Louvain-la-Neuve, Belgium
Louvain-la-Neuve, Belgium

Time filter

Source Type

Nieberding C.M.,Leiden University | Nieberding C.M.,Earth and Life Institute | Fischer K.,University of Greifswald | Saastamoinen M.,Leiden University | And 7 more authors.
Ecology Letters | Year: 2012

Although olfaction is a primary mode of communication, its importance in sexual selection remains understudied. Here, using the butterfly Bicyclus anynana, we address all the parameters of importance to sexual selection for a male olfactory signal. We show that variation in the male sex pheromone composition indicates male identity and male age. Courting males of different ages display small absolute (c. 200ng) but large relative (100%) change of one specific pheromone component (hexadecanal) which, unlike the other components, showed no heritability. Females prefer to mate with mid-aged over younger males and the pheromone composition is sufficient to determine this preference. Surprisingly refined information is thus present in the male olfactory signal and is used for sexual selection. Our data also reveal that there may be no 'lek paradox' to resolve once the precise signal of importance to females is identified, as hexadecanal is, as expected, depleted in additive genetic variation. © 2012 Blackwell Publishing Ltd/CNRS.

Stevens A.,Earth and Life Institute | Nocita M.,Earth and Life Institute | Nocita M.,European Commission - Joint Research Center Ispra | Toth G.,European Commission - Joint Research Center Ispra | And 2 more authors.
PLoS ONE | Year: 2013

Soil organic carbon is a key soil property related to soil fertility, aggregate stability and the exchange of CO2 with the atmosphere. Existing soil maps and inventories can rarely be used to monitor the state and evolution in soil organic carbon content due to their poor spatial resolution, lack of consistency and high updating costs. Visible and Near Infrared diffuse reflectance spectroscopy is an alternative method to provide cheap and high-density soil data. However, there are still some uncertainties on its capacity to produce reliable predictions for areas characterized by large soil diversity. Using a large-scale EU soil survey of about 20,000 samples and covering 23 countries, we assessed the performance of reflectance spectroscopy for the prediction of soil organic carbon content. The best calibrations achieved a root mean square error ranging from 4 to 15 g C kg-1 for mineral soils and a root mean square error of 50 g C kg-1 for organic soil materials. Model errors are shown to be related to the levels of soil organic carbon and variations in other soil properties such as sand and clay content. Although errors are ∼5 times larger than the reproducibility error of the laboratory method, reflectance spectroscopy provides unbiased predictions of the soil organic carbon content. Such estimates could be used for assessing the mean soil organic carbon content of large geographical entities or countries. This study is a first step towards providing uniform continental-scale spectroscopic estimations of soil organic carbon, meeting an increasing demand for information on the state of the soil that can be used in biogeochemical models and the monitoring of soil degradation. © 2013 Stevens et al.

Mathiot P.,Earth and Life Institute | Goosse H.,Earth and Life Institute | Fichefet T.,Earth and Life Institute | Barnier B.,Joseph Fourier University | Gallee H.,CNRS Laboratory for Glaciology and Environmental Geophysics
Ocean Science | Year: 2011

One of the main features of the oceanic circulation along Antarctica is the Antarctic Slope Current (ASC). This circumpolar current flows westwards and contributes to communication between the three major oceanic basins around Antarctica. The ASC is not very well known due to remote location and the presence of sea ice during several months, allowing in situ studies only during summertime. Moreover, only few modelling studies of this current have been carried out. Here, we investigate the sensitivity of this simulated current to four different resolutions in a coupled ocean-sea ice model and to two different atmospheric forcing sets. Two series of simulations are conducted. For the first series, global model configurations are run at coarse (2°) to eddy-permitting (0.25°) resolutions with the same atmospheric forcing. For the second series, simulations with two different atmospheric forcings are performed using a regional circumpolar configuration (south of 30° S) at 0.5° resolution. The first atmospheric forcing is based on a global atmospheric reanalysis and satellite data, while the second is based on a downscaling of the global atmospheric reanalysis by a regional atmospheric model calibrated to Antarctic meteorological conditions. Sensitivity experiments to resolution indicate that a minimum model resolution of 0.5° is needed to capture the dynamics of the ASC in terms of water mass transport and recirculation. Sensitivity experiments to atmospheric forcing fields shows that the wind speed along the Antarctic coast strongly controls the water mass transport and the seasonal cycle of the ASC. An increase in annual mean of easterlies by about 30 % leads to an increase in the mean ASC transport by about 40 %. Similar effects are obtained on the seasonal cycle: using a wind forcing field with a larger seasonal cycle (+30 %) increases by more than 30 % the amplitude of the seasonal cycle of the ASC. To confirm the importance of wind seasonal cycle, a simulation without wind speed seasonal cycle is carried out. This simulation shows a decrease by more than 50 % of the amplitude of the ASC transport seasonal cycle without changing the mean value of ASC transport. © 2011 Author(s).

Dufour C.O.,CEA Saclay Nuclear Research Center | Sommer J.L.,French National Center for Scientific Research | Zika J.D.,French National Center for Scientific Research | Gehlen M.,CEA Saclay Nuclear Research Center | And 3 more authors.
Journal of Climate | Year: 2012

To refine the understanding of how the Southern Ocean responds to recent intensification of the southern annularmode (SAM), a regional oceanmodel at two eddy-permitting resolutions was forced with two synthetic interannual forcings. The first forcing corresponds to homogeneously intensified winds, while the second concerns their poleward intensification, consistent with positive phases of the SAM. Resulting wind-driven responses differ greatly between the nearly insensitive Antarctic Circumpolar Current (ACC) and the more sensitivemeridional overturning circulation (MOC).As expected, eddiesmitigate the response of theACC and MOC to poleward-intensified winds. However, transient eddies do not necessarily play an increasing role in meridional transport with increasing resolution. As winds and resolution increase, meridional transport from standing eddies becomes more efficient at balancing wind-enhanced overturning. These results question the current paradigms on the role of eddies and present new challenges for eddy flux parameterization. Results also indicate that spatial patterns of wind anomalies are at least as important as the overall change in intensity in influencing the Southern Ocean's dynamic response to wind events. Poleward-intensified wind anomalies from the positive trend in the SAMare farmore efficient in accelerating the ACCthan homogeneouswind anomalies. © 2012 American Meteorological Society.

Stevens A.,Earth and Life Institute | Miralles I.,Earth and Life Institute | Van Wesemael B.,Earth and Life Institute
Soil Science Society of America Journal | Year: 2012

Soil organic carbon (SOC) is considered to influence important processes affecting soil, air, and water quality. The management of this valuable resource could be assisted by remote sensing techniques able to provide highresolution spatial estimates of SOC. Such estimations are usually based on empirical regressions that are likely to have poor extrapolation abilities and hence it is important to properly estimate their accuracy in unsampled fields. Based on an imaging spectroscopy image acquired over the Luxembourg (c. 420 km2), several multivariate calibration models (partial least square [PLSR], penalized-spline signal [PSR], and support vector machine [SVMR] regressions) were developed to predict SOC content of topsoil bare agricultural fields and compared. The performance of the models was evaluated by means of cross-validation (k-fold[KFO], leave-one-out [LOO], leave-one-group-out [LOGO], and leave-one-field-out [LOFO]) and these estimates were compared with model performance obtained by validation. The validation set excluded the fields used in the training set, to provide realistic measures of prediction error in unsampled fields. All cross-validation techniques, except LOFO, strongly underestimate validation error. In large areas, training samples are often not a representative subset of the soil and spectral variation. Leave-one-field-out cross-validation, by repeatedly leaving samples belonging to one field out of the calibration, better simulates model error at unknown locations than other cross-validation strategies. The root mean square error (RMSE) of the best models, obtained with a stringent validation procedure (leave-fields-out), was equal to 4.7 g C kg-1. This is higher than most of previous studies using imaging spectroscopy for SOC prediction, suggesting that measures of accuracy obtained by KFO, LOO, and LOGO are likely over-optimistic in large areas. Finally, a SOC content map for the topsoil of croplands was produced that may assist soil monitoring and/or management efforts in this region in the future. © Soil Science Society of America.

Ligot G.,University of Liège | Balandier P.,IRSTEA | Courbaud B.,IRSTEA | Jonard M.,Earth and Life Institute | And 2 more authors.
Forest Ecology and Management | Year: 2014

Close-to-nature management of forests has been increasingly advocated. However forest managers often face difficulties in maintaining mixtures of species with different shade tolerance. In uneven aged stand management, understory light can be manipulated by modifying stand structure and composition, in addition to stand density. Using a forest radiative transfer model, we analyzed how different cutting strategies could modify light availability under the post-harvest canopy. To calibrate the model, we measured and mapped trees in 27 plots with structures ranging from secondary-successional oak forests to late-successional beech forests. We measured understory light and crown openness and verified that our forest radiative transfer model well captured the variability of understory light among the studied stands (R2=87%). We then compared cutting strategies varying in type and intensity and provided indications to promote the regeneration of mixtures of species of different shade tolerances. In particular, creating gaps of about 500m2 provided adequate light for small regeneration clumps. Cutting from below, species-specific cutting and uniform cutting were also appropriate for tree regeneration but uniform cutting required higher harvest intensity. Cutting from above slightly increased understory light and promoted more shade tolerant species. © 2014 Elsevier B.V.

Soulsbury C.D.,University of Lincoln | Kervinen M.,University of Jyväskylä | Lebigre C.,Earth and Life Institute
Behavioral Ecology | Year: 2016

There is growing evidence that achromatic plumage can act as honest indicators of male quality. In some species with areas of white plumage, black melanin spots can be found on parts of the feathers. The functional significance of these spots and the relationship with male quality is yet poorly understood. We investigated the relationship between black melanin spots in an otherwise totally white ornament, the undertail covert, in relation to age, fitness, and covariance with past and present expression of sexual traits, in the lekking black grouse Lyrurus tetrix. We found that spots at tips of feathers (tip spots) were negatively related to survival and reproductive success, and covaried negatively with current fighting rate. They also covaried positively with past fighting rate, suggesting high investment in fighting leads to carryover effects on male condition. In contrast, spots found further down the feather (vane spots) were unrelated to fitness and morphological and behavioral trait expression. Our results show that melanin spots can reflect overall male quality, but their adaptive value is dependent on their location on the feather. The exact drivers of melanin spot expression and how these link to male quality are currently unknown. © 2016 The Author.

Bitume E.V.,Earth and Life Institute | Bitume E.V.,Montpellier University | Bonte D.,Ghent University | Ronce O.,Montpellier University | And 4 more authors.
Ecology Letters | Year: 2013

Although dispersal distance plays a major role in determining whether organisms will reach new habitats, empirical data on the environmental factors that affect dispersal distance are lacking. Population density and kin competition are two factors theorised to increase dispersal distance. Using the two-spotted spider mite as a model species, we altered these two environmental conditions and measured the mean dispersal distance of individuals, as well as other attributes of the dispersal kernel. We find that both density and relatedness in the release patch increase dispersal distance. Relatedness, but not density, changes the shape of the dispersal kernel towards a more skewed and leptokurtic shape including a longer 'fat-tail'. This is the first experimental demonstration that kin competition can shape the whole distribution of dispersal distances in a population, and thus affect the geographical spread of dispersal phenotypes. © 2013 Blackwell Publishing Ltd/CNRS.

Bitume E.V.,Earth and Life Institute | Bitume E.V.,Montpellier University | Bonte D.,Ghent University | Ronce O.,Montpellier University | And 2 more authors.
Proceedings of the Royal Society B: Biological Sciences | Year: 2014

Non-genetic transmission of information across generations, so-called parental effects, can have significant impacts on offspring morphology, physiology, behaviour and life-history traits. In previous experimental work using the two-spotted spider mite Tetranychus urticae Koch, we demonstrated that dispersal distances increase with local density and levels of genetic relatedness. We here show that manipulation of parental and grand-parental density has a significant effect on offspring dispersal distance, of the same order of magnitude as manipulation of offspring density. We demonstrate that offspring exposed to the same density disperse further if they were born to parents exposed to higher density compared with parents exposed to low density. Offspring dispersal distance also increases when grand-parents were exposed to higher density, except for offspring exposed to lowdensities, which disperse at shorter distances whatever the grand-parental density. We also show that offspring from mothers exposed to higher densities were overall larger, which suggests that parents in high densities invest more in individual offspring, enabling them to disperse further. We propose that our findings should be included in models investigating the spread rate of invasive species or when predicting the success of conservation measures of species attempting to track changing climates. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Henrard A.,Royal Museum for Central Africa | Henrard A.,Earth and Life Institute | Jocque R.,Royal Museum for Central Africa
Zootaxa | Year: 2015

A new genus, Suffrica, is described from Tanzania and Kenya. It contains three new species occurring in the Eastern Arc Mountains and the adjacent Mkomazi Game Reserve: S. exotica, S. chawia and S. gus. They are characterized by a remarkable combination of features which has not been documented in spiders so far: a pair of femoral organs on each leg, a gland on the dorsal side of the abdomen in both sexes and a dorsal abdominal groove in males. A dual femoral organ appears to occur in species of the genus Suffasia Jocqué, 1991 and Asceua Thorell, 1887. The discovery of a new African genus close to Suffasia is remarkable since the latter genus is known only from Asia. Copyright © 2015 Magnolia Press.

Loading Earth and Life Institute collaborators
Loading Earth and Life Institute collaborators