COS 72-3
Life history and environmental determinants of desert annual plant responses to rainfall variability

Wednesday, August 12, 2015: 8:40 AM
342, Baltimore Convention Center
Robert K. Shriver, University Program in Ecology, Duke University

Despite widespread predictions of changing environmental variability both within and across years, little attention had been given to how variability within years will affect populations. Increasing environmental variability is often assumed to drive down long-term population growth, but the generality of this is contingent on an organism’s life history. Relying on a unique set of daily demographic models, I used integral projection models to simulate the response of four summer annual plants in the Chihuahuan desert to changes in daily environmental variability with climate change. Namely, changes in the timing and intensity of rainfall (i.e. fewer rainfall events, but more rain in each event) across low, average, and high rainfall years. Although all of these are relatively short-lived annual plants, they exhibit differing life history strategies, with two being comparatively fast-growers with low-survival, and the other two being slower-growers with higher-survival. 


Changes stochastic population growth differed across life histories, but the changes were not always consistent.  Population growth of both fast-growing, low-survival species declined 20% with increasing intra-annual variability, relative to current average conditions. However, the slow-growing, high-survival species differed with one species predicted to have a slight, 10%, decline in population growth while the other had a more dramatic, 50%, decline in population growth with increasing variability.  Interestingly, in all species a doubling of only intra-annual rainfall variability led to nearly the same predicted decline in population growth as a 50% reduction in total rainfall.  These predictions include only the single species direct responses to precipitation, and interactions among species may further worsen the situation for some species. My results provide evidence that intra-annual variability will be important in determining plant responses to climate change, even without changes in average annual conditions.