A questionnaire survey for the assessment of wild-domestic pig interactions in a context oedema disease outbreaks among wild boars (Sus scrofa) in South-Eastern France.

Pig outdoor farming is gaining popularity and commercial success in the European Union, and its expansion, together with an increasing wild boar population, facilitates interactions between domestic and wild suids. In the Southern French Department of Ardèche, several episodes of mass mortalities due to infection with an enteropathogenic strain of Escherichia coli causing oedema disease (OD) were reported in wild boar populations between 2013 and 2016. In order to investigate a potential link between those events and the frequency of interactions between wild boar and domestic pig, we analyzed regional vegetation and hunting bag data and implemented a semi-structured questionnaire survey among a total of 30 outdoor pig farmers and 30 hunters distributed inside and outside the identified area of OD emergence. One third of interviewed farmers (11/30) had experienced intrusions of wild boars in domestic pig premises during the previous year. Similarly, 23% of interviewed hunters reported interactions between wild boar and feral free-ranging pigs in recent years, and 60% reported the observation of free-ranging pigs with a phenotypic feature of Vietnamese pot-bellied pigs (55%). Our analysis identified that in the OD emergence area, several factors could facilitate the transmission of pathogens between wild and domestic suids including a predominance of forested vegetation, a higher estimated wild boar density, weaker levels of farm biosecurity, a higher level of reported wild boar intrusions in pig farms and several reports of feral pot-bellied pig presence. Although our sample was limited, our study suggested a widespread occurrence of situations facilitating the transmission of pathogens between wild and domestic suids. Similar studies in other rural regions in the European Union are recommended, in order to promote preparedness for the emergence and circulation of shared swine pathogens.

Financial Impacts of Priority Swine Diseases to Pig Farmers in Red River and Mekong River Delta, Vietnam.

A study was conducted between May 2013 and August 2014 in three provinces of Vietnam to investigate financial impacts of swine diseases in pig holdings in 2010-2013. The aim of the study was to quantify the costs of swine diseases at producer level in order to understand swine disease priority for monitoring at local level. Financial impacts of porcine reproductive and respiratory syndrome (PRRS), foot and mouth disease (FMD), and epidemic diarrhoea were assessed for 162 pig holders in two Red River Delta provinces and in one Mekong River Delta province, using data on pig production and swine disease outbreaks at farms. Losses incurred by swine diseases were estimated, including direct losses due to mortality (100% market value of pig before disease onset) and morbidity (abortion, delay of finishing stage), and indirect losses due to control costs (treatment, improving biosecurity and emergency vaccination) and revenue foregone (lower price in case of emergency selling). Financial impacts of swine diseases were expressed as percentage of gross margin of pig holding. The gross margin varied between pig farming groups (P < 0.0001) in the following order: large farm (USD 18 846), fattening farm (USD 7014) and smallholder (USD 2350). The losses per pig holding due to PRRS were the highest: 41% of gross margin for large farm, 38% for fattening farm and 63% for smallholder. Cost incurred by FMD was lower with 19%, 25% and 32% of gross margin of pig holding in large farm, fattening farm and smallholder, respectively. The cost of epidemic diarrhoea was the lowest compared to losses due to PRRS and FMD and accounted for around 10% of gross margin of pig holding in the three pig farming groups. These estimates provided critical elements on swine disease priorities to better inform surveillance and control at both national and local level.

Multivariate analysis of traditional pig management practices and their potential impact on the spread of infectious diseases in Corsica.

Corsica is a French Mediterranean island with traditional extensive pig farming oriented towards the production of high quality cured meat products. The increasing success of these cured products in continental Europe has triggered the development and organisation of an extensive pig farming industry. However, these pig farming practices have seldom been described and analysed to understand the potential risk of introduction and spread of infectious diseases. We conducted a cross-sectional study in Corsica in 2013 to characterise the main pig management practices and to identify groups of farms with similar practices and therefore homogeneous risk of introduction and spread of infectious diseases. We interviewed 68 pig farmers and investigated different farm management practices which could lead to contact between herds, such as trading animals, sharing pastures, feed and reproduction management (direct contacts), slaughtering and carcass waste management, and contacts with people and vehicles (indirect contacts). The practices were described and the farms grouped by multiple factor and hierarchical clustering analyses. Results revealed interesting patterns in the introduction and spread of infectious disease, such as the seasonality of pig production, the potential local spread of diseases in pastures due to the presence of free-ranging boars, carcasses, and animal waste. Multivariate analyses identified four groups of farms with different levels of risk of the spread of infectious disease, illustrating changes in farmers' customs from free-range uncontrolled farming systems to more controlled systems aimed at the production of high quality pork products. These results will be useful to more realistically simulate the spread of infectious diseases among Corsican pig farms and highlight the need for awareness raising campaigns among the stakeholders to reduce risky practices.

When private actors matter: Information-sharing network and surveillance of Highly Pathogenic Avian Influenza in Vietnam.

The effectiveness of animal health surveillance systems depends on their capacity to gather sanitary information from the animal production sector. In order to assess this capacity we analyzed the flow of sanitary information regarding Highly Pathogenic Avian Influenza (HPAI) suspicions in poultry in Vietnam. Participatory methods were applied to assess the type of actors and likelihood of information sharing between actors in case of HPAI suspicion in poultry. While the reporting of HPAI suspicions is mandatory, private actors had more access to information than public actors. Actors of the upstream sector (medicine and feed sellers) played a key role in the diffusion of information. The central role of these actors and the influence of the information flow on the adoption by poultry production stakeholders of behaviors limiting (e.g. prevention measures) or promoting disease transmission (e.g. increased animal movements) should be accounted for in the design of surveillance and control programs.

Evaluation of enzyme-linked immunosorbent assays and a haemagglutination inhibition tests for the detection of antibodies to Newcastle disease virus in village chickens using a Bayesian approach.

Newcastle disease (ND) is an endemic disease in village chickens in Ethiopia with substantial economic importance. The sensitivity (Se) and specificity (Sp) of a blocking enzyme-linked immunosorbent assay (bELISA, Svanova Biotech), indirect ELISA (iELISA, Laboratoire Service International) and haemagglutination inhibition (HI) test for ND virus (NDV) antibody detection were evaluated in a Bayesian framework in the absence of a gold standard test, on sera collected from unvaccinated chickens kept under the village production system in household flocks and at markets in two woredas (i.e. districts) of the Eastern Shewa zone, Ethiopia. The outcomes of the iELISA test differed dramatically from those of the two other tests with 92% of the samples testing positive as compared with less than 15% for bELISA and HI. iELISA results were also inconsistent with previous estimations of Newcastle serological prevalence. The information provided by the iELISA test was thus considered as highly unreliable, probably due to an extremely low specificity, and thus not considered in the Bayesian models aiming at estimating serological prevalence and test performance parameters. Bayesian modelling of HI and bELISA test results suggested that bELISA had both the highest Se (86.6%; 95% posterior credible interval (PCI): 61.8%; 98.5%), and the highest Sp (98.3%; 95% PCI: 97.2%; 99.5%), while HI had a Se of 80.2% (95% PCI: 59.1%; 94.3%), and a Sp of 96.1% (95% PCI: 95.1%; 97.4%). Model selection and the range of the posterior distribution of the correlation between bELISA and HI test outcomes for truly seropositive animals (median at 0.461; PCI: -0.055; 0.894) suggested a tendency for bELISA and HI to detect the same truly positive animals and to fail to detect the same truly positive animals. The use of bELISA in screening and surveillance for NDV antibodies is indicated given its high Se and Sp, in addition to its ease of automation to handle large numbers of samples compared to HI. The latter can be used as confirmatory test where an ELISA test with moderate or low specificity is used although the likely positive dependence with bELISA implies that HI and bELISA provide similar information on truly positive animals. Evaluation of commercial ELISAs is indicated before their wider use in village chicken populations to avoid erroneous inferences.

Bridge hosts for avian influenza viruses at the wildlife/domestic interface: an eco-epidemiological framework implemented in southern Africa.

Wild terrestrial birds can act as potential local spreaders or bridge hosts for avian influenza viruses (AIVs) between waterfowl (the maintenance hosts of AIVs) and domestic avian populations in which AIVs may cause disease. Few studies have investigated this hypothesis, although it is an important knowledge gap in our understanding of AIV spread within socio-ecosystems. We designed a simple and reproducible approach in an agro-ecosystem in Zimbabwe based on: (1) bird counts at key target sites (i.e., wetlands, villages, intensive poultry production buildings and ostrich farms) to identify which wild birds species co-occur in these different sites and seasons when the risk of AIV transmission through these potential bridge hosts is maximal and (2) targeted sampling and testing for AIV infection in the identified potential bridge hosts. We found that 12 wild bird species represented the vast majority (79%) of co-occurrences in the different sites, whereas 230 bird species were recorded in this ecosystem. Specifically, three species - barn swallow, Hirundo rustica, red-billed quelea, Quelea quelea and cattle egret, Bubulcus ibis - represented the main potential bridge host species (65% of co-occurrences). In two out of these three species (i.e., barn swallow and red-billed quelea), we detected AIV infections, confirming that they can play a bridge function between waterfowl and domestic species in the ecosystem. Our approach can be easily implemented in other ecosystems to identify potential bridge hosts, and our results have implications in terms of surveillance, risk management and control of AIV spread in socio-ecosystems.

Evaluation of the vaccination efficacy against H5N1 in domestic poultry in the Red River Delta in Vietnam.

The domestic poultry population in Vietnam has been vaccinated against highly pathogenic avian influenza (HPAI) H5N1 since 2005. Since then, outbreaks have continued to occur without a clear understanding of the mechanisms involved. The general objective of this study was to understand the epidemiology of the disease in the context of vaccination and to draw some conclusions about vaccination efficacy in the domestic poultry population of the Red River Delta area. Five cross-sectional surveys to measure the serological and virological prevalence in vaccinated and unvaccinated poultry were performed from the end of 2008 to June 2010. The global seroprevalence was 24% (95% confidence interval 19·9-28·2). Determinants of vaccine immunogenicity were identified separately in chickens and ducks as well as determinants of the seroconversion in unvaccinated birds. The results highlight the difficulties in maintaining good flock immunity in poultry populations using inactivated vaccine in the field with two vaccination rounds per year, and in preventing circulation of virus in co-existing unvaccinated poultry.

A meta-analysis of observational epidemiological studies of Newcastle disease in African agro-systems, 1980-2009.

Newcastle disease (ND) is one of the most important and widespread avian pests. In Africa, backyard poultry production systems are an important source of protein and cash for poor rural livelihoods. ND mortality in these production systems is important and seriously disrupts benefits derived from it. This study undertook an African continental approach of ND epidemiology in backyard poultry. After a systematic literature review of studies published from 1980 to 2009, a meta-analysis of spatio-temporal patterns of serological prevalence and outbreak occurrence was performed. Average ND serological prevalence was estimated at 0·67 [95% confidence interval (CI) 0·58-0·75] in regions characterized by humid ecosystems, high human and poultry densities and low altitudes; 0·36 (95% CI 0·30-0·41) in dry ecosystems at intermediate altitude where human and poultry densities are low and 0·27 (95% CI 0·19-0·38) in mountain ecosystems where human and poultry densities are intermediate. In terms of seasonality, ND outbreaks occur mostly during the dry seasons in Africa, when environmental conditions are likely to be harshest for backyard poultry. In addition, a phylogeographical analysis revealed the regionalization of ND virus strains, their potential to evolve towards a higher pathogenicity from the local viral pool and suggests a risk for vaccine strains to provide new wild strains. These results present for the first time a continent-wide approach to ND epidemiology in Africa. More emphasis is needed for ND management and control in rural African poultry production systems.

Lumpy skin disease in Ethiopia: seroprevalence study across different agro-climate zones.

A cross-sectional study was conducted to estimate the seroprevalence of lumpy skin disease (LSD) in the different agro-climatic zones prevailing in Ethiopia. A total of 2368 serum samples were collected from 42 kebeles located in 15 districts and tested using indirect fluorescent antibody test (IFAT) and virus neutralization test (VNT). The herd and animal true LSD serological prevalence were estimated in each agro-climate zone using a Bayesian model. The intra-cluster correlation coefficient (ICC) was evaluated using a random-effect model. According to the serological prevalence estimations, LSD affected differently the three agro-climatic zones considered. Herd level seroprevalence was higher in the midland agro-climate zone 64% (95% CI: 53-74) as compared to the highland 26% (95% CI: 17-36) and the lowland 50% (95% CI: 40-60) agro-climates. Animal level seroprevalence in infected herds was also higher in the midland agro-climate zone 31% (95% CI: 24-40) than in the highland and lowland zones (24% (95% CI: 18-31) and 23% (95% CI: 18-29), respectively). Higher ICC value in the highland agro-climate zone implies that increased sample sizes should be particularly required for this zone in future studies to estimate LSD prevalence or incidence with a desired precision level. This seroprevalence study also suggests that the prevalence of LSD infection in Ethiopia is higher than what has been previously reported. In the light of these updated estimations, we discuss options to trigger appropriate control measures in the future.

Evaluating the efficiency of participatory epidemiology to estimate the incidence and impacts of foot-and-mouth disease among livestock owners in Cambodia.

The economic and social impacts of foot-and-mouth disease (FMD) for livestock owners of developed countries have been extensively documented over the past few years. In developing countries such as Cambodia, this evaluation is often lacking due to the scarcity of accurate data. In the present study, we used a range of participatory tools to infer farmers' knowledge and perception, and the relative incidence of FMD from January 2009 to June 2010 in fifty-one villages of Svay Rieng province, Cambodia. In addition, the detection of non-structural protein at village level was used to cross-validate the results from the participatory epidemiology (PE) study. A quantitative assessment using Bayesian modeling was carried out to assess the ability of PE to retrospectively determine the FMD-infected status of a village in Cambodia. Our study shows that even if FMD is ranked second in the list of priority diseases, livestock owners did not see any benefit in reporting it since the disease entailed low direct losses. The average clinical incidence rates at individual level for cattle-buffaloes and pigs in infected villages were assessed by proportional piling at 18% and 11%, respectively for the year 2009. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of PE study were estimated at 87%, 30%, 51% and 74%, respectively. This approach seems to largely overestimate the presence of the disease but proves useful in evaluating the impact of FMD at household level and in understanding the reasons for not reporting it. This information may be important in establishing well-adapted disease prevention and control strategies in Cambodia.

Evidence for freedom from swine influenza in a remote area of Northern Vietnam.

Swine influenza is responsible for one of the most prevalent disease affecting the swine industry worldwide. Epidemiological surveys rarely focus on remote areas, because traditional farming systems characterized by locally consumed production and low pig densities are considered as having little influence on the emergence, re-emergence, persistence or spread of swine influenza viruses. In addition, routine disease investigations in remote areas are often neglected due to logistic and economical constraints. A bank of swine sera collected in 2005 in the ethnic minorities households of Ha Giang province (Northern Vietnam) located adjacent to the Chinese border was analyzed to estimate the seroprevalence of swine influenza (SI) and to identify potential risk factors for infection. The results suggest that this specific agro-ecological system is free from SI and is not favourable to SI spread either through pig-to-pig transmission, or through poultry-to-pig transmission.

Understanding the ecological drivers of avian influenza virus infection in wildfowl: a continental-scale study across Africa.

Despite considerable effort for surveillance of wild birds for avian influenza viruses (AIVs), empirical investigations of ecological drivers of AIV prevalence in wild birds are still scarce. Here we used a continental-scale dataset, collected in tropical wetlands of 15 African countries, to test the relative roles of a range of ecological factors on patterns of AIV prevalence in wildfowl. Seasonal and geographical variations in prevalence were positively related to the local density of the wildfowl community and to the wintering period of Eurasian migratory birds in Africa. The predominant influence of wildfowl density with no influence of climatic conditions suggests, in contrast to temperate regions, a predominant role for inter-individual transmission rather than transmission via long-lived virus persisting in the environment. Higher prevalences were found in Anas species than in non-Anas species even when we account for differences in their foraging behaviour (primarily dabbling or not) or their geographical origin (Eurasian or Afro-tropical), suggesting the existence of intrinsic differences between wildfowl taxonomic groups in receptivity to infection. Birds were found infected as often in oropharyngeal as in cloacal samples, but rarely for both types of sample concurrently, indicating that both respiratory and digestive tracts may be important for AIV replication.

Looking for avian influenza in remote areas. A case study in Northern Vietnam.

Epidemiological surveys of avian influenza infections rarely focus on backyard poultry systems in remote locations because areas with low levels of poultry production are considered to have little influence on the emergence, re-emergence, persistence or spread of avian influenza viruses. In addition, routine disease investigations in remote areas often are neglected due to the lower availability and relatively high cost of veterinary services there. A bank of avian sera collected in 2005 from ethnic minority households in Ha Giang province (Northern Vietnam), located on the Chinese border, was analysed to estimate the seroprevalence of avian influenza virus (AIV) during a H5N1 epidemic and to identify potential risk factors for infection. The results suggest that the chicken population had been exposed to AIV with a seroprevalence rate of 7.2% [1.45; 10.5]. The H5 and H9 subtypes were identified with a seroprevalence of 3.25% [2.39; 4.11] and 1.12% [0.61; 1.63], respectively. The number of inhabitants in a village and the distance to the main national road were the most influential risk factors of AIV infection, and high-risk clusters were located along the road leading to China. These two results suggest a virus spread through commercial poultry exchanges and a possible introduction of AIV from southern China. Remote areas and small-scale farms may play an under-estimated role in the spread and persistence of AIV.

Risk factors of highly pathogenic avian influenza H5N1 occurrence at the village and farm levels in the Red River Delta Region in Vietnam.

A case-control study at both village and farm levels was designed to investigate risk factors for highly pathogenic avian influenza H5N1 during the 2007 outbreaks in one province of Northern Vietnam. Data related to human and natural environments, and poultry production systems were collected for 19 case and 38 unmatched control villages and 19 pairs of matched farms. Our results confirmed the role of poultry movements and trading activities. In particular, our models found that higher number of broiler flocks in the village increased the risk (OR = 1.49, 95% CI: 1.12-1.96), as well as the village having at least one poultry trader (OR = 11.53, 95% CI: 1.34-98.86). To a lesser extent, in one of our two models, we also identified that increased density of ponds and streams, commonly used for waterfowl production, and greater number of duck flocks in the village also increased the risk. The higher percentage of households keeping poultry, as an indicator of households keeping backyard poultry in our study population, was a protective factor (OR = 0.95, 95% CI: 0.91-0.98). At the farm level, three risk factors at the 5% level of type I error were identified by univariate analysis: a greater total number of birds (P = 0.006), increase in the number of flocks having access to water (P = 0.027) and a greater number of broiler flocks in the farm (P = 0.049). Effect of vaccination implementation (date and doses) was difficult to investigate because of a poor recording system. Some protective or risk factors with limited effect may not have been identified owing to our limited sample size. Nevertheless, our results provide a better understanding of local transmission mechanisms of HPAI H5N1 in one province of the Red River Delta region in Vietnam and highlight the need to reduce at-risk trading and production practices.

Risk factors associated with observed clinical lumpy skin disease in Ethiopia.

A cross-sectional study based on a questionnaire survey was conducted to determine the distribution of lumpy skin disease (LSD) and associated risk factors in three main agro-climatic zones of Ethiopia. A total of 330 questionnaire surveys were collected from 44 peasant associations (PA) distributed in 15 districts. Across agro-climate zones, herd-level LSD prevalence in the midland agro-climate was significantly higher 55.2% [95% confidence interval (CI) 47.5-62.6] than in highland and lowland agro-climate zones. Overall observed LSD prevalence at animal-level was 8.1% (95% CI 7.3-8.9) and observed mortality was 2.12% (95% CI 1.73-2.6). The odds ratio (OR) of LSD occurrence in midland vs. highland and lowland vs. highland zones was 3.86 (95% CI 2.61-5.11) and 4.85 (95% CI 2.59-7.1), respectively. Significantly high risk of LSD occurrence was associated with communal grazing and watering management (OR 4.1, 95% CI 2.02-6.18) and introduction of new cattle (OR 8.5, 95% CI 6.0-11.0). Our findings describe the distribution of LSD in different agro-climates in Ethiopia along with associated risk factors, and can help shed light on the epidemiology of LSD in other African countries suffering from the disease.

Environmental risk factors of West Nile virus infection of horses in the Senegal River basin.

In 2005, a serological study was carried out on horses in five ecologically contrasted zones of the Senegal River basin (Senegal) to assess West Nile virus (WNV) transmission and investigate underlying environmental risk factors. In each study zone, horses were randomly selected and blood samples taken. A land-cover map of the five study areas was built using two satellite ETM+ images. Blood samples were screened by ELISA for anti-WNV IgM and IgG and positive samples were confirmed by seroneutralization. Environmental data were analysed using a principal components analysis. The overall IgG seroprevalence rate was 85% (n=367; 95% CI 0.81-0.89). The proximity to sea water, flooded banks and salted mudflats were identified as protective factors. These environmental components are unfavourable to the presence of Culex mosquitoes suggesting that in Senegal, the distribution of the vector species is more limiting for WNV transmission than for the hosts' distribution.

Modeling survival at multi-population scales using mark-recapture data.

The demography of vertebrate populations is governed in part by processes operating at large spatial scales that have synchronizing effects on demographic parameters over large geographic areas, and in part, by local processes that generate fluctuations that are independent across populations. We describe a statistical model for the analysis of individual monitoring data at the multi-population scale that allows us to (1) split up temporal variation in survival into two components that account for these two types of processes and (2) evaluate the role of environmental factors in generating these two components. We derive from this model an index of synchrony among populations in the pattern of temporal variation in survival, and we evaluate the extent to which environmental factors contribute to synchronize or desynchronize survival variation among populations. When applied to individual monitoring data from four colonies of the Atlantic Puffin (Fratercula arctica), 67% of between-year variance in adult survival was accounted for by a global spatial-scale component, indicating substantial synchrony among colonies. Local sea surface temperature (SST) accounted for 40% of the global spatial-scale component but also for an equally large fraction of the local-scale component. SST thus acted at the same time as both a synchronizing and a desynchronizing agent. Between-year variation in adult survival not explained by the effect of local SST was as synchronized as total between-year variation, suggesting that other unknown environmental factors acted as synchronizing agents. Our approach, which focuses on demographic mechanisms at the multi-population scale, ideally should be combined with investigations of population size time series in order to characterize thoroughly the processes that underlie patterns of multi-population dynamics and, ultimately, range dynamics.

How does farmer connectivity influence livestock genetic structure? A case-study in a Vietnamese goat population.

Assessing how genes flow across populations is a key component of conservation genetics. Gene flow in a natural population depends on ecological traits and the local environment, whereas for a livestock population, gene flow is driven by human activities. Spatial organization, relationships between farmers and their husbandry practices will define the farmer's network and so determine farmer connectivity. It is thus assumed that farmer connectivity will affect the genetic structure of their livestock. To test this hypothesis, goats reared by four different ethnic groups in a Vietnamese province were genotyped using 16 microsatellites. A Bayesian approach and spatial multivariate analysis (spatial principal component analysis, sPCA) were used to identify subpopulations and spatial organization. Ethnic group frequencies, husbandry practices and altitude were used to create cost maps that were implemented in a least-cost path approach. Genetic diversity in the Vietnamese goat population was low (0.508) compared to other local Asian breeds. Using a Bayesian approach, three clusters were identified. sPCA confirmed these three clusters and also that the genetic structure showed a significant spatial pattern. The least-cost path analysis showed that genetic differentiation was significantly correlated (0.131-0.207) to ethnic frequencies and husbandry practices. In brief, the spatial pattern observed in the goat population was the result of complex gene flow governed by the spatial distribution of ethnic groups, ethnicity and husbandry practices. In this study, we clearly linked the livestock genetic pattern to farmer connectivity and showed the importance of taking into account spatial information in genetic studies.

Assessing the impact of climate variation on survival in vertebrate populations.

The impact of the ongoing rapid climate change on natural systems is a major issue for human societies. An important challenge for ecologists is to identify the climatic factors that drive temporal variation in demographic parameters, and, ultimately, the dynamics of natural populations. The analysis of long-term monitoring data at the individual scale is often the only available approach to estimate reliably demographic parameters of vertebrate populations. We review statistical procedures used in these analyses to study links between climatic factors and survival variation in vertebrate populations. We evaluated the efficiency of various statistical procedures from an analysis of survival in a population of white stork, Ciconia ciconia, a simulation study and a critical review of 78 papers published in the ecological literature. We identified six potential methodological problems: (i) the use of statistical models that are not well-suited to the analysis of long-term monitoring data collected at the individual scale; (ii) low ratios of number of statistical units to number of candidate climatic covariates; (iii) collinearity among candidate climatic covariates; (iv) the use of statistics, to assess statistical support for climatic covariates effects, that deal poorly with unexplained variation in survival; (v) spurious detection of effects due to the co-occurrence of trends in survival and the climatic covariate time series; and (vi) assessment of the magnitude of climatic effects on survival using measures that cannot be compared across case studies. The critical review of the ecological literature revealed that five of these six methodological problems were often poorly tackled. As a consequence we concluded that many of these studies generated hypotheses but only few provided solid evidence for impacts of climatic factors on survival or reliable measures of the magnitude of such impacts. We provide practical advice to solve efficiently most of the methodological problems identified. The only frequent issue that still lacks a straightforward solution was the low ratio of the number of statistical units to the number of candidate climatic covariates. In the perspective of increasing this ratio and therefore of producing more robust analyses of the links between climate and demography, we suggest leads to improve the procedures for designing field protocols and selecting a set of candidate climatic covariates. Finally, we present recent statistical methods with potential interest for assessing the impact of climatic factors on demographic parameters.

An explicit approach to evolutionarily stable dispersal strategies: no cost of dispersal.

The evolution of dispersal is examined by looking at evolutionarily stable strategies (ESS) for dispersal parameters in discrete time multisite models without any cost of dispersal. ESS are investigated analytically, based on explicit results on sensitivity analysis of matrix models. The basic model considers an arbitrary number of sites and a single age class. An ESS for dispersal parameters is obtained when the spatial reproductive values, calculated at the density-dependent population equilibrium, are equal across sites. From this basic formulation, one derives equivalently that all local populations should be at equilibrium in the absence of migration, and that dispersal between sites should be balanced, i.e., the numbers of individuals arriving to and leaving a site are equal. These results are then generalized to a model with several age classes. Equal age-specific reproductive values do not however imply balanced dispersal in this case. Our results generalize to any number of sites and age classes those available ¿M. Doebeli, Dispersal and dynamics, Theoret. Popul. 47 (1995) 82 for two sites and one age class.