Climatic niche breadth can explain variation in geographical range size of alpine and subalpine plants

Understanding the environmental factors determining the distribution of species with different range sizes can provide valuable insights for evolutionary ecology and conservation biology in the face of expected climate change. However, little is known about what determines the variation in geographical and elevational ranges of alpine and subalpine plant species. Here, we examined the relationship between geographical and elevational range sizes for 80 endemic rhododendron species in China using Spearman’s rank-order correlation. We ran the species distribution model – maximum entropy modelling (MaxEnt) – with 27 environmental variables. The importance of each variable to the model prediction was compared for species groups with different geographical and elevational range sizes. Our results showed that the correlation between geographical and elevational range sizes of rhododendron species was not significant. Climate-related variables were found to be the most important factors in shaping the distributional ranges of alpine and subalpine plant species across China. Species with geographically and elevationally narrow ranges had distinct niche requirements. For geographical ranges, the narrow-ranged species showed less tolerance to niche conditions than the wide-ranged species. For elevational ranges, compared with the wide-ranged species, the narrow-ranged species showed an equivalent niche breadth, but occurred at different niche position along the environmental gradient. Our findings suggest that over large spatial extents the elevational range size can be a complementary trait of alpine and subalpine plant species to geographical range size. Climatic niche breadth, especially the range of seasonal variability, can explain species’ geographical range sizes. Changes in climate may influence the distribution of rhododendrons, with the effects likely being felt most by species with either a narrow geographical or narrow elevational range

Adaptations of plant species to environmental changes

The future climate change represents the biggest challenge for plant and animal species. The scenarios forecasted by the IPCC predict a global increase in temperatures and regional changes in rainfall during this century. Therefore, studying the relationship between climate and several traits of species is crucial in our understanding of the effects that future changes may have on plants. Species growing along a wide environmental gradient are a suitable study model to verify the relationship between intraspecific variability and both current and future climate. The aim of my PhD project is to analyse the relationship between environmental variability and variation in morphological traits, germination capacity and genetic structure of Lilium pomponium, using a multidisciplinary approach. The results of this study may enhance our understanding about the possible responses of this threatened species to environmental changes. Lilium pomponium is an endemism of the Ligurian and Maritime Alps spanning along a wide altitudinal gradient (100 and 2000 m a.s.l.), ranging from a Mediterranean to a subalpine climate. Our results show that the populations exposed to different environmental pressures have variations in floral characteristics, these variations likely play an important role in reducing among-populations variability in reproductive output. Germination tests show that the increase in temperature may negatively affect seeds germination capacity. Nevertheless, projections of thermal requirement for seed germination under future climatic conditions suggest that populations will probably respond to future temperature increase shifting their germination phenology. Moreover, in the future the species may find suitable ecological conditions for seed germination in new areas at higher altitudes. Finally, genetic analysis suggests that there is no clear pattern of diversity and differentiation between populations, which may be related to the topographic complexity of the areas and to the biogeographical history of the species. Overall, the results obtained suggest that high among-populations variability found in L. pomponium may be a bet-hedging strategy to cope with unpredictable environmental conditions occurring in Mediterranean climate and that it might also represent a successful strategy to face the future environmental change

Retreat to refugia: Severe habitat contraction projected for endemic alpine plants of the Olympic Peninsula

Abstract: Premise of the study- The unique geography of the Olympic Peninsula has created a flora with exceptional endemism that may face high rates of extinction due to climate change. Conserving endemic taxa requires a deeper understanding of general and individual species’ responses to warming in topographically complex environments. The Olympic Mountains provide an unparalleled opportunity to test predicted responses and inform conservation plans for threatened alpine taxa. Methods- I developed Species Distribution Models (SDMs) for five endemic alpine plants of the Olympic Peninsula to estimate the potential impact of climate change on these rare taxa. First, I created high-resolution raster surfaces on the Olympic Peninsula with climatic and topographic variables for the current period and the year 2080. I used Principal Components Analysis to visualize changes in climate niche-space in the Olympic alpine and the exposure of the five endemics to changing conditions. I then constructed climate and topographic-based SDMs, to estimate changes in the distribution of habitat for each taxon. Finally, I identified potential thermal refugia as areas where suitable habitat conditions would remain by the year 2080. Key Results- The Olympic alpine will experience novel environmental conditions in the future, with a pronounced decrease in winter snow and an increase in growing season moisture stress. Suitable habitat will be greatly reduced for all five focal taxa, with thermal refugia remaining only on the highest peaks of the eastern Olympics. Topographic SDMs suggested further decreases in the total amount of projected suitable habitat. Furthermore, I identified differences in the proportion of suitable micro-topography within each taxon’s climate envelope that greatly affect the species-specific climate change prognosis. Conclusions- The Olympic alpine endemics are stranded on ever shrinking habitat islands, and are projected to lose 85-99% of their suitable habitat by 2080. Their survival depends on their ability to persist in isolated thermal refugia on the highest peaks. Within these refugia, the distribution of micro-topography may be a critical factor in determining the long term survival prospects of threatened taxa. The Olympic Mountains and their endemic taxa are a model system illustrating the biogeographic characteristics that underpin vulnerability to climate change. Globally, taxa with narrow distributions that are already occupying the coldest locally available habitats should be considered extremely vulnerable, and may be at the forefront of climate-driven extinctions

Tackling intraspecific genetic structure in distribution models better reflects species geographical range

Genetic diversity provides insight into heterogeneous demographic and adaptive history across organisms' distribution ranges. For this reason, decomposing single species into genetic units may represent a powerful tool to better understand biogeographical patterns as well as improve predictions of the effects of GCC (global climate change) on biodiversity loss. Using 279 georeferenced Iberian accessions, we used classes of three intraspecific genetic units of the annual plant Arabidopsis thaliana obtained from the genetic analyses of nuclear SNPs (single nucleotide polymorphisms), chloroplast SNPs, and the vernalization requirement for flowering. We used SDM (species distribution models), including climate, vegetation, and soil data, at the whole-species and genetic-unit levels. We compared model outputs for present environmental conditions and with a particularly severe GCC scenario. SDM accuracy was high for genetic units with smaller distribution ranges. Kernel density plots identified the environmental variables underpinning potential distribution ranges of genetic units. Combinations of environmental variables accounted for potential distribution ranges of genetic units, which shrank dramatically with GCC at almost all levels. Only two genetic clusters increased their potential distribution ranges with GCC. The application of SDM to intraspecific genetic units provides a detailed picture on the biogeographical patterns of distinct genetic groups based on different genetic criteria. Our approach also allowed us to pinpoint the genetic changes, in terms of genetic background and physiological requirements for flowering, that Iberian A. thaliana may experience with a GCC scenario applying SDM to intraspecific genetic units

Postglacial range expansion of high‐elevation plants is restricted by dispersal ability and habitat specialization

Aim: Species' ecological traits influence their spatial genetic patterns. Bedrock preference strongly shapes the phylogeography of alpine plants, but its interactions with other ecological traits have rarely been disentangled. Here, we explore whether dispersal ability and degree of habitat specialization account for divergent postglacial expansion patterns of high-elevation plants in spite of similar bedrock preference. Location: The Pyrenees, southwestern Europe. Taxon: Cirsium glabrum (Asteraceae), Salix pyrenaica (Salicaceae) and Silene borderei (Caryophyllaceae). Methods: Phylogenetic, genetic structure and demographic modelling analyses based on restriction-site- associated DNA sequencing (RADseq) data from a range-wide populational sampling were conducted. Occurrence data and environmental variables were used to construct species distribution models, which were projected under current and Last Glacial Maximum conditions, and were combined with RADseq data to reconstruct the postglacial history of the study species. The degree of habitat specialization of each species was estimated based on the plant communities within which they occur, and their climatic niche breadth. Results: Salix pyrenaica, which occupies a broad range of habitats, shows a high level of range filling, a blurred genetic structure and an admixture cline between the two main genetic groups, congruent with rapid postglacial expansion. The microsite specialists C. glabrum and S. borderei exhibit a strong genetic structure and low levels of range filling, indicative of slow postglacial expansion. The good disperser C. glabrum shows higher levels of admixture between genetic groups and weaker population differentiation than the poor disperser S. borderei. Main Conclusions: Factors other than bedrock preference have a strong impact on the postglacial range dynamics of high-elevation species. Habitat specialization plays an important role, allowing species occupying a broad range of habitats to more rapidly expand their ranges after environmental change. The effect of dispersal ability is lower than expected for the study species

Environmental Niche Divergence In The Kalmia Lineage: Integrating Phylogeny, Community Composition And Ecology To Understand Patterns Of Regional Plant Diversity

The ongoing synthesis of the formerly disparate fields of ecology and evolution is resulting in a proliferation of insights, highlighting the interdependence and feedback between ecological and evolutionary processes. There is increasing evidence that evolutionary processes can influence community dynamics through geographic patterns of speciation, mutualist interactions, and other processes governing community phylogenetic patterns (Weber et al., 2017; Weeks et al., 2016). Here we adopt a clade-focused perspective to understand patterns of niche evolution in a single lineage, and subsequently address the regional community context of habitats which have facilitated the persistence and diversification of members of the genus. Hypothesized to have originated in eastern North America, the genus Kalmia contains ten species exhibiting widely varying and disjunct distributions while occupying a large spectrum of habitats- from alpine bogs to xeric sandhill scrub (Gillespie & Kron, 2013; Weakley, 2015). Given the extent of ecological and geographic divergence, we asked the following questions: what potential processes or factors underlie the patterns of lineage bifurcation and habitat differentiation in Kalmia, and what has been the role of phylogenetic niche conservatism in these lineage divergences? We constructed ecological niche models for seven of ten species of Kalmia using available climatic and topographic variables, and identified the variables contributing most to the observed distributions. We calculated niche overlap among all species, and subsequently used these metrics to assess the potential geographic pattern of divergence using a recent molecular phylogeny for the genus. We then subjected these results to an age-range correlation (ARC) test. We assessed the extent of niche conservatism in both morphological as well as abiotic traits that we could further use to infer processes underlying niche evolution. We suggest that the long evolutionary history of the Kalmia lineage in eastern North America coinciding with climatic and/or topographic changes has resulted in considerable niche lability, subsequently allowing Kalmia species to track suitable oligotrophic habitats while diverging in larger-scale climatic and topographic niche characteristics as well as less ecologically important morphological traits.To understand speciation and niche evolution in a community context, we investigated the habitat use among three of these closely related taxa that exhibit overlapping disjunct ranges. We assessed the taxonomic and phylogenetic patterns of local communities along an elevation gradient among three distinct floristic regions of the southeastern US that all contain at least one Kalmia species. We asked if there were differences in abiotic and biotic attributes among coastal plain, piedmont and mountain habitats, given that they all support the same focal taxa. Using community data from both field collection and an open-source vegetation database, we find that differences in edaphic and phylogenetic patterns among regions were minimal with only soil pH exhibiting differences. Our results of taxonomic and phylogenetic beta diversity support the prevalence of allopatric speciation patterns from closely related lineages establishing in similar habitats. This research highlights the importance of considering habitat-specific lineage pools when interpreting patterns of regional diversity and local community assembly, as well as consideration for lineage-specific history when evaluating regional diversity patterns

Biogeography and ecology of geographically distant populations of sibling Cryptocephalus leaf beetles

Different populations of two closely related species, Cryptocephalusflavipes and C. bameuli, from western (Alps, Apennines and Pyrenees) and central Europe (Poland, Ukraine and Pannonia) were analysed. On the basis of DNA sequences from two genes, cox1 and ef1-alpha, distinctiveness of both species was confirmed. Nevertheless, possible hybrids were identified in Carpathian mountains. We found a significant genetic differentiation among populations of C. flavipes and C. bameuli from distant regions but a high genetic similarity between populations of C. bameuli from north and south of the Carpathians. Demographic estimates suggest a past population expansion in the case of C. bameuli and a recent one for C. flavipes, possibly occurred during Pleistocene and Holocene, respectively. Distribution modelling showed that C. flavipes is typically present in the mountain systems, whereas C. bameuli is associated with hilly areas of central and eastern Europe. Based on the present data, Last Glacial Maximum refugia of both species were located in the Alpine region and Black Sea coasts, but on different elevations. The characterization of the insect diet, through a DNA metabarcoding approach targeting the trnL plant intron, demonstrated a significant differentiation of food preferences between the two species, as well as between geographic populations within the species