Éditeur(s) : HAL CCSD
Résumé :   Diplôme : DEA
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
L'étude de la répartition géographique de la diversité génétique résultant de l'histoire des populations apparaît comme fondamentale pour la conservation des espèces. Ainsi, la mise en évidence des relations phylo-géographiques au court du Quaternaire récent, au sein d'une espèce modèle Vouacapoua americana (Caesalpiniaceae), en Guyane française apporte des informations importantes sur la dynamique des populations naturelles. Dans cette étude les loci trn Q-trn S et trn Sa-trn fM sont utilisés afin de déterminer l'histoire évolutive des populations issues des refuges forestiers tropicaux. Le but principal est l'obtention des séquences après amplification PCR. L'analyse de ces séquences chez cinq populations testées a permis de mettre en évidence leur caractère hypervariable, ainsi que des régions présentant des motifs conservés répétés plusieurs fois. Les constructions phylogéographiques obtenues à partir de celles-ci accentuent la régionalisation des différents chlorotypes, existant en Guyane pour cette espèce, mise en évidence au cours de travaux précédents. Ainsi, les informations apportées par cette approche apparaissent comme complémentaires aux résultats obtenus par d'autres techniques d'analyse moléculaire.
https://hal.archives-ouvertes.fr/hal-01189224

hal-01189224
https://hal.archives-ouvertes.fr/hal-01189224
PRODINRA : 16622

Éditeur(s) : HAL CCSD Wiley
Résumé :  
Aims: Astrocaryum sciophilum (Miq.) Pulle (Arecaceae) is an understorey palm, endemic to north-eastern South America with a patchy distribution. We tested the hypothesis that the spatial distribution of this palm species is not in equilibrium but is slowly colonizing the forest understorey. Location: Inventories and seed dispersal studies were conducted in the undisturbed tropical forest close to the Nouragues research station, French Guiana. Additional data were collected in the entire territory of French Guiana. Methods: We studied the demography of A. sciophilum on a 20-ha plot located at the edge of its distribution. The age of the palms was estimated by postulating an exponentially decreasing abundance by age class. Direct seed dispersal experiments were also conducted, to estimate dispersal parameters. The seeds of A. sciophilum were dispersed only by rodents. This information was used to parameterize a forest growth simulator, to study the spatial spread of this species. Results: Within the sampling plot, the density of A. sciophilum dropped sharply from about 500 individuals per hectare to zero. The maturation age was estimated to be 170 ± 70 years, and over 55 years with 95% confidence. Seed-dispersal experiments yielded an average seed dispersal distance of 11 m and a maximum estimated dispersal distance of 125 m across a generational span of 55 years to maturity. Therefore, the maximal estimated colonization speed is 2.3 m/y. Conclusions: Empirical results and numerical simulations suggest that the boundary of the A. sciophilum population is a colonization front, and that the range of this species is slowly expanding. The implications of this result in respect of palaeoenvironmental changes in this region are discussed.
ISSN: 1466-822X

hal-01032154
https://hal.archives-ouvertes.fr/hal-01032154
DOI : 10.1046/j.1466-822X.2003.00020.x

Éditeur(s) : HAL CCSD
Résumé : The main objective of this thesis was to study the influence of Guianan terra firme rainforests types on medium- and large-sized vertebrates community organization. First, we choose a model species which permitted to develop an appropriate abundance estimation method which take into account the imperfect detection and temporary immigration of mobile species, and to test environmental conditions effects at different spatial scales of analysis. Second, given that bias due to animal detection can be important in the abundance estimation, we determinated the relative role of environmental conditions and species biological traits on detection probability. From this methodological framework, we studied then processes of community organization, by identifying the main determinants involved in community organization, using composition and alpha and beta diversities, and, in a complementary manner, three metrics (taxonomic, functional, and phylogenetic). We sought from these general framework to determinate the relative role of environmental conditions and historical contingency, responsible for the current community organization, and to test the forest refugia hypothesis. Finally, we downscaled the analysis to determinate, and tried to disentangle the effects of environmental conditions and interspecific interactions on species co-occurrence. We used then functional traits to test the relationship between species co-occurrence and similarities.This thesis highlights the important role of historical contingency and facilitation in the structure of regional diversity and the local assembly processes of medium- and large-sized vertebrates, respectively, in French Guiana.
Cette thèse a pour but d’étudier l'influence de l'hétérogénéité des forêts de terre ferme en Guyane sur l'organisation des communautés de moyens et grands vertébrés. Nous avons, d'abord, choisi une espèce modèle afin de déterminer une méthode adéquate d'estimation d'abondance prenant en compte la détection imparfaite et l'immigration temporaire des espèces, et de tester l'effet des conditions environnementales à différentes échelles d'analyse. Puis, partant du constat que les biais dus à la détection dans l'estimation d'abondance pouvaient être importants, nous avons déterminé l'importance relative des conditions environnementales et des traits biologiques des espèces sur la probabilité de détection. A partir de ce cadre d'étude, nous avons étudié la composition et les diversités alpha et beta en utilisant de façon complémentaire les métriques taxonomique, fonctionnelle, et phylogénétique pour déterminer le rôle relatif de l'environnement et de la contingence historique dans l'organisation des communautés, et de tester l’hypothèse des refuges forestiers. Enfin, en descendant dans l'échelle d'analyse, nous avons tenté de démêler l'effet de l'environnement et des interactions interspécifiques sur la cooccurrence des espèces, et utilisé les traits fonctionnels des espèces pour tester le lien entre cooccurrence et similitude fonctionnelle. Cette thèse met en avant les rôles prépondérants de la contingence historique et de la facilitation dans, respectivement, la structuration de la diversité régionale et les processus d’assemblages locaux des communautés de moyens et grands vertébrés en Guyane.
https://tel.archives-ouvertes.fr/tel-01537779

NNT : 2017YANE0004
tel-01537779
https://tel.archives-ouvertes.fr/tel-01537779
https://tel.archives-ouvertes.fr/tel-01537779/document
https://tel.archives-ouvertes.fr/tel-01537779/file/these_thomas_denis.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : URL de l'article : http://www.sciencedirect.com/science/article/B6WPN-4XY3KDK-2/2/fd8508af63d82e29b4f9829c65194e26
The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C4 savannas) occurred in northern French Guiana during the Holocene. We measured variations in the δ13C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C4 savannahs or C4 forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the 13C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties.
ISSN: 0033-5894

halshs-00551758
https://halshs.archives-ouvertes.fr/halshs-00551758
DOI : 10.1016/j.yqres.2009.11.007

Éditeur(s) : HAL CCSD Wiley
Résumé :  
The chloroplast genome has been widely used to describe genetic diversity in plant species. Its maternal inheritance in numerous angiosperm species and low mutation rate are suitable characters when inferring historical events such as possible recolonization routes. Here we have studied chloroplast DNA variation using PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) with seven pairs of primers and four restriction enzymes in 14 populations of Vouacapoua americana (Caesalpiniaceae) a neotropical tree sampled throughout French Guiana. Population diversity (Hs), total gene diversity (Ht) and differentiation among populations (GST) were estimated using Nei's method as 0.09, 0.87 and 0.89, respectively. This is consistent with the limited gene flow associated with synzoochory in this species. The genetic structure observed in the north of French Guiana suggests that historical events such as contractions and recent recolonizations have had a large impact on the distribution of genetic diversity in this species.
ISSN: 0962-1083

hal-01032176
https://hal.archives-ouvertes.fr/hal-01032176
DOI : 10.1046/j.1365-294x.2000.01027.x