Investigating connectivity and seasonal differences in wind assistance in the migration of Common Sandpipers

Many migratory bird species have undergone recent population declines, but there is considerable variation in trends between species and between populations employing different migratory routes. Understanding species-specific migratory behaviours is therefore of critical importance for their conservation. The Common Sandpiper Actitis hypoleucos is an Afro-Palaearctic migratory bird species whose European populations are in decline. We fitted geolocators to individuals breeding in England or wintering in Senegal to determine their migration routes and breeding or non-breeding locations. We used these geolocator data in combination with previously published data from Scottish breeding birds to determine the distributions and migratory connectivity of breeding (English and Scottish) and wintering (Senegalese) populations of the Common Sandpiper, and used simulated random migrations to investigate wind assistance during autumn and spring migration. We revealed that the Common Sandpipers tagged in England spent the winter in West Africa, and that at least some birds wintering in Senegal bred in Scandinavia; this provides insights into the links between European breeding populations and their wintering grounds. Furthermore, birds tagged in England, Scotland and Senegal overlapped considerably in their migration routes and wintering locations, meaning that local breeding populations could be buffered against habitat change, but susceptible to large-scale environmental changes. These findings also suggest that contrasting population trends in England and Scotland are unlikely to be the result of population-specific migration routes and wintering regions. Finally, we found that birds used wind to facilitate their migration in autumn, but less so in spring, when the wind costs associated with their migrations were higher than expected at random. This was despite the wind costs of simulated migrations being significantly lower in spring than in autumn. Indeed, theory suggests that individuals are under greater time pressures in spring than in autumn because of the time constraints associated with reproduction.     

Towards the extremes: A critical analysis of pointer year detection methods

To study growth responses of trees to extreme events, analyses of so-called ‘pointer years’ are often performed. Thereby, the term pointer year refers to years in which a majority of trees shows extraordinary growth responses, like very narrow (or wide) ring widths. A wide variety of methods has been used to analyze pointer years, hampering comparisons between studies. The latter illustrates that there is a strong need to harmonize pointer year detection methods. This review contributes to that by describing and comparing the main methods (and variants thereof) found in the literature for the last two decades, both in a qualitative and quantitative way. We discuss methodological considerations and provide recommendations how to proceed with pointer year detection in future. Given that the individual methods for pointer year detection were found to highlight different aspects of extraordinary growth, the one method cannot completely substitute the other. Hence, we suggest to use multiple methods in a harmonized way to get the deepest insight into the nature of pointer years.     

A novel approach for the identification of pointer years

In the context of extreme event ecology, identification of pointer years has become a central aspect of tree-ring research. However, the variety of methods employed for pointer year detection since the introduction of the concept in 1979 impedes a direct comparison among studies. Moreover, most commonly used methods partly rely on arbitrarily selected thresholds, resulting in a potentially inconsistent application of those means. To overcome these discrepancies, we here introduce the “standardized growth change” method SGC, which relies on probability density functions of standardized year-to-year ring width differences and internationally accepted significance levels. To evaluate the performance of SGC, it is applied to 1000 pseudo-populations with known properties as well as to an existing Scots pine tree ring data set and compare the results derived from SGC to the four most frequently applied pointer year detection methods. Our comparative evaluation indicates SGC to supersede the other considered methods. In particular, it identified all artificially introduced pointer years in the pseudo-populations, whereas the other methods missed between 3 and 96 percent of known events. A detailed evaluation of misclassifications by the other approaches points out method-specific weaknesses. Finally, we provide technical aspects and recommendations for the application of SGC in a broader context.     

陕西长武玉米降水指数保险设计

天气指数保险能有效规避传统农业保险的弊端.本研究基于陕西长武长序列产量数据和气象数据,采用统计分析的方法进行种植面积、产量、单产、趋势产量、相对气象产量以及玉米生育期需供水的分析;采用基于损失的风险评估方法评价种植风险;采用基于Logistic模型的费率厘定方法进行纯费率厘定;根据降水指数和减产率的相关性,设计降水指数...     

Plasticity and cross‐tolerance to heterogeneous environments: divergent stress responses co‐evolved in an African fruit fly

Plastic adjustments of physiological tolerance to a particular stressor can result in fitness benefits for resistance that might manifest not only in that same environment but also be advantageous when faced with alternative environmental stressors, a phenomenon termed ‘cross‐tolerance’. The nature and magnitude of cross‐tolerance responses can provide important insights into the underlying genetic architecture, potential constraints on or versatility of an organism's stress responses. In this study, we tested for cross‐tolerance to a suite of abiotic factors that likely contribute to setting insect population dynamics and geographic range limits: heat, cold, desiccation and starvation resistance in adult Ceratitis rosa following acclimation to all these isolated individual conditions prior to stress assays. Traits of stress resistance scored included critical thermal (activity) limits, chill coma recovery time (CCRT), heat knockdown time (HKDT), desiccation and starvation resistance. In agreement with other studies, we found that acclimation to one stress typically increased resistance for that same stress experienced later in life. A more novel outcome, however, is that here we also found substantial evidence for cross‐tolerance. For example, we found an improvement in heat tolerance (critical thermal maxima, CT_max) following starvation or desiccation hardening and improved desiccation resistance following cold acclimation, indicating pronounced cross‐tolerance to these environmental stressors for the traits examined. We also found that two different traits of the same stress resistance differed in their responsiveness to the same stress conditions (e.g. HKDT was less cross‐resistant than CT_max). The results of this study have two major implications that are of broader importance: (i) that these traits likely co‐evolved to cope with diverse or simultaneous stressors, and (ii) that a set of common underlying physiological mechanisms might exist between apparently divergent stress responses in this species. This species may prove to be a valuable model for future work on the evolutionary and mechanistic basis of cross‐tolerance.     

Weather-induced changes in moth activity bias measurement of long-term population dynamics from light trap samples

Interpretation of light trap catches of moths is complicated by daily variation in weather that alters flight activity and numbers caught. Light trap efficiency is also modified by wind and fog, and daily weather may effect absolute abundance (numbers actually present). However, actograph experiments and other sampling methods suggest that changes in daily activity are large by comparison to changes in absolute abundance. Daily variation in weather (other than wind and fog) is therefore a form of sampling error in absolute abundance estimates. We investigated the extent of this sampling bias in 26 years of population dynamics from 133 moth species. In a subset of 20 noctuid and geometrid species, daily numbers caught were positively correlated with temperature in 14 species, and negatively correlated with rainfall in 11 species. The strength of correlations varied between species, making it difficult to standardize catches to constant conditions. We overcame this by establishing how weather variation changed with time and duration of the flight period. Species flying later in the summer and for shorter periods experienced more variable temperatures, making sampling error greater for these species. Of the 133 moth species, those with shorter flight periods had greater population variability and more showed significant temporal density dependence. However, these effects were weak, which is encouraging because it suggests that population analyses of light trap data largely reflect factors other than sampling error.     

Demographic responses to weather fluctuations are context dependent in a long‐lived amphibian

Weather fluctuations have been demonstrated to affect demographic traits in many species. In long‐lived organisms, their impact on adult survival might be buffered by the evolution of traits that reduce variation in interannual adult survival. For example, skipping breeding is an effective behavioral mechanism that may limit yearly variation in adult survival when harsh weather conditions occur; however, this in turn would likely lead to strong variation in recruitment. Yet, only a few studies to date have examined the impact of weather variation on survival, recruitment and breeding probability simultaneously in different populations of the same species. To fill this gap, we studied the impact of spring temperatures and spring rainfall on survival, on reproductive skipping behavior and on recruitment in five populations of a long‐lived amphibian, the yellow‐bellied toad (Bombina variegata). Based on capture–recapture data, our findings demonstrate that survival depends on interactions between age, population and weather variation. Varying weather conditions in the spring result in strong variation in the survival of immature toads, whereas they have little effect on adult toads. Breeding probability depends on both the individual's previous reproductive status and on the weather conditions during the current breeding season, leading to high interannual variation in recruitment. Crucially, we found that the impact of weather variation on demographic traits is largely context dependent and may thus differ sharply between populations. Our results suggest that studies predicting the impact of climate change on population dynamics should be taken with caution when the relationship between climate and demographic traits is established using only one population or few populations. We therefore highly recommend further research that includes surveys replicated in a substantial number of populations to account for context‐dependent variation in demographic processes.     

Population suppression for control of the blowfly Lucilia sericata and sheep blowfly strike

Abstract.

• 1 The control of ovine myiasis by suppression of populations of the blowfly Lucifia sericata was investigated experimentally on three farms in the south-west of England in 1992 and 1993.
• 2 In blind trials, sheep on one farm (control) were given two doses of placebo, on a second two doses of the larvicide cyromazine (Vetrazin®, CibaGeigy), and on a third cyromazine and a subsequent dose of placebo.
• 3 The first treatment was given shortly before the predicted spring emergence of L.sericata and the second shortly before the predicted emergence of the second generation. Previous simulation analysis had identified strategic early-season treatment as the optimum for blowfly population suppression.
• 4 On both treatment farms significantly smaller L.sericata populations were recorded throughout 1992 and the incidence of strike was significantly lower than on the control farm. The results show that appropriate early-season timing of sheep treatment can suppress populations of L.sericata and could be used by farmers to reduce the incidence of blowfly strike.
• 5 The results suggest, however, that the effectiveness of population suppression and strike incidence may have been influenced by immigration into the control areas and by adverse weather, the latter changing the susceptibility of sheep to strike and resulting in rising strike incidence even when L.sericata population densities were low. In practice, therefore, blowfly population suppression should be employed as a component of an integrated strike management programme.