Structure of communities of ground-living spiders along altitudinal gradients

Differences in the altitudinal composition of ground-living spider communities were studied by pitfall trapping in western Norway. These data plus compilations of information from the literature were used to investigate features in the size composition, temporal appearance and spatial distribution of species. Spiders at the highest altitude had the widest distribution both in terms of geographical and altitudinal range. At the lowest altitude species were more often stenochronous than at higher altitudes. The size composition, reflecting food choice of the spiders, tended to be bimodal with increasing altitude. It is argued that small spiders are segregated mainly along the habitat dimension (searchers), while the larger ones are segregated with respect to diel activity patterns and food choice (pursuers). We suggest that mountain spider faunas in temperate regions at high latitudes mainly consist of widely distributed and easily dispersed species.     

Performance of two alpine plant species along environmental gradients in an alpine meadow ecosystem in central Tibet

Understanding how biotic interactions and abiotic conditions affect plant performance is important for predicting changes in ecosystem function and services in variable environments. We tested how performances of Astragalus rigidulus and Potentilla fruticosa change along gradients of biotic interactions (represented by plant species richness, abundance of the dominant plant species Kobresia pygmaea, and herbivory intensity) and abiotic conditions (represented by elevation, aspect, and slope steepness) across a semi-arid landscape in central Tibet. Redundancy analyses showed that the biotic variables explained 30 and 39 % of the variation in overall performance of A. rigidulus (P = 0.03) and P. fruticosa (P = 0.01), respectively. Abiotic variables did not contribute significantly to variation among A. rigidulus populations. Plant size decreased with species richness in both species and was larger on south- rather than north-facing slopes. Reproductive effort for both species was significantly negatively related to the abundance of K. pygmaea and both species had larger reproductive effort on south- rather than north- and west-facing slopes. The proportion of biomass allocated to sexual reproduction in P. fruticosa was negatively correlated with K. pygmaea abundance and herbivory intensity. The population density of P. fruticosa was positively related to elevation, species richness, and K. pygmaea abundance. We conclude that plant performance at a local scale was more strongly related to biotic than abiotic conditions, but different components of plant performance responded differently to predictor variables and the responses were species-specific. These findings have important implications for rangeland management under changing environmental conditions.     

Effects of disturbance on plant regrowth along snow pack gradients in alpine habitats

Human disturbance in alpine habitats is expected to increase, and improved knowledge of short-term recovery after disturbance events is necessary to interpret vegetation responses and formulate planning and mitigation efforts. The ability of a plant community to return to its original state after a disturbance (community resilience) depends on species composition and environmental conditions. The aim of this study is to analyze initial short-term effects of disturbance in alpine plant communities in contrasting climates (oceanic vs. continental; central Norway). We used a nested block-design to examine vegetative regrowth and seedling recruitment after experimental perturbation. Three plant community types along the snow pack gradient were exposed to (1) no disturbance, (2) clipping, and (3) clipping and uprooting. Slow vegetative regrowth and low seedling establishment rates were found in dry alpine ridges and late-melting oceanic snowbed communities. Leeside habitats with intermediate snow conditions were found more resilient. The difference was related to growth form and species diversity. Woody species, which dominated in ridges and oceanic snowbeds, showed the most negative response to disturbance. Species-rich plant communities dominated by graminoids and herbs showed higher rates of regrowth. Species richness seems to cause resilience to the plant communities through higher response diversity. Plant communities at the extreme ends of abiotic gradients, ridges and late-melting snowbeds, will be most sensitive to both disturbance and environmental change. In an up-scaled human-used landscape disturbance effects will be amplified and further limit recovery to a pre-disturbance state.     

Variations in species and functional plant diversity along climatic and grazing gradients

Different components of biodiversity may vary independently of each other along environmental gradients giving insights into the mechanisms that regulate species coexistence. In particular, the functional diversity (FD) or the presence of rare or endemic species in natural assemblages do not necessarily increase with species diversity. We studied if different components of plant species diversity (species richness, Simpson diversity, evenness) varied similarly to FD (measured as a generalization of the Simpson index) and rarity along grazing intensity and climatic gradients. Plots under different sheep grazing regimes (high and low intensity, abandonment) were surveyed in five locations along a climatic gradient in north-eastern Spain, from semi-arid lowland to moist upland locations. Variation in species diversity, functional diversity and rarity followed different patterns. Species diversity was lowest in water-stressed environments (arid locations and southern aspects) and increased with grazing more makedly in humid locations. The FD was comparable between the most species-poor and species-rich locations and decreased with grazing in the moistest location, i.e. where species diversity markedly increased. The FD did not show a strong correlation with species richness nor with the Simpson index and less specious communities could show the highest functional diversity. The rarest species in the region were more frequently found in the abandoned areas, which held the lowest species diversity. Consequently, the mechanisms that enhance the diversity of species do not necessarily support a functional differentiation among those species or the maintenance of rare species in a region. We hypothesize that the degree of dependence of functional diversity on species diversity might be mostly related to the amplitude of the species' traits pool and on how species partition the niche space available.     

高寒草甸不同草地群落物种多样性与生产力关系研究

生态系统的结构和功能、生物多样性与生产力的关系问题是近年来群落生态学中研究的中心问题,其中,生态系统生产力水平是其功能的重要表现形式,用4种不同草地类型探讨自然群落的物种多样性与生产力关系.结果表明,矮嵩草草甸、小嵩草草甸和金露梅灌丛群落中物种多样性与生产力的关系呈线性增加关系,藏嵩草沼泽化草甸群落中线性增加关系不显著,这表明群落生产力除受物种多样性的影响外,也受物种本身特征和环境资源的影响.不同的环境资源和环境异质性是形成群落结构特征、物种多样性分布格局差异的主要原因之一.     

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.     

Testing limits to adaptation along altitudinal gradients in rainforest Drosophila

Given that evolution can generate rapid and dramatic shifts in the ecological tolerance of a species, what prevents populations adapting to expand into new habitat at the edge of their distributions? Recent population genetic models have focused on the relative costs and benefits of migration between populations. On the one hand, migration may limit adaptive divergence by preventing local populations from matching their local selective optima. On the other hand, migration may also contribute to the genetic variance necessary to allow populations to track these changing optima. Empirical evidence for these contrasting effects of gene flow in natural situations are lacking, largely because it remains difficult to acquire. Here, we develop a way to explore theoretical models by estimating genetic divergence in traits that confer stress resistance along similar ecological gradients in rainforest Drosophila. This approach allows testing for the coupling of clinal divergence with local density, and the effects of genetic variance and the rate of change of the optimum on the response to selection. In support of a swamping effect of migration on phenotypic divergence, our data show no evidence for a cline in stress-related traits where the altitudinal gradient is steep, but significant clinal divergence where it is shallow. However, where clinal divergence is detected, sites showing trait means closer to the presumed local optimum have more genetic variation than sites with trait means distant from their local optimum. This pattern suggests that gene flow also aids a sustained response to selection.     

Central boreal mire plant communities along soil nutrient potential and water content gradients

Peatlands have traditionally been exploited in forestry and agriculture over the boreal region, yet they also provide substantial source of fuel production. The large-scale exploitation of peatlands has raised a concern about the diversity of mire plant communities. We studied composition of mire plant communities along soil nutrient potential and water content gradients, to recognize the areas with the high plant diversity. Soil electrical conductivity (EC_b) was measured to characterise soil nutrient regimes and soil dielectric permittivity (DP) the soil (volumetric) water regimes. A total of 115 mire sites were studied in the central boreal region of south-western Finnish Lapland. We found that Ward’s hierarchical cluster analysis produced eight stable EC_b and DP clusters with discrete vegetation compositions. On the basis of a locally weighted regression analysis (Loess), Carex dioica L., Comarum palustre L., Equisetum fluviatile L., Menyanthes trifoliata L., and Scorpidium scorpioides (Hedw.) Limpr. were found as indicator species for nutrient-rich regimes as designated by high soil EC_b. The soil EC_b is a diagnostic measure of plant diversity as EC_b?>?7 mSm^?1 resulted in a considerable increase in species richness. Our classification method, based on electrical measurements, provides a simple way to classify mires and focus detailed research to areas with potentially high conservation value.     

Geomorphological disturbance affects ecological driving forces and plant turnover along an altitudinal stress gradient on alpine slopes

The altitudinal gradient is considered as a stress gradient for plant species because the development and fitness of plant communities tend to decrease as a result of the extreme environmental conditions present at high elevations. Abiotic factors are predicted to be the primary filter for species assemblage in high alpine areas, influencing biotic interactions through both competition for resources and positive interactions among species. We hypothesised that the relative importance of the ecological driving forces that affect the biotic interactions within plant communities changes along an elevation gradient on alpine debris slopes. We used multiple gradient analyses of 180 vegetation plots along an altitudinal range from ~1,600 to 2,600 m and single 100 m-bands in the Adamello-Presanella Group (Central Alps) to investigate our hypothesis; we measured multiple environmental variables related to different ecological driving forces. Our results illustrate that resource limitations at higher elevations affect not only the shift from competition to facilitation among species. A geomorphological disturbance regime along alpine slopes favours the resilience of the high-altitude species within topographic/geomorphological traps. An understanding of the ecological driving forces and positive interactions as a function of altitude may clarify the mechanisms underlying plant responses to present and future environmental changes.     

Vascular plant species richness along latitudinal and altitudinal gradients: a contribution from New Zealand temperate rainforests

Vascular plant species richness is known to often decrease with both increasing latitude and increasing altitude. However, a number of studies have shown the reverse trend and the primary cause of these gradients remains unknown. In the present work, generalized linear models were used to assess the relative importance of latitude and altitude as well as of a number of other factors (mean annual precipita-tion, slope, substrate and forest type) on species richness in temperate rainforests of New Zealand. The effect of Southern beech ( Nothofagus spp.) as dominant canopy species on total species richness was shown to be much smaller than postulated in most previous studies. Within the region studied, altitude had by far the strongest effect on species richness. This effect was independent of latitude and was significant for woody but not for herbaceous vegetation.     

阿尔卑斯山黄花茅(Anthoxanthum alpinum)沿海拔梯度的基因频率分布

在瑞士阿尔卑斯山的2个定点样地,黄花茅从森林线（海拔1700 m）到山顶（海拔2830 m）呈连续分布。在海拔梯度样带的最高和最低定样场所间的垂直距离差不多为1000 m,但2个定样场所间相距仅仅1.4 km。在所研究的3个海拔梯度样带中,3个同工酶位点（Px_1, Got_2和 Mdh_1）被观察到有统计意义的倾群变异。研究结果显示：沿海拔梯度样带的亚居群间的基因流可能太弱不足以克服自然选择的影响,后者促使对局部环境的适应。在这种情况下,温度因子至少可能作为一种主要的自然选择力起作用。     

On the use of weather data in ecological studies along altitudinal and latitudinal gradients

Global warming has created a need for studies along climatic gradients to assess the effects of temperature on ecological processes. Altitudinal and latitudinal gradients are often used as such, usually in combination with air temperature data from the closest weather station recorded at 1.5–2 m above the ground. However, many ecological processes occur in, at, or right above the soil surface. To evaluate how representative the commonly used weather station data are for the microclimate relevant for soil surface biota, we compared weather station temperatures for an altitudinal (500–900 m a.s.l.) and a latitudinal gradient (49–68°N) with data obtained by temperature sensors placed right below the soil surface at five sites along these gradients. The mean annual temperatures obtained from weather stations and adjusted using a lapse rate of ?5.5°C km^?1 were between 3.8°C lower and 1.6°C higher than those recorded by the temperature sensors at the soil surface, depending on the position along the gradients. The monthly mean temperatures were up to 10°C warmer or 5°C colder at the soil surface. The within‐site variation in accumulated temperature was as high as would be expected from a 300 m change in altitude or from a 4° change in latitude or a climate change scenario corresponding to warming of 1.6–3.8°C. Thus, these differences introduced by the decoupling are significant from a climate change perspective, and the results demonstrate the need for incorporating microclimatic variation when conducting studies along altitudinal or latitudinal gradients. We emphasize the need for using relevant temperature data in climate impact studies and further call for more studies describing the soil surface microclimate, which is crucial for much of the biota.     

Variation in the abundance of fungal endophytes in fescue grasses along altitudinal and grazing gradients

Epichloë festucae, a common fungal symbiont of the genus Festuca (family Poaceae), can provide its host plant with protection against herbivores. However, infection might also be associated with a cost to its host plant. We examined the distribution of Epichloë festucae infection in natural populations of three fescue grasses, Festuca rubra , F. ovina and F. vivipara, on mountains in northern Sweden to determine whether infection frequency varied with reindeer Rangifer tarandus grazing pressure and altitude. Two differently-scaled approaches were used: 1) infection frequency was measured at a local scale along ten elevational transects within a ca 400 km² area and 2) infection frequency was measured on a regional scale along elevational transects on 17 mountains classified as having a history of high or low reindeer grazing pressure. Mean infection frequencies in F. rubra were 10% (vegetative tillers at a local scale), and 23% (flowering culms at a regional scale), and in F. ovina they were 13% (local scale) and 15% (regional scale). Endophyte infection frequency in F. vivipara , was, on average, 12% (local scale) and 37% (regional scale). In F. rubra , infection decreased significantly with increasing altitude at both the local and regional scale, and was positively correlated with grazing pressure. In F. ovina , an opposite trend was found at the regional scale: infection frequency increased significantly with increasing altitude, while no discernible distribution pattern was observed at the local scale. No elevational trends were observed in infection of F. vivipara . These patterns in the distribution of endophyte-infected grasses in non-agricultural ecosystems may be explained by both biotic (grazing) and abiotic factors (altitude). Differences in ecology and life history of the studied grass species may also be of importance for the different results observed among species.     

Classification and ordination of plant communities along an altitudinal gradient on the Presidential Range,New Hampshire,USA

An analysis of vegetation along an altitudinal gradient on the Presidential Range, New Hampshire, USA, using the Braun–Blanquet approach followed by multivariate data analysis is presented. Twelve main plant communities have been distinguished. Floristic information is presented in twelve tables and one appendix. The relationships of the communities to complex environmental gradients are analyzed using Correspondence Analysis. Floristic composition and community structure are controlled primarily by the altitudinal gradient (temperature, precipitation), and by mesotopographic conditions (snow accumulation, exposure and cryoturbation, slope position, and soil moisture).     

Plant diversity and dry-matter dynamics of peri-urban plant communities in an Indian dry tropical region

The emergence of variety of land-use changes due to continuous anthropogenic pressure in peri-urban areas may concomitantly result in modification of the structure of associated plant communities for their sustainable growth. In the present study, plant diversity, and above- and belowground biomass distribution among species were investigated to understand their dynamics across different season, soil, and site conditions in a dry tropical peri-urban region in India. From four study sites that covered contrasting land uses: abandoned brick kiln (ABK), grazing land (GL), Kali river bank (KRB), and agricultural land (AL), a total of 360 monoliths were randomly extracted in three seasons, and dry weights were estimated for aboveground and belowground parts of species individuals. Seasonal soil samples of the sites were analyzed for physico-chemical characteristics. Of the total 87 recorded species that were mainly annual weeds and ruderals, 77% were forbs and 23% grasses. The ranges of plant biomass recorded across all sites and seasons were: aboveground 228–738 g m⁻², belowground 83–288 g m⁻², and a total of 344–1,026 g m⁻². The dominance of species differed between above- and belowground; some species dominated only above- or belowground, and others dominated in both layers. Above- and belowground biomass of the sites, differential community-biomass allocation to above- and belowground parts and species dominants varied significantly with site and season. ABK and AL sites showed lower species diversity and soil nutrients compared to GL and KRB sites. Belowground biomass significantly declined with increasing soil organic C and total N, indicating altered dry matter allocation under resource-scarce habitat conditions. Higher diversity occurred at both low- and high-biomass sites, reflective of enhanced ability of these plant communities to exploit resources maximally in spatio-temporal pattern.     

Phenological and growth responses of Papaver radicatum along altitudinal gradients in the Canadian High Arctic

Phenology and growth of Papaver radicatum Rottb. was monitored over four summers (1990–1993) at 12 sites, along a dolomitic and a granitic altitudinal gradient (330 m a.s.l.–770 m a.s.l.) at Sverdrup Pass, central Ellesmere Island, Canada. The gradients provided substantial differences in environmental characteristics. Three of the four seasons (1990, 1991 and 1993) had more than 400 thawing degree-days (TDD) in the valley, while the 1992 season had less than 300. The granitic sites had consistently higher temperatures than the dolomitic sites, despite their northerly aspect. Increasing elevation reduced total degree-day accumulation ( c . 40 degree-days/100 m) and length of potential growing season. The proportion of the population producing flower buds was similar at all sites in any given year, but there were differences among years. Production of flowers and fruits per site, decreased with altitude along the dolomitic gradient in 1991 and 1992. There was no difference in the number of buds or flowers produced per plant with increasing altitude, although larger plants with multiple flowers were found only on low elevation granitic sites. Plants from the dolomitic sites were smaller and flowered, on average, after the site accumulated 150 degree-days, while plants on the granitic sites were larger and bloomed after 200 degree-days. Papaver is able to grow and reproduce over a wide range of environmental conditions and moderate climate warming would likely promote its growth and establishment, unless other factors, especially snow-free periods and water availability, become limiting.     

Woodland mollusc communities along environmental gradients in the East Carpathians

Mollusc communities were sampled quantitatively at eleven sites representing different environmental conditions in the Bieszczady National Park (East Carpathians Mts, Poland). Overall 61 species were recorded. Alder forest in the valleys (AF; Alnetum incanae carpathicum, Caltho-Alnetum, secondary alder forest) hosted the richest fauna, with up to 41 species occurring sympatrically on 100 m² of forest floor and average density ca. 750 specimens m⁻². Three important ecological controllers of species composition and community structure were found. The main predictor of mollusc assemblage composition was calcium content; the first DCA axis of molluscs most significantly and highly correlated with calcium content in the leaf litter and organic matter in the upper layer. The second axis significantly correlated with altitude and negatively with annual temperature, and thus can be explained as an elevational gradient. We observed slope aspect to constitute the third significant gradient. On the basis of forward selection in CCA analysis organic matter in the upper layer of soil was the best predictor of species composition, which explained 26% of total variance. It comes to prove that in mountain forest on non-calcareous bedrock molluscs obtain calcium mainly from leaf litter.     

Effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura, central Japan

We investigated the effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura (3026 m a.s.l.), Japan. We examined the vegetation of herb and tree species shorter than 1.3 m along roadsides and adjacent natural vegetation at 200 m intervals between 1600 and 3000 m a.s.l. The timberline was at 2500 m a.s.l. Although the canopy opening was greater at the roadsides than in the natural vegetation, it was similar above the timberline. Soil cover and litter depth of the soil surface were less at roadsides than the natural vegetation, and gravel and rock cover were greater at roadsides. Species composition changed in similar directions from natural vegetation to roadsides along the altitudinal gradient. This direction was related to canopy opening and litter depth. Liliaceae, Ericaceae and Pinaceae were dominant families in the natural vegetation, and Asteraceae and Poaceae were greatest at the roadsides. Roadside plants were mostly herb species, while tree species increased in natural vegetation. Five exotic species were also observed at the roadsides. Sunny plant species gradually increased with altitude in the natural vegetation, indicated by the increase in canopy opening. By contrast, roadside plants were mostly sunny plant species irrespective of altitude. The number of lowland and montane species increased at the roadsides in the subalpine zone. Thus, roads strongly altered species composition of the natural vegetation along the altitudinal gradient probably because of changes in light and soil-surface conditions for growth and seedling establishment.     

Global gradients in moss and vascular plant diversity

Knowledge on the distribution and hotspots of different taxon groups is indispensable for improving the state of biodiversity protection. Our aim was to determine if the relations between major environmental factors and species richness of two plant groups, mosses and vascular plants differ on a global scale. The dependence of species richness on environmental factors in 50 regions, covering 17 % of the global terrestrial territory, was analysed with SAS statistical software. Species richness of vascular plants increases significantly towards the equator, but for mosses the increase is not significant. Species richness of mosses and vascular plants are significantly positively correlated only in the near equator zone. Although there were similarities in the trends of mosses and vascular plant diversities at a global scale, their relations with some factors differ with distance from the equator. The effect of precipitation on species richness is similar for both plant groups, but coastline length has a significant positive influence only on moss richness, whereas species richness of vascular plants was related strongly to area and energy input. Therefore, effective conservation policy at both local and global scale demands consideration of all diversity drivers of different taxon groups.