Low-elevation Populations Research Articles

Climate change and the conservation of marmots

Conservation of marmots, large ground-dwelling squirrels restricted to the northern hemisphere, was impacted by direct human activity through hunting or modifying ecosystem dynamics. Regulating human activities reduced the threat of extinction. Climate change, an indirect human impact, threatens marmot survival through global warming and extreme weather events. Most marmot species occupy a harsh environment characterized by a short growing season and a long, cold season without food. Marmots cope with seasonality by hibernating. Their large size increases the efficiency of fat accumulation and its use as the sole energy source during hibernation. Marmot physiology is highly adapted to coping with low environmental temperatures; they are stressed by high heat loads. Global warming since the last ice age reduced the geographic distribution of some of the 15 species of marmots. Recent warming resulted in a movement upslope of their lower elevation boundary. This process likely will continue because warming is associated with drier unpalatable vegetation. Drought reduces reproduction and increases mortality; thus decreased summer rainfall in the montane environments where marmots live may cause local extinction. Snow cover, a major environmental factor, is essential to insulate hibernation burrows from low, stressful temperatures. However, prolonged vernal snow cover reduces reproduction and increases mortality. Montane areas currently lacking marmot populations because vernal snow cover persists beyond the time that marmots must begin foraging may become colonized if warming causes earlier snow melt. This benefit will be short-lived because decreased precipitation likely will result in unpalatable vegetation. Although some marmot populations are physiologically adapted to a warmer climate, global warming will increase too rapidly for any significant evolutionary response to dryness. The species that live in high, alpine meadows where tree and shrub invasions occur are most threatened with extinction. Captive breeding can preserve marmot species in the shortrun, but is impractical over the long-term. Widespread species are unlikely to be endangered in the foreseeable future, but local, low elevation populations will be lost.

Response to artificial drying until drought‐induced death in different elevation populations of a high‐mountain plant

Climate change is imposing warmer and more arid conditions on high-mountain Mediterranean pastures. The severity of these conditions is more intense in lower elevation populations and may be critical for their survival. In this context, we asked whether local adaptation plays an important role in the response of these populations to climate change, and if so, what mechanisms are involved. Previous works, involving reciprocal sowings suggested the existence of local adaptation in lower elevation populations of Silene ciliata, a perennial representative of high-mountain Mediterranean pastures. To determine if this local advantage is due to better adaptation to more intense water stress conditions, an experiment was conducted in which S.ciliata plants from three populations located at different elevations (Low, Intermediate and High) were subjected to severe artificial water stress. Results showed that plants from the Low population had greater tolerance to water stress than plants from the High population in the earliest stages of water shortage. Furthermore, responses of proteins to specific antibodies related to drought were evaluated. Two representative late-embryogenesis abundant (LEA) proteins known to play a role in water stress tolerance were expressed throughout the drought treatment in plants from the three populations, with some pattern differences among individuals within populations. This study detected slight evidence of local adaptation to water stress in populations from different elevations.

Post‐introduction evolution in the biological control agent Longitarsus jacobaeae (Coleoptera: Chrysomelidae)

Rapid evolution has rarely been assessed in biological control systems despite the similarity with biological invasions, which are widely used as model systems. We assessed post-introduction climatic adaptation in a population of Longitarsus jacobaeae, a biological control agent of Jacobaea vulgaris, which originated from a low-elevation site in Italy and was introduced in the USA to a high-elevation site (Mt. Hood, Oregon) in the early 1980s. Life-history characteristics of beetle populations from Mt. Hood, from two low-elevation sites in Oregon (Italian origin) and from a high-elevation site from Switzerland were compared in common gardens. The performance of low- and high-elevation populations at a low- and a high-elevation site was evaluated using reciprocal transplants. The results revealed significant changes in aestival diapause and shifts in phenology in the Mt. Hood population, compared with the low-elevation populations. We found increased performance of the Mt. Hood population in its home environment compared with the low-elevation populations that it originated from. The results indicate that the beetles at Mt. Hood have adapted to the cooler conditions by life-history changes that conform to predictions based on theory and the phenology of the cold-adapted Swiss beetles.

Geographic and temporal patterns in white spruce climate–growth relationships in Yukon, Canada

A growing body of evidence suggests that climate change will have complex effects on the boreal forests of western Canada. Studies that examine historical species responses over large geographic and climatic distances may provide insights into the temporal and spatial complexities underlying forest vulnerabilities to climate change. We analyzed annual tree-ring data collected from 56 white spruce (Picea glauca (Moench) Voss) populations across the species’ distribution in Yukon, Canada. Regional growth patterns were identified and correlation and response functions were computed to determine primary climatic influences on growth within each region. The temporal stability of climate–growth relationships was also tested in regions with sufficient climate records. Key results showed that white spruce radial growth shows strong geographic patterns across Yukon, likely reflecting large-scale climatic influences on growth. Drought appears to be a primary limitation to white spruce growth across much of southern Yukon, whereas snowfall and summer temperatures may be more important limitations in other regions. Spruce populations growing at high-elevations in central Yukon may be changing their climatic sensitivity over time and are converging with low-elevation populations in terms of climate–growth relationships. The considerable spatial and temporal complexity of climate–growth responses suggest that climate change will have varying implications for white spruce growth across Yukon.

Growth Sensitivity to Drought of Co-OccurringPinusspp. along an Elevation Gradient in Northern Mexico

Climate change is predicted to increase the frequency of severe drought, yet little information exists on the impacts of drought on dominant trees of Mexican pine forests, which are among the most biologically diverse forests in the world. We conducted the first comparison of growth sensitivity to drought of two co-occurring Pinus species in Mexico to understand whether growth of dominant pines of the Sierra Madre Occidental in northern Mexico is sensitive to drought and temperature variation and to understand how sensitivity differs between tree species and elevations. We sampled and analyzed tree-ring data across a 400-m elevation gradient for the years 1945–2004 for co-occurring Pinus engelmannii and Pinus lumholtzii at Basaseachi National Park, Chihuahua, Mexico. We hypothesized that growth sensitivity to drought would be highest at low elevations, annual basal area increment (BAI) would be lowest at low elevations, and winter precipitation would covary positively with BAI at all elevations. Growth sensitivity to drought, as measured by a wet-dry ring-width index ratio (W:D), was significantly higher for both species at low elevations (W:D range 2.2–2.8) than at intermediate and high elevations (WD range 1.5–1.9). Pinus engelmannii had significantly higher W:D (2.2) than P. lumholtzii (1.8). Annual BAI did not differ between elevations or species. Annual ring—width index was positively and significantly associated with winter (December–April) precipitation. This association was stronger at low elevations than at high elevations. Other seasons of precipitation and other climatic variables were not significantly associated with annual growth. Our results suggest that the increasing frequency and severity of drought predicted for this region in the coming decades will reduce growth of P. engelmannii and P. lumholtzii, with greater impacts on low-elevation populations and on P. engelmannii.

Population differentiation and plasticity in vegetative ontogeny: Effects on life‐history expression in Erysimum capitatum (Brassicaceae)

Distinguishing the contributions of phenotypic plasticity vs. population differentiation to variation in the life history of plants throughout their range is important for predicting their performance after dispersal or their responses to environmental change. In Erysimum capitatum, plants in alpine environments are iteroparous perennials, but those below tree line are semelparous perennials. We tested population differentiation and plasticity of life-history variation and explored the effects of plastic responses at the prereproductive stage on life-history expression. Plants from alpine and below tree-line populations were grown in a common greenhouse environment. Soil water content at the prereproductive stage was manipulated to simulate field condition. Because rosette ontogeny of E. capitatum (i.e., production of multiple rosettes, reproductive allocation, and degeneration of rosettes) was highly associated with in situ life-history variation, water effects on rosette ontogeny and life history were assessed. Plants from alpine populations showed higher postreproductive survival than those from low-elevation populations in the greenhouse environment, and such difference can be explained by differential rosette ontogeny at both the prereproductive and reproductive stage. In addition, rosette development at the reproductive stage was plastic to water availability at the prereproductive stage, which influences life-history expression as adults. Because water availability is lower at low-elevation sites, in situ population differentiation is likely caused by plasticity to water availability as well as by genetic differentiation or maternal effects. Plastic or evolutionary changes of prereproductive traits are expected to influence adult life-history expression, which possibly influence population demography.

Temporal variation in genetic diversity and effective population size of Mediterranean and subalpine Arabidopsis thaliana populations

Currently, there exists a limited knowledge on the extent of temporal variation in population genetic parameters of natural populations. Here, we study the extent of temporal variation in population genetics by genotyping 151 genome-wide SNP markers polymorphic in 466 individuals collected from nine populations of the annual plant Arabidopsis thaliana during 4 years. Populations are located along an altitudinal climatic gradient from Mediterranean to subalpine environments in NE Spain, which has been shown to influence key demographic attributes and life cycle adaptations. Genetically, A. thaliana populations were more variable across space than over time. Common multilocus genotypes were detected several years in the same population, whereas low-frequency multilocus genotypes appeared only 1 year. High-elevation populations were genetically poorer and more variable over time than low-elevation populations, which might be caused by a higher overall demographic instability at higher altitudes. Estimated effective population sizes were low but also showed a significant decreasing trend with increasing altitude, suggesting a deeper impact of genetic drift at high-elevation populations. In comparison with single-year samplings, repeated genotyping over time captured substantially higher amount of genetic variation contained in A. thaliana populations. Furthermore, repeated genotyping of populations provided novel information on the genetic properties of A. thaliana populations and allowed hypothesizing on their underlying mechanisms. Therefore, including temporal genotyping programmes into traditional population genetic studies can significantly increase our understanding of the dynamics of natural populations.

The effect of water temperature on gamete maturation and gamete quality in the European grayling (Thymalus thymallus) based on experimental data and on data from wild populations

To investigate the effect of water temperature on gamete maturation and gamete quality, European grayling (Thymalus thymallus) were held under different temperature regimes prior to spawning. Maturation of males and females and their gamete quality depended strongly on temperature regime. The highest percentages of maturing fish and highest gamete quality were obtained under a creek water temperature regime with natural seasonal fluctuations. In warmed creek water (3-4°C), at a constant temperature of 8-9°C, and under an abruptly increasing temperature, regime maturation rates and gamete quality were reduced. The effect was more pronounced in females than in males. The spawning dates of different wild Austrian grayling populations were also correlated with water temperature data collected during the last 10-15 years. The mean spawning date expressed as the number of days from 21 December until spawning ranged from 98 to 111 days for lower elevation populations, while it was considerably delayed for an alpine population. All populations spawned at water temperatures of 5.5-7.2°C. Regression analysis indicated that spawning date correlated with (1) the overall mean water temperature from 21 December until spawning, (2) the mean water temperature during both the last 10 days and 15 days before spawning, and (3) the difference between mean January temperature and that of the last 15 days before spawning. The regression functions indicate that an increase in water temperature from 21 December to spawning of 1°C advances spawning by 5½ days, and an increase of 1°C in the last 10-15 days advances spawning by 3½ days.

Adaptability to elevated temperature and nitrogen addition is greater in a high-elevation population than in a low-elevation population of Hippophae rhamnoides

Hippophae rhamnoides L. is a broadleaf deciduous woody shrub occurring in southwest China, where it has been widely used in ecological restoration. In this study we investigated growth and physiological responses of 2-year-old healthy seedlings to elevated temperature, nitrogen (N) addition and their combination in two contrasting populations from high and low elevations. In closed-top chamber experiments, two populations were subjected to two temperature conditions (ambient temperature and temperature elevated by 2.2 +/- 0.2 degrees C) and two N levels (0 and 25 g N m(-2) a(-1)). Compared with the control, increases in total leaf area (TLA), total chlorophyll content (TC), light-saturated photosynthetic rate (P-max), guaiacol peroxidase activity (POD), catalase activity (CAT) and carbon isotope composition (delta C-13) were greater in the high-elevation population than in the low-elevation population under elevated temperature. On the other hand, decreases in root and shoot biomass ratio (RS), TC, P-max, light saturation point (L-SP), light compensation point (L-CP), superoxide dismutase (SOD), POD, CAT and delta C-13 were lower in the high-elevation population than in the low-elevation population under N addition. Moreover, the combination of elevated temperature and N addition decreased RS, P-max, apparent quantum efficiency (Phi), SOD, POD and delta C-13 significantly more in the low-elevation population than in the high-elevation population. These results demonstrated that there are different adaptive strategies among H. rhamnoides populations, the high-elevation population exhibiting higher adaptability to elevated temperature and N addition than the low-elevation population.

Major histocompatibility complex class II gene diversity and tolerance to avian malaria in Hawaiian honeycreepers (Drepanidinae) (99.15)

Abstract Susceptibility to avian malaria differs both within and between species of Hawaiian honeycreepers. Due to their critical function in adaptive immunity, proteins encoded by Mhc genes may be key in the development of tolerance to Plasmodium relictum in low elevation populations of `amakihi (Hemignathus virens). To evaluate gene copy number, 263 Mhc class II peptide-binding region clones were sequenced from a captive family of `amakihi. Phylogenetic analysis suggests a minimum of 10 Mhc class II genes with detection of 35 unique alleles. Species comparisons (total 503 clones, eight birds/species) reveal that Mhc diversity is highest in `amakihi [d = 0.085(0.015)] with 98 distinct alleles detected (average 13.5/bird), followed by `apapane (Himatione sanguinea) [d = 0.068(0.012)] with 66 distinct alleles detected (average 11/bird) and in a highly susceptible species, the i`iwi (Vestiaria coccinea) diversity appears lowest with d = 0.057(0.011) and 66 distinct alleles detected (average 10.6/bird). Within `amakihi, Mhc sequences from birds from low elevation (56 distinct alleles, average 14.25 alleles/bird) and high elevation (50 distinct alleles, average 12.75 alleles/bird) subpopulations appear distinct with detection of only one shared allele. Microarray-based population level analysis (~1,000 individuals) of Mhc diversity in `amakihi detected at least one allele with a significantly higher frequency in low elevation populations than mid or high elevation subpopulations.

Genetic Variation in Ecophysiological and Survival Responses to Drought in Two Native Grasses:Koeleria macranthaandElymus elymoides

ABSTRACT. Genetic variation in ecophysiological and survival responses to drought was studied in 2 northern Arizona native grass species, Koeleria macrantha (Ledeb.) Schult, (prairie Junegrass) and Elymus elymoides (Raf.) Swezey. ssp. elymoides (squirreltail). Low- and high-elevation populations of each species were compared in a greenhouse common garden experiment that included simulated drought. Leaf gas-exchange characteristics were significantly affected by simulated drought and often by population elevation, but gas-exchange responses to drought were similar for high- and low-elevation populations. Compared to high-elevation populations, low-elevation populations of both species had higher net photosynthetic rate and predawn water potential, and for E. elymoides had higher stomatal conductance. Leaf-level water-use efficiency did not differ between populations for either species. Populations also differed significantly in leaf morphological characteristics related to water use. Compared to high-eleva...

Demography, reproduction, and dormancy along altitudinal gradients in three intermountain Allium species with contrasting abundance and distribution

Little is known about the variation in demographics, flower number, fruit set, and summer dormancy in Allium species native to the Intermountain West region of the United States. The purpose of this study was to investigate demographic patterns, summer dormancy traits, and variation in reproductive characteristics among habitats. Three populations of each of three species, Allium acuminatum, A. brandegei, and A. passeyi, were studied along an altitudinal gradient in northern Utah, USA, from 2004 to 2006. Demographic data were collected from individuals in permanent plots established in each population. Individual flowering plants were periodically monitored and used to calculate reproductive characteristics. Leaf area measurements throughout the 2005 growing season and soil temperature sensors were used to assess the relationship between habitat and dormancy characteristics. Populations of the widely distributed species, A. acuminatum and A. brandegei, were dominated by individuals in seedling and flowering stages while the restricted A. passeyi had populations containing a majority of individuals in the post-seedling, but non-flowering stage-class. There was a strong directional trend in A. acuminatum reproductive traits, with flower number and fruit set decreasing with increasing elevation. The mid-elevation A. brandegei populations were reproductively more successful than the high and low-elevation populations. The high-elevation A. passeyi population had more flowers per plant and higher fruit set in comparison to the lower elevation populations. The onset of summer dormancy as indicated by the timing of leaf senescence, was associated with high soil temperatures specific to each species. In general, the timing of leaf senescence was later in higher elevation populations in all species. A smaller proportion of non-flowering individuals in A. acuminatum and A. brandegei may indicate a high seedling mortality rate or a shorter juvenile phase in comparison to A. passeyi. The A. passeyi populations exhibit demographic characteristics of rare taxa; low seed production and low seedling recruitment. The high number of non-flowering plants in A. passeyi likely includes many reproductively mature individuals which are influenced by the unique habitat and environment of this species. Temperature is likely the key environmental cue inducing summer dormancy in all three species.

Genetic Variation in Cold Hardiness and Phenology Between and Within Turkish Red Pine (Pinus brutia Ten.) Populations: Implications for Seed Transfer

AbstractWind-pollinated seeds from 40 trees (half-sib families) were collected from each of six Turkish red pine (Pinus brutia Ten.) populations in southern Turkey. Two-year old seedlings were evaluated for growth, phenology and cold resistance in a common garden experiment established in Ankara, located outside the species’ natural range. Each family was represented with a six-tree row plot within each of the three replications. The below freezing temperatures (-15.2°C) observed in January and February of 2000 were sufficient to observe visually- assessable-cold damage to the seedlings. The populations significantly differed in all traits under investigation except for second flushing in 1999. Populations originating from more inland and higher elevation areas were more resistant to cold than coastal low elevation populations. Families within populations were significantly different as regards all traits except HT00. Family heritability for bud burst was 0.40, and ranged from 0.12 to 0.37 for height, and from 0.20 to 0.23 for bud set. Final height of cold damage prone seedlings was shorter than cold tolerant seedlings. Families with early bud-set, later bud-burst and shorter second flush shoots suffered less from cold damage. Considering the expected climate change in the eastern Mediterranean, there is a potential for using this species outside its natural range, especially in sites experiencing more continental climate since it will be possible to move the species 200-300 m in altitude and 2-3 degrees in latitude.

Geographic variation in growth response of Douglas‐fir to interannual climate variability and projected climate change

AbstractWe used 179 tree ring chronologies of Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] from the International Tree‐Ring Data Bank to study radial growth response to historical climate variability. For the coastal variety of Douglas‐fir, we found positive correlations of ring width with summer precipitation and temperature of the preceding winter, indicating that growth of coastal populations was limited by summer dryness and that photosynthesis in winter contributed to growth. For the interior variety, low precipitation and high growing season temperatures limited growth. Based on these relationships, we chose a simple heat moisture index (growing season temperature divided by precipitation of the preceding winter and current growing season) to predict growth response for the interior variety. For 105 tree ring chronologies or 81% of the interior samples, we found significant linear correlations with this heat moisture index, and moving correlation functions showed that the response was stable over time (1901–1980). We proceeded to use those relationships to predict regional growth response under 18 climate change scenarios for the 2020s, 2050s, and 2080s with unexpected results: for comparable changes in heat moisture index, the most southern and outlying populations of Douglas‐fir in Mexico showed the least reduction in productivity. Moderate growth reductions were found in the southern United States, and strongly negative response in the central Rocky Mountains. Growth reductions were further more pronounced for high than for low elevation populations. Based on regional differences in the slope of the growth–climate relationship, we propose that southern populations are better adapted to drought conditions and could therefore contain valuable genotypes for reforestation under climate change. The results support the view that climate change may impact species not just at the trailing edges but throughout their range due to genetic adaptation of populations to local environments.

Geographic variation in seed mass within and among nine species of Pedicularis (Orobanchaceae): effects of elevation, plant size and seed number per fruit

Summary 1. We examined geographic variation in mean individual seed mass (MISM) among 38 populations within and across nine Pedicularis species in the eastern Tibetan Plateau, measuring the effects of one extrinsic factor (elevation) and two intrinsic factors (plant size and mean seed number per fruit). 2. Across all populations, elevation is negatively correlated with MISM; within eight of nine species, this pattern is also observed among populations. This relationship, however, is not significant when controlling for variation in plant size or seeds per fruit. High‐elevation populations produce smaller plants with more seeds per fruit than low‐elevation populations; controlling for these variables eliminates the negative correlation between elevation and MISM. 3. Across all populations, the predicted trade‐off between MISM and seeds per fruit is consistently strong, with or without controlling for the effects of plant size. By contrast, the trade‐off between MISM and total seasonal fecundity can be detected only when controlling for plant size. 4. Independent of plant size, populations that produce small seeds do not support individuals with particularly low reproductive yield (fecundity × MISM). Accordingly, high‐elevation populations exhibit neither lower reproductive yield nor smaller seeds than expected given their lower biomass. 5. Synthesis. In Pedicularis, elevation, plant size and seeds per fruit are all correlated with MISM among populations across species. Elevation is less important, however, than intrinsic factors in determining the MISM of a population; the effect of elevation on MISM disappears when the effects of intrinsic factors are controlled statistically. The observed decline in MISM with increasing elevation is therefore partly mediated by the decline in plant size and partly by an increase in mean seed number per fruit with elevation. Altitudinal variation in MISM across populations or species has been described before, but this is the first study to control for the effect of intrinsic factors simultaneously. This result calls into question the conclusions of studies that have detected geographic variation in MISM without controlling for variation in intrinsic factors.

Changing demography and dispersal behaviour: ecological adaptations in an alpine butterfly

High mountain ecosystems are extreme habitats for all organisms and therefore demand specific adaptations. In this context, we studied the ecology of the butterfly Euphydryas aurinia debilis in the High Tauern (Austria) and compared the obtained data against the ecology of the species in lower elevation habitats. We performed mark-release-recapture studies over the entire flight periods (end of June to end of July) in 2007 and 2008 to analyse the fundamental ecological parameters of a population. The demography of males and females was similar in both years, and no indication of typical protandry was detected. We observed a generally low dispersal of the individuals in both years, but males dispersed significantly more than females in 2008; this finding of low vagility was supported by allozyme analyses. Furthermore, butterflies survived periods of several days of continuously closed snow cover without any indication of increased mortality rates. In these three traits, this alpine population of E. aurinia apparently has ecological and physiological adaptations to the extreme requirements of high-altitude habitats and strongly deviates from the lower elevation populations.

Evolutionary diversification of cryophilic Grylloblatta species (Grylloblattodea: Grylloblattidae) in alpine habitats of California

BackgroundClimate 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.ResultsOur analysis reveals a pattern of deep genetic subdivision among geographically isolated populations of Grylloblatta in California. Alpine populations diverged from low elevation populations and subsequently diversified. Using a Bayesian relaxed clock model and both uncalibrated and calibrated measurements of time to most recent common ancestor, we reconstruct the temporal diversification of alpine Grylloblatta populations. Based on calibrated relaxed clock estimates, evolutionary diversification of Grylloblatta occurred during the Pliocene-Pleistocene epochs, with an initial dispersal into California during the Pliocene and species diversification in alpine clades during the middle Pleistocene epoch.ConclusionsGrylloblatta species exhibit a high degree of genetic subdivision in California with well defined geographic structure. Distinct glacial refugia can be inferred within the Sierra Nevada, corresponding to major, glaciated drainage basins. Low elevation populations are sister to alpine populations, suggesting alpine populations may track expanding glacial ice sheets and diversify as a result of multiple glacial advances. Based on relaxed-clock molecular dating, the temporal diversification of Grylloblatta provides evidence for the role of a climate-driven species pump in alpine species during the Pleistocene epoch.

Age structure and body size of the Chuanxi Tree Frog Hyla annectans chuanxiensis from two different elevations in Sichuan (China)

Age, body size, and growth patterns in the subtropical anuran Hyla annectans chuanxiensis from high (Dengchigou Protection Station) and low (Lingguan Town) elevations in Baoxing County of Sichuan province (China) were described using skeletochronology. Females were significantly older than males at the low-elevation site, but there was no significant difference between the sexes at the high-elevation site. Age at sexual maturity of both males and females was 2 years at the high-elevation site, whereas males matured at 1 year and females at 2 years at the low-elevation site. Males and females from the low-elevation population reached a maximum age of 3 and 4 years, respectively, whereas males and females from the high-elevation population reached a maximum age of 4 and 5 years, respectively. At both sites, females were significantly larger than males. Females and males from the high-elevation population were larger than individuals from the low-elevation population. When the effect of age was controlled, the differences in body size of the two populations were significant only for females. Von Bertalanffy growth curves indicated that the growth rates in males was greater than in females in both populations. They also showed that the growth of both sexes slowed at an earlier age in the low-elevation population than in the high-elevation population. The findings suggest that age is a major factor underlying body size patterns for both sexes, but that the elevation of the locality affects the body size of females.

Competition and drought limit the response of water-use efficiency to rising atmospheric carbon dioxide in the Mediterranean fir Abies pinsapo

The gas-exchange and radial growth responses of conifer forests to climatic warming and increasing atmospheric CO2 have been widely studied. However, the modulating effects of variables related to stand structure (e.g., tree-to-tree competition) on those responses are poorly explored. The basal-area increment (BAI) and C isotope discrimination (C stable isotope ratio; delta13C) in the Mediterranean fir Abies pinsapo were investigated to elucidate the influences of stand competition, atmospheric CO2 concentrations and climate on intrinsic water-use efficiency (WUEi). We assessed the variation in delta13C of tree-rings from dominant or co-dominant trees subjected to different degrees of competition. A high- (H) and a low-elevation (L) population with contrasting climatic constraints were studied in southern Spain. Both populations showed an increase in long-term WUEi. However, this increase occurred more slowly at the L site, where a decline of BAI was also observed. Local warming and severe droughts have occurred in the study area over the past 30 years, which have reduced water availability more at lower elevations. Contrastingly, trees from the H site were able to maintain high BAI values at a lower cost in terms of water consumption. In each population, trees subjected to a higher degree of competition by neighboring trees showed lower BAI and WUEi than those subjected to less competition, although the slopes of the temporal trends in WUEi were independent of the competitive micro-environment experienced by the trees. The results are consistent with an increasing drought-induced limitation of BAI and a decreasing rate of WUEi improvement in low-elevation A. pinsapo forests. This relict species might not be able to mitigate the negative effects of a decrease in water availability through a reduction in stomatal conductance, thus leading to a growth decline in the more xeric sites. An intense and poorly asymmetric competitive environment at the stand level may also act as an important constraint on the adaptive capacity of these drought-sensitive forests to climatic warming.

Correlated trait responses to multiple selection pressures in larval amphibians reveal conflict avoidance strategies

Abstract1. Larval amphibians frequently experience simultaneous, conflicting selection pressures from ultraviolet‐B (UV‐B) radiation and predation risk, two stressors that can select for opposing defence strategies. When both UV‐B and predators are present, individuals can reconcile potential conflicts by correlating particular trait responses (e.g. combining dark or light body colouration with increased or decreased activity rates to create an appropriate multiple stressor strategy). Optimal combinations of body colour and activity rate are predicted to change across an elevation gradient with increasing UV‐B exposure.2. In this study, we tested how larval amphibians combine changes in body colouration and activity rates to create a correlated response to potentially conflicting selection pressures. We quantified activity and colour response in two amphibian species, the pacific treefrog (Hyla regilla) and the long‐toed salamander (Ambystoma macrodactylum), from both high and low elevation populations, and exposed individuals to both a common predator and naturally relevant levels of UV‐B.3. Hyla regilla and A. macrodactylum individuals from low elevation populations responded with correlated response strategies while high elevation populations did not. Low elevation H. regilla coupled decreased activity rates to reduce predator detection with dark body colouration to screen out UV‐B. Low elevation A. macrodactylum adopted cryptic colouration when predators were present and decreased activity in response to UV‐B. Individuals from high elevation H. regilla and A. macrodactylum populations responded only with changes in activity and not colour change.4. The observed population differences may reflect variation in selection strengths across an elevation gradient. High elevation habitats may require individuals to focus defence efforts on the greatest potential risk. Additionally, pigmentation changes may not be an adequate defence in these UV‐B intense habitats.