Post-doctoral Researcher Western Sydney University, Australia
Historically, the field of comparative (or functional) ecology has focused on understanding how environments contribute to variation in plant morphology and physiology across species spanning a range of environments. Consequently, much is now known regarding how plant species vary across broad environmental gradients, including at the local, regional, and global scale, yet little is known regarding how within-species variation in plant traits compares to across-species variation across spatial scales, and fewer still have clarified how this variation influences higher order ecological processes. Using three case studies, I show how environments shape intraspecific trait variation (hereafter, ITV) with downstream consequences for whole-plant biomass allocation, population dynamics, and invasion success. First, I found that the allocation of biomass towards leaves versus wood decreases strongly with plant size but also with climatic moisture for native Australian plants spanning a broad climate gradient (mean annual precipitation ranging from 384 to 1753 mm). Interestingly, while all species more than doubled their allocation to wood at large sizes, the extent to which they became woodier was only weakly influenced by moisture, suggesting generality in how species allocate carbon towards tissues with distinct functions. Given that ecosystem carbon budgets depend strongly on estimates of whole-plant biomass allocation to wood versus leaves, more research is thus needed to better understand how ITV influences ecosystem properties. In a second case study, I studied light-driven variation in leaf photosynthesis for herbs spanning a range of sizes, and found that populations dominated by individuals with high rates of leaf photosynthesis were likely to grow faster than populations dominated by individuals with low rates of photosynthesis, but only when the light environment was allowed to vary naturally. This suggests that intraspecific variation in photosynthesis, coupled with variation in light availability, directly influences rates of population growth and therefore fitness. In a third study, I examined ITV across environmental gradients in Hawaii and found that the drivers of ITV were uncoupled in natives and invasives. Preliminary results from a companion study show that soil fertility influences the extent of ITV, particularly at smaller spatial scales, and therefore the degree to which native and invasive species overlap in their traits at the regional scale. Together, the findings from these case studies show that variation in environmental properties underlies variation in plant traits within species at both local and regional scale, with important consequences for ecological processes including population spread and invasion.
