Evolutionary perspectives on plant responses and sensitivity to environmental change
Global change is putting unprecedented pressure on plants to adapt or migrate to avoid extinction. Studying the past responses of plants to environmental change can shed light on the potential evolutionary outcomes and sensitivity of species to future environmental change. These processes are especially relevant to highly diverse, evolutionarily rich, and ecologically vulnerable alpine ecosystems. My PhD aims to narrow the uncertainty about how plant lineages with a range of lowland and alpine species will be impacted by global change by studying the historical biogeography, trait and species diversification, and ecological strategies of alpine species in a phylogenetic framework. Chapter 1 reviews current knowledge about the relative roles of migration and adaptation in plant responses to climate change and how historical biogeographical and evolutionary modeling provide novel insights to these questions. Chapter 2 applies recent developments in sequencing methods to construct a new, near-complete phylogeny of a diverse species radiation, New Zealand Veronica, also addressing questions about how to resolve difficulties in reconstructing phylogenetic relationships in recent, rapid radiations such as Veronica. This group serves as an important case study for further evolutionary questions about the relationships between habitat, species diversity, and environmental change. Chapter 3 estimates the contributions of in situ cladogenesis (i.e., the formation of new species) and colonization from lowland habitat in generating mountain diversity in Veronica. Further, the chapter explores the importance of niche adaptation and divergence in contributing to cladogenesis, and presents a general, conceptual model to understand how mountain diversity accumulates. Chapter 4 compares the potential range and niche change required for plant species to respond to future climate change relative to the change undergone since the mid-Holocene. It also determines which niche traits can predict “winners” and “losers” under climate change. Chapter 5 discusses the main findings of the thesis and ends with proposed avenues for future research.