Biogeografía y conservación de dos especies de la flora relicta del Mediterráneo OccidentalAbies pinsapo Boiss. y Cedrus atlantica (Endl.) Carrière

Abstract

This thesis focuses on the habitat distribution of Abies pinsapo Boiss. and Cedrus atlantica (Endl.) Carrière in the Western Mediterranean. The possible distribution that both species might have occupied during the last glacial period (Würm, 110-10 ka) and the Holocene Climate Optimum (Hypsithermal, 8-4.5 ka) is proposed; and the causes of the biogeographic pattern that have driven to the current distribution are discussed. In addition, the feasibility of current populations is predicted under the foreseeable conditions of climate change. In the study, ecoinformatics tools for modeling and niche overlap analyses have been used as a complement to the traditional paleobiological tools with whose results have been contrasted. The results indicate that the biogeographic dynamics of A. pinsapo and C. atlantica at the end of the Quaternary in the Western Mediterranean has consisted of a series of altitudinal migrations determined by temperature variation. Such shifts in the altitudinal gradient have been geographically reflected in phenomena of expansion, connection, contraction, isolation, refuge and local extinction. Since the Pleistocene, the suitable habitat for C. atlantica has remained uninterrupted in the Betic mountain range until the present, which suggests the implication of non-climatic causes in its local extinction in the Iberian Peninsula. In this sense, it cannot be ruled out that the higher prevalence of Pinus nigra on the European continent would have desplaced Cedrus. Currently, the European and African lineages of A. pinsapo complex show divergence between their niches, expressed by differences in the habitat they occupy on both sides of the Mediterranean. The African lineage, represented by A. marocana, supports a seasonal rainfall regime characterized by low rainfall during the summer months. This restricts its presence to the mountainous summits of the Rif, in wich the annual water balance is higher than that existing in the Betica mountain range where A. pinsapo lives. The isolation of the two lineages, without gene flow between them since the Middle Miocene, would have favored allopatric segregation. Differential climatic evolution, with the manifestation of out-of-step events on both sides of the Mediterranean, would have given rise to successive bottlenecks for the populations, at the same time that it would have promoted the occupation of ecological gaps that would end up defining the current niches of A. pinsapo and A. marocana. In Serranía de Ronda, current environmental conditions do not allow to complete its life cycle to A. pinsapo in much of its current distribution. The differences between the realized niche and the reproductive niche could reveal a shift in altitude of their populations due to climate change, in whose dynamics a pattern appears with greater retraction at the trailing-edge than expansion at the leading-edge. This behavior is typical of sessile species with a long life cycle and does not lead to the extinction of populations in the short term, but it can endanger their viability if the conditions that cause the contraction in the lower limit remain in time. The foreseeable future habitat of A. pinsapo and C. atlantica in the western Mediterranean will be considerably reduced compared to their current habitats, although A. pinsapo will be able to maintain cohesion of the main current stands under strict conservation measures. Meanwhile, C. atlantica will find the best natural refuges in those currently most threatened areas, so it will be necessary to adopt measures aimed at the special protection of these localities.