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Salas-Lopez, A., Violle, C., Mallia, L., & Orivel, J. (2018). Land-use change effects on the taxonomic and morphological trait composition of ant communities in French Guiana. Insect Conserv Divers, 11(2), 162–173.
Abstract: Abstract Land-use changes frequently lead to major changes in the composition and diversity of organisms. A reduction in the range of strategies enabling organisms to survive in a given environment and changes in the average trait values of species may potentially be associated with variations in species? number and identity. We investigated the variation in ant taxonomic composition and morphological trait diversity along a land-use gradient in French Guiana. We measured 13 core ant morphological traits on all species sampled. We then selected the set of five traits that best captured changes along the land-use gradient. Potential effects of the variation in morphological trait diversity and average values were evaluated by examining morphological traits individually as well as in combination. We found that variation in taxonomic diversity was unrelated to the plot-level morphospace. Conversely, a significant shift in taxonomic composition was accompanied by changes in the average values of community traits along the studied gradient, examined both individually and in combination. We argue that morphological trait values may be related to the success of different species in surviving in a given environment and, therefore, are indicative of the taxonomic turnover in ants along the land-use gradient. Nevertheless, in contradiction with theoretical expectations, the morphospace is only slightly affected by habitat filtering and loosely impacted by taxonomic changes. Examining the sensitivity of the morphospace to abiotic and biotic factors and how it reflects varying ecological pressures for species is thus of the utmost importance.
Keywords: Community assembly; Formicidae; functional diversity; gradient analysis; habitat filtering; land-use intensification; n-dimensional hypervolume approach
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Leponce, M., Dejean, A., Mottl, O., & Klimes, P. (2021). Rapid assessment of the three-dimensional distribution of dominant arboreal ants in tropical forests. Insect Conservation and Diversity, 14(4), 426–438.
Abstract: Ants are omnipresent in tropical forests, especially territorially dominant arboreal ants whose territories are spatially segregated forming ‘ant mosaics’. These ecologically important species are rarely used in conservation monitoring because of the difficulty in collecting them. We developed a standardised baitline protocol to study the distribution of dominant ants on canopy trees and also a procedure to objectively define species dominance, even in unknown ant assemblages.
Besides eliminating the need to climb trees, this protocol allows live arboreal ant specimens to be sampled at different heights. Behavioural aggressiveness assays between the collected workers provide data on the three-dimensional distribution of colonies and on interactions between species. We compared the results of the behavioural tests to those from null models.
In the New Guinean lowland forest studied, we show that the canopy was either shared by multiple territorial species or inhabited by a single species with a large territory. The baitline protocol collected up to half of the arboreal ant species found in a felling census. However, the proportion of species collected at baits decreased with the increasing spatial dominance of single territorial species.
Behavioural observations used in the protocol allowed a more efficient detection of ant mosaics than null models. Territorially dominant ants were active on both understorey and canopy trees.
The protocol is fast and easy to replicate. It is a potential tool for understanding and monitoring the spatiotemporal dynamics of arboreal ant assemblages and can detect populous colonies, including those of invasive species
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Lebrini, M., Mbomekallé, I. M., Dolbecq, A., Marrot, J., Berthet, P., Ntienoue, J., et al. (2011). Manganese(III)-containing wells-dawson sandwich-type polyoxometalates: Comparison with their manganese(II) counterparts. Inorg. Chem., 50(14), 6437–6448.
Abstract: We present the synthesis and structural characterization, assessed by various techniques (FTIR, TGA, UV-vis, elemental analysis, single-crystal X-ray diffraction for three compounds, magnetic susceptibility, and electrochemistry) of five manganese-containing Wells-Dawson sandwich-type (WDST) complexes. The dimanganese(II)-containing complex, [Na2(H2O) 2MnII2(As2W15O 56)2]18- (1), was obtained by reaction of MnCl2 with 1 equiv of [As2W15O 56]12- in acetate medium (pH 4.7). Oxidation of 1 by Na2S2O8 in aqueous solution led to the dimanganese(III) complex [Na2(H2O)2Mn III2(As2W15O56) 2]16- (2), while its trimanganese(II) homologue, [Na(H2O)2MnII(H2O)Mn II2(As2W15O56) 2]17- (3), was obtained by addition of ca. 1 equiv of MnCl2 to a solution of 1 in 1 M NaCl. The trimanganese(III) and tetramanganese(III) counterparts, [MnIII(H2O)Mn III2(As2W15O56) 2]15- (4) and [MnIII2(H 2O)2MnIII2(As2W 15O56)2]12- (6), are, respectively, obtained by oxidation of aqueous solutions of 3 and [MnII2(H2O)2MnII2(As 2W15O56)2]16- (5) by Na2S2O8. Single-crystal X-ray analyses were carried out on 2, 3, and 4. BVS calculations and XPS confirmed that the oxidation state of Mn centers is +II for complexes 1, 3, and 5 and +III for 2, 4, and 6. A complete comparative electrochemical study was carried out on the six compounds cited above, and it was possible to observe the distinct redox steps MnIV/III and MnIII/II. Magnetization measurements, as a function of temperature, confirm the presence of antiferromagnetic interactions between the Mn ions in these compounds in all cases with the exception of compound 2. © 2011 American Chemical Society.
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de Thoisy, B., Duron, O., Epelboin, L., Musset, L., Quénel, P., Roche, B., et al. (2021). Ecology, evolution, and epidemiology of zoonotic and vector-borne infectious diseases in French Guiana: Transdisciplinarity does matter to tackle new emerging threats. Infection, Génétics and Evolution, 93, 104916.
Abstract: French Guiana is a European ultraperipheric region located on the northern Atlantic coast of South America. It constitutes an important forested region for biological conservation in the Neotropics. Although very sparsely populated, with its inhabitants mainly concentrated on the Atlantic coastal strip and along the two main rivers, it is marked by the presence and development of old and new epidemic disease outbreaks, both research and health priorities. In this review paper, we synthetize 15 years of multidisciplinary and integrative research at the interface between wildlife, ecosystem modification, human activities and sociodemographic development, and human health. This study reveals a complex epidemiological landscape marked by important transitional changes, facilitated by increased interconnections between wildlife, land-use change and human occupation and activity, human and trade transportation, demography with substantial immigration, and identified vector and parasite pharmacological resistance. Among other French Guianese characteristics, we demonstrate herein the existence of more complex multi-host disease life cycles than previously described for several disease systems in Central and South America, which clearly indicates that today the greater promiscuity between wildlife and humans due to demographic and economic pressures may offer novel settings for microbes and their hosts to circulate and spread. French Guiana is a microcosm that crystallizes all the current global environmental, demographic and socioeconomic change conditions, which may favor the development of ancient and future infectious diseases.
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Dubois-Fernandez, P. C., Le Toan, T., Daniel, S., Oriot, H., Chave, J., Blanc, L., et al. (2012). The tropiSAR airborne campaign in French Guiana: Objectives, description, and observed temporal behavior of the backscatter signal. IEEE Trans Geosci Remote Sens, 50(8), 3228–3241.
Abstract: The TropiSAR campaign has been conducted in August 2009 in French Guiana with the ONERA airborne radar system SETHI. The main objective of this campaign was to collect data to support the Phase A of the 7th Earth Explorer candidate mission, BIOMASS. Several specific questions needed to be addressed to consolidate the mission concept following the Phase 0 studies, and the data collection strategy was constructed accordingly. More specifically, a tropical forest data set was required in order to provide test data for the evaluation of the foreseen inversion algorithms and data products. The paper provides a description of the resulting data set which is now available through the European Space Agency website under the airborne campaign link. First results from the TropiSAR database analysis are presented with two in-depth analyses about both the temporal radiometric variation and temporal coherence at P-band. The temporal variations of the backscatter values are less than 0.5 dB throughout the campaign, and the coherence values are observed to stay high even after 22 days. These results are essential for the BIOMASS mission. The observed temporal stability of the backscatter is a good indicator of the expected robustness of the biomass estimation in tropical forests, from cross-polarized backscatter values as regarding environmental changes such as soil moisture. The high temporal coherence observed after a 22-day period is a prerequisite for SAR Polarimetric Interferometry and Tomographic applications in a single satellite configuration. The conclusion then summarizes the paper and identifies the next steps in the analysis. © 2012 IEEE.
Keywords: Forestry; interferometry; polarimetric synthetic aperture radar
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Essebtey, S. E. I., Villard, L., Borderies, P., Koleck, T., Burban, B., & Le Toan, T. (2021). Long-Term Trends of P-Band Temporal Decorrelation Over a Tropical Dense Forest-Experimental Results for the BIOMASS Mission. IEEE Transactions on Geoscience and Remote Sensing, 60, 1–15.
Abstract: Fostered by the upcoming BIOMASS mission, this article explores long-term trends of P-band temporal decorrelation over a tropical forest due to a time series of 617 days acquired during the TropiScat-2 experiment. The interest in this unique time series is twofold. First, it provides consistent statistics to monitor the yearly evolution of temporal coherences according to specific time scales of the BIOMASS tomographic and interferometric phases. Second, it provides key insights to explore new processing approaches with the combination of data from different orbit directions (ascending/descending) and different mission cycles separated by about seven months according to the current acquisition plan. For the first time, this study shows that 18-day coherences (corresponding to the time interval between the first and last acquisitions of the BIOMASS tomographic processing) can vary significantly according to rainy and dry seasons (medians from 0.3 to 0.9). The extension to time intervals of up to 90 days within both seasons and over two consecutive years puts forward the key role of the typical sporadic rainfalls occurring during dry periods in tropical rainforests, with a stronger impact on temporal coherence evolution compared to the more reproducible rainy seasons. Furthermore, outstanding values significantly above zero have been obtained for the 7- and 14-month coherences (medians of 0.35 and 0.2, respectively), opening the way to new methods of change detection. Overall, this study highlights the role of P-band temporal decorrelation not only as a disturbance factor for coherent applications but also as a relevant indicator of forest changes.
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Campillo, F., & Rossi, V. (2009). Convolution Particle Filter for Parameter Estimation in General State-Space Models. IEEE Trans. Aerosp. Electron. Syst., 45(3), 1063–1072.
Abstract: The state-space modeling of partially observed dynamical systems generally requires estimates of unknown parameters. The dynamic state vector together with the static parameter vector can be considered as an augmented state vector. Classical filtering methods, such as the extended Kalman filter (EKF) and the bootstrap particle filter (PF), fail to estimate the augmented state vector. For these classical filters to handle the augmented state vector, a dynamic noise term should be artificially added to the parameter components or to the deterministic component of the dynamical system. However, this approach degrades the estimation performance of the filters. We propose a variant of the PF based on convolution kernel approximation techniques. This approach is tested on a simulated case study.
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Aubry-Kientz, M., Laybros, A., Weinstein, B., Ball, J. G. C., Jackson, T., Coomes, D., et al. (2021). Multisensor data fusion for improved segmentation of individual tree crowns in dense tropical forests. IEEE Journal of Selected topics in Applied Earth Observations and Remote Sensing, 14, 3927–3936.
Abstract: Automatic tree crown segmentation from remote sensing data is especially challenging in dense, diverse, and multilayered tropical forest canopies, and tracking mortality by this approach is even more difficult. Here, we examine the potential for combining airborne laser scanning (ALS) with multispectral and hyperspectral data to improve the accuracy of tree crown segmentation at a study site in French Guiana. We combined an ALS point cloud clustering method with a spectral deep learning model to achieve 83% accuracy at recognizing manually segmented reference crowns (with congruence >0.5). This method outperformed a two-step process that involved clustering the ALS point cloud and then using the logistic regression of hyperspectral distances to correct oversegmentation. We used this approach to map tree mortality from repeat surveys and show that the number of crowns identified in the first that intersected with height loss clusters was a good estimator of the number of dead trees in these areas. Our results demonstrate that multisensor data fusion improves the automatic segmentation of individual tree crowns and presents a promising avenue to study forest demography with repeated remote sensing acquisitions.
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Hamadi, A., Borderies, P., Albinet, C., Koleck, T., Villard, L., Ho Tong Minh, D., et al. (2015). Temporal coherence of tropical forests at P-band: Dry and rainy seasons. IEEE Geosci. Remote Sens. Lett., 12(3), 557–561.
Abstract: In this letter, the temporal coherence of tropical forest scattering at P-band is addressed by means of a ground-based experiment. The study is based on the TropiScat campaign in French Guiana, designed to support the Biomass mission, which will be the ESA 7th Earth Explorer mission. For Biomass, temporal coherence is a crucial parameter for coherent processing of polarimetric synthetic aperture radar (SAR) interferometry and SAR tomography in repeat-pass acquisitions. During the experiment, data were continuously collected for six months during both the rainy and dry seasons. For the rain-free days in both seasons, the coherence exhibits a daily cycle showing a high decorrelation during daytime, which is likely due to motion in the canopy. Up to a 20-day baseline, the coherence is much higher in the dry season than in the rainy season (> 0.8). From 20 to 40 days, it presents the same order of magnitude in both seasons [0.6, 0.7]. For larger temporal baselines, it becomes lower in the dry season. The results can be used to assess the long-term coherence of repeat-pass observations over a tropical forest. However, an extension of this study to several years and over other forest spots would be necessary to draw more general conclusions.
Keywords: Biomass mission; forest scattering; ground-based experiment; P-band; range impulse response; temporal coherence
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Ruelle, J., Clair, B., Beauchene, J., Prevost, M. F., & Fournier, M. (2006). Tension wood and opposite wood in 21 tropical rain forest species 2. Comparison of some anatomical and ultrastructural criteria. IAWA J., 27(4), 341–376.
Abstract: The anatomy of tension wood and opposite wood was compared in 21 tropical rain forest trees from 21 species belonging to 18 families from French Guyana. Wood specimens were taken from the upper and lower sides of naturally tilted trees. Measurement of the growth stress level ensured that the two samples were taken from wood tissues in a different mechanical state: highly tensile-stressed wood on the upper side, called tension wood and normally tensile-stressed wood on the lower side, called opposite wood. Quantitative parameters relating to fibres and vessels were measured on transverse sections of both tension and opposite wood to check if certain criteria can easily discriminate the two kinds of wood. We observed a decrease in the frequency of vessels in the tension wood in all the trees studied. Other criteria concerning shape and surface area of the vessels, fibre diameter or cell wall thickness did not reveal any general trend. At the ultrastructural level, we observed that the microfibril angle in the tension wood sample was lower than in opposite wood in all the trees except one (Licania membranacea).
Keywords: tension wood; opposite wood; tropical rain forest; vessels; wood anatomy; wood fibre
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