Plant population differentiation and climate change: responses of grassland species along an elevational gradient

Mountain ecosystems are particularly susceptible to climate change. Characterizing intraspecific variation of alpine plants along elevational gradients is crucial for estimating their vulnerability to predicted changes. Environmental conditions vary with elevation, which might influence plastic responses and affect selection pressures that lead to local adaptation. Thus, local adaptation and phenotypic plasticity among low and high elevation plant populations in response to climate, soil and other factors associated with elevational gradients might underlie different responses of these populations to climate warming. Using a transplant experiment along an elevational gradient, we investigated reproductive phenology, growth and reproduction of the nutrient‐poor grassland species Ranunculus bulbosus, Trifolium montanum and Briza media. Seeds were collected from low and high elevation source populations across the Swiss Alps and grown in nine common gardens at three different elevations with two different soil depths. Despite genetic differentiation in some traits, the results revealed no indication of local adaptation to the elevation of population origin. Reproductive phenology was advanced at lower elevation in low and high elevation populations of all three species. Growth and reproduction of T. montanum and B. media were hardly affected by garden elevation and soil depth. In R. bulbosus, however, growth decreased and reproductive investment increased at higher elevation. Furthermore, soil depth influenced growth and reproduction of low elevation R. bulbosus populations. We found no evidence for local adaptation to elevation of origin and hardly any differences in the responses of low and high elevation populations. However, the consistent advanced reproductive phenology observed in all three species shows that they have the potential to plastically respond to environmental variation. We conclude that populations might not be forced to migrate to higher elevations as a consequence of climate warming, as plasticity will buffer the detrimental effects of climate change in the three investigated nutrient‐poor grassland species.     

Smaller,more diverse and on the way to the top: Rapid community shifts of montane wild bees within an extraordinary hot decade

Aim

Global warming is assumed to restructure mountain insect communities in space and time. Theory and observations along climate gradients predict that insect abundance and richness, especially of small-bodied species, will increase with increasing temperature. However, the specific responses of single species to rising temperatures, such as spatial range shifts, also alter communities, calling for intensive monitoring of real-world communities over time.

Location

German Alps and pre-alpine forests in south-east Germany.

Methods

We empirically examined the temporal and spatial change in wild bee communities and its drivers along two largely well-protected elevational gradients (alpine grassland vs. pre-alpine forest), each sampled twice within the last decade.

Results

We detected clear abundance-based upward shifts in bee communities, particularly in cold-adapted bumble bee species, demonstrating the speed with which mobile organisms can respond to climatic changes. Mean annual temperature was identified as the main driver of species richness in both regions. Accordingly, and in large overlap with expectations under climate warming, we detected an increase in bee richness and abundance, and an increase in small-bodied species in low- and mid-elevations along the grassland gradient. Community responses in the pre-alpine forest gradient were only partly consistent with community responses in alpine grasslands.

Main Conclusion

In well-protected temperate mountain regions, small-bodied bees may initially profit from warming temperatures, by getting more abundant and diverse. Less severe warming, and differences in habitat openness along the forested gradient, however, might moderate species responses. Our study further highlights the utility of standardized abundance data for revealing rapid changes in bee communities over only one decade.     

Effect of altitude on the genetic structure of an Alpine grass, Poa hiemata

Background and Aims

The persistence of plants inhabiting restricted alpine areas under climate change will depend upon many factors including levels of genetic variation in adaptive traits, population structure, and breeding system.

Methods

Using microsatellite markers, the genetic structure of populations of a relatively common alpine grass, Poa hiemata, is examined across three altitudinal gradients within the restricted Australian alpine zone where this species has previously been shown to exhibit local adaptation across a narrow altitudinal gradient.

Key Results

Genetic variation across six microsatellite markers revealed genetic structuring along altitudinal transects, and a reduction in genetic variation at high and low altitude extremes relative to sites central within transects. There was less genetic variation among transect sites compared with altitudinal gradients within transects, even though distances among transects were relatively larger. Central sites within transects were less differentiated than those at extremes.

Conclusions

These patterns suggest higher rates of gene flow among sites at similar altitudes than along transects, a process that could assist altitudinal adaptation. Patterns of spatial autocorrelation and isolation by distance changed with altitude and may reflect altered patterns of dispersal via pollen and/or seed. There was evidence for selfing and clonality in neighbouring plants. Levels of gene flow along transects were insufficient to prevent adaptive changes in morphological traits, given previously measured levels of selection.Key words: Poa hiemata, genetic structure, altitudinal gradient, microsatellite, gene flow, climate change     

Evolutionary diversification of cryophilic <Emphasis Type="Italic">Grylloblatta</Emphasis>species (Grylloblattodea: Grylloblattidae) in alpine habitats of California

Background  

Climate in alpine habitats has undergone extreme variation during Pliocene and Pleistocene epochs, resulting in repeated expansion and contraction of alpine glaciers. Many cold-adapted alpine species have responded to these climatic changes with long-distance range shifts. These species typically exhibit shallow genetic differentiation over a large geographical area. In contrast, poorly dispersing organisms often form species complexes within mountain ranges, such as the California endemic ice-crawlers (Grylloblattodea: Grylloblattidae: Grylloblatta). The diversification pattern of poorly dispersing species might provide more information on the localized effects of historical climate change, the importance of particular climatic events, as well as the history of dispersal. Here we use multi-locus genetic data to examine the phylogenetic relationships and geographic pattern of diversification in California Grylloblatta.     

Past vegetation dynamics in the Yellowstone region highlight the vulnerability of mountain systems to climate change

Aim

Reconstruct the long‐term ecosystem dynamics of the region across an elevational gradient as they relate to climate and local controls. In particular, we (1) describe the dominant conifers' history; (2) assess changes in vegetation composition and distribution; and (3) note periods of abrupt change versus stability as means of better understanding vegetation responses to environmental variability.

Location

Greater Yellowstone Ecosystem (GYE; USA).

Time period

16.5 ka bp ‐present.

Major taxa studied

Juniperus, Picea, Abies, Pinus, Pseudotsuga.

Methods

The vegetation reconstruction was developed from 15 pollen records. Results were interpreted based on modern pollen–vegetation relationships estimated from a suite of regression‐based approaches.

Results

Calibrated pollen data suggest that late‐glacial vegetation, dominated by shrubs and Juniperus, lacks a modern counterpart in the area. Picea, Abies and Pinus expanded at 16 ka bp in association with postglacial warming and co‐occurred in mixed‐conifer parkland/forest after 12 ka bp . This association along with Pinus contorta forest, which was present after 9 ka bp , has persisted with little change at middle and high elevations to the present day. This stability contrasts with the dynamic history of plant communities at low elevations, where shifts between parkland, steppe and forest over the last 8,000 years were likely driven by variations in effective moisture and fire.

Main conclusions

The postglacial vegetation history of the GYE highlights the dynamic nature of mountain ecosystems and informs on their vulnerability to future climate change: (1) most of the conifers have been present in the area for >12,000 years and survived climate change by adjusting their elevational ranges; (2) some plant associations have exhibited stability over millennia as a result of nonclimatic controls; and (3) present‐day forest cover is elevationally more compressed than at any time in history, probably due to the legacy of the Medieval Climate Anomaly and the Little Ice Age.     

Climate change shifts natural selection and the adaptive potential of the perennial forb Boechera stricta in the Rocky Mountains

Heritable genetic variation is necessary for populations to evolve in response to anthropogenic climate change. However, antagonistic genetic correlations among traits may constrain the rate of adaptation, even if substantial genetic variation exists. We examine potential genetic responses to selection by comparing multivariate genetic variance–covariances of traits and fitness (multivariate Robertson–Price identities) across different environments in a reciprocal transplant experiment of the forb Boechera stricta in the Rocky Mountains. By transplanting populations into four common gardens arrayed along an elevational gradient, and exposing populations to control and snow removal treatments, we simulated future and current climates and snowmelt regimes. Genetic variation in flowering and germination phenology declined in plants moved downslope to warmer, drier sites, suggesting that these traits may have a limited ability to evolve under future climates. Simulated climate change via snow removal altered the strength of selection on flowering traits, but we found little evidence that genetic correlations among traits are likely to affect the rate of adaptation to climate change. Overall, our results suggest that climate change may alter the evolutionary potential of B. stricta, but reduced expression of genetic variation may be a larger impediment to adaptation than constraints imposed by antagonistic genetic correlations.     

Enough space in a warmer world? Microhabitat diversity and small‐scale distribution of alpine plants on mountain summits

Aim

Global warming is predicted to shift distributions of mountain species upwards, driven by a release from climatic restrictions at their upper distribution limit and increased biotic pressure at their lower distribution limit. In alpine ecosystems, which are characterized by large microclimatic diversity and sparse vegetation cover, the relative importance of abiotic and biotic drivers for species distribution is poorly understood. To disentangle abiotic and biotic mechanisms affecting distributions of alpine species, we investigated how alpine plant species with differing elevational ranges and frequency trends over the past century differ in their microhabitat distribution, and how they respond to neighbouring vegetation.

Location

A total of 11 summits (2635—3410 m a.s.l.) in SE‐Switzerland.

Methods

We quantified the microscale abundance of 12 species in relation to biogeographic (frequency trend, i.e., change in occurrences over the past century, and elevational range on summits) and local microhabitat characteristics (temperature, substrate type). We assessed species size traits in relation to neighbouring vegetation characteristics to investigate possible neighbour interactions.

Results

Species with increasing frequency on summits over the past century were most abundant on scree and warmer slopes. Species with negative or stable frequency trends on summits were more abundant on organic soil and colder slopes. The preferred microhabitats of the latter were rarest overall, decreased with increasing elevation, and had the most competitive neighbours. Size of one high‐alpine specialist, Ranunculus glacialis was negatively related to cover of neighbouring vegetation, whereas other species showed no response to neighbours.

Main conclusions

Long‐term frequency trends of species correlate with their microhabitat association. Species with most negative frequency trends show preferences for the rarest microhabitat conditions, where they likely experience higher competitive pressure in a warming climate. This finding emphasizes the importance of characterizing microhabitat associations and microclimatic diversity to assess present and future distributions of alpine plant species.

     

Distribution,species diversity and life-form spectra of plant communities along an altitudinal gradient in the northern slopes of Qilianshan Mountains,Gansu, China

We studied the distribution pattern, species diversity and life-formspectra of plant communities along an altitudinal gradient in the mid-sectionofthe northern slopes of Qilianshan Mountains by means of multivariate analyses.Two data sets (167 species × 75 plots, 10 environmental variables ×75 plots), originated from the fieldworks in 1998–1999, were subjected toTWINSPAN and DCCA, resulting in 8 major plant communities: 1)Asterothamnus centraliasiaticus–Halogetonarachnoideus desert grassland on azonal substrates from 1450 to 1600m and 2) zonal Reaumuria soogorica desertgrassland on gravels from 1470 to 1900 m; 3) Stipaprzewalskii–Stipa purpurea montane grassland from 2200 to 2900m; 4) Polygonum viviparum alpine grasslandfrom 2900 to 3700 m; 5) Caraganastenophylla–Ajaniafruticulosa dry-warm shrubland from 2350 to 2800 m; 6)Sabina przewalskii mid-wet warm forest from 2700 to 3300m; 7) Picea crassifolia cold coniferousforestfrom 2450 to 3200 m; 8) Caragana jubatawet-cold alpine shrubland from 3100 to 3700 m. Species diversityand species richness of both grasslands and forests peaked at the intermediateportion of the elevational gradient. Evenness might be strongly influenced byeither biotic or abiotic factors at a local scale, while seems quiteindependentof an elevational gradient at landscape scales. Beta-diversity decreased from1500 to 3700 m, indicating that species turnover declined withincreased elevation. Both richness of life-form and total species richness in agiven altitudinal belt (gamma-diversity) peaked at intermediate elevations,while relative species richness of different life-form varied differently alongthe altitudinal gradient.     

西藏东达山3种嵩草属植物气孔特征沿海拔的变化

嵩草属(Kobresia)植物是藏东南高山草甸的优势种和建群种,对该区畜牧业发展和维持生态系统平衡起着重要作用。选择西藏左贡县东达山为研究地点,从林线开始,海拔每升高约100m设置1个样带直至高山草甸分布边缘,共8个样带,调查各样带中物种的组成及盖度,并依据相对盖度和相对频度计算3种嵩草植物矮生嵩草(K.humilis)、线叶嵩草(K.capillifolia)和大花嵩草(K.macrantha)在群落中的重要值,同时取样观察它们叶片远、近轴面表皮细胞形态,测量气孔长度及保卫细胞宽度,计算气孔密度,探讨嵩草属植物对海拔梯度的适应性。结果表明:(1)3种嵩草属植物叶表皮细胞均呈波浪状,气孔器仅分布于远轴面,近轴面无气孔器分布。(2)3种嵩草属植物气孔密度沿海拔梯度的变化均呈单峰曲线分布格局,且在海拔4 537m样带处达到最大值,并表现为矮生嵩草(777.6个/mm2)线叶嵩草(476.4个/mm2)大花嵩草(414.3个/mm2)。(3)随海拔的增加,矮生嵩草和线叶嵩草气孔长度显著增大(P0.05),而保卫细胞宽度显著减小;但大花嵩草气孔长度随海拔的升高而显著减小,保卫细胞宽度基本保持不变。(4)矮生嵩草和线叶嵩草气孔密度、长度和保卫细胞宽度与海拔梯度均显著相关,气孔特征对海拔梯度变化的敏感程度高,与其在群落中重要值高的分布特征一致;而大花嵩草仅气孔密度和长度与海拔梯度显著相关,气孔特征对海拔梯度变化的敏感性低,与其在群落中重要值低的分布特征一致;嵩草属植物气孔密度、长度和保护细胞宽度与海拔梯度之间的相关性,反映出它们在海拔梯度上对生境的适应程度。可见,3种嵩草属植物气孔特征对海拔梯度上生境变化的适应性不同,从而影响它们在群落中的分布范围和物种优势度,其中矮生嵩草和线叶嵩草对环境变化敏感,而大花嵩草对环境变化相对不敏感;保卫细胞宽度与气孔长度同样对植物适应环境变化起重要作用。     

Local environment,not local adaptation,drives leaf‐out phenology in common gardens along an elevational gradient in Acadia National Park,Maine

Premise of the Study

Climate‐driven changes in phenology are substantially affecting ecological relationships and ecosystem processes. The role of variation among species has received particular attention; for example, variation among species’ phenological responses to climate can disrupt trophic interactions and can influence plant performance. Variation within species in phenological responses to climate, however, has received much less attention, despite its potential role in ecological interactions and local adaptation to climate change.

Methods

We constructed three common gardens across an elevation gradient on Cadillac Mountain in Acadia National Park, Maine, to test population‐level responses in leaf‐out phenology in a reciprocal transplant experiment. The experiment included three native species: low bush blueberry (Vaccinium angustifolium), sheep's laurel (Kalmia angustifolia), and three‐toothed cinquefoil (Sibbaldiopsis tridentata).

Key Results

Evidence for local adaptation of phenological response to temperature varied among the species, but was weak for all three. Rather, variation in phenological response to temperature appeared to be driven by local microclimate at each garden site and year‐to‐year variation in temperature.

Conclusions

Population‐level adaptations in leaf‐out phenology appear to be relatively unimportant for these species in Acadia National Park, perhaps a reflection of strong genetic mixing across elevations, or weak differences in selection on phenological response to spring temperatures at different elevations. These results concur with other observational data in Acadia and highlight the utility of experimental approaches to understand the importance of annual and local site variation in affecting phenology both among and within plant species.     

Climate,host phylogeny and the connectivity of host communities govern regional parasite assembly

Aim

Identifying barriers that govern parasite community assembly and parasite invasion risk is critical to understand how shifting host ranges impact disease emergence. We studied regional variation in the phylogenetic compositions of bird species and their blood parasites (Plasmodium and Haemoproteus spp.) to identify barriers that shape parasite community assembly.

Location

Australasia and Oceania.

Methods

We used a data set of parasite infections from >10,000 host individuals sampled across 29 bioregions. Hierarchical models and matrix regressions were used to assess the relative influences of interspecies (host community connectivity and local phylogenetic distinctiveness), climate and geographic barriers on parasite local distinctiveness and composition.

Results

Parasites were more locally distinct (co‐occurred with distantly related parasites) when infecting locally distinct hosts, but less distinct (co‐occurred with closely related parasites) in areas with increased host diversity and community connectivity (a proxy for parasite dispersal potential). Turnover and the phylogenetic symmetry of parasite communities were jointly driven by host turnover, climate similarity and geographic distance.

Main conclusions

Interspecies barriers linked to host phylogeny and dispersal shape parasite assembly, perhaps by limiting parasite establishment or local diversification. Infecting hosts that co‐occur with few related species decreases a parasite's likelihood of encountering related competitors, perhaps increasing invasion potential but decreasing diversification opportunity. While climate partially constrains parasite distributions, future host range expansions that spread distinct parasites and diminish barriers to host shifting will likely be key drivers of parasite invasions.     

The role of selection and historical factors in driving population differentiation along an elevational gradient in an island bird

Adaptation to local environmental conditions and the range dynamics of populations can influence evolutionary divergence along environmental gradients. Thus, it is important to investigate patterns of both phenotypic and genetic variations among populations to reveal the respective roles of these two types of factors in driving population differentiation. Here, we test for evidence of phenotypic and genetic structure across populations of a passerine bird (Zosterops borbonicus) distributed along a steep elevational gradient on the island of Réunion. Using 11 microsatellite loci screened in 401 individuals from 18 localities distributed along the gradient, we found that genetic differentiation occurred at two spatial levels: (i) between two main population groups corresponding to highland and lowland areas, respectively, and (ii) within each of these two groups. In contrast, several morphological traits varied gradually along the gradient. Comparison of neutral genetic differentiation (F_ST) and phenotypic differentiation (P_ST) showed that P_ST largely exceeds F_ST at several morphological traits, which is consistent with a role for local adaptation in driving morphological divergence along the gradient. Overall, our results revealed an area of secondary contact midway up the gradient between two major, cryptic, population groups likely diverged in allopatry. Remarkably, local adaptation has shaped phenotypic differentiation irrespective of population history, resulting in different patterns of variation along the elevational gradient. Our findings underscore the importance of understanding both historical and selective factors when trying to explain variation along environmental gradients.     

Upward elevation and northwest range shifts for alpine Meconopsis species in the Himalaya–Hengduan Mountains region

Climate change may impact the distribution of species by shifting their ranges to higher elevations or higher latitudes. The impacts on alpine plant species may be particularly profound due to a potential lack of availability of future suitable habitat. To identify how alpine species have responded to climate change during the past century as well as to predict how they may react to possible global climate change scenarios in the future, we investigate the climatic responses of seven species of Meconopsis, a representative genus endemic in the alpine meadow and subnival region of the Himalaya–Hengduan Mountains. We analyzed past elevational shifts, as well as projected shifts in longitude, latitude, elevation, and range size using historical specimen records and species distribution modeling under optimistic (RCP 4.5) and pessimistic (RCP 8.5) scenarios across three general circulation models for 2070. Our results indicate that across all seven species, there has been an upward shift in mean elevation of 302.3 m between the pre‐1970s (1922–1969) and the post‐1970s (1970–2016). The model predictions suggest that the future suitable climate space will continue to shift upwards in elevation (as well as northwards and westwards) by 2070. While for most of the analyzed species, the area of suitable climate space is predicted to expand under the optimistic emission scenario, the area contracts, or, at best, shows little change under the pessimistic scenario. Species such as M. punicea, which already occupy high latitudes, are consistently predicted to experience a contraction of suitable climate space across all the models by 2070 and may consequently deserve particular attention by conservation strategies. Collectively, our results suggest that the alpine high‐latitude species analyzed here have already been significantly impacted by climate change and that these trends may continue over the coming decades.     

Variation of biomass and morphology of the cushion plant Androsace tapete along an elevational gradient in the Tibetan Plateau

Alpine ecosystems are among those biomes that are most vulnerable to climate change. Cushion plants are an important life form of alpine ecosystems and will likely play a critical role for the resilience of these habitats to climate change. We studied cushion size distribution and different measures of the compactness of cushions (biomass and rosette density, leaf area index) of the cushion plant, Androsace tapete along an elevational gradient from 4500 to 5200 m a.s.l. in the Nyainqentanglha Mountains of the central Tibetan Plateau. Cushion size distribution, total cover, and compactness of cushions varied substantially along the elevational gradient. At the driest site at low elevation we found the lowest total cushion cover, a particularly high proportion of very small cushions, and the most compact cushions (highest rosette and biomass densities, and leaf area index (LAI) per cushion). Our results indicate that in the semi‐arid Tibetan Plateau water availability is the more important climate factor than temperature affecting cushion plant traits and morphology.     

The role of climate in constraining the elevational range of the Water Pipit Anthus spinoletta in an alpine environment

The study of determinants of species’ ranges along elevational gradients may shed light on the ecological factors that constrain their distribution and fundamental niche. We analysed the influence of the climate, habitat at different spatial scales and topography on Water Pipit Anthus spinoletta density in mountain landscapes across a wide elevational gradient. Variables associated with spring and annual temperature values were the main determinants of Water Pipit density, especially at the lower distributional limit (700–1200 m asl), where the species avoided warmer areas. At high‐elevation sites (1600–2300 m asl), the main constraint to the species’ distribution was habitat structure and composition, with steep rocky areas being avoided. Highest densities were found in open but locally heterogeneous habitat at intermediate to high elevations, and the habitat variables that played a major role at the landscape scale were medium‐tall shrublands and woodlands, but with contrasting effects depending on elevation. These results suggest that different sets of variables may constrain density, and effects may differ at the upper and lower elevational limits, with climate being more important at lower elevations and local habitat more important at higher elevations. Ongoing global warming is likely to cause an upward shift in range boundaries of alpine species, but local habitat features could constrain the upward expansion, resulting in range contractions accompanying range shift.     

A weak upward elevational shift in the distributions of breeding birds in the Italian Alps

Aim To test whether bird assemblages are shifting upwards in their elevational distribution in synchrony with current climate warming and/or habitat changes. Location A gradient of elevation in the Italian Alps (Alta Valsessera, Piedmont). Methods We used data from two recent atlas surveys performed on a 1 × 1 km grid at an 11‐year interval (1992–94 and 2003–05). We modelled the elevational gradient of avifaunal composition, using a sample‐based approach, in an effort to detect evidence for an upward elevational shift of bird zonation. Changes in species richness were controlled for. The results from this analysis were compared with those obtained using a species‐based approach. Changes in climate and landscape between the two surveys were assessed using local meteorological data and Corine Land Cover maps, respectively. Results We detected small avifaunal changes between the two surveys: (1) mean elevations increased for the majority of species, but the average change was not significantly different from zero; (2) the species richness increased, but this was mainly due to an increase in sampling effort; and (3) a change in species composition was detected, which was at the limit of significance and corresponded on average to a 29‐m upward elevational shift in the distribution of the avifauna. The shift was the same for open land and forest bird communities. During the same period, the mean temperature increased by c. 1 °C in the area, and a slight trend towards vegetation closure by woody plants was detected. Main conclusions The use of fine‐scale breeding bird atlases in mountainous regions, together with ordination methods, provides a sensitive tool to test and measure elevational shifts in species ranges, but the results have to be interpreted carefully. In our case, the observed elevational shift in the distributions of the avifauna cannot unambiguously be attributed to climate warming. This shift is smaller than expected from the regional increase in temperature, which raises the question of how closely bird distributions match climate change.     

Evolutionary response of cold-adapted chasmophytic plants to Quaternary climatic oscillations in the Mountains of Central Asia (a world hotspot of biodiversity)

Aim

Past climatic oscillations are the main driving force of evolutionary changes in alpine species. Species' response to paleoclimatic oscillations is crucial in forecasting their future response in face of climate warming. The aim of this research is to explore the effect of climatic fluctuations on the evolutionary history, demography, and distribution of high-mountain bellflowers (Campanula lehmanniana complex), the flagship and taxonomically problematic members of chasmophytic vegetation within an underexplored biodiversity hotspot, the Mountains of Central Asia.

Location

Central Asia (Tian Shan, Alai and Zeravshan-Hissar Mountains).

Methods

We used molecular data (ITS, cpDNA, DArTseq-based SNPs) of 262 individuals (70 for the phylogeny reconstruction, and 247 from 31 localities for population studies). We analysed the data using phylogenetic and molecular clock reconstructions, coalescent simulations, and ecological niche modelling.

Results

Tertiary isolation between the Tian-Shanian and Pamir-Alaian populations led to the differentiation of the two main lineages (~5–6 Mya) corresponding to C. eugeniae and C. lehmanniana, whereas further Quaternary isolation into subregions led to intraspecific genetic differentiation, which starts almost simultaneously for both species (~2.7–1.5 Mya). The relatively small genetic admixture among populations indicates rare historic events of connectivity. In response to Holocene warming, the analysed species experienced a substantial decline in effective population size. Currently, the distribution of both taxa is highly influenced by precipitation in the coldest and driest quarters.

Main Conclusions

Our results highlight a general principle that glacial–interglacial cycles and contemporary island-like habitats distribution, shape the genomic variation of high-mountain species. The similar declining demographic trend of examined taxa may suggest the overall response to ongoing climate warming. The results underline also the urgent need for conservation action in alpine regions to preserve their biodiversity.     

Climate change and recent genetic flux in populations of <Emphasis Type="Italic">Drosophila robusta</Emphasis>

Background  

Studied since the early 1940's, chromosomal polymorphisms in the deciduous woods species Drosophila robusta have been characterized by well-defined latitudinal, longitudinal, and elevational clines, but – until at least ten years ago – stable, local population frequencies. Recent biogeographical analyses indicate that D. robusta invaded North America from southeast Asia and has persisted in eastern temperate forests for at least 20–25 my without speciating. The abundant chromosome polymorphisms found across the range of D. robusta are thus likely to be relatively ancient, having accumulated over many well known climatic cycles in North America. Sufficient long-term data are now available such that we can now gauge the rate of these evolutionary changes in natural populations due to environmental change.     

Elevational gradients in bird diversity in the Eastern Himalaya: an evaluation of distribution patterns and their underlying mechanisms

Background

Understanding diversity patterns and the mechanisms underlying those patterns along elevational gradients is critically important for conservation efforts in montane ecosystems, especially those that are biodiversity hotspots. Despite recent advances, consensus on the underlying causes, or even the relative influence of a suite of factors on elevational diversity patterns has remained elusive.

Methods and Principal Findings

We examined patterns of species richness, density and range size distribution of birds, and the suite of biotic and abiotic factors (primary productivity, habitat variables, climatic factors and geometric constraints) that governs diversity along a 4500-m elevational gradient in the Eastern Himalayan region, a biodiversity hotspot within the world''s tallest mountains. We used point count methods for sampling birds and quadrats for estimating vegetation at 22 sites along the elevational gradient. We found that species richness increased to approximately 2000 m, then declined. We found no evidence that geometric constraints influenced this pattern, whereas actual evapotranspiration (a surrogate for primary productivity) and various habitat variables (plant species richness, shrub density and basal area of trees) accounted for most of the variation in bird species richness. We also observed that ranges of most bird species were narrow along the elevation gradient. We find little evidence to support Rapoport''s rule for the birds of Sikkim region of the Himalaya.

Conclusions and Significance

This study in the Eastern Himalaya indicates that species richness of birds is highest at intermediate elevations along one of the most extensive elevational gradients ever examined. Additionally, primary productivity and factors associated with habitat accounted for most of the variation in avian species richness. The diversity peak at intermediate elevations and the narrow elevational ranges of most species suggest important conservation implications: not only should mid-elevation areas be conserved, but the entire gradient requires equal conservation attention.     

Use of intraspecific variation in thermal responses for estimating an elevational cline in the timing of cold hardening in a sub‐boreal conifer

To avoid winter frost damage, evergreen coniferous species develop cold hardiness with suitable phenology for the local climate regime. Along the elevational gradient, a genetic cline in autumn phenology is often recognised among coniferous populations, but further quantification of evolutionary adaptation related to the local environment and its responsible signals generating the phenological variation are poorly understood. We evaluated the timing of cold hardening among populations of Abies sachalinensis, based on time series freezing tests using trees derived from four seed source populations × three planting sites. Furthermore, we constructed a model to estimate the development of hardening from field temperatures and the intraspecific variations occurring during this process. An elevational cline was detected such that high‐elevation populations developed cold hardiness earlier than low‐elevation populations, representing significant genetic control. Because development occurred earlier at high‐elevation planting sites, the genetic trend across elevation overlapped with the environmental trend. Based on the trade‐off between later hardening to lengthen the active growth period and earlier hardening to avoid frost damage, this genetic cline would be adaptive to the local climate. Our modelling approach estimated intraspecific variation in two model components: the threshold temperature, which was the criterion for determining whether the trees accumulated the thermal value, and the chilling requirement for trees to achieve adequate cold hardiness. A higher threshold temperature and a lower chilling requirement could be responsible for the earlier phenology of the high‐elevation population. These thermal responses may be one of the important factors driving the elevation‐dependent adaptation of A. sachalinensis.