Dottorato in BIOLOGIA AMBIENTALE ED EVOLUZIONISTICA

Titolo della tesi: Late Quaternary population dynamics and present distribution of Mediterranean-Atlantic woody taxa

This thesis investigates the distribution patterns and long-term population dynamics of Arbutus and Ilex, two emblematic evergreen broadleaved genera with a Mediterranean-Atlantic distribution, by adopting a methodological approach that includes the collection of a variety of data from literature, databases, and repositories, the critical evaluation of the collected information, statistical analysis, mapping, and geographic processing. Arbutus and Ilex exhibit intricate biogeographic patterns shaped by diverse climatic and edaphic gradients, whose complexity is amplified in transitional biogeographic zones. The nature of the distribution patterns of the strawberry tree and holly has long been the subject of international debate and deals with broad questions of continental-scale interest that can be only tackled through a multidisciplinary approach, including systematic botany, phytogeography, palaeobotany, and ecological modelling. Thus, the main objective is contributing to the knowledge of the range evolution of Arbutus and Ilex during the Late Pleistocene and Holocene, up to the present day. Late Quaternary climate oscillations have been one of the main drivers in shaping the current distribution and range fluctuations of trees at the continental scale. During the last glaciation, many tree populations experienced severe range contractions, followed by a total or partial recovery of the pre-glacial extent, starting from refuge areas with different sizes and locations and showing different re-colonization routes. The new occurrence record maps for the present distribution of Arbutus and Ilex in the Old World provide new biogeographical insights, such as details on peripheral stands, the variability of population density, continuity vs gaps in distribution, plausible centres of gravity of the species, and long-term vulnerability, as well as potential resilience of populations. A major result was recognising the importance of peripheral populations that provide helpful hints to reconstruct the diversity and range history of the species. These populations are extremely sensitive to climate change and human impact and therefore deserve particular attention in conservation strategies. Extending this perspective on marginal populations of other plant taxa with fragmented distributions across Europe and the Mediterranean Basin will certainly provide a comprehensive view of the long-term vulnerability of trees in relation to the ongoing climate change, hopefully leading to shared conservation strategies at the continental scale. A holistic understanding of the link between modern occurrence records and past spatiotemporal patterns offers significant scientific potential for better understanding ecological niches. This approach enables reliable assessments of potentially vulnerable populations and supports informed conservation actions in response to ongoing and predicted climate change and increasing human pressures. A critical comparison of different modelling approaches evaluated the accuracy and coherence of spatial predictions of environmental suitability over time. It demonstrated that using multiple methods to predict past environmental suitability provides more informed interpretations of both past and present distribution patterns. The wealth of data processed for both past and present distributions, along with the diversity of ecological modelling and the wide geographical and temporal scales, has enabled the exploration of a broad interdisciplinary research field. This spans from evolutionary questions and past climate change to species nativeness, potential population recovery, mapping methods, biogeographical divides, predicted ranges, and long-term persistence in climatic refugia. A wider availability of published phylogeographical analyses for Arbutus and Ilex would promote more in-depth interpretations in some cases. To answer biogeographical issues and test hypotheses about spatiotemporal trends in plant population dynamics, new molecular research is welcomed to complement palaeobotanical investigations and ecological modelling.