覆被，在0～40cm，羊草草地、退化草地和碱斑地随盐渍化程度的加重，含盐量剖面变异逐渐减小，而农田的三种土地覆被之间变异比较接近。整个采样期，向日葵地储盐量随时间的变化呈下降趋势，其他土地覆被波动变化一致，都经历了下降-上升-下降过程，但波动幅度不同，且羊草草地在7月7日出现上升，其他4种土地覆被在9月8日开始出现滞后于含水量的变化。相对于采样初期，不同土地覆被含盐量的相对变率均为负值，农田的下降幅度大，草地次之，碱斑地最小。协方差分析表明：95％置信度下，土地覆被、土壤剖面和两者的交互作用对含盐量的影响差异显著。     

Tests for a biased sex ratio when the data are clustered

In behavioral ecology the overall sex ratio in a population of birds is often tested to see if it differs from a 50/50 ratio. In recent publications the binomial test or the ² test are carried out although the sexes of chicks within the same nest may not be independent. The lack of independence occurs since female birds can adjust the sex ratio in an adaptive way as demonstrated in recent studies. In order to take dependence into consideration the Wilcoxon signed rank test based on the within-brood differences between the proportions of sons and daughters was performed in a study investigating great tit hatchling sex ratios. We compare this test with a test based on an optimally weighted estimator recently proposed for medical studies with clustered binary data. According to our simulation results, this novel test is more powerful than the Wilcoxon signed rank test and should be used for the analysis of avian sex ratios. The methods are illustrated with real data from the great reed warbler.     

Multistate models for monitoring individual trees in permanent observation plots

This interdisciplinary research on forest ecosystems begins with some characteristics of ecosystems which are the basis for the derivation of statistical models for the development and vitality of trees. Several ecological problems which could be solved by longitudinal studies are mentioned. Statistical methods for the evaluation of the crowns of spruce trees (Picea abies Karst) in three permanent observation plots in Switzerland are described. In particular, the time-dependent proportional odds model and a transitional model are used. Through application of these multistate models the data give information on the dependence of an ordered categorical response variable on covariates characterizing the ecosystem. The response variable is observed through infrared aerial photographs. This monitoring system gives insight into the dynamic behaviour of the forest ecosystem. The need for more eco-systematically motivated statistical research using longitudinal studies is identified.