Phylogenetic history and global diversity patterns of plantsDoctoral thesis
Date of Examination:2023-09-25
Date of issue:2024-01-26
Advisor:Prof. Dr. Holger Kreft
Referee:Prof. Dr. Holger Kreft
Referee:Prof. Dr. Hermann Behling
Referee:Prof. Dr. Wolf Eiserhardt
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EnglishUnderstanding where and how biodiversity originates and how it is maintained is one of the central questions in biogeography and macroecology. Phylogenies capture the evolutionary history of how lineages have diversified over evolutionary time. Integrating information on phylogenetic positions and evolutionary uniqueness of species into biodiversity assessments thus provides insights into biogeographic and evolutionary mechanisms underlying biodiversity, and is of paramount importance for biodiversity conservation. Plants are key elements of terrestrial ecosystems and are essential for biodiversity and humanity in terms of controlling ecosystem functioning and providing essential ecosystem services. Despite their crucial importance, knowledge of plant diversity on a global scale, accounting for evolutionary history, remains limited. In this thesis, I fill this important gap in our understanding of plant diversity by integrating a comprehensive global dataset of regional plant inventories across different geographic regions comprising up to 320,000 plant species with broad plant phylogenies. I explored global patterns and drivers of three key aspects of plant diversity accounting for evolutionary history in particular: (i) species and phylogenetic richness (Chapter 1); (ii) phylogenetic endemism that accounts for the phylogenetic uniqueness of range-restricted species (Chapter 2); (iii) phylogenetic turnover that quantifies dissimilarities in the evolutionary relatedness of assemblages (Chapter 3). In Chapter 1, integrating current knowledge of regional vascular plant diversity with past and present environmental variables, I tested environment-related hypotheses of broad-scale vascular plant diversity gradients, and modeled and predicted global species and phylogenetic richness using advanced machine learning techniques. Global patterns of plant diversity are shaped by a range of past and present environmental variables that interact in complex ways. While current climate and environmental heterogeneity emerged as the most important drivers, past environmental conditions left discernible legacies on current diversity patterns. The updated global maps produced as a result of the models at multiple grain sizes provide accurate estimates of vascular plant diversity, which will be a foundation for large-scale biodiversity monitoring, research, and conservation. In Chapter 2, I uncovered patterns and determinants of phylogenetic endemism, and distinguished the drivers and centers of evolutionarily young (neoendemism) and evolutionarily old endemism (paleoendemism) for seed plants worldwide. Phylogenetic endemism was predominantly driven by environmental heterogeneity. Warm and wet climates, geographic isolation, and long-term climatic stability were also important drivers of phylogenetic endemism. Long-term climatic stability promoted the persistence of paleoendemics, while isolation promoted neoendemism, leading to islands and mountain regions in the tropics and subtropics as global centers. These findings highlight the key role of climatic and geological history in diversification and maintenance of biodiversity, and reinforce the urgency of conserving areas occupied by narrow-ranged species with unique evolutionary histories. In Chapter 3, I tested hypotheses of environmental filtering and dispersal history on global patterns of phylogenetic and species turnover in seed plants, and assessed the contributions of these processes to phylogenetic turnover along the phylogenetic timescale. Past and present dispersal limitations promoted compositional dissimilarity among regions, but its effect was smaller for phylogenetic turnover than for species turnover, and further diminished when moving back along the phylogenetic timescale. In contrast, environmental filtering strongly promoted both species turnover and phylogenetic turnover at different phylogenetic timescales. The findings highlight the significant influence of environmental constraints on the distribution of major seed plant lineages and the important impact of dispersal limitation on the younger lineages towards the tips of the phylogeny. In conclusion, the integration of unprecedented plant distribution and phylogenetic information allows to reveal global patterns and drivers of plant diversity and compositions in terms of evolutionary history. The thesis uncovers global distributions of plant species and phylogenetic richness and phylogenetic endemism, and disentangles the complex effects of past and present environmental drivers. Global patterns of regional seed plant composition result from complex dispersal history related to past and present dispersal limitations and phylogenetically conserved environmental constraints, and further the relative impacts of the processes vary along the phylogenetic timescale. Notably, the findings highlight the importance of past climate change and geological history (e.g. past plate tectonics) on regional plant diversity and composition via altering key evolutionary and ecological processes of diversity generation and maintenance. Consequently, these findings enhance our understanding of biogeographical and evolutionary mechanisms structuring biodiversity and provide essential information for future biodiversity science and conservation.
Keywords: Biodiversity; Plant diversity; Phylogenetic diversity; Phylogenetic endemism; Phylogenetic beta diversity; Past climate change; Geological history