PhD Thesis

Eco-evolutionary responses of plants to spatial and temporal climatic variation

David Harter (07/2010-07/2015)

Support: Carl Beierkuhnlein, Heike Feldhaar, Cyrus Samimi

Spatial and temporal variation of climate determines ecological and evolutionary trajectories of plants. This can be seen e.g. in arrangements of plant species and functional traits along climate gradients, in palynological records, phylogeographic patterns or in plant responses to contemporary climate change. Current and expected future climatic alterations are special in their potential to influence plant life, due to particularly high rates of change but also to co-occurring and synergistic anthropogenic stressors to species and ecosystems. This thesis aims to enhance the understanding of past, present and future response capacities of plants. It is based on six manuscripts that study different aspects of plant responses to climatic variation in space and time and combines conceptual literature reviewing, experimental studies, population and landscape genetic analyses, phylogeographic approaches, as well as field studies and biogeographic pattern analyses. Studies include continental systems on different scales, as well as oceanic islands on a global perspective and in case studies from La Palma, Canary Islands. Oceanic islands are important contributors to global biodiversity and have played pivotal roles in biogeographical, ecological and evolutionary research. However, knowledge about the outcomes of climate change on oceanic islands is very scarce. Within this thesis, a conceptual overview depicts the wide range of impacts and reveals a large threat potential of anthropogenic climate change to island floras. Research needs and potentials are identified. On La Palma, population structures in two species of the evolutionarily significant genus Aeonium, as well as patterns of endemic species distributions are shown to be determined by climatic and topographic landscape heterogeneity. This highlights the importance of climatic variation in shaping evolutionary pathways and generating biodiversity patterns. Heterogeneous selection and divergent adaptation interact with various effects of landscape structures. These range from sheltering local species and gene pools from climatic variability or human-induced influences (introduced herbivores, fire, land use) in (micro-)refugia over provisioning of habitat diversity to acting as gene flow barriers and increasing reproductive isolation between divergent populations. Phenotypic plasticity is a direct and rapid response of organisms to environmental change and is known to vary intraspecifically in many species. Potential links of such variation to the history of populations and their resultant genetic make-up are experimentally studied and discussed. In Fagus sylvatica, genetically diverse populations from regions that acted as glacial refugia tend to show higher plasticity towards extreme weather conditions than populations from re-colonised regions. This hints to the importance of phylogeographical histories for the capacity of populations to respond to climate change and to a role of genetic diversity besides promoting adaptability. In a study on Corynephorus canescens, phylogeography-dependent patterns of genetic diversity were shown to be modified by range centre-periphery gradients. Additionally, the species’ uncommon ecology affected the population genetic structure. To allow for adequate models of genetic diversity, e.g. for assessing eco-evolutionary response capacities, those factors need to be integrated. Furthermore, a consideration of transgenerational effects of extreme weather events on perennial species is given. It shows changes in germination timing and success, but also modifications in growth and leaf stoichiometry in offspring plants of Genista tinctoria and Calluna vulgaris after their mother plants were exposed to drought and heavy rain treatments. Perennial species rely on plastic responses to environmental changes due to long generation times and low rates of possible genetic adaptation and/or range shifts, making (adaptive) transgenerational plasticity an important mechanism for population persistence. It can increase individual fitness from the seedling stage and thereby provide new variants for selection to act on and potentially induce evolutionary change. To sum up, the thesis elaborates a conceptual overview over plant responses to climatic variation on different spatial and temporal scales. It mainly focusses on processes and their drivers, and how past and current biogeographic, evolutionary, natural or anthropogenic factors can influence current and future response capabilities, thereby facilitating the mechanistic understanding of climate change influences on plants. Resulting from this thesis, new research questions arise in climate change ecology and island biology that particularly address the value and driving forces of plasticity within and among plant populations in changing environments, landscape effects on evolutionary processes on the scale of single islands, and the impacts of climate change on oceanic islands.