Empirical Predictability of Community Responses to Climate Change

Robust predictions of ecosystem responses to climate change are challenging. To achieve such predictions, ecology has extensively relied on the assumption that community states and dynamics are at equilibrium with climate. However, empirical evidence from Quaternary and contemporary data suggest that species communities rarely follow equilibrium dynamics with climate change. This discrepancy between the conceptual foundation of many predictive models and observed community dynamics casts doubts on our ability to successfully predict future community states. Here we used community response diagrams (CRDs) to empirically investigate the occurrence of different classes of disequilibrium responses in plant communities during the Late Quaternary, and bird communities during modern climate warming in North America. We documented a large variability in types of responses including alternate states, suggesting that equilibrium dynamics are not the most common type of response to climate change. Bird responses appeared less predictable to modern climate warming than plant responses to Late Quaternary climate warming. Furthermore, we showed that baseline climate gradients were a strong predictor of disequilibrium states, while ecological factors such as species’ traits had a substantial, but inconsistent effect on the deviation from equilibrium. We conclude that (1) complex temporal community dynamics including stochastic responses, lags, and alternate states are common; (2) assuming equilibrium dynamics to predict biodiversity responses to future climate changes may lead to unsuccessful predictions

Habitat filtering by landscape and local forest composition in native and exotic New Zealand birds : Habitat filtering in New Zealand birds

Untangling the relative influences of environmental filtering and biotic interactions on species coexistence at various spatial scales is a long-held issue in community ecology. Separating these processes is especially important to understand the influences of introduced exotic species on the composition of native communities. For this aim, we investigated coexistence patterns in New Zealand exotic and native birds along multiple-scale habitat gradients. We built a Bayesian hierarchical model, contrasting the abundance variations of 10 native and exotic species in 501 point counts spread along landscape and local-scale gradients of forest structure and composition. Although native and exotic species both occurred in a wide range of habitats, they were separated by landscape-level variables. Exotic species were most abundant in exotic conifer plantations embedded in farmland matrices, while native birds predominated in areas dominated by continuous native forest. In exotic plantation forests, and to a lesser extent in native forests, locally co-occurring exotic and native species were segregated along a gradient of vegetation height. These results support the prediction that exotic and native bird species are segregated along gradients related to anthropogenic disturbance and habitat availability. In addition, native and exotic species overlapped little in a multivariate functional space based on 10 life history traits associated with habitat selection. Hence, habitat segregation patterns were probably mediated more by environmental filtering processes than by competition at landscape and local scales

Empirical Predictability of Community Responses to Climate Change

Robust predictions of ecosystem responses to climate change are challenging. To achieve such predictions, ecology has extensively relied on the assumption that community states and dynamics are at equilibrium with climate. However, empirical evidence from Quaternary and contemporary data suggest that species communities rarely follow equilibrium dynamics with climate change. This discrepancy between the conceptual foundation of many predictive models and observed community dynamics casts doubts on our ability to successfully predict future community states. Here we used community response diagrams (CRDs) to empirically investigate the occurrence of different classes of disequilibrium responses in plant communities during the Late Quaternary, and bird communities during modern climate warming in North America. We documented a large variability in types of responses including alternate states, suggesting that equilibrium dynamics are not the most common type of response to climate change. Bird responses appeared less predictable to modern climate warming than plant responses to Late Quaternary climate warming. Furthermore, we showed that baseline climate gradients were a strong predictor of disequilibrium states, while ecological factors such as species' traits had a substantial, but inconsistent effect on the deviation from equilibrium. We conclude that (1) complex temporal community dynamics including stochastic responses, lags, and alternate states are common; (2) assuming equilibrium dynamics to predict biodiversity responses to future climate changes may lead to unsuccessful predictions

Behavioural responses of humpback whales to food-related chemical stimuli

Publisher's version (útgefin grein)Baleen whales face the challenge of finding patchily distributed food in the open ocean. Their relatively well-developed olfactory structures suggest that they could identify the specific odours given off by planktonic prey such as krill aggregations. Like other marine predators, they may also detect dimethyl sulfide (DMS), a chemical released in areas of high marine productivity. However, dedicated behavioural studies still have to be conducted in baleen whales in order to confirm the involvement of chemoreception in their feeding ecology. We implemented 56 behavioural response experiments in humpback whales using two food-related chemical stimuli, krill extract and DMS, as well as their respective controls (orange clay and vegetable oil) in their breeding (Madagascar) and feeding grounds (Iceland and Antarctic Peninsula). The whales approached the stimulus area and stayed longer in the trial zone during krill extract trials compared to control trials, suggesting that they were attracted to the chemical source and spent time exploring its surroundings, probably in search of prey. This response was observed in Iceland, and to a lesser extend in Madagascar, but not in Antarctica. Surface behaviours indicative of sensory exploration, such as diving under the stimulus area and stopping navigation, were also observed more often during krill extract trials than during control trials. Exposure to DMS did not elicit such exploration behaviours in any of the study areas. However, acoustic analyses suggest that DMS and krill extract both modified the whales’ acoustic activity in Madagascar. Altogether, these results provide the first behavioural evidence that baleen whales actually perceive prey-derived chemical cues over distances of several hundred metres. Chemoreception, especially olfaction, could thus be used for locating prey aggregations and for navigation at sea, as it has been shown in other marine predators including seabirds.This research was funded by the Fondation Total (www.fondation.total.com), grant #144903 to A.C., and the Ministère de l'Enseignement Supérieur et de la Recherche (www.enseignementsup-recherche.gouv.fr) to B.B., Bourse doctorale. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer Reviewe

Relating Habitat and Climatic Niches in Birds

Predicting species' responses to the combined effects of habitat and climate changes has become a major challenge in ecology and conservation biology. However, the effects of climatic and habitat gradients on species distributions have generally been considered separately. Here, we explore the relationships between the habitat and thermal dimensions of the ecological niche in European common birds. Using data from the French Breeding Bird Survey, a large-scale bird monitoring program, we correlated the habitat and thermal positions and breadths of 74 bird species, controlling for life history traits and phylogeny. We found that cold climate species tend to have niche positions in closed habitats, as expected by the conjunction of the biogeographic history of birds' habitats, and their current continent-scale gradients. We also report a positive correlation between thermal and habitat niche breadths, a pattern consistent with macroecological predictions concerning the processes shaping species' distributions. Our results suggest that the relationships between the climatic and habitat components of the niche have to be taken into account to understand and predict changes in species' distributions

L'avifaune commune face aux changements anthropiques : comprendre les facteurs de vulnérabilité à travers la structure et les variations de la niche écologique

Deciphering the processes by which human activities influence the diversity of ecological systems, at various temporal and spatial scales, is at the foreground of research in conservation biology. The ecological niche appears in that respect as a relevant conceptual interface. My work addresses the implications of the structure and variations of this interface for our interpretation of the consequences of changes in landscapes, habitats and climatic conditions on biotic communities. I examine this issue through the model of European common birds, for which large-scale data bases allow quantifying the niche in a multivariate and multiscale way. My reasoning holds with three main results. First, beyond the multiplicity of niche axes, exploring their relations and structures allow inferences on the processes that drive the segregation of species along environmental gradients. Second, crossing habitat and climatic niches reveal interactions between sources of vulnerability which seem at a first glance to operate at distinct scales. Last, the breadth of the habitat niche is not only a cause, but also a consequence of species' responses to environmental variations. I explore the consequences of these three major results on our understanding of processes that sustain the taxonomic and functional diversity of biotic communities. I suggest that, beyond the traditional view of the niche as a network of nested filters, accounting explicitly for interactions between these filters and their variations would sensibly improve our ability to explain and predict the ecological effects of global changes.Comprendre les processus par lesquels les activités humaines influent sur la diversité écologique, à des échelles spatiales et temporelles diverses, est une priorité en biologie de la conservation. La niche écologique constitue à cette fin une interface conceptuelle pertinente. Ma thèse traite de l'influence de la structure et des variations de cette interface, et de leur propension à affecter notre interprétation des conséquences des modifications des paysages, des habitats et du climat sur les communautés biotiques. A partir du modèle de l'avifaune commune, pour lequel de vastes bases de données permettent une quantification de la niche multivariée et multi-échelle, je développe un argumentaire en trois volets. Le premier propose qu'au-delà de la multiplicité des axes de la niche, leurs relations et leurs structures permettent d'inférer des processus qui conduisent à la ségrégation des espèces communes le long de gradients d'habitats. Deuxièmement, croiser la niche climatique et la niche d'habitat révèle des interactions entre des sources de vulnérabilité qui semblent de prime abord opérer à des échelles différentes. Enfin, la largeur de la niche d'habitat est non seulement une cause, mais aussi une conséquence de la réponse des espèces aux variations de leur environnement. J'explore les conséquences de ces trois résultats principaux sur notre compréhension des processus qui sous-tendent la diversité taxonomique et fonctionnelle des communautés. Je propose en conclusion de dépasser la vision classique de la niche comme un ensemble de filtres aux effets spatialement et temporellement hiérarchisés, pour prendre explicitement en compte les interactions entre ces filtres et leurs variations dans l'explication et la prédiction des effets écologiques des changements globaux

Common birds facing anthropogenic changes : assessing factors of vulnerability through the structure and variations of the ecological niche

Comprendre les processus par lesquels les activités humaines influent sur la diversité écologique, à des échelles spatiales et temporelles diverses, est une priorité en biologie de la conservation. La niche écologique constitue à cette fin une interface conceptuelle pertinente. Ma thèse traite de l'influence de la structure et des variations de cette interface, et de leur propension à affecter notre interprétation des conséquences des modifications des paysages, des habitats et du climat sur les communautés biotiques. A partir du modèle de l'avifaune commune, pour lequel de vastes bases de données permettent une quantification de la niche multivariée et multi-échelle, je développe un argumentaire en trois volets. Le premier propose qu'au-delà de la multiplicité des axes de la niche, leurs relations et leurs structures permettent d'inférer des processus qui conduisent à la ségrégation des espèces communes le long de gradients d'habitats. Deuxièmement, croiser la niche climatique et la niche d'habitat révèle des interactions entre des sources de vulnérabilité qui semblent de prime abord opérer à des échelles différentes. Enfin, la largeur de la niche d'habitat est non seulement une cause, mais aussi une conséquence de la réponse des espèces aux variations de leur environnement. J'explore les conséquences de ces trois résultats principaux sur notre compréhension des processus qui sous-tendent la diversité taxonomique et fonctionnelle des communautés. Je propose en conclusion de dépasser la vision classique de la niche comme un ensemble de filtres aux effets spatialement et temporellement hiérarchisés, pour prendre explicitement en compte les interactions entre ces filtres et leurs variations dans l'explication et la prédiction des effets écologiques des changements globaux.Deciphering the processes by which human activities influence the diversity of ecological systems, at various temporal and spatial scales, is at the foreground of research in conservation biology. The ecological niche appears in that respect as a relevant conceptual interface. My work addresses the implications of the structure and variations of this interface for our interpretation of the consequences of changes in landscapes, habitats and climatic conditions on biotic communities. I examine this issue through the model of European common birds, for which large-scale data bases allow quantifying the niche in a multivariate and multiscale way. My reasoning holds with three main results. First, beyond the multiplicity of niche axes, exploring their relations and structures allow inferences on the processes that drive the segregation of species along environmental gradients. Second, crossing habitat and climatic niches reveal interactions between sources of vulnerability which seem at a first glance to operate at distinct scales. Last, the breadth of the habitat niche is not only a cause, but also a consequence of species' responses to environmental variations. I explore the consequences of these three major results on our understanding of processes that sustain the taxonomic and functional diversity of biotic communities. I suggest that, beyond the traditional view of the niche as a network of nested filters, accounting explicitly for interactions between these filters and their variations would sensibly improve our ability to explain and predict the ecological effects of global changes

Dynamiques temporelles de la diversité taxonomique des Oiseaux d’eau sur un marais salant protégé

Les marais salants reconvertis en réserves naturelles forment des habitats clés pour les Oiseaux d’eau nicheurs et en halte migratoire. Les variations abiotiques de ces milieux sont, pour une large part, contrôlées par le gestionnaire de site, offrant des conditions quasi-expérimentales pour l’étude de la dynamique des écosystèmes aquatiques littoraux. La présente étude vise à estimer l’effet des variations hydrauliques et physico-chimiques du milieu sur la diversité des Oiseaux d’eau, dans un complexe de marais salants du littoral méditerranéen (salins d’Hyères, Var). Nous avons pour cela quantifié la diversité de la communauté d’Oiseaux d’eau à partir de comptages décadaires (2013 à 2016), et l’avons corrélée à des relevés physico-chimiques (salinité, oxygénation, niveau d’eau) à partir de modèles de régression. Notre étude montre des variations temporelles de richesse spécifique, d’abondance et d’équitabilité distinctes entre groupes fonctionnels, attribuables à des fluctuations de la disponibilité en ressources et en habitat. Elle révèle par ailleurs une complémentarité dans l’usage par les Oiseaux des deux marais composant le site d’étude. Dans leur ensemble, les patrons observés décrivent une dynamique de communauté multi-échelle susceptible de contribuer à orienter une approche écosystémique de la gestion de ce type de site, tenant compte des processus régionaux et des fonctions écologiques des espèces.Saltpans converted into protected areas form key habitats for breeding and migrating waterbirds. Their abiotic variations are mainly controlled by site managers, offering near-experimental templates for the study of coastal ecosystem dynamics. The present study aims to estimate the effects of hydraulic and physico-chimical variations of water conditions in saltpans on the taxonomic diversity of waterbirds, on a study site located on the French Mediterranean shore (salins d’Hyères, Var). We quantified the species richness, total abundance and Pielou’s equitability of the local bird assemblage from standardized decadal bird counts from 2013 to 2016. We subsequently regressed these indices against measurements of water level, salinity and oxygen concentration. Our results show temporal variations in bird diversity that differ among functional guilds and match with fluctuations in resource and habitat availability. They reveal patterns of complementarity in site use within the study area. Overall, our results describe a pattern of multiscale community dynamics which could contribute to orient site management towards an ecosystem approach, accounting for regional processes and species’ ecological functions.</p

Interactions entre gestionnaires d'espaces naturels et éco-statisticiens : exemple d'une étude sur l'avifaune des salins d'Hyères, réserve Naturelle de Port-Cros

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Effets des îlots de feuillus sur les assemblages de papillons de jour dans un paysage de plantation de pins

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