Consequences of Changing Rainfall Variability for the Chihuahuan Desert Annual Plant Community

Abstract

Climate change is expected to increase climate variability over much of the world, including the timing and magnitude of weather events such as droughts and heat waves. Although ecologists have made great strides in quantifying how climate conditions at annual or longer timescales regulate populations and communities, the role of individual weather events and intra-annual variability is still relatively unknown. In this dissertation I seek to quantify how the Chihuahuan desert summer annual plant community responds to intra-annual variability, and in doing so better understand how biodiversity is maintained in this community and how this community may respond to climate change. In chapter one, I present a general approach to quantify how plants respond to short-term variability. Using this approach, I find that species in this community show an environmentally dependent life history tradeoff between growth in wet conditions and survival in dry conditions. This tradeoff could have important implications for both species coexistence and responses to climate change, as I show in chapters two and three. In chapter two, I seek to understand how a diverse community of annual plants is maintained in an environment with a single primary limiting resource, water. I show that the tradeoffs found in chapter one and environmental variability lead to conditions in which each life history is favored. The differences in life history are explained in part by tradeoffs in balancing carbon uptake and water use. In chapter three I forecast how this community of annual plants may respond to climate change. I find that while increasing variability is likely to lead to reduced growth, survival, and reproduction in almost all species, it favors species with slower growth in wet conditions but and high survival in dry condition which do comparatively better in increasingly variable conditions.