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Pointeau S.,CNRS Laboratory of Woody Plants and Crops Biology | Ameline A.,CNRS Edysan, Ecology and Dynamics of Human-influenced Systems Laboratory | Salle A.,CNRS Laboratory of Woody Plants and Crops Biology | Bankhead-Dronnet S.,CNRS Laboratory of Woody Plants and Crops Biology | Lieutier F.,CNRS Laboratory of Woody Plants and Crops Biology
Journal of Economic Entomology | Year: 2013

The woolly poplar aphid, Phloeomyzus passerinii (Signoret) (Hemiptera: Aphididae), is a major pest of poplar plantations in the Mediterranean basin and the Near East. Aphids colonize poplar trunks and feed upon the cortical parenchyma. Despite the economic importance of poplar, little is known about the mechanisms involved in poplar resistance to this pest. However, Populus x canadensis Moench genotypes show various levels of resistance to P. passerinii. This study has investigated the type of poplar resistance (antibiosis or antixenosis) by assessing aphid settlement, physiology (survival, development, and reproduction), and stylet penetration behavior (electrical penetration graph) on three P. x canadensis genotypes; 'I214' (susceptible), 'Brenta' (resistant), and 'I45/51' (intermediate). Because settlement was reduced, the highly resistant genotype Brenta exhibited surface antixenosis. In addition, nymphal survival was null on Brenta, and twice less adult aphid initiated a sustained intracellular phase in the cortical parenchyma of that genotype compared with the other two genotypes. Thus, Brenta also showed parenchyma-located antixenosis coupled with antibiosis characteristic. In contrast, P. passerinii had no difficulty to initiate a sustained ingestion in the cortical parenchyma of the intermediate genotype I45/51, but decreased fecundity and lower intrinsic rate of natural increase were clear expressions of antibiosis. © 2013 Entomological Society of America. Source

Sandom C.,University of Aarhus | Dalby L.,University of Aarhus | Flojgaard C.,University of Aarhus | Flojgaard C.,CSIC - National Museum of Natural Sciences | And 7 more authors.
Ecology | Year: 2013

Predator-prey interactions play an important role for species composition and community dynamics at local scales, but their importance in shaping large-scale gradients of species richness remains unexplored. Here, we use global range maps, structural equation models (SEM), and comprehensive databases of dietary preferences and body masses of all terrestrial, non-volant mammals worldwide, to test whether (1) prey bottom-up or predator top-down relationships are important drivers of broad-scale species richness gradients once the environment and human influence have been accounted for, (2) predator-prey richness associations vary among biogeographic regions, and (3) body size influences large-scale covariation between predators and prey. SEMs including only productivity, climate, and human factors explained a high proportion of variance in prey richness (R2 = 0.56) but considerably less in predator richness (R2 = 0.13). Adding predator-to-prey or prey-topredator paths strongly increased the explained variance in both cases (prey R2 = 0.79, predator R2 = 0.57), suggesting that predator-prey interactions play an important role in driving global diversity gradients. Prey bottom-up effects prevailed over productivity, climate, and human influence to explain predator richness, whereas productivity and climate were more important than predator top-down effects for explaining prey richness, although predator top-down effects were still significant. Global predator-prey associations were not reproduced in all regions, indicating that distinct paleoclimate and evolutionary histories (Africa and Australia) may alter species interactions across trophic levels. Stronger crosstrophic- level associations were recorded within categories of similar body size (e.g., large prey to large predators) than between them (e.g., large prey to small predators), suggesting that mass-related energetic and physiological constraints influence broad-scale richness links, especially for large-bodied mammals. Overall, our results support the idea that trophic interactions can be important drivers of large-scale species richness gradients in combination with environmental effects. © 2013 by the Ecological Society of America. Source

Le Roux P.C.,University of Helsinki | Lenoir J.,CNRS Edysan, Ecology and Dynamics of Human-influenced Systems Laboratory | Pellissier L.,University of Lausanne | Pellissier L.,University of Aarhus | And 3 more authors.
Ecology | Year: 2013

Studies of species range determinants have traditionally focused on abiotic variables (typically climatic conditions), and therefore the recent explicit consideration of biotic interactions represents an important advance in the field. While these studies clearly support the role of biotic interactions in shaping species distributions, most examine only the influence of a single species and/or a single interaction, failing to account for species being subject to multiple concurrent interactions. By fitting species distribution models (SDMs), we examine the influence of multiple vertical (i.e., grazing, trampling, and manuring by mammalian herbivores) and horizontal (i.e., competition and facilitation; estimated from the cover of dominant plant species) interspecific interactions on the occurrence and cover of 41 alpine tundra plant species. Adding plant-plant interactions to baseline SDMs (using five field-quantified abiotic variables) significantly improved models' predictive power for independent data, while herbivore-related variables had only a weak influence. Overall, abiotic variables had the strongest individual contributions to the distribution of alpine tundra plants, with the importance of horizontal interaction variables exceeding that of vertical interaction variables. These results were consistent across three modeling techniques, for both species occurrence and cover, demonstrating the pattern to be robust. Thus, the explicit consideration of multiple biotic interactions reveals that plant-plant interactions exert control over the fine-scale distribution of vascular species that is comparable to abiotic drivers and considerably stronger than herbivores in this low-energy system. © 2013 by the Ecological Society of America. Source

Solefack M.C.M.,CNRS Edysan, Ecology and Dynamics of Human-influenced Systems Laboratory | Solefack M.C.M.,University of Yaounde I | Chabrerie O.,CNRS Edysan, Ecology and Dynamics of Human-influenced Systems Laboratory | Gallet-Moron E.,CNRS Edysan, Ecology and Dynamics of Human-influenced Systems Laboratory | And 3 more authors.
Acta Botanica Gallica | Year: 2012

Habitat destruction and land use change are major causes of biodiversity erosion on Earth, especially in tropical regions. Monitoring studies or even surveys of species and community diversity in changing landscapes or disturbed areas require an assessment of the land cover changes over time. Here, we present a method combining remote sensing and structural equation models (SEM) to describe and analyse landscape dynamics. We focus on the mount Oku as an example, which is a mountain area located in north-west Cameroon. This site hosts the largest remaining tract of Central African cloud forest, a biodiversity hotspot threatened by contemporary land-use changes. Our aim is to characterize land cover changes over the last three decades and to quantify and elucidate the causes of deforestation and forest fragmentation. For this purpose, we integrate several Landsat satellite images taken between 1978 and 2007 in a Geographic Information System (GIS), and compare changes in land-use types. We assess forest fragmentation over this period by comparing the number, the area and the perimeter of forest fragments, and derive a forest fragmentation index. Finally, we quantify the respective effects of natural (altitude, slope) and human (human density, distance to villages) factors on deforestation using SEM. We evidence two periods in the dynamics of the cloud forest cover: a period of intense deforestation (1978-2001), followed by a period of re-afforestation (2001-2007). The forest cover lost 62.1% of its area (12,060 ha) between 1978 and 2001, corresponding to an averaged deforestation rate of 579 ha.yr-1. Deforested areas were mainly converted into crop lands (+75.6% between 1978 and 1988), under the pressure of an increasing human density, which was multiplied by 20 between 1921 and 2005 and doubled during the last 18 years. After 2001, the forest cover stabilized with the appearance of numerous small fragments of secondary forest, reflecting the success of the local biodiversity protection programs. Despite this recent progression of the forest cover, the proportion of ancient forest has continuously decreased from 1978 to 2007, indicating that deforestation is still ongoing. In 2007, the forest cover was a mosaic composed of 66% of recent secondary forests (i.e. forests appeared after 1978) and only 34% of ancient forests (i.e. present before 1978). Between 1978 and 2007, the number of forest fragments increased from 2627 to 5183, their average area decreased from 7.4 to 1.8 ha, and perimeter from 912 to 446 m, and the forest fragmentation index increased by 285.7%. Deforestation started from lower altitudes (<2300 m, before 1988) and progressed towards higher altitudes (2100-2900 m) between 1988 and 2001. SEM showed that altitude and slope had a significant negative effect on human density, explaining why the deforestation has been low on steep slopes and/or at higher altitudes. Our study reveals that the last fragments of the primary cloud forest of mount Oku could be definitively lost in the next decades. As tropical primary forests are irreplaceable ecosystems that host numerous endemic species, we recommend (1) to urgently protect the last remnants of ancient forest for their biological value; clear-cuts, grazing in forest interior and fires should be excluded from these areas, and (2) to extend secondary forests around ancient forest fragments so that they can act as a protective buffer and be managed as community forests and used for hunting and logging activities. Copyright © 2012 Société botanique de France. Source

Lenoir J.,University of Aarhus | Lenoir J.,CNRS Edysan, Ecology and Dynamics of Human-influenced Systems Laboratory | Graae B.J.,Norwegian University of Science and Technology | Aarrestad P.A.,Norwegian Institute for Nature Research | And 38 more authors.
Global Change Biology | Year: 2013

Recent studies from mountainous areas of small spatial extent (<2500 km2) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m2 units (community-inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1-km2 units; (2) the relationship between CiT range and topographically and geographically derived predictors at 1-km resolution; and (3) whether spatial turnover in CiT is greater than spatial turnover in GiT within 100-km2 units. Ellenberg temperature indicator values in combination with plant assemblages explained 46-72% of variation in LmT and 92-96% of variation in GiT during the growing season (June, July, August). Growing-season CiT range within 1-km2 units peaked at 60-65°N and increased with terrain roughness, averaging 1.97 °C (SD = 0.84 °C) and 2.68 °C (SD = 1.26 °C) within the flattest and roughest units respectively. Complex interactions between topography-related variables and latitude explained 35% of variation in growing-season CiT range when accounting for sampling effort and residual spatial autocorrelation. Spatial turnover in growing-season CiT within 100-km2 units was, on average, 1.8 times greater (0.32 °C km-1) than spatial turnover in growing-season GiT (0.18 °C km-1). We conclude that thermal variability within 1-km2 units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains. © 2012 Blackwell Publishing Ltd. Source

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