TITLE 1 Disjunct populations of European vascular plant species keep the same climatic 2 niches 3 4

122 Aim Research on how the climatic niche varies across a species range has focused on a 123 limited number of species, mostly invasive, and has not been very conclusive so far. Here, we 124 assess the degree of niche conservatism between distant populations of alpine plant species 125 that have been established for thousands of years. 126 Location European Alps and Fennoscandia. 127 Methods Focusing on a representative sample (n = 389) of the pool of terrestrial vascular 128 plant species (n = 888) occurring in both the Alps and Fennoscandia, we used two 129 complementary approaches to test for and quantify climatic-niche shifts for species with 130 Alpine and Fennoscandian populations that are either strictly disjunct (n = 31) or at least 131 distant (n = 358). First, we used a species distribution modelling approach to test for a region 132 effect on each species’ climatic niche. Second, we quantified niche overlap and shifts in niche 133 width (i.e., ecological amplitude) and position (i.e., ecological optimum) within a bi134 dimensional climatic space. 135 Results Only one species (3%) with strictly disjunct populations and 58 species (16%) with at 136 least distant populations showed a region effect on their climatic niche. Niche overlap was 137 higher for species with strictly disjunct populations (0.50±0.1) than for species with distant 138 populations (0.42±0.1), and highest for Arctic-alpine species (0.55±0.06). Estimated climatic 139 niches were, on average, larger and located towards warmer and wetter conditions in the Alps. 140 Main conclusion Climatic niches seem to be generally conserved between populations that 141 are separated between the Alps and Scandinavia and likely have been so for 10,-15,000 years, 142 despite the fact that populations in the Alps and Fennoscandia became adapted over time to 143 their respective sets of regional climatic conditions. Therefore, the basic assumption of 144 species distribution models that species’ climatic niche is constant in space and time – at least 145 one time scales 10 years or less – seems to be largely valid for arctic-alpine plants. 146 6