Escalfament i biologia de la conservació a les Terres Altes de la Guayana: paleoecologia, biogeografia i modelització SIG

Abstract

This thesis uses the combined study of past and present to the future applied to the vascular plants of the Guayana Highlands, a remote area of northern South America constituted by a set of tabular mountains (known as tepui ), with an exceptional degree of endemism. The tepuian flora is so unique that constitutes a phytogeographical province by itself, called Pantepui. Chapter 1 uses the analysis of pollen grains, fern spores and charcoal, among others, to provide new data of the temporal trends of the vegetation during the Tardiglacial and the Holocene. The results show that the moisture variation detected, did not significantly affect the plant community, suggesting a buffering capacity. The absence of biotic changes may be attributed also to the absence of environmental disturbances of enough intensity to affect plant communities. Throughout the thesis, it has been analyzed the potential vertical displacement of vascular plants in both the past and future. For the first case, chapter 2 has provided relevant data on the species that may have migrated during the Quaternary (70%) and those that remained isolated (8%) in the tops of tepui. These data have been obtained thanks to the identification for each tepui of an historical factor known as critical limit for topographic isolation during the last Glacial Maximum (LGM). In chapter 3, it has been analyzed the elevation patterns and the relationship between species richness with area and elevation. This analysis was conducted for both non-endemic and endemic species. The results show that the elevation pattern for the Pantepui endemic species suggests that isolation and habitat fragmentation has had a major influence on their distribution. This conclusion can not be applied for the non-endemic species. Local endemic species (occurring in one tepui) show a certain independence of these geographical factors but show a relationship with the historical factor defined above: the critical limit topographic isolation during LGM, suggesting that maximum levels of local endemism occurred at altitudes with small or null connexion possibilities. Finally, it has been calculated the potential vertical displacement caused by global warming for the end of this century (2100). The results show that the expected increase in temperature will have severe consequences on the tepuian vascular plants. On chapter 4 and 5 it has been used three complementary analysis to quantify the consequences of the global warming: the species-area relationship (SAR), the Altitude Range Displacement analysis (ARD) and habitat fragmentation. Both the SAR and the ARD predicted a decrease of the vascular plant species due to habitat loss at the end of the century. Moreover, on the warmest scenario, the results of the fragmentation analysis show a reduction of the 80% of the Pantepui habitat. The remaining habitat would be comprised in more than 40% in one patch. These results suggest the combination of in situ conservation strategies (prevention of introduction of invasive species) and ex situ (seed bank and assisted migration).

Date of Award	21 Sept 2009
Original language	Undefined/Unknown
Supervisor	Teresa Vegas Vilarrúbia (Director) & Valentí Rull del Castillo (Director)