•Traditional hedgerow landscapes are profoundly affected by agricultural intensification.•Amphibian richness is determined by both landscape and breeding site attributes.•Crop farming negatively ...influence landscape heterogeneity and amphibian diversity.•Wood patches have a positive effects even within areas with intensive practices.•High habitat structural heterogeneity is favorable to a diversity of amphibians.
Agricultural intensification is responsible for major habitat degradation and is a primary cause of biodiversity loss. Amphibians are currently facing a global decline induced by multiple pressures, including notably habitat degradation and land conversion. In western Europe, traditional farming systems involve a dense hedgerow network with a mosaic of pastures, cultivated fields, ponds, and small woods. These heterogeneous landscapes are particularly favorable for biodiversity but their role for amphibian conservation remain understudied.
We studied the amphibian community (15 species) of a hedgerow network landscape in western France. We described 79 cattle ponds and tested the influence of ponds characteristics as well as the surrounding landscape composition on species occurrence. Amphibian diversity was positively influenced by breeding site vegetation and also ponds density in the surrounding landscape. We also found positive effects of wood patches and hedgerow linear at a small spatial scale. In turn, crop cover and road linear negatively influenced amphibian richness at large spatial scale. Important variation were detected among species reflecting contrasted life history traits. Our results underline that traditional pastoral landscapes provide a high density of breeding sites and habitats favorable for a diversity of amphibian species.
Understanding the population dynamics of aquatic species and how inter‐specific variation in demographic and life history traits influence population dynamics is crucial to define their conservation ...status and design appropriate protection measures.
The abundance and biomass growth rates for 18 common European freshwater fish species were estimated using data spanning 1990–2011 for 546 sites across France. Fish‐length trends were assessed using quantile regressions and correlations with life history traits were investigated.
Amongst the 18 species, eleven of them have exhibited a significant decline in abundance and 14 species declined in biomass, seven remained stable or exhibited positive abundance growth rates; for four species, biomass was stable or increased. Of the demographic and ecological traits investigated, life‐history strategy and maximum length were significantly correlated with species’ population growth rates, revealing that the decline mainly concerned large‐bodied species with slow life‐histories.
These results focus on 18 common European species representing 94% of fish captured during the study period within the French national monitoring programme and underline that more attention should be paid to the decline in common species. Population dynamics of widely distributed common species are key drivers of communities and of importance to ecosystem function.
This study provides evidence of declines in common European freshwater fish species at a national scale and recommends conservation measures to favour recovery of most declining species. We highlight the crucial value of electrofishing monitoring programmes to assess freshwater fish species population trajectories and to support environmental management and conservation policy based on scientific evidences.
The marine realm suffers from cumulative causes of biodiversity erosion and world seabird community declined by 50 % since 1970. Seabirds routinely transgress regional and international boundaries ...and threat assessments should be performed at large spatial scales. We studied the demographic consequences of transnational Spanish longline fisheries bycatch on vulnerable Scopoli's shearwater (Calonectris diomedea) populations in the French Mediterranean. First, we assessed space use for 174 shearwaters breeding in the Calanques National Park (NP) using GPS-tracking between 2011 and 2022. By matching this information with a published bycatch risk map for Mediterranean Spain, we found that shearwaters largely overlapped with Spanish longline fisheries. Second, we calculated Spanish demersal longline bycatch on shearwater populations of Calanques and Port-Cros NPs, using bycatch reports, ring recoveries and ringing effort. Annually, Spanish demersal longline fisheries killed 5.3 birds (95 % CI = 0.4–14.2; 0.5 % of the population) from the Calanques NP and 8.1 birds (0.5–21.6; 2.6 % of the population) from Port-Cros NPs. Third, we assessed the demographic consequences of this bycatch using multi-event capture-recapture models and matrix population modeling based on long-term nest monitoring. Adult survival was low (0.84 to 0.92) relative to other Procellariiforms. Even though annual shearwater casualties on Spanish demersal longline seem modest, they may compromise the persistence of several French Scopoli's populations within 50 years. We demonstrate the importance of designing marine conservation at international scales for highly mobile species, to fully embrace the cumulative effects of marine anthropogenic threats on adult seabird survival, the main leverage effect for long-lived vulnerable populations.
•Seabirds suffer from the transnational cumulative impacts of fisheries bycatch.•The French Scopoli's shearwater population largely overlaps with Spanish fisheries.•Demersal Spanish longliners kill up to 3 % of French colonies annually on average.•Spanish bycatch therefore accelerates French shearwater population decline.•Highly mobile species require an international approach to marine conservation.
The estimation of population size and its variation across space and time largely relies on counts of individuals, generally carried out within spatial units such as quadrats or sites. Missing ...individuals during counting (i.e. imperfect detection) results in biased estimates of population size and trends. Imperfect detection has been shown to be the rule in animal studies, and most studies now correct for this bias by estimating detection probability. Yet this correction remains exceptional in plant studies, suggesting that most plant ecologists implicitly assume that all individuals are always detected.
To assess if this assumption is valid, we conducted a field experiment to estimate individual detection probability in plant counts conducted in 1 × 1 m quadrats. We selected 30 herbaceous plant species along a gradient of conspicuousness at 24 sites along a gradient of habitat closure, and asked groups of observers to count individuals in 10 quadrats using three counting methods requiring progressively increasing times to complete (quick count, unlimited count and cell count). In total, 158 participants took part in the experiment, allowing an analysis of the results of 5024 counts.
Over all field sessions, no observer succeeded in detecting all the individuals in the 10 quadrats. The mean detection rate was 0.44 (ranging from 0.11 to 0.82) for the quick count, 0.59 for the unlimited count (range 0.18–0.87) and 0.74 for the cell count (range 0.46–0.94).
Detection probability increased with the conspicuousness of the target species and decreased with the density of individuals and habitat closure. The observer's experience in botany had little effect on detection probability, whereas detection was strongly affected by the time observers spent counting. Yet although the more time‐consuming methods increased detection probability, none achieved perfect detection, nor did they reduce the effect on detection probability of the variables we measured.
Synthesis. Our results show that detection is imperfect and highly heterogeneous when counting plants. To avoid biased estimates when assessing the size, temporal or spatial trends of plant populations, plant ecologists should use methods that estimate the detection probability of individuals rather than relying on raw counts.
Résumé
L'estimation de la taille d'une population et de ses variations dans l'espace et dans le temps repose en grande partie sur des comptages d'individus, généralement effectués dans des unités spatiales telles que des quadrats ou des sites. Manquer des individus lors de comptages (c'est‐à‐dire la détection imparfaite) entraîne des estimations biaisées des tailles et des tendances des populations. Il a été montré que la détection imparfaite est la règle dans les études sur les animaux, et la plupart des études corrigent désormais ce biais en estimant la probabilité de détection. Pourtant, cette correction reste exceptionnelle dans les études sur les plantes, ce qui suggère que la plupart des écologues des plantes supposent implicitement que tous les individus sont toujours détectés.
Pour évaluer la validité de cette hypothèse, nous avons mené une expérience sur le terrain afin d'estimer la probabilité de détection des individus lors de comptages de plantes effectués dans des quadrats de 1 × 1 m. Nous avons sélectionné 30 espèces de plantes herbacées réparties sur un gradient de visibilité au sein de 24 sites présentant un gradient de fermeture de l'habitat. Pour chaque espèce, nous avons demandé à un groupe d'observateurs de compter les individus dans 10 quadrats à l'aide de trois méthodes de comptage nécessitant un temps de prospection croissant (le comptage rapide, le comptage sans limite de temps et le comptage par cellule). Au total, 158 participants ont pris part à l'expérience, ce qui a permis d'analyser les résultats de 5024 comptages.
Sur l'ensemble des sessions de terrain, aucun observateur n'a réussi à détecter tous les individus dans les 10 quadrats. Le taux de détection moyen était de 0,44 (variant de 0,11 à 0,82) pour le comptage rapide, de 0,59 pour le comptage sans limite de temps (variant de 0,18 à 0,87) et de 0,74 pour le comptage par cellule (variant de 0,46 à 0,94).
La probabilité de détection augmentait avec la visibilité de l'espèce ciblée et diminuait avec la densité des individus et la fermeture de l'habitat. L'expérience en botanique de l'observateur avait peu d'effet sur la probabilité de détection, alors que la détection était fortement influencée par le temps que les observateurs consacraient au comptage. Cependant, bien que les méthodes nécessitant le plus de temps augmentaient la probabilité de détection, aucune n'a permis d'atteindre la détection parfaite, ni de réduire l'effet sur la probabilité de détection des variables que nous avons mesurées.
Synthèse. Nos résultats montrent que la détection est imparfaite et très hétérogène lorsque l'on compte des plantes. Afin d'éviter des estimations biaisées lorsque l'on évalue la taille, les tendances temporelles ou spatiales des populations de plantes, les écologues des plantes devraient utiliser des méthodes qui estiment la probabilité de détection des individus plutôt que de se baser sur des comptages bruts.
To assess whether imperfect detection is the rule in plant studies, the authors conducted a field experiment on 30 herbaceous plant species at 24 sites, and 158 participants counted plants on 1 × 1 m quadrats. Detection was imperfect and highly heterogeneous, thus to avoid biased estimates of the size, temporal or spatial trends of plant populations, ecologists need to correct for imperfect detection.
Quantifying the demographic impact of anthropogenic fatalities on animal populations is a key component of wildlife conservation. However, such quantification remains rare in environmental impact ...assessments (EIA) of large-infrastructure projects, partly because of the complexity of implementing demographic models. Providing user-friendly demographic tools is thus an important step to fill this gap.
We developed an application called EolPop to run demographic simulations and assess population-level impacts of fatalities. This tool, freely available online, is easy to use and requires minimal input data from the user. As an output, it provides an estimate, with associated uncertainty, of the relative deficit in population size at a given time horizon. Because this impact metric is relative to a baseline scenario without fatalities, it is robust to uncertainties.
We showcase the tool using examples on two species that are affected by collisions with wind turbines: Lesser kestrel (Falco naumanni) and Eurasian skylark (Alauda arvensis). After 30 years, the kestrel's population is expected to suffer a deficit of ca. 48%. In contrast, the impact on skylarks, which are already declining in France, is estimated to be fairly low (ca. 7%).
EolPop aims at providing a robust quantification of the relative impact of fatalities. This tool was originally built for windfarm EIA, with a focus on birds, but it can be used to assess the demographic consequences of any type of fatalities on any species.
•Birds and bats are susceptible to collisions with wind turbines.•Assessing population impacts of collisions is mandatory, but it remains difficult.•Current practices are based on expert judgment, a method that lacks objectivity.•EolPop is an operational and standardized tool that quantifies demographic impacts.•This tool improves the quality and objectivity of environmental impact assessments.
Effective conservation management of wildlife species depends on understanding their space and habitat use. Telemetry has become the primary source of data for information on how species use space ...and habitats. However, animals can be difficult to capture, leading to limited sample sizes and thus low quality inferences. As some individuals may be easier to capture than others, it may be tempting to use them to make inferences about the studied population as a whole. Juvenile birds, in contrast to adults, are easy to capture while they are still in the nest. However, there are few studies on when and how they might serve to obtain a representative characterization of the habitat or space use of adults. This study investigated this by using GPS‐tracking data of 35 adult/juvenile dyads of golden eagles Aquila chrysaetos, with the juvenile and adult in a dyad sharing the same home‐range. We assessed juvenile‐to‐adult home‐range overlap and also compared their relative use of habitats within that space. We also analysed how these metrics evolved throughout the post‐fledging dependence period (PFDP). During this period, juvenile‐to‐adult similarity was more than 80% for the entire home‐range, whereas it was lower for the core area (approximately 60%). Habitat‐use similarity was high, at approximately 90% for both the home‐range and core area, both in land‐cover and topography. The similarity increased following the improvement of juvenile flight skills over a period of two months, to the extent that two months after fledging and until the end of the PFDP, habitat and space use of juveniles can be used to infer the home‐range and habitat requirements of adults. It would be valuable to study this ‘adult‐by‐juvenile replacement' approach in other species to determine whether it could be generalized, notably for species with a shorter dependence period or more complex social interactions.
Dispersal (i.e. movement from a natal or breeding site to another breeding site) is a central process in ecology and evolution as it affects the eco‐evolutionary dynamics of spatially structured ...populations. Dispersal evolution is regulated by the balance between costs and benefits, which is influenced by the individual phenotype (i.e. phenotype‐dependent dispersal) and environmental factors (i.e. condition‐dependent dispersal). Even though these processes have been extensively studied in species with simple life cycles, our knowledge about these mechanisms in organisms displaying complex life cycles remains fragmentary. In fact, little is specifically known about how the interplay between individual and environmental factors may lead to alternative dispersal strategies that, in turn, lead to the coexistence of contrasted site fidelity phenotypes. In this paper, we examined breeding dispersal in a pond‐breeding amphibian, the great crested newt Triturus cristatus, within usual walking distances for a newt. We took advantage of recent developments in multi‐event capture–recapture models and used capture–recapture data (946 newts marked) collected in a spatially structured population occupying a large pond network (73 ponds). We showed a high rate of breeding site infidelity (i.e. pond use) and the coexistence of two dispersal phenotypes, namely, a highly pond faithful phenotype and a dispersing phenotype. Individuals that were site faithful at time t – 1 were therefore more likely to remain site faithful at time t. Our results also demonstrated that the probability that individuals belong to one or the other dispersal phenotypes depended on environmental and individual factors. In particular, we highlighted the existence of a dispersal syndrome implying a covariation pattern among dispersal behavior, body size, and survival. Our work opens new research prospects in the evolution of dispersal in organisms displaying complex life cycles and raises interesting questions about the evolutionary pathways that contribute to the diversification of movement strategies in the wild.
The post‐fledging dependence period (PFDP), which extends from a fledgling's first flight out of the nest to its departure from the parents' territory, is crucial in the lifecycle of birds. During ...this period, juveniles develop their flight and foraging skills to become fully independent. Despite the importance of this life stage in basic bird ecology and conservation, it remains largely overlooked – notably its link with the acquisition of flight skills. In this study, we modeled the variation in seven proxies describing flight skills of 84 GPS‐tracked golden eagle juveniles in France between 2016 and 2020. Juveniles had a long but highly variable PFDP, averaging 177.9 (± 62.2) days after departure from the nest. This period is divided into two phases: a first phase of rapid increase in flight skills over the first 60 days after departure from the nest, followed by a plateau in which flight skills no longer develop until independence. These results suggest that the full development of flight skills is not a constraining factor during the PFDP and that it is advantageous for juveniles to choose to remain in their natal territory. We posit that parents' tolerance of fledged juveniles is a type of parental care that may maximize their own fitness by improving the survival of their descendants. In future studies, it may be of interest to investigate the factors that may explain the high variability in the duration of this stage between individuals within the same population.
Abstract Population monitoring programmes typically rely on sampling because it is impossible to survey all the sites within the study area. In such a situation, the general recommendation to obtain ...unbiased estimates of population trends is to select monitoring sites using probability sampling. However, site selection not based on probability sampling, such as selecting sites with the largest abundance of individuals at the beginning of the monitoring programme, is common in practice. Nevertheless, these methods carry the risk of obtaining biased trend estimates. Using simulations, McClure & Rolek (2023) investigated whether three non‐probability sampling site selection methods can yield unbiased trend estimates under some specific conditions. For two of these methods, that is selecting high quality sites and selecting sites known to be occupied, the authors conclude that there is a major risk of obtaining biased trend estimates. For the third method, that is selecting sites with the largest initial abundance, they found conditions in which unbiased estimates can be obtained. They conclude that the general recommendation to use probability sampling should be revised. Here, we show that the authors' results, although perfectly correct, do not invalidate this recommendation. First, we point out that the authors made strong assumptions about the populations' functioning in their simulations, especially that inter‐annual variance in abundance is similar for all sites, which is unlikely in most real populations. We show through simple simulations that even slightly relaxing this assumption invalidates the authors' results. We also point out that for most of the hypotheses made by the authors, it is generally not known at the beginning of a study whether they will be respected. Furthermore, the authors did not provide evidence that selecting sites based on high initial abundance leads to more precise trend estimates than probability sampling methods. Therefore, neither the benefits nor the risks of this method are known. We conclude that until evidence is provided that abundance‐based site selection improves estimate precision and the situations in which it provides unbiased estimates are clearly identified, using probability sampling should remain the rule.
Résumé Les programmes de suivi des populations reposent généralement sur de l'échantillonnage car il est impossible de suivre tous les sites de la zone d'étude. Dans de telles situations, la recommandation générale pour obtenir des estimations non biaisées des tendances de population est de sélectionner les sites suivis via une méthode d'échantillonnage probabiliste. Cependant, dans la pratique il est courant que les sites ne soient pas sélectionnés sur la base d'un échantillonnage probabiliste, par exemple en choisissant les sites présentant la plus grande abondance d'individus de l'espèce cible au début du programme de suivi. Néanmoins, ces méthodes engendrent un risque élevé d'obtenir des estimations biaisées des tendances. En utilisant des simulations, McClure & Rolek (2023) ont cherché à savoir si trois méthodes de sélection des sites par échantillonnage non probabiliste peuvent produire des estimations non biaisées des tendances dans certaines conditions spécifiques. Pour deux de ces méthodes, à savoir sélectionner des sites de haute qualité et sélectionner des sites connus pour être occupés par l'espèce cible, les auteurs concluent qu'il y a un risque majeur d'obtenir des estimations biaisées des tendances. Pour la troisième méthode, c'est‐à‐dire sélectionner les sites avec la plus grande abondance initiale, ils ont trouvé des conditions dans lesquelles des estimations non biaisées peuvent être obtenues. Ils concluent que la recommandation générale d'utiliser l'échantillonnage probabiliste devrait être révisée. Nous montrons ici que les résultats des auteurs, bien que parfaitement corrects, n'invalident absolument pas cette recommandation. Tout d'abord, nous signalons que les auteurs ont fait des hypothèses fortes sur le fonctionnement des populations dans leurs simulations, et en particulier que la variance interannuelle de l'abondance est similaire pour tous les sites, ce qui est peu probable pour la plupart des populations réelles. Nous montrons à l'aide de simulations simples que même un léger relâchement de cette hypothèse invalide les résultats des auteurs. Nous soulignons également que pour la plupart des hypothèses formulées par les auteurs, il n'est généralement pas possible de savoir au début d'une étude si elles seront respectées ou non. En outre, les auteurs n'ont pas apporté de preuve que sélectionner les sites sur la base d'une abondance initiale élevée conduit à des estimations plus précises des tendances que les méthodes d'échantillonnage probabiliste. Ainsi, les avantages et les risques de cette méthode sont inconnus. Nous concluons que jusqu'à ce qu'il soit prouvé que sélectionner les sites suivis en fonction de l'abondance améliore la précision des estimations des tendances de population et que les situations dans lesquelles cette méthode fournit des estimations non biaisées soient clairement identifiées, utiliser l'échantillonnage probabiliste pour sélectionner les sites suivis doit rester la règle.
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