852 research outputs found
Determining range edges: habitat quality, climate or climate extremes?
No full textAimClimate change is predicted to adversely affect wildlife populations at the trailing edge of their range, with extreme weather events acting as a catalyst for local extinctions and range contractions. We assessed the relative importance of long-term climate averages, short-term drought and habitat in predicting species occupancy and range edge, using the koala (Phascolarctos cinereus) as a case study
The effects of environment and niche on the distributions of dwarf chameleons, present and future
No full textIncludes bibliographical references.The niche and niche breadth of Dwarf Chameleons, Bradypodion, was assessed in terms of broad scale climatic factors. A niche-based modelling method was then used to construct present and future habitat suitability maps for 2050 and 2080, for species in the genus. Additionally, the relationship between environment and morphology was analysed for a representative Bradypodion species, the Cape Dwarf Chameleon, B. pumilum. The niche and niche breadth of species and phylogenetic clades were analysed and described via an ordination technique, the outlying mean index (OMI) analysis. Maxent (v2.3), a presence only niche modelling method, proved very useful in the construction of present and future habitat suitability maps for species within the genus. For analysis of the correspondence between environment and morphology for B. pumilum, regression trees were employed. Rainfall seasonality and maximum annual temperatures were shown to strongly effect the current distributions of the genus Bradypodion at both the species and clade level. Additionally, as closely related species inhabited similar environmental niches, the genus was shown to display a degree of niche conservatism. All species and clades were shown to respond to climate change scenarios for 2050 and 2080, but responses were individualistic. However, most demonstrated range contractions under predicted climate scenarios. Additionally, a strong correlation (p < 0.05) was found between the morphology of B. pumilum and its environment. Environmental factors explained over 40% of the variation in snout-vent length and tail length, and over 20% of the variation in head width and head height, thus supporting the hypothesis of a correspondence between vegetation and morphology in Bradypodion. These results have provided an understanding of the relationship between Bradypodion and their environments that could provide valuable information regarding their ecology. Additionally, the habitat suitability maps for 2050 and 2080 could prove useful in the construction of any future conservation plans for these species. Furthermore, the results support the hypothesis of a correspondence between environmental factors and morphological traits within the genus Bradypodion
The contribution of vegetation and landscape configuration for predicting environmental change impacts on Iberian birds
No full textAlthough climate is known to be one of the key factors determining animal species distributions amongst others, projections of global change impacts on their distributions often rely on bioclimatic envelope models. Vegetation structure and landscape configuration are also key determinants of distributions, but they are rarely considered in such assessments. We explore the consequences of using simulated vegetation structure and composition as well as its associated landscape configuration in models projecting global change effects on Iberian bird species distributions. Both present-day and future distributions were modelled for 168 bird species using two ensemble forecasting methods: Random Forests (RF) and Boosted Regression Trees (BRT). For each species, several models were created, differing in the predictor variables used (climate, vegetation, and landscape configuration). Discrimination ability of each model in the present-day was then tested with four commonly used evaluation methods (AUC, TSS, specificity and sensitivity). The different sets of predictor variables yielded similar spatial patterns for well-modelled species, but the future projections diverged for poorly-modelled species. Models using all predictor variables were not significantly better than models fitted with climate variables alone for ca. 50% of the cases. Moreover, models fitted with climate data were always better than models fitted with landscape configuration variables, and vegetation variables were found to correlate with bird species distributions in 26–40% of the cases with BRT, and in 1–18% of the cases with RF. We conclude that improvements from including vegetation and its landscape configuration variables in comparison with climate only variables might not always be as great as expected for future projections of Iberian bird species
Vulnerability of mountainous ecosystems to global change - a spatially explicit modeling approach and conservation implications
No full textLes conséquences des récents changements environnementaux sont déjà observables sur les écosystèmes du monde entier et menacent la biodiversité. Dans l'objectif de conserver les bénéfices que nous procurent les écosystèmes, l'enjeu est de comprendre et prédire la dynamique spatiale et temporelle des paysages et de la biodiversité afin de mieux anticiper les changements possibles et adapter les décisions de conservation. En zone de montagne, où l'environnement est très hétérogène, les effets combinés des modifications du climat et de l'agriculture sont susceptibles d'avoir un impact important sur les écosystèmes. La présente thèse a pour objectif principal de caractériser les espèces et les habitats vulnérables aux changements climatiques et changements d'utilisation des terres dans les Alpes Françaises. Elle apporte sa contribution en se basant sur des données accumulées par le Conservatoire Botanique National Alpin et le Parc national des Ecrins (PNE), et en utilisant trois angles d'approche complémentaires. Dans une première partie, les cadres théoriques expliquant la coexistence des espèces et leur répartition spatiale ont été testés empiriquement. Les patrons de rareté des plantes des Alpes françaises ont ainsi été reliés aux caractéristiques des espèces, mettant en évidence les compromis entre différentes stratégies fonctionnelles. Une seconde analyse de la répartition de 21 espèces cibles a démontré la différence entre les facteurs expliquant la présence d'une espèce à un endroit donné et ceux expliquant son abondance. Cette analyse a également permis de souligner l'importance de la dispersion et mis en évidence des dynamiques source-puits chez certaines espèces. La deuxième partie s'appuie sur les mêmes cadres théoriques et a consisté à développer un modèle dynamique de la structure et de la diversité de la végétation. Ce modèle a été calibré et validé sur la végétation du PNE. Une troisième partie porte son attention sur les évolutions possibles de la végétation sous plusieurs scénarios de changements climatiques et d'utilisation des terres. Les simulations ont montré qu'il est nécessaire de considérer la dynamique temporelle du fait que les conséquences d'un changement climatique peuvent être observées bien après la phase du changement. D'autre part, l'analyse a montré les effets conjugués que peuvent avoir les changements climatiques et la déprise agricole sur la structure de la végétation. Un tel modèle ouvre la voie à l'exploration de multiples scenarios, en permettant non seulement de décrire des paysages futurs potentiels mais aussi les états de transition qui devraient y mener.On-going global changes have already affected ecosystems and threaten the biodiversity all over the world. In order to maintain the ecosystems services provided to humans and adapt conservation planning, the challenge is to improve our understanding of the mechanisms underlying the maintenance of biodiversity and to predict its response to global changes. In mountainous areas, where the environment is very heterogeneous, the modifications of both climate and land use are expected to strongly influence the landscapes and current biodiversity. This PhD thesis has for main objective to assess the vulnerability of species and habitat to environmental changes in the French Alps. It uses three different approaches and relies on the large databases accumulated by two institutions: the National Alpine Botanical Conservatory and the Ecrins National Park (PNE). The first part of the PhD confronts theoretical hypotheses for species coexistence to observations and describes the characteristics of the regional flora. The species ecological niche breadth has been estimated and related to other rarity facets and trade-off between plant functional strategies. A second analysis disentangles the drivers of the presence or the local abundance of 21 focal species and highlights the importance of the dispersion and the source-sink dynamics. The second part is based on the same conceptual background and aims to develop a dynamic model of the vegetation structure and diversity. The model has been validated for the vegetation of the PNE. The last part proposes an application of this dynamic model to provide multiple biodiversity scenarios in respect to change in both climate and land management. The simulations showed that the consequences of climate change might be visible only after a certain time-lag, demonstrating the interest of considering the spatial but also temporal vegetation dynamics. Furthermore, the analysis pointed out the importance of the interplay effects between climate and land use abandonment. Such a model should pave the way for the exploration of multiples scenarios and will be able to describe not only the potential future landscapes but also the transition states leading to it
Why would plant species become extinct locally if growing conditions improve?
No full textwo assumptions underlie current models of the geographical ranges of perennial plant species: 1. current ranges are in equilibrium with the prevailing climate, and 2. changes are attributable to changes in macroclimatic factors, including tolerance of winter cold, the duration of the growing season, and water stress during the growing season, rather than to biotic interactions. These assumptions allow model parameters to be estimated from current species ranges. Deterioration of growing conditions due to climate change, e.g. more severe drought, will cause local extinction. However, for many plant species, the predicted climate change of higher minimum temperatures and longer growing seasons means, improved growing conditions. Biogeographical models may under some circumstances predict that a species will become locally extinct, despite improved growing conditions, because they are based on an assumption of equilibrium and this forces the species range to match the species-specific macroclimatic thresholds. We argue that such model predictions should be rejected unless there is evidence either that competition influences the position of the range margins or that a certain physiological mechanism associated with the apparent improvement in growing conditions negatively affects the species performance. We illustrate how a process-based vegetation model can be used to ascertain whether such a physiological cause exists. To avoid potential modelling errors of this type, we propose a method that constrains the scenario predictions of the envelope models by changing the geographical distribution of the dominant plant functional type. Consistent modelling results are very important for evaluating how changes in species areas affect local functional trait diversity and hence ecosystem functioning and resilience, and for inferring the implications for conservation management in the face of climate change
Dataset on 10 common alien plants in French grasslands
No full textData to build a multi-species hierarchical model of
the distribution of the ten most widespread alien plants in French grasslands, based on a subset of the DIVGRASS dataset of more than 50000 plant community plots. It allows testing how plant traits (height, specific leaf area (SLA) and seed mass) affect alien species occurrence along
gradients of human pressure, environmental conditions and native community
composition.Dataset from the paper:Carboni, M., Calderon-Sanou, I., Pollock, L., Violle, C., Thuiller, W. 2018. Functional traits modulate alien species response to environmental, biotic and human gradients. Global Ecology and Biogeography</div
Towards a better understanding of soil multi-trophic biodiversity through the use of environmental DNA metabarcoding
No full textBien que les organismes du sol représentent un quart de la biodiversité totale de la planète, notre compréhension actuelle des principaux moteurs de la biodiversité du sol le long des gradients environnementaux est principalement limitée à un ensemble restreint de macro-organismes de surface. À la lumière des menaces mondiales croissantes qui pèsent sur les écosystèmes, l'inclusion des organismes du sol dans les études macroécologiques est cruciale pour améliorer les prévisions des réponses écologiques des écosystèmes terrestres aux changements globaux et pour soutenir leur conservation. En outre, les approches multitrophiques qui tiennent compte de plusieurs groupes d'organismes en interaction dans l'écosystème permettent une compréhension plus holistique de la biodiversité du sol et de ses moteurs.Dans ma thèse, j'ai cherché à mieux comprendre la réponse de la diversité multitrophique du sol aux changements environnementaux rapides à l'échelle régionale et locale, en combinant les données de métabarcodage de l'ADN environnemental du sol, les outils mathématiques et statistiques dérivés de la théorie des réseaux et l'écologie des réseaux alimentaires.La thèse est développée en quatre chapitres. Tout d'abord, parce que la plupart des analyses sont basées sur des données de métabarcodage de l'ADN environnemental, j'ai eu besoin de mieux comprendre les incertitudes associées à l'utilisation du métabarcodage de l'ADN environnemental dans les analyses empiriques. Dans le premier chapitre, j'ai montré que l'utilisation de la diversité de Shannon permettait d'obtenir des résultats plus fiables dans différentes analyses écologiques. J'ai ensuite proposé une feuille de route des étapes cruciales à inclure dans le nettoyage des données pour différents types d'analyses écologiques. Ensuite, à l'aide de données d'ADN environnemental du sol provenant de forêts de bouleaux subarctiques du nord de la Norvège, j'ai montré que l'effet des épidémies de papillons s'est propagé localement des communautés végétales à l'ensemble du réseau trophique du sol, créant un changement dans l'état de l'écosystème. Ensuite, j'ai étudié comment la diversité multitrophique du sol répondait aux gradients environnementaux en utilisant un observatoire de la biodiversité à grande échelle dans les Alpes françaises (chapitres 3 et 4). Dans le troisième chapitre, j'ai mené une analyse comparative entre les principaux groupes trophiques du sol pour évaluer les moteurs de la diversité du sol à la lumière d'hypothèses écologiques bien connues appliquées au contexte du sol. J'ai constaté que les hypothèses d’energie et de tolerance physiologique étaient particulièrement pertinentes pour prédire la variation spatiale de la biodiversité du sol. Enfin, dans le quatrième chapitre, j'ai décrit comment la structure et la composition des réseaux trophiques du sol variaient le long des gradients environnementaux et spaciaux et j'ai évalué les principaux moteurs de cette variation.Je pense que mon doctorat a ouvert de nouvelles voies de recherche dans la compréhension de la biodiversité multi-trophique des sols. Passer du niveau de l'espèce à une définition plus robuste des groupes trophiques et fonctionnels permet d'inclure davantage de groupes multiples et d'atteindre l'objectif ultime de comprendre la distribution et la composition de la biodiversité du sol dans son ensemble.Although soil organisms represent one-quarter of the whole biodiversity on earth, our current understanding of the main drivers of soil biodiversity along environmental gradients is mostly restricted to a limited set of aboveground macro-organisms. In light of increasing global threats to ecosystems, the inclusion of soil organisms into macroecological studies is crucial to improve predictions of ecological responses of terrestrial ecosystems to global changes and support their conservation. Moreover, multitrophic approaches that account for multiple groups of interacting organisms in the ecosystem allow a more holistic understanding of soil biodiversity and its drivers.In my PhD, I aimed at getting a better understanding of the response of soil multitrophic diversity to rapid environmental changes at regional and local scales, by combining soil environmental DNA metabarcoding data, mathematical and statistical tools derived from network theory, and food web ecology.The thesis is developed in four chapters. First, because most of the analyses were based on eDNA metabarcoding data, I needed to gain a better understanding of the uncertainties associated with the use of eDNA metabarcoding in empirical analyses. In the first chapter, I showed that the use of Shannon diversity led to more reliable results from different ecological analyses. I then proposed a roadmap of crucial curation steps for different types of ecological analyses. Second, using eDNA soil data from subarctic birch forests of Northern Norway, I showed that the effect of severe moth outbreaks has cascaded locally from plant communities to the entire soil food web, creating a shift in the ecosystem state. Next, I studied how soil multitrophic diversity responded to environmental gradients using a large-scale biodiversity observatory in the French Alps (chapters 3 and 4). In the third chapter, I conducted a comparative analysis across major soil trophic groups to assess the drivers of soil diversity in the light of well known ecological hypotheses applied to the soil context. I found that the energy and physiological tolerance hypotheses were particularly relevant in predicting the spatial variation in soil biodiversity. Finally, in the fourth chapter, I described how soil food webs structure and composition varied along environmental gradients and in the function of human activities and assessed the main drivers of this variation.I believe my PhD has opened new research avenues in the understanding of multi-trophic soil biodiversity. Zooming out from the species level to a more robust definition of trophic and functional groups allows a larger inclusion of multiple groups and to reach the ultimate goal of understanding all-in-end soil biodiversity distribution and composition
Impacts of past habitat loss and future climate change on the range dynamics of South African Proteaceae
No full textAim To assess how habitat loss and climate change interact in affecting the range dynamics of species and to quantify how predicted range dynamics depend on demographic properties of species and the severity of environmental change. Location South African Cape Floristic Region. Methods We use data-driven demographic models to assess the impacts of past habitat loss and future climate change on range size, range filing and abundances of eight species of woody plants (Proteaceae). The species-specific models employ a hybrid approach that simulates population dynamics and long-distance dispersal on top of expected spatio-temporal dynamics of suitable habitat. Results Climate change was mainly predicted to reduce range size and range filling (because of a combination of strong habitat shifts with low migration ability). In contrast, habitat loss mostly decreased mean local abundance. For most species and response measures, the combination of habitat loss and climate change had the most severe effect. Yet, this combined effect was mostly smaller than expected from adding or multiplying effects of the individual environmental drivers. This seems to be because climate change shifts suitable habitats to regions less affected by habitat loss. Interspecific variation in range size responses depended mostly on the severity of environmental change, whereas responses in range filling and local abundance depended mostly on demographic properties of species. While most surviving populations concentrated in areas that remain climatically suitable, refugia for multiple species were overestimated by simply overlying habitat models and ignoring demography. Main conclusions Demographic models of range dynamics can simultaneously predict the response of range size, abundance and range filling to multiple drivers of environmental change. Demographic knowledge is particularly needed to predict abundance responses and to identify areas that can serve as biodiversity refugia under climate change. These findings highlight the need for data-driven, demographic assessments in conservation biogeography
Effects of Harvesting Flowers from Shrubs on the Persistence and Abundance of Wild Shrub Populations at Multiple Spatial Extents
No full textWildflower harvesting is an economically important activity of which the ecological effects are poorly understood. We assessed how harvesting of flowers affects shrub persistence and abundance at multiple spatial extents. To this end, we built a process-based model to examine the mean persistence and abundance of wild shrubs whose flowers are subject to harvest (serotinous Proteaceae in the South African Cape Floristic Region). First, we conducted a general sensitivity analysis of how harvesting affects persistence and abundance at nested spatial extents. For most spatial extents and combinations of demographic parameters, persistence and abundance of flowering shrubs decreased abruptly once harvesting rate exceeded a certain threshold. At larger extents, metapopulations supported higher harvesting rates before their persistence and abundance decreased, but persistence and abundance also decreased more abruptly due to harvesting than at smaller extents. This threshold rate of harvest varied with species' dispersal ability, maximum reproductive rate, adult mortality, probability of extirpation or local extinction, strength of Allee effects, and carrying capacity. Moreover, spatial extent interacted with Allee effects and probability of extirpation because both these demographic properties affected the response of local populations to harvesting more strongly than they affected the response of metapopulations. Subsequently, we simulated the effects of harvesting on three Cape Floristic Region Proteaceae species and found that these species reacted differently to harvesting, but their persistence and abundance decreased at low rates of harvest. Our estimates of harvesting rates at maximum sustainable yield differed from those of previous investigations, perhaps because researchers used different estimates of demographic parameters, models of population dynamics, and spatial extent than we did. Good demographic knowledge and careful identification of the spatial extent of interest increases confidence in assessments and monitoring of the effects of harvesting. Our general sensitivity analysis improved understanding of harvesting effects on metapopulation dynamics and allowed qualitative assessment of the probability of extirpation of poorly studied species
Beyond species, how to preserve evolutionary history, ecosystem functioning and the direct benefit human obtain from nature
No full textLa biodiversité est définie comme la variété et la variabilité du monde vivant sous toutes ses formes. Elle est souvent appréhendée par la richesse en espèces. Pourtant il existe d'autres « facettes » de la biodiversité (telles que la diversité phylogénétique et fonctionnelle) qui sont à considérer pour comprendre la plupart des processus évolutifs et écologiques. Aujourd'hui, la prise en compte de ces différentes facettes ainsi que les services des écosystèmes –bénéfices que les humains retirent directement des écosystèmes – sont au cœur de l'agenda européen de la conservation. Cependant pour mettre en place de nouvelles actions, une meilleure compréhension des variations spatiales de ces différentes facettes et de leurs relations avec les services des écosystèmes est nécessaire. Ce travail visait à quantifier, décrire et comprendre la distribution de la richesse spécifique et de la diversité phylogénétique et fonctionnelle des tétrapodes d'Europe et leurs liens avec les services écosystémiques. L'étude des patrons spatiaux de la diversité phylogénétique pour différents groupes taxonomiques a montré une absence de recouvrement, une protection inégale et a permis d'identifier des zones particulières d'histoire évolutive indétectables par le prisme unique de la richesse spécifique. Alors que les facteurs environnementaux liés au climat (comme la température ou la productivité primaire) semblent être prépondérant pour expliquer la distribution de chaque facette de diversité, leurs influences respectives varient selon la facette considérée. Enfin, la comparaison de différents scénarios de conservation dans lesquels plus d'importance est donnée soit à la protection de la biodiversité soit à celle des services écosystémiques a mis en avant des relations complexes (synergies et compromis) et non prédictibles mettant en évidence les enjeux liés à la protection simultanée de plusieurs groupes d'espèces, plusieurs facettes de diversité et d'un éventail de services écosystémiques.Biodiversity is defined as the variety and variability of living organisms on Earth and is often measured through species richness. However, biodiversity is composed of other facets (e.g. phylogenetic and functional diversity) that need to be considered to account for evolutionary and ecological processes. Considering these multiple facets of biodiversity together with ecosystem services – direct benefit human obtain from nature – is central in the European conservation agenda. However, to propose new planning strategies, a better understanding of the spatial variation of these different facets and their relationships to ecosystem services is crucial. The objective of this Ph. D. project was to better quantify, describe and understand the spatial variation of different biodiversity facets and analyse their links to ecosystem services. The study of spatial pattern of phylogenetic diversity showed a low overlap between the different taxonomic groups and an unequal protection within the current European protected areas system. This analysis allowed identifying areas of particular evolutionary history, which would be undetectable through the unique lens of species richness. Although environmental factors related to climate (e.g. temperature, primary productivity) seemed to best explain each facet, their relative importance varied across biodiversity facets. Finally a comparison of conservation scenarios where priority was given either to protecting biodiversity protection or to protecting ecosystem services highlighted complex and unpredictable relationships (synergies and trade-offs) and stressed out the stakes linked to the simultaneous protection of different facets of diversity of multiple taxonomic groups and a set of ecosystem services
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