1,721,168 research outputs found
Supplemental Material - Explaining willingness to pay taxes: The role of income, education, ideology
No full textSupplemental Material for Explaining willingness to pay taxes: The role of income, education, ideology by Olivier Jacques in Journal of European Social Policy.</p
Retour sur la journée "Jeunes Chercheur (e) s" au Mémorial de Caen
No full textCette année encore, tel un marronnier, la journée « Jeunes chercheurs et nouvelles recherches sur la Seconde Guerre mondiale », a trouvé sa place dans l'un des amphithéâtres du Mémorial de Caen, grâce au partenariat avec l'Université de Caen et le laboratoire HisTeMé. Placée sous les présidences de François Rouquet, Gaël Eismann et Françoise Passera, cette journée a permis à six jeunes chercheurs, venant de différentes universités, de présenter en public leurs travaux. Olivier Jacques et Pie..
Plant-plant interactions in tropical alpine environments.
No full textPlant–plant interactions are increasingly recognized as a key driver of community organization and ecosystem processes in alpine environments. However, patterns and mechanisms of plant–plant interactions remain largely uncharacterized in tropical alpine ecosystems (TAE) which represent as much as 10% of the total surface area of alpine ecosystems worldwide. In this paper, we review (1) the ecological and environmental features that are specific to TAE in comparison with other alpine ecosystems, (2) the existing literature on plant–plant interactions in TAE, and (3) whether patterns and mechanisms of plant–plant interactions established in extratropical alpine zones can be extended to TAE. TAE are located predominantly in South America, East Africa, and South-East Asia where they show a unique combination of environmental characteristics, such as absence of persisting snow cover, high frequency of diurnal freeze–thaw cycles and needle-ice activity, and a decrease in precipitation with increasing altitude. These environmental characteristics result in the presence of giant growth forms with a great architectural diversity. These biotic and abiotic characteristics influence the outcome of plant–plant interactions by imposing other types of environmental constraints than those found in extratropical alpine environments, and by potentially generating distinctive patterns of niche differentiation/complementarity between species and populations. To generalize the conceptual framework of plant–plant interactions in alpine environments, we advocate that TAE should be investigated more thoroughly by applying designs, methods and hypotheses that are used currently in temperate areas and by conducting studies along large latitudinal gradients that include tropical regions
Temporal scaling of high flow effects on benthic fauna: insights from equatorial glacier-fed streams
Get PDFWe used equatorial glacier-fed streams as a model system to investigate the relationships between flow fluctuation and benthic fauna at different temporal scales. Water level was measured at 30 min intervals over 29 months (942 d) and benthic macroinvertebrates were sampled 14 times over the study period. We performed wavelet analyses on water-level time series to identify temporal scales at which significant flow variation occurs, and calculated three indices: intensity, frequency and temporal clustering of the diurnal flow variation for periods from 2 d to 50 d. We determined the effect of temporal scaling (length of the periods considered) on relationships between benthic community dissimilarity (using Sørensen index) and differences in flow indices among the 14 sampling dates. Temporal scaling affected flow-variation frequency and temporal clustering and their subsequent relationships with benthic community dissimilarity. A time scale of 15 d before benthic sampling was relevant to the assessment of flow-biota relationships. Community dissimilarity significantly increased with increasing difference in flow-fluctuation intensity. This dissimilarity was associated with a decrease in the density of dominant taxa and a taxa turnover along the temporal gradient in flow-fluctuation intensity. Although flow fluctuations are frequent and highly predictable in equatorial glacier-fed streams, macroinvertebrate communities exhibited a temporal variability in taxon assemblage, which was linked to the intensity of flow fluctuation. We explain these patterns by downstream displacement during high flow events and upstream displacement during low flow periods, thereby highlighting the need of considering temporal scaling effects on benthic fauna to understand the ecological dynamics of lotic systems
Differences in morphometry and activity among horse fly populations in an Andean tropical montane cloud forest: indication of altitudinal migration.
No full textExiste evidencia científica que sugiere que las variaciones de un gradiente ecológico moldean algunas características propias de cada organismo como su comportamiento o morfometría. En este estudio, analizamos el efecto de la altura sobre la actividad de vuelo de poblaciones de una especie de tábano del género Stypommisa Enderlein a lo largo de 1 km de gradiente altitudinal en las estribaciones nor-orientales de los Andes ecuatorianos. Nuestros objetivos fueron (1) evaluar la hipótesis que los individuos de zonas altas presentan mayor tamaño en sus estructuras corporales asociadas al vuelo, y (2) comparar los patrones de actividad de vuelo de las diferentes poblaciones y correlacionarlas con factores climáticos. Para esto recolectamos especímenes en trampas Malaise a 1180, 1680 y 2180 m de altura desde las 0600 h hasta las 1800 h por 20 días en cada sitio. Se midieron siete variables climáticas en intervalos de una hora, y la actividad de vuelo fue inferida a partir de los datos de abundancia relativa/hora en las trampas. Dentro de las medidas morfométricas de las moscas incluimos el tamaño del cuerpo, el volumen torácico, el área alar y la carga alar. Los patrones de vuelo de las moscas revelaron una distribución bimodal a 1680 m, y dos distribuciones unimodales y asíncronas a 1180 m y 2180 m. Los análisis GLM mostraron que la temperatura, la neblina, y la pluviosidad fueron los factores climáticos que mejor predijeron los diferentes tipos de actividad de vuelo entre las alturas. Por otra parte, los análisis morfométricos demostraron que tanto el tamaño del cuerpo como el volumen torácico aumentan significativamente de tamaño con la altura. Se encontró que los grupos de moscas con actividad sincrónica a diferentes alturas (1180–1680(pm) m, y 1680(am)–2180 m) fueron morfológicamente similares lo que sugiere que las moscas pueden ser capaces de migrar de las zonas altas hacia las zonas bajas en horas específicas del día dependiendo del clima
Temperature-dependent shift in herbivore performance and interactions drive non-linear changes in crop damages.
No full textUnderstanding how and to what extent the influence of temperature on physiological performance scales up to interspecific interactions and process rate patterns remains a major scientific challenge faced by ecologists. Here, we combined approaches developed by two conceptual frameworks in ecology, the stress-gradient hypothesis (SGH), and the biodiversity–ecosystem functioning relationship (B-EF), to test the hypothesis that interspecific difference in thermal performance modulates multiple species interactions along a thermal stress (SGH) and the subsequent richness effects on process rates (B-EF). We designed an experiment using three species of herbivorous agricultural pests with different thermal optima for which we determined how temperature influences the direction and the strength of interaction and subsequent richness effects on crop damage (7 species interaction treatments × 6 temperature treatments × 10 replicates). We showed that both biotic interactions and species richness effects drive variations in crop damages along a thermal stress gradient, and thus have the potential to drive agro-system responses to climate change. To help explain and generalize underlying mechanisms of richness effects on process rates, we further proposed a conceptual model that views interaction outcomes as shifting between positive and negative along a thermal stress depending on species thermal optima. Overall, our study demonstrates that nonlinear effects of temperature on process rates must be a major concern in terms of prediction and management of the consequences of global warming
Adaptive management in crop pest control in the face of climate variability: an agent-based modeling approach
Get PDFClimate changes are occurring rapidly at both regional and global scales. Farmers are faced with the challenge of developing new agricultural practices to help them to cope with unpredictable changes in environmental, social, and economic conditions. Under these conditions, adaptive management requires a farmer to learn by monitoring provisional strategies and changing conditions, and then incrementally adjust management practices in light of new information. Exploring adaptive management will increase our understanding of the underlying processes that link farmer societies with their environment across space and time, while accounting for the impacts of an unpredictable climate. Here, we assessed the impacts of temperature and crop price, as surrogates for climate and economic changes, on farmers’ adaptive management in crop pest control using an agent-based modeling approach. Our model simulated an artificial society of farmers that relied on field data obtained in the Ecuadorian Andes. Farmers were represented as heterogeneous autonomous agents who interact with and influence each other, and who are capable of adapting to changing environmental conditions. The results of our simulation suggest that variable temperatures led to less effective pest control strategies than those used under stable temperatures. Moreover, farmers used information gained through their own past experience or through interactions with other farmers to initiate an adaptive management approach. At a broader scale, this study generates more than an increased understanding of adaptive management; it highlights how people depend on one another to manage common problems
Entomology in Ecuador: Recent developments and future challenges.
No full textWe review and analyze the recent development and future challenges facing entomology as a science in Ecuador, a country with limited fi nancial and human resources and numerous environmental problems. Taxonomic studies of the Ecuadorian insect fauna have been well developed for only a few groups (e.g. Papilionoidea, Carabidae) and remains in its infancy for most insect orders. This is due to the huge diversity of species living in a great diversity of habitats and the diffi culty to identify most species. There is a lack of published basic biological information and to a high rate of endemism of many groups, especially in the Andes. The development of ecological entomology as a formal discipline in Ecuador is a very recent phenomenon, and has been mostly limited to descriptive studies of the environmental factors that govern insect diversity and abundance. We outline a set of research challenges regarding the impact of global environmental changes on insect communities and habitats they live in and propose potential strategies for the development of entomology in Ecuador. Both basic and applied research will be important in this context as well as international collaboration to strengthen the role of entomological science in decision making processes in the country
Experimental support of the stress-gradient hypothesis in herbivore-herbivore interactions.
No full textThe stress-gradient hypothesis (SGH) postulates an increase in the frequency of positive species interactions at increasing amounts of stress. While theSGHhas been extensively tested in plant–plant interactions along abiotic stresses, it remains unclear whether this hypothesis could apply to higher trophic levels, such as herbivores, along biotic stress gradients.
To address this issue,weinvestigatedhowthe interaction between two potato herbivoresmay change along a stress gradient created by an assortment of potato varieties with different tuber palatability. We used a tuber resistance trait as a measure for biotic stress and one herbivore as the facilitator to gain access to the tuber of the other herbivore.
Our experiment revealed a switch from neutral to positive interactions with increasing stress, confirming for the first time the predictions of the SGH for herbivores. Moreover, the intensity of facilitation decreased at high stress levels, suggesting that benefits by the facilitating species were dampened in the most stressful environment.
In view of the ubiquitous role played by positive interactions among herbivores, broadening our search image for facilitative effects among other plant enemies will allow a better awareness of the importance of the SGH in structuring plant communities
A comparative analysis reveals weak relationships between ecological factors and beta diversity of stream insect metacommunities at two spatial levels
No full textThe hypotheses that beta diversity should increase with decreasing latitude and increase with spatial extent of a region have rarely been tested based on a comparative analysis of multiple datasets, and no such study has focused on stream insects. We first assessed how well variability in beta diversity of stream insect metacommunities is predicted by insect group, latitude, spatial extent, altitudinal range, and dataset properties across multiple drainage basins throughout the world. Second, we assessed the relative roles of environmental and spatial factors in driving variation in assemblage composition within each drainage basin. Our analyses were based on a dataset of 95 stream insect metacommunities from 31 drainage basins distributed around the world. We used dissimilarity-based indices to quantify beta diversity for each metacommunity and, subsequently, regressed beta diversity on insect group, latitude, spatial extent, altitudinal range, and dataset properties (e.g., number of sites and percentage of presences). Within each metacommunity, we used a combination of spatial eigenfunction analyses and partial redundancy analysis to partition variation in assemblage structure into environmental, shared, spatial, and unexplained fractions. We found that dataset properties were more important predictors of beta diversity than ecological and geographical factors across multiple drainage basins. In the within-basin analyses, environmental and spatial variables were generally poor predictors of variation in assemblage composition. Our results revealed deviation from general biodiversity patterns because beta diversity did not show the expected decreasing trend with latitude. Our results also call for reconsideration of just how predictable stream assemblages are along ecological gradients, with implications for environmental assessment and conservation decisions. Our findings may also be applicable to other dynamic systems where predictability is low
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