Range-wide variation in life-history phenotypes: spatiotemporal plasticity across the latitudinal gradient of the evergreen oak Quercus ilex

Aim Stressful environments, like those at the limits of species ranges, are closely associated with the selective establishment of particular traits, yet the mechanisms behind this relationship are poorly understood. Our main aim was to investigate spatial and temporal phenotypic plasticity related to environmental conditions and biogeographical origin. Location A latitudinal gradient along Iberian Peninsula and Morocco, western Mediterranean Basin. Methods We investigate the intra-specific variability in the Mediterranean oak Quercus ilex subsp. ballota, covering most of its latitudinal range. Acorns were collected in the years 2009, 2011, 2012 and 2013 from natural populations and were grown under controlled conditions. We measured acorn mass and germination dynamics, as well as seedling morphology. Results Field data showed significant differences in stand structure among populations. The southernmost population presented the smallest trees, followed by the northernmost population. Core-range trees registered higher values for leaf-nitrogen concentration. Leaf size showed latitudinal variation, with the lowest values at the northern range limit. In addition, the germination pattern also significantly differed among populations, showing a latitudinal pattern of variation ( i.e. the southern populations germinated earlier). Fresh acorn mass showed significant within- and among-population differences, displaying a range margin pattern ( i.e. similarities between the edge populations). Furthermore, seedling total weight and biomass allocation also followed the same pattern. The models explaining the most part of the trait variance were related mainly to climatic variables ( reflecting temporal variability), while the random effect of the models ( population) showed a range margin pattern with lower values in edge populations compared with core populations. Main conclusions Similar phenotypic traits among individuals native to the periphery of the distribution range were found despite the temporal variability, suggesting adaptation to stressful environments at the range edges.