DEMOGRAPHIC APPROACHES TO UNDERSTAND PLANT COMMUNITY RESPONSES TO CLIMATE CHANGE

Abstract

Anthropogenic climate change is impacting all aspects of plant life, from shifting species’ spatial and temporal distributions, to altering their functional traits and the way they interact with one another. Understanding how the structure and diversity of plant communities will respond to these myriad impacts may seem daunting. But in this dissertation, we show that focusing on the demographic responses of individual species is a powerful and scalable approach to understand the responses of entire communities. In Chapter 1, we develop a mathematical model of population spread to show that demographic changes interact with evolutionary processes at the leading range edge of populations tracking climate change, giving rise to complex range shift dynamics. In Chapter 2, we explore the demographic consequences of species’ phenological plasticity under experimental climate change and show that, contrary to expectations, advancing flowering phenology as climate warms is not necessarily advantageous. In Chapter 3, we use field experiments to quantify how alpine species’ demography depends on climate and on interactions with neighbors, and use this information to build models of climate-dependent community dynamics. With these models, we show how community responses to gradual climate change differ from the responses to abrupt change that we typically observe in experiments, and also quantify the role of demographic and competitive lags in shaping the trajectory of dynamics. Finally, in Chapter 4, we use a similar combination of field experiments and models to quantify how fast species migrating from lower elevations will threaten the persistence of alpine species. Moreover, we show that plant height is an important predictor of the timescale of lowland species invasion of alpine communities. Overall, these chapters combine the strengths of mathematical models and experiments to understand how climate alters the dynamics of plant communities through its impacts on species’ demography.