Demographic compensation arises when vital rates change in opposite directions across populations, buffering the variation in population growth rates, and is a mechanism often invoked to explain the stability of species geographic ranges. However, studies on demographic compensation have disregarded the effects of temporal variation in vital rates and their temporal correlations, despite theoretical evidence that stochastic dynamics can affect population persistence in temporally varying environments. We carried out a seven-year-long demographic study on the perennial plant Arabis alpina (L.) across six populations encompassing most of its elevational range. We discovered demographic compensation in the form of negative correlations between the means of plant vital rates, but also between their temporal coefficients of variation, correlations and elasticities. Even if their contribution to demographic compensation was small, this highlights a previously overlooked, but potentially important, role of stochastic processes in stabilising population dynamics at range margins. N, number of individuals. Daily mean temperature (T mean ) and daily temperature range (T range ) were measured with in-situ data-loggers. Values are means and (minimum and maximum) over plots and years for the month of July. Means and 95% confidence interval for the stochastic population growth rate (logk s ) were calculated by randomly sampling the values calculated using matrix populations models constructed using predicted vital rates from 200 bootstrapped demographic datasets and 10 resampled imputed datasets. The N per site per year is shown in Figure S2.

No abstract

 Due to its genetic proximity with Arabidopsis thaliana, Arabis alpina (Brassicaceae) is increasingly used as a perennial model species in studies of molecular evolution and adaptation. We studied the demography of A. alpina in six natural sites widely differing in their degree of disturbance, slope and vegetation, and encompassing the full altitudinal range of the species. We estimated three vital rates (growth, reproductive effort and survival) for individuallymarked plants, studied for six years (2008)(2009)(2010)(2011)(2012)(2013)(2014). We characterized the thermic conditions of each site with different thermal variables obtained using in situ continuous-time data loggers. Although A. alpina is described as a perennial species, the average life expectancy was only 1.82 years and most plants died before setting seeds. Plant size was a strong predictor of all three vital rates. Mean daily temperature showed a positive effect on growth and a negative effect on survival.Furthermore, reproductive effort covaried negatively with survival, suggesting a mechanism of demographic compensation acting on an elevational gradient. Synthesis. These results are informative of the selective pressures experienced by A. alpina in natural conditions and will help design experimental and molecular studies of local adaptation in this species.

No abstract