Piñon and juniper tree species have species-specific climatic requirements, resulting in unique distributions and differential responses to climate change. Piñons and junipers co-dominate the arid woodlands of North America as groups with widespread hybridization. Two piñons, Pinus edulis; P. monophylla, and four junipers, Juniperus deppeana var. deppeana; J. monosperma; J. occidentalis; J. osteosperma, are endemic to the midlatitude interior west and form three groups of hybridizing sister species, P. edulis-P. monophylla; J. deppeana var. deppeana-J. monosperma; J. occidentalis-J. osteosperma. Recent droughts have caused widespread mortality among piñons, but have had less impact on junipers and indicate shifts in co-occurrence have already begun in response to global climate change. Within these groups hybridization likely plays an important role in such distribution changes. The central objective of this thesis is to forecast the distributions of piñons and junipers endemic to the US under modeled climate change for the 21st century. Species distribution models are built with an emphasis placed on aligning the life cycle dynamics of the species within the temporal and spatial resolution of predictor variables, and within the modeling technique. Two concerns surrounding species distribution modeling are addressed. First, concerns regarding the extent to which species are at equilibrium with the current climate are addressed by incorporating dispersal into the model building process. Second, concerns regarding the potential role of hybridization between closely related species are addressed by building distribution models for each of the three sister species groups as well as the six component species. Species distribution models exhibited individualistic responses to modeled climate change. Modeled areal loss was greater than gain for all species, which is reflected in changes of co-occurrence. Piñon-juniper richness is forecast to increase in the northern Colorado Plateau, eastern Great Basin, and Rocky Mountains. The sister-species models forecast greater areal gain, and less areal loss, along hybridization zones for P. edulis-P. monophylla and for J. occidentalis-J. osteosperma, but forecast greater areal loss along the periphery of the component species distributions. The sister-species model for J. deppeana var. deppeana-J. monosperma forecasts overall greater areal loss than the component species. In general, forecast changes in latitude and elevation are about one third of the changes inferred, from the fossil record, to have occurred following the transition to the current interglacial ~10,000 years ago.

Global change profoundly alters biological communities and increases species extinction rates. Recent reports show that odonate species (dragonflies and damselflies) are declining globally, however, odonates can also respond strongly to climate and land use change through shifts in range and phenology - i.e., the timing of life history events. Understanding how and when species respond to rapid environmental change is critical to address conservation risks in a timely way. I assembled a dataset of ~2 million odonate records between 1901 and 2021 and investigated a series of research questions about odonate persistence within historically occupied regions, how species respond across continents, and mechanisms leading to these responses. I discovered that non-target effects of pesticides interacted with temperature increases, leading to higher rates of odonate declines across the United States. Species with greater capacities in shifting their range northward may be more robust to impacts of global change (Chapter 2). Converging across Europe and North America, stronger range limit shifts were associated with stronger shifts in emergence phenology towards earlier spring dates, even though land use histories are highly divergent among regions. It is temperature variability and range geography, determinants of habitat conditions to which species are exposed, rather than ecological traits, that facilitated or hindered range shifts (Chapter 3). Temperature variability interacted with pesticide applications to hinder persistence or establishment in new areas that were otherwise climatically suitable, providing further evidence of impacts of extreme weather to insect declines. Tests of methods commonly used to predict species' distributions under future climate change (Species Distribution Models) revealed that species most likely to decline were also less likely to be well modeled, in terms of their temporal transferability (Chapter 4). This work deepens knowledge of spatial and temporal interspecific variation in species distributions as humans continue to reshape the Earth's ecosystems and climatic processes. This thesis can help improve species-specific conservation planning for species that decline in the face of anthropogenic activities.

No description available.

No description available.

No description available.

Testing ecological theory at macroecological scales may be useful for disentangling abiotic influences from anthropogenic disturbances, and thus provide insights into fundamental processes that structure ecological communities. In tropical coral reef systems, our understanding of community structure is limited to small-scale studies conducted in moderately degraded regions, while larger regional or ocean scale analyses have typically focused on identifying human drivers of reef degradation. In this thesis, my collaborators and I combined stable isotope specimens, underwater visual censuses, and remote sensing data from 43 Pacific islands and atolls in order to examine the relative roles of natural environmental variation and anthropogenic pressures in structuring coral reef fish and benthic communities. First, at unexploited sites on Kiritimati Atoll (Kiribati), isotope estimates indicated that trophic level increased with body size across species and individuals, while negative abundance ~ body size relationships (size spectra) revealed distinct energetic constraints between energy-competing carnivores and energy-sharing herbivores. After demonstrating size structuring of reef fish communities in the absence of humans, we then examined evidence for size-selective exploitation impacts on coral reefs across the Pacific Ocean. Size spectra 'steepened' as human population density increased and proximity to market center decreased, reflecting decreases in large-bodied fish abundance, biomass, turnover rate, and mean trophic level. Depletion of large fish abundances likely diminishes functions such as bioerosion by grazers and food chain connectivity by top predators, further degrading reef community resilience. Next, we considered the relative strengths of abiotic, biotic and anthropogenic influences in determining reef benthic state across spatial scales. We found that from fine (0.25 km2) to coarse (1,024 km2) grain scales the phase shift index (a multivariate metric of the relative cover of hard coral and macroalgal) was primarily predicted by local abiotic and bottom-up influences, such that coral-dominated reefs occurred in warm, productive regions at sites exposed to low wave energy, irrespective of grazing or human impacts. Our size- based analyses of reef fish communities revealed novel exploitation impacts at ocean-basin scales, and provide a foundation for delineating energetic pathways and feeding interactions in complex tropical food webs. Furthermore, we demonstrate that abiotic constraints underpin natural variation among fish and benthic communities of remote uninhabited reefs, emphasizing the importance of accounting for local environmental conditions when developing quantitative baselines for coral reef ecosystems. / Graduate / 0329

Quels sont les grands patrons de distribution des espèces et quels sont les facteurs qui les contrôlent? Ces questions sont au cœur des problématiques macroécologiques et prennent un intérêt tout particulier au regard du réchauffement climatique global actuel. L’objectif principal de ce travail de thèse était de déterminer les patrons de distribution actuels des espèces d’oursins antarctiques et subantarctiques à l’échelle de l’océan Austral et de mettre en évidence les facteurs qui contrôlent ces distributions. La modélisation des niches écologiques d’une vingtaine d’espèces d’oursins a permis de mettre en évidence deux grands patrons de distribution : (1) un premier représenté par les espèces dont la distribution n’est pas limitée au sud du Front Polaire et s’étend des côtes antarctiques aux zones subantarctiques et tempérées froides et (2) un deuxième constitué d’espèces restreintes à la zone antarctique. Au sein de ces deux patrons, cinq sous-patrons ont également pu être défini sur la base de différences de distribution latitudinale et bathymétrique entre groupes d’espèces. Cette approche biogéographique par modélisation de niche écologique a été complétée par l’analyse de similarité de l’ensemble des faunes d’oursins, de bivalves et de gastéropodes, au niveau spécifique et générique, entre biorégions de l’océan Austral. Cette analyse démontre qu’il existe chez les oursins et les bivalves des connexions fauniques entre l’Amérique du Sud et les zones subantarctiques ainsi qu’une séparation entre l’Est et l’Ouest antarctique. Au contraire, les faunes de gastéropodes subantarctiques montrent des affinités plutôt antarctiques que sud-américaines, l’Antarctique ne formant qu’une unique province pour ce clade. Ces différences entre clades sont interprétées comme étant le résultat d’histoires évolutive et biogéographique distinctes entre oursins et bivalves d’une part et gastéropodes d’autre part. L’hypothèse d’une réponse évolutive différente des clades aux changements environnementaux survenus au cours du Cénozoïque est avancée. Enfin, l’existence de connexions fauniques trans-antarctiques est mise en évidence dans l’étude des trois clades ; celles-ci sont interprétées comme le résultat de la dislocation de la calotte ouest-antarctique et l’ouverture de bras de mer trans-antarctiques au cours du Pléistocène. Parmi les paramètres environnementaux utilisés dans la modélisation des niches écologiques, les résultats montrent que trois paramètres jouent un rôle majeur dans la distribution des oursins : la profondeur, la couverture de glace et la température des eaux de surface. Toutefois, l’importance relative de ces paramètres diffère selon les espèces d’oursins étudiées. L’étude du genre Sterechinus souligne tout particulièrement ces différences. En effet, l’espèce S. neumayeri est plus sensible aux conditions environnementales qui prédominent près des côtes antarctiques (température des eaux de surface et couverture de glace), alors que S. antarcticus semble être beaucoup moins contraint par ces mêmes paramètres. La distribution potentielle de S. antarcticus est d’ailleurs beaucoup plus étendue en latitude. Cependant, S. antarcticus n’est pas présent sur l’ensemble de son aire de distribution potentielle, ceci pouvant être expliqué alternativement par le résultat (1) de facteurs océanographiques (rôle de barrière biogéographique joué par le Front Polaire), (2) d’interactions biotiques (phénomènes de compétition inter-spécifique) et (3) du contexte temporel (colonisation toujours en cours). / What are the forcing factors and main patterns of species distribution? This question is the core of macroecological issues and is of particular interest in the present context of global warming. The main objectives of this thesis were to determine the current distribution patterns of Antarctic and sub-Antarctic echinoid species at the scale of the whole Southern Ocean and to highlight the forcing factors that control them. The ecological niche modelling of 19 echinoid species showed that distribution is mainly structured in two patterns: (1) a first one represented by species that are not limited to the south of the Polar Front and distributed from the Antarctic coasts to the sub-Antarctic and cold temperate areas, and (2) a second one with species restricted to the Antarctic area. Within these two main patterns, five sub-patterns were also identified that depend on differences in the latitudinal and depth range of species groupings. In addition to this approach of biogeography by ecological niche modelling, a similarity analysis of echinoid, bivalve and gastropod fauna between bioregions of the Southern Ocean was performed at species and genus levels. This analysis reveals faunal connections between southern South America and sub-Antarctic areas in echinoids and bivalves, along with a partition between the East and West Antarctic. On the contrary, sub-Antarctic gastropod fauna show Antarctic rather than South American affinities and the Antarctic form a sole and unique province in this clade. These differences between clades are interpreted as the result of distinct biogeographic and evolutionary histories between echinoids and bivalves on the one hand, and gastropods on the other hand. The proposed hypothesis is that clades developped different evolutionary responses to the environmental changes that occurred during the Cenozoic. Finally, in the three clades, trans-Antarctic faunal connections are shown and interpreted as a result of West Antarctic Ice Sheet collapses and the setting up of trans-Antarctic sea-ways during the Pleistocene. Among the environmental parameters used for the ecological niche modelling, results show that the three following parameters play the main part in echinoid distribution: depth, sea-ice cover and sea surface temperature. However, the relative importance of these parameters depends on the species under studies. These differences are particularly emphasized in the case study of the genus Sterechinus. The species S. neumayeri is indeed the most dependent on environmental conditions that prevail along the Antarctic coasts (sea surface temperature and sea-ice cover), while S. antarcticus doesn’t seem to be so much under the control of these parameters. Accordingly, the potential distribution of S. antarcticus in latitude is the most extended. However, S. antarcticus is not present over the whole area of its potential distribution, what can be explained as the result of either (1) oceanographic factors (role of the Polar Front as a biogeographical barrier), (2) biotic interactions (inter-specific competition) or (3) the temporal context (still ongoing colonization).

Na presente tese investigamos o papel de alguns dos fatores mais importantes na estruturação da fauna de EPT em riachos. No primeiro capítulo, abordamos os efeitos do tamanho do riacho, do tipo de mesohabitat (corredeira e remanso) e da estação do ano (seca e chuva) sobre a abundância, riqueza e composição de Ephemeroptera, Plecoptera e Trichoptera (EPT). Segundo os nossos resultados, a abundância respondeu de forma significativa às interações entre o tipo de mesohabitat e o tamanho do riacho; e entre estação do ano e o tamanho do riacho. A riqueza foi influenciada significativamente pelo tamanho do riacho. Adicionalmente, tanto o tipo de mesohabitat quanto o tamanho do riacho afetaram significativamente a composição faunística (DCA I). O tipo de mesohabitat pode ser considerado um bom preditor da fauna de EPT, mesmo em um sistema altamente sazonal como é o caso dos riachos aqui estudados. No segundo capítulo, apresentamos equações representativas da relação tamanho corpóreo (comprimento do corpo e largura da cápsula cefálica) para táxons de EPT. Considerando os dados obtidos, recomendamos, sempre que possível, a utilização do comprimento do corpo e apenas as equações com o R2 acima de 0,65, as quais podem ser úteis em trabalhos onde informações gerais sobre a biomassa de EPT são necessárias. Este capítulo serviu de base para o capítulo III. No terceiro capítulo, abordamos os padrões de distribuição de frequência do tamanho corpóreo e a relação entre tamanho corpóreo e abundância de EPT. Os nossos resultados mostraram que independente do riacho, do tipo de mesohabitat e da estação do ano, no geral, as distribuições se encaixaram em uma distribuição normal. Considerando as relações entre o tamanho corpóreo e abundância, os dados de 50% das assembleias de EPT analisadas individualmente se encaixaram numa forma piramidal. Em nenhum dos casos, observamos relações lineares negativas, portanto, os nossos dados discordam da Regra de Equivalência Energética. Nossos resultados sugerem que um único fator (e.g. balanço energético) é insuficiente para explicar a relação tamanho-abundância de EPT em ambientes altamente variáveis como os riachos aqui estudados. / In this thesis we investigate the role of some of the most important factors in structuring EPT fauna in streams. In the first chapter, we discuss the effects of stream size, type of mesohabitat (riffles and pools) and season (rainy and dry) on the abundance, richness and composition of Ephemeroptera, Plecoptera and Trichoptera (EPT). According to our results, the abundance responded significantly to the interactions between mesohabitat type and size of the stream, and between season and size of the stream. Richness was significantly influenced by the size of the stream. Additionally, both the mesohabitat type and size of the stream significantly affected the faunal composition (DCA I). The type of mesohabitat can be considered a good predictor of EPT fauna, even in a highly seasonal system like the streams studied here. In the second chapter, we present equations representing the relative body size (body length and width of head capsule) for EPT taxa. Considering the data obtained, it is recommended, where possible, using the length of the body and only equations with R2 above 0.65, which may be useful when general information on the EPT biomass is necessary. This chapter supported the Chapter III. In third chapter we discuss the patterns of frequency distribution of body size and the relationship between body size and abundance of EPT. Our results show that regardless of the stream, the type of mesohabitat and the season, in general, the data on body size fit the normal distribution. Considering the relations between body size and abundance, the data of 50% of EPT assemblages analyzed individually fit the pyramidal shape. In any case, we observed negative linear relationship, therefore, our data disagree with the Energy Equivalence Rule. Our results suggest that a single factor (e.g. energy balance) is insufficient to explain the relationship between size and abundance of EPT in highly variable environments such as streams studied here.

Cette thèse a pour objectif de combiner plusieurs théories opérant à différentes échelles spatiales afin de mieux prédire l'effet des changements globaux, tels que la modification du climat, l’exploitation intensive des ressources ou la disparition des espaces naturels, sur la structure et le fonctionnement des écosystèmes. L'originalité de ce travail est l'utilisation de la masse corporelle des espèces pour caractériser à la fois leur dynamique spatiale, leurs interactions trophiques ainsi que les flux de biomasse au sein de l’écosystème. Cette approche offre l'avantage de relier les propriétés des écosystèmes à un trait fonctionnel mesurable à l'échelle de l'espèce, voire même de l'individu.J'étudie dans un premier temps le lien entre la diversité des écosystèmes et leur stabilité, qui est une question centrale dans le domaine de l’écologie. Il a été démontré que les écosystèmes très diversifiés en espèces ne devraient pas perdurer du fait de leur trop grande sensibilité aux perturbations, ce qui soulève un paradoxe puisque les écosystèmes riches en espèces abondent dans la nature. Grâce à la compilation et à l'analyse d'un important jeu de données d'écosystèmes empiriques, je montre qu'il n'existe pas de relation entre la stabilité, la diversité et la complexité des écosystèmes. Une analyse détaillée des données démontre que la structure très organisée des flux de biomasse observés entre les prédateurs et leurs proies est l’un des principaux fondements de la stabilité des écosystèmes.Je relie ensuite ces propriétés stabilisantes à des caractéristiques mesurables à l’échelle de l’espèce. À partir de la masse corporelle des espèces, je détermine les interactions trophiques, les besoins énergétiques ainsi que les biomasses à l’équilibre des espèces d’un écosystème afin de modéliser des réseaux trophiques réalistes. Je trouve que les écosystèmes composés d’espèces de masses corporelles très différentes sont caractérisés par un nombre important d'interactions proie-prédateur de faible intensité et sont plus stables que ceux possédant des espèces de masse corporelle similaires.J'étudie enfin l’effet de la taille et de l’isolement d’un habitat sur la moyenne et la variance de la masse corporelle des espèces qui y coexistent à partir de modèles intégrant les différences interspécifiques de dispersion, de vulnérabilité aux extinctions et la position trophique des espèces. Je compare les prédictions des modèles aux distributions de masse corporelle observées dans les assemblages de poissons récifaux tropicaux en me basant sur une base de données globale. L'analyse de ces données démontre que les assemblages locaux de poissons ne correspondent pas à un sous-ensemble aléatoire du pool régional et valident les prédictions de la théorie allométrique et trophique de la biogéographie des îles.L’intégration de l’écologie fonctionnelle, de la biogéographie et de la théorie sur la stabilité des systèmes dynamiques ouvre de nouvelles perspectives pour la conservation des écosystèmes puisqu'elle met en évidence l'effet de la fragmentation des espaces naturels sur la diversité fonctionnelle, et par extension sur la structure et le fonctionnement des écosystèmes. / The general objective of this thesis is to combine theories acting at different spatial scales in order to better predict the effect of global changes, such as such as resource overexploitation, climate change or habitat fragmentation, on ecosystem functioning. The unique feature of this work is the use of species body mass to describe both spatial dynamics, trophic interactions and biomass flows between the species of an ecosystem. An advantage to this approach is that it links ecosystem properties to a functional trait, measured at the species or even the individual level.First, I study the relationship between the diversity and the stability of ecosystems. It has been demonstrated that species-rich, complex ecosystems should be too sensitive to perturbations to persist through time, which raises a paradox as many species-rich ecosystems are observed in nature. With the compilation and the analysis of a large dataset of empirically measured ecosystems, I show that there is no relationship between stability and diversity or complexity in real ecosystems. A further analysis demonstrates that the non-random organization of energy flows between predators and prey allows complex ecosystem to be stable.A second step is to link this stabilizing structure to species functional traits. I derive food web topology, species energetic needs and equilibrium densities from body mass to build quantitative realistic food webs. I find that food webs composed of species with very different body masses are characterized by a high number of weak trophic interactions and are more stable than food webs with more similar species.Finally, I study the effect of habitat area and isolation of the mean and variance of species body mass distribution, using models integrating the interspecific variability of dispersal ability, vulnerability to extinctions and trophic position. I compare model predictions to observed body mass distributions of fish assemblages found on tropical reefs with a global database. I find that body mass distribution in local fish assemblages does not correspond to a random sample of the regional species pool, which confirms the predictions of the allometric and trophic theory of island biogeography.The integration of functional ecology, island biogeography and theory on the stability of complex systems open new perspectives in the fields of macroecology and ecosystem management since it highlights the potential impact of habitat destruction and fragmentation on the functional reorganization of species assemblages and therefore on the structure and functioning of ecosystems.

Na presente tese investigamos o papel de alguns dos fatores mais importantes na estruturação da fauna de EPT em riachos. No primeiro capítulo, abordamos os efeitos do tamanho do riacho, do tipo de mesohabitat (corredeira e remanso) e da estação do ano (seca e chuva) sobre a abundância, riqueza e composição de Ephemeroptera, Plecoptera e Trichoptera (EPT). Segundo os nossos resultados, a abundância respondeu de forma significativa às interações entre o tipo de mesohabitat e o tamanho do riacho; e entre estação do ano e o tamanho do riacho. A riqueza foi influenciada significativamente pelo tamanho do riacho. Adicionalmente, tanto o tipo de mesohabitat quanto o tamanho do riacho afetaram significativamente a composição faunística (DCA I). O tipo de mesohabitat pode ser considerado um bom preditor da fauna de EPT, mesmo em um sistema altamente sazonal como é o caso dos riachos aqui estudados. No segundo capítulo, apresentamos equações representativas da relação tamanho corpóreo (comprimento do corpo e largura da cápsula cefálica) para táxons de EPT. Considerando os dados obtidos, recomendamos, sempre que possível, a utilização do comprimento do corpo e apenas as equações com o R2 acima de 0,65, as quais podem ser úteis em trabalhos onde informações gerais sobre a biomassa de EPT são necessárias. Este capítulo serviu de base para o capítulo III. No terceiro capítulo, abordamos os padrões de distribuição de frequência do tamanho corpóreo e a relação entre tamanho corpóreo e abundância de EPT. Os nossos resultados mostraram que independente do riacho, do tipo de mesohabitat e da estação do ano, no geral, as distribuições se encaixaram em uma distribuição normal. Considerando as relações entre o tamanho corpóreo e abundância, os dados de 50% das assembleias de EPT analisadas individualmente se encaixaram numa forma piramidal. Em nenhum dos casos, observamos relações lineares negativas, portanto, os nossos dados discordam da Regra de Equivalência Energética. Nossos resultados sugerem que um único fator (e.g. balanço energético) é insuficiente para explicar a relação tamanho-abundância de EPT em ambientes altamente variáveis como os riachos aqui estudados. / In this thesis we investigate the role of some of the most important factors in structuring EPT fauna in streams. In the first chapter, we discuss the effects of stream size, type of mesohabitat (riffles and pools) and season (rainy and dry) on the abundance, richness and composition of Ephemeroptera, Plecoptera and Trichoptera (EPT). According to our results, the abundance responded significantly to the interactions between mesohabitat type and size of the stream, and between season and size of the stream. Richness was significantly influenced by the size of the stream. Additionally, both the mesohabitat type and size of the stream significantly affected the faunal composition (DCA I). The type of mesohabitat can be considered a good predictor of EPT fauna, even in a highly seasonal system like the streams studied here. In the second chapter, we present equations representing the relative body size (body length and width of head capsule) for EPT taxa. Considering the data obtained, it is recommended, where possible, using the length of the body and only equations with R2 above 0.65, which may be useful when general information on the EPT biomass is necessary. This chapter supported the Chapter III. In third chapter we discuss the patterns of frequency distribution of body size and the relationship between body size and abundance of EPT. Our results show that regardless of the stream, the type of mesohabitat and the season, in general, the data on body size fit the normal distribution. Considering the relations between body size and abundance, the data of 50% of EPT assemblages analyzed individually fit the pyramidal shape. In any case, we observed negative linear relationship, therefore, our data disagree with the Energy Equivalence Rule. Our results suggest that a single factor (e.g. energy balance) is insufficient to explain the relationship between size and abundance of EPT in highly variable environments such as streams studied here.