Demographic differences across the range of a xeric-adapted alpine plant

Background/Question/Methods

Investigation of the demographic differences between populations across a species’ range will inform our mechanistic understanding of potential range shifts. The magnitude of range shifts resulting from climate change will be driven by an interaction of each demographic rates’ proportional influence on the overall population growth rate (elasticity), the magnitude of fluctuations in demographic rates driven by climate (environmental sensitivity), and the extent of change in climate in the local area. Each of these values may change independently across a species’ range. In 2013, I surveyed populations of a long-lived alpine perennial (Ivesia lycopodioides var. scandularis, Rosaceae) across the entirety of its arid altitudinal range in the White Mountains, CA. In the last two decades there has been a significant increase in temperature and decrease in precipitation in the White Mountains, and it is suggested that this species is vulnerable to extensive range contraction. In twenty plots across six sites, the following measurements for each individual were taken: number of rosettes, leaves, stalks, inflorescences, seeds and longest leaf length. I asked if the stage structure and fecundity rates of the populations were different depending on microclimatic growing-season soil moisture and temperature in both the range center and edge.

Results/Conclusions

My results suggest a complex interaction between environmental conditions and population dynamics across the range of Ivesia lycopodioides var. scandularis. There is significant increase in plant size (p = 0.00172), but decrease in population density at higher elevations, (p = 0.0387).  At the lower range edge the population is skewed toward a much smaller age class, corroborating previous work on this species. However, compared to the 1988 study, the current population density is greater at lower elevations and reduced at higher elevation. Average number of leaves per individual and average number of flowering stalks per individual increase with elevation (p = 0.00533). These relationships indicate increased vigor and fecundity in the more central part of the species range compared to the lower trailing edge. Future work includes a full factorial, landscape- scale Life Table Response Experiment (LTRE) in which I will quantify and compare population sensitivity to augmented precipitation and temperature across this species’ range, allowing a novel inference of the probability and direction of range shifts in a warmer, drier future in eastern California.