Hampe, A. | Search bioRxiv

bioRxiv2019

Asymmetry in marginal population performance foreshadows widespread species range shifts

AimRange shifts are expected to occur when populations at one range margin perform better than those at the other margin, yet no global trend in population performances at range margins has been demonstrated empirically across a wide range of taxa and biomes. Here we test the prediction that, if impacts of ongoing climate change on population performance are widespread, then populations from the high-latitude margin (HLM) should perform as well as or better than central populations, whereas populations at low-latitude margins (LLM) populations should perform worse. LocationGlobal Time period1898-2020 Major taxa studiedPlants and animals MethodsTo test our prediction, we used a meta-analysis quantifying the empirical support for asymmetry in the performance of high- and low-latitude margin populations compared to central populations. Performance estimates were derived from 51 papers involving 113 margin-centre comparisons from 54 species and 705 populations. We then related these performance differences to climatic differences among populations. We also tested whether patterns are consistent across taxonomic kingdoms (plants vs. animals) and across habitats (marine vs. terrestrial). ResultsPopulations at margins performed significantly worse than central populations and this trend was primarily driven by the low-latitude margin. Although the difference was of small magnitude, it was largely consistent across biological kingdoms and habitats. The differences in performance were positively related to the difference in average temperatures between populations during the period 1985-2016. Major conclusionsThe observed asymmetry in marginal population performance confirms predictions about the effects of global climate change. It indicates that changes in demographic rates in marginal populations, despite extensive short-term variation, can serve as early-warning signals of impending range shifts.

ecology↗

bioRxiv2019

Range-wide variation in local adaptation and phenotypic plasticity of fitness-related traits in Fagus sylvatica and their implications under climate change

AimTo better understand and more realistically predict future species distribution ranges, it is critical to account for local adaptation and phenotypic plasticity in populations responses to climate. This is challenging because local adaptation and phenotypic plasticity are trait-dependent and traits co-vary along climatic gradients, with differential consequences for fitness. Our aim is to quantify local adaptation and phenotypic plasticity of vertical and radial growth, leaf flushing and survival across Fagus sylvatica range and to estimate each trait contribution to explain the species occurrence.\n\nLocationEurope\n\nTime period1995 - 2014; 2070\n\nMajor taxa studiedFagus sylvatica L.\n\nMethodsWe used vertical and radial growth, flushing phenology and mortality of Fagus sylvatica L. recorded in BeechCOSTe52 (>150,000 trees). Firstly, we performed linear mixed-effect models that related trait variation and co-variation to local adaptation (related to the planted populations climatic origin) and phenotypic plasticity (accounting for the climate of the plantation), and we made spatial predictions under current and RCP 8.5 climates. Secondly, we combined spatial trait predictions in a linear model to explain the occurrence of the species.\n\nResultsThe contribution of plasticity to intra-specific trait variation is always higher than that of local adaptation, suggesting that the species is less sensitive to climate change than expected; different traits constrain beechs distribution in different parts of its range: the northernmost edge is mainly delimited by flushing phenology (mostly driven by photoperiod and temperature), the southern edge by mortality (mainly driven by intolerance to drought), and the eastern edge is characterised by decreasing radial growth (mainly shaped by precipitation-related variables in our model); considering trait co-variation improved single-trait predictions.\n\nMain conclusionsPopulation responses to climate across large geographical gradients are trait-dependent, indicating that multi-trait combinations are needed to understand species sensitivity to climate change and its variation across distribution ranges.

ecology↗