Costs of reproduction in common eiders ( Somateria mollissima ): an assessment of relationships between reproductive effort and future survival and reproduction based on observational and experimental studies

The two traditional approaches to the study of costs of reproduction, correlational and experimental, have been used in parallel in a breeding colony of common eiders ( Somateria mollissima ) and were compared in this paper. The analysis of the observational data was based on a two-strata capture-recapture model, the strata being defined on the basis of the clutch size laid by individual females in a given year. The best model according to AIC C indicated substantial variation in survival, recapture and transition rates, but overall a pattern emerged: females laying large clutches have a somewhat higher survival and much higher capture rate than females laying small clutches, and transition from large to small clutch size occurs much more frequently than the reverse transition. The analysis of the experimental data (adding/removing one egg) showed that no clear effect was found on either survival or transition rates. We conclude by suggesting (1) that condition should be included in multi-strata models in addition to reproductive effort; (2) that a specific study design for estimating the proportion of non-breeding females should be implemented, and (3) that non-breeding (a non-observable state in this study) may be influenced by previous reproduction events.     

Costs of reproduction: Assessing responses to brood size manipulation on life-history and behavioural traits using multi-state capture-recapture models

Costs of reproduction are fundamental trade-offs shaping the evolution of life histories. There has been much interest, discussion and controversy about the nature and type of reproductive costs. The manipulation of reproductive effort (e.g. brood size manipulation) may alter not only life-history traits such as future adult survival rate and future reproductive effort, but also behavioural decisions affecting recapture/resighting and dispersal probabilities. We argue that many previous studies of the costs of reproduction may have erroneously concluded the existence or non-existence of such costs because of their use of local return rates to assess survival. In this paper, we take advantage of the modern multistate capture-recapture methods to highlight how the accurate assessment of the costs of reproduction requires incorporating not only recapture probability, but also behavioural 'state' variables, for example dispersal status and current reproductive investment. The inclusion of state-dependent decisions can radically alter the conclusions drawn regarding the costs of reproduction on future survival or reproductive investment. We illustrate this point by re-analysing data collected to address the question of the costs of reproduction in the collared flycatcher and the great tit. We discuss in some detail the methodological issues and implications of the analytical techniques.     

Effects of neckbands on survival and fidelity of white-fronted and Canada geese captured as non-breeding adults

We conducted an experiment to examine the effect of neckbands, controlling for differences in sex, species and year of study (1991-1997), on probabilities of capture, survival, reporting, and fidelity in non-breeding small Canada ( Branta canadensis hutchinsi ) and white-fronted ( Anser albifrons frontalis ) geese. In Canada's central arctic, we systematically double-marked about half of the individuals from each species with neckbands and legbands, and we marked the other half only with legbands. We considered 48 a priori models that included combinations of sex, species, year, and neckband effects on the four population parameters produced by Burnham's (1993) model, using AIC for model selection. The four best approximating models each included a negative effect of neckbands on survival, and effect size varied among years. True survival probability of neckbanded birds annually ranged from 0.006 to 0.23 and 0.039 to 0.22 (Canada and white-fronted geese, respectively) lower than for conspecifics without neckbands. Changes in estimates of survival probability in neckbanded birds appeared to attenuate more recently, particularly in Canada Geese, a result that we suspect was related to lower retention rates of neckbands. We urge extreme caution in use of neckbands for estimation of certain population parameters, and discourage their use for estimation of unbiased survival probability in these two species.     

Population reproduction during Poland's millennium

An attempt is made to summarize birth and death rates as well as population growth, life expectancy, gross reproduction rates, and theoretical birth rates for Poland during its 1,000-year history. The author concentrates on estimates for the period from the year 1000 to 1900, since the rates and coefficients for the twentieth century are much better documented and are well known.     

Disentangling the sources of variation in the survival of the European dipper

The population growth rate of the European dipper has been shown to decrease with winter temperature and population size. We examine here the demographic mechanism for this effect by analysing how these factors affect the survival rate. Using more than 20 years of capture-mark-recapture data (1974-1997) based on more than 4000 marked individuals, we perform analyses using open capture-mark-recapture models. This allowed us to estimate the annual apparent survival rates (probability of surviving and staying on the study site from one year to the next one) and the recapture probabilities. We partitioned the variance of the apparent survival rates into sampling variance and process variance using random effects models, and investigated which variables best accounted for temporal process variation. Adult males and females had similar apparent survival rates, with an average of 0.52 and a coefficient of variation of 40%. Chick apparent survival was lower, averaging 0.06 with a coefficient of variation of 42%. Eighty percent of the variance in apparent survival rates was explained by winter temperature and population size for adults and 48% by winter temperature for chicks. The process variance outweighed the sampling variance both for chick and adult survival rates, which explained that shrunk estimates obtained under random effects models were close to MLE estimates. A large proportion of the annual variation in the apparent survival rate of chicks appears to be explained by inter-year differences in dispersal rates.     

Disentangling the sources of variation in the survival of the European dipper

The population growth rate of the European dipper has been shown to decrease with winter temperature and population size. We examine here the demographic mechanism for this effect by analysing how these factors affect the survival rate. Using more than 20 years of capture-mark-recapture data (1974-1997) based on more than 4000 marked individuals, we perform analyses using open capture-mark-recapture models. This allowed us to estimate the annual apparent survival rates (probability of surviving and staying on the study site from one year to the next one) and the recapture probabilities. We partitioned the variance of the apparent survival rates into sampling variance and process variance using random effects models, and investigated which variables best accounted for temporal process variation. Adult males and females had similar apparent survival rates, with an average of 0.52 and a coefficient of variation of 40%. Chick apparent survival was lower, averaging 0.06 with a coefficient of variation of 42%. Eighty percent of the variance in apparent survival rates was explained by winter temperature and population size for adults and 48% by winter temperature for chicks. The process variance outweighed the sampling variance both for chick and adult survival rates, which explained that shrunk estimates obtained under random effects models were close to MLE estimates. A large proportion of the annual variation in the apparent survival rate of chicks appears to be explained by inter-year differences in dispersal rates.     

Survival rates of Hungarian sand martins and their relationship with Sahel rainfall

Since 1986, I have carried out an intensive field survey of 10 000-30 000 pairs of a sand martin ( Riparia riparia ) population. Direct survey of the size and distribution of the breeding population and estimation of adult survival rates by SURGE, based on extensive ringing data sets, allow us to analyze the effects of different environmental factors with high precision. The model selection showed that the S s+t , P t model, in which the survival rates differ by sex for adults and vary in parallel by year and the capture rate varies by year, fits the data. The adult females had a lower survival rate compared to the males. The capture rate could be modelled as a quotient of the number of captured birds and the number of breeding birds along the upper part of the river Tisza. The survival rates of adults were related to the rainfall of the southern Sahel, which has an important role in the extension of the winter foraging habitat in the Sahel. Although the severe decrease in the population size, which may reach 50%, coincided with a large decline in the adult survival rate, there was not a significant relation between the adult survival rate and population size during the studied period. The population recruitment by first breeders and immigrant-emigrant adults could have a key role in the determination of population size. In the case of the studied subpopulation along the river, which is a core of the Carpathian Bend population, the immigration-emigration of adults had an important effect on the population size. The significant difference between juvenile male and female dispersal indicates the importance of separate estimation of juvenile survival for the sexes in further studies.     

Estimation of trade-offs with capture-recapture models: A case study on the lesser snow goose

Trade-offs between traits such as fecundity or survival are fundamental to much of our understanding of the evolution of life histories. There has been much renewed interest and controversy concerning methods for estimating trade-offs, in the wild or in captivity, and with or without experimental manipulations. In this paper, we assess the general question of the utility of modern capture-recapture methods as a robust tool for estimating trade-offs in natural populations. We present results from analyses of two forms of trade-offs: the cost of present reproduction on future survival and the cost of present reproduction on the probability of breeding in the future. We apply the methods to data from a long-term study of a snow goose population, and generally discuss the advantages and potential problems with various approaches.     

Separation of survival and movement rates in multi-state tag-return and capture-recapture models

There has been growing interest in the estimation of transition probabilities among stages (Hestbeck et al. , 1991; Brownie et al. , 1993; Schwarz et al. , 1993) in tag-return and capture-recapture models. This has been driven by the increasing interest in meta-population models in ecology and the need for parameter estimates to use in these models. These transition probabilities are composed of survival and movement rates, which can only be estimated separately when an additional assumption is made (Brownie et al. , 1993). Brownie et al. (1993) assumed that movement occurs at the end of the interval between time i and i + 1. We generalize this work to allow different movement patterns in the interval for multiple tag-recovery and capture-recapture experiments. The time of movement is a random variable with a known distribution. The model formulations can be viewed as matrix extensions to the model formulations of single open population capturerecapture and tag-recovery experiments (Jolly, 1965; Seber, 1965; Brownie et al. , 1985). We also present the results of a small simulation study for the tag-return model when movement time follows a beta distribution, and later another simulation study for the capture-recapture model when movement time follows a uniform distribution. The simulation studies use a modified program SURVIV (White, 1983). The Relative Standard Errors (RSEs) of estimates according to high and low movement rates are presented. We show there are strong correlations between movement and survival estimates in the case that the movement rate is high. We also show that estimators of movement rates to different areas and estimators of survival rates in different areas have substantial correlations.     

Fledging size and survival in snow geese: Timing is everything (or is it?)

In many birds, body size at fledging is assumed to predict accurately the probability of subsequent survival, and size at fledging is often used as a proxy variable in analyses attempting to assess the pattern of natural selection on body size. However, in some species, size at fledging can vary significantly as a function of variation in the environmental component of growth. Such developmental plasticity has been demonstrated in several species of Arctic-breeding geese. In many cases, slower growth and reduced size at fledging has been suggested as the most parsimonious explanation for reduced post-fledging survival in goslings reared under poor environmental conditions. However, simply quantifying a relationship between mean size at fledging and mean survival rate (Francis et al ., 1992) may obscure the pattern of selection on the interaction of the genetic and environmental components of growth. The hypothesis that selection operates on the environmental component of body size at fledging, rather than the genetic component of size per se, was tested using data from the long-term study of Lesser Snow Geese ( Anser c. caerulescens ) breeding at La Pérouse Bay, Manitoba, Canada. Using data from female goslings measured at fledging, post-fledging survival rates were estimated using combined live encounter and dead recovery data (Burnham, 1993). To control for the covariation between growth and environmental factors, survival rates were constrained to be functions of individual covariation of size at fledging, and various measures of the timing of hatch; in all Arctic-breeding geese studied to date, late hatching goslings grow significantly more slowly than do early hatching goslings. The slower growth of late-hatching goslings has been demonstrated to reflect systematic changes in the environmental component of growth, and thus controlling for hatch date controls for a significant proportion of variation in the environmental component of growth. The relationship between size at fledging, hatch date and survival was found to be significantly non-linear; among early hatching goslings, there was little indication of significant differences in survival rate among large and small goslings. However, with increasingly later hatch dates, there was progressively greater mortality selection against smaller, slower growing goslings in most years. This would appear to suggest that body size matters, but not absolutely; small size leads to reduced survival for late-hatching goslings only at La Pe´rouse Bay. Since at least some of the variation in size among goslings for a given hatch date reflects genetic differences, this suggests selection may favour larger size at fledging, albeit only among late-hatching goslings.     

Bias in transition-specific survival and movement probabilities estimated using capture-recapture data

Transition probabilities can be estimated when capture-recapture data are available from each stratum on every capture occasion using a conditional likelihood approach with the Arnason-Schwarz model. To decompose the fundamental transition probabilities into derived parameters, all movement probabilities must sum to 1 and all individuals in stratum r at time i must have the same probability of survival regardless of which stratum the individual is in at time i + 1. If movement occurs among strata at the end of a sampling interval, survival rates of individuals from the same stratum are likely to be equal. However, if movement occurs between sampling periods and survival rates of individuals from the same stratum are not the same, estimates of stratum survival can be confounded with estimates of movement causing both estimates to be biased. Monte Carlo simulations were made of a three-sample model for a population with two strata using SURVIV. When differences were created in transition-specific survival rates for survival rates from the same stratum, relative bias was <2% in estimates of stratum survival and capture rates but relative bias in movement rates was much higher and varied. The magnitude of the relative bias in the movement estimate depended on the relative difference between the transition-specific survival rates and the corresponding stratum survival rate. The direction of the bias in movement rate estimates was opposite to the direction of this difference. Increases in relative bias due to increasing heterogeneity in probabilities of survival, movement and capture were small except when survival and capture probabilities were positively correlated within individuals.     

Testing the Null Hypothesis of Nonstationary Long Memory Against the Alternative Hypothesis of a Nonlinear Ergodic Model

Interest in the interface of nonstationarity and nonlinearity has been increasing in the econometric literature. This paper provides a formal method of testing for nonstationary long memory against the alternative of a particular form of nonlinear ergodic processes; namely, exponential smooth transition autoregressive processes. In this regard, the current paper provides a significant generalization to existing unit root tests by allowing the null hypothesis to encompass a much larger class of nonstationary processes. The asymptotic theory associated with the proposed Wald statistic is derived, and Monte Carlo simulation results confirm that the Wald statistics have reasonably correct size and good power in small samples. In an application to real interest rates and the Yen real exchange rates, we find that the tests are able to distinguish between these competing processes in most cases, supporting the long-run Purchasing Power Parity (PPP) and Fisher hypotheses. But, there are a few cases in which long memory and nonlinear ergodic processes display similar characteristics and are thus confused with each other in small samples.     

Multivariate Two-Sided Tests for Normal Mean Vectors with Unknown Covariance Matrix

A numerically stable method is developed which computes seemingly tight bounds at a small computational cost relative to the model size, when that model size is large, for the unreliability and bounds for the unreliability using, respectively, exact and bounding failure/repair continuous-time Markov chain models of fault-tolerant systems with exponential failure and repair time distributions, in which repair is deferred until some condition on the collection of failed components is satisfied, and, then, proceeds until reaching the state without failed components, with failure rates much smaller than repair rates and not too different output rates from states with deferred repair.     

Sample size calculation for an agreement study

It is often necessary to compare two measurement methods in medicine and other experimental sciences. This problem covers a broad range of data. Many authors have explored ways of assessing the agreement of two sets of measurements. However, there has been relatively little attention to the problem of determining sample size for designing an agreement study. In this paper, a method using the interval approach for concordance is proposed to calculate sample size in conducting an agreement study. The philosophy behind this is that the concordance is satisfied when no more than the pre‐specified k discordances are found for a reasonable large sample size n since it is much easier to define a discordance pair. The goal here is to find such a reasonable large sample size n. The sample size calculation is based on two rates: the discordance rate and tolerance probability, which in turn can be used to quantify an agreement study. The proposed approach is demonstrated through a real data set. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of correlation and missing data on sample size estimation in longitudinal clinical trials

In longitudinal clinical trials, a common objective is to compare the rates of changes in an outcome variable between two treatment groups. Generalized estimating equation (GEE) has been widely used to examine if the rates of changes are significantly different between treatment groups due to its robustness to misspecification of the true correlation structure and randomly missing data. The sample size formula for repeated outcomes is based on the assumption of missing completely at random and a large sample approximation. A simulation study is conducted to investigate the performance of GEE sample size formula with small sample sizes, damped exponential family of correlation structure and non‐ignorable missing data. Copyright © 2008 John Wiley & Sons, Ltd.     

The demography of the decline in the British willow warbler population

Since 1989, there has been a major and unprecedented decline in the breeding population of willow warblers ( Phylloscopus trochilus ) in southern Britain. Between 1986 and 1993 the numbers of willow warbler territories counted on monitoring plots declined by 47% in southern Britain, compared to a decline of 7% in northern Britain. Breeding densities of willow warblers are generally higher in the north and west of Britain, than in the south. Data from nest record cards provided evidence of only minor regional differences in breeding performance with a small but significant increase in the loss rate of nests during the nestling stage in 1989-1992 in southern Britain, compared with 1974-1988. Mark-recapture data collected at 18 constant effort sites and from one intensive study were used to estimate apparent survival rates of adults during the period 1987-1993. Program SURGE4 was used to test for differences in survival rates and recapture probabilities between years, sexes, sites and regions. Recapture probabilities differed between sites and between the sexes but not between years. Survival rates differed significantly between years (in southern Britain) but not between sexes or sites. In southern Britain, adult survival declined from 45% during 1987-1988 to 24% during 1991-1992, while in northern Britain there was no evidence that survival changed during the same period. Although the pattern of annual variation in survival differed between northern and southern Britain, this was due mainly to a much lower survival rate in southern Britain during 1991-1992. Declining survival rates of adult willow warblers have probably been a major cause of the observed population decline.     

Ultimate Extinction of the Promiscuous Bisexual Galton—Watson Metapopulation

A variant of a sexual Gallon–Watson process is considered. At each generation the population is partitioned among n‘hosts’ (population patches) and individual members mate at random only with others within the same host. This is appropriate for many macroparasite systems, and at low parasite loads it gives rise to a depressed rate of reproduction relative to an asexual system, due to the possibility that females are unmated. It is shown that stochasticity mitigates against this effect, so that for small initial populations the probability of ultimate extinction (the complement of an ‘epidemic’) displays a tradeoff as a function of n between the strength of fluctuations which overcome this ‘mating’ probability, and the probability of the subpopulation in one host being ‘rescued’ by that in another. Complementary approximations are developed for the extinction probability: an asymptotically exact approximation at large n, and for small n a short‐time probability that is exact in the limit where the mean number of offspring per parent is large.     

金融要素扭曲与企业创新活动

本文利用世界银行的企业调查数据并将四大国有商业银行的市场份额作为金融要素市场化的代理指标,分析了金融要素扭曲对企业创新活动的影响。实证研究发现：金融要素扭曲对企业的研发投入和创新成果都具有抑制作用,这种抑制作用在不同所有制企业间具有异质性,相比国有企业,私营企业的创新活动受金融要素扭曲的抑制作用更大。中小企业的研发投入对金融要素的扭曲的敏感性要高于大型企业,在过程创新中,金融要素扭曲对中小型企业的影响更大,但在产品创新过程中,金融要素的扭曲的对大型企业的影响则更强。本文的研究提供了金融要素扭曲对经济增长有负面的影响的来自企业创新的微观证据。因此,全面推进的金融要素市场化改革有助于企业的创新活动,从而为国家经济转型提供持续创新与发展的动力。     

Combining estimates from multiple early studies to obtain estimates of response: using shrinkage estimates to obtain estimates of response

Development of anti-cancer therapies usually involve small to moderate size studies to provide initial estimates of response rates before initiating larger studies to better quantify response. These early trials often each contain a single tumor type, possibly using other stratification factors. Response rate for a given tumor type is routinely reported as the percentage of patients meeting a clinical criteria (e.g. tumor shrinkage), without any regard to response in the other studies. These estimates (called maximum likelihood estimates or MLEs) on average approximate the true value, but have variances that are usually large, especially for small to moderate size studies. The approach presented here is offered as a way to improve overall estimation of response rates when several small trials are considered by reducing the total uncertainty.The shrinkage estimators considered here (James-Stein/empirical Bayes and hierarchical Bayes) are alternatives that use information from all studies to provide potentially better estimates for each study. While these estimates introduce a small bias, they have a considerably smaller variance, and thus tend to be better in terms of total mean squared error. These procedures provide a better view of drug performance in that group of tumor types as a whole, as opposed to estimating each response rate individually without consideration of the others. In technical terms, the vector of estimated response rates is nearer the vector of true values, on average, than the vector of the usual unbiased MLEs applied to such trials.     

A note on the sample size required in sequential tests for the generalized binomial distribution

In this paper, we discuss the sample size needed to perform Wald's sequential statistical test for the proportion of non-conforming items generated by a process when the results of the inspections are correlated and the generalized binomial distribution proposed by Madsen (1993) is used. It will be shown that, in the presence of correlation, the sample size increases as the value of the coefficient of correlation increases--being much higher for processes with small failure rates.