Nitrogen Cycling Responses to Mountain Pine Beetle Disturbance in a High Elevation Whitebark Pine Ecosystem

Ecological disturbances can significantly affect biogeochemical cycles in terrestrial ecosystems, but the biogeochemical consequences of the extensive mountain pine beetle outbreak in high elevation whitebark pine (WbP) (Pinus albicaulis) ecosystems of western North America have not been previously investigated. Mountain pine beetle attack has driven widespread WbP mortality, which could drive shifts in both the pools and fluxes of nitrogen (N) within these ecosystems. Because N availability can limit forest regrowth, understanding how beetle-induced mortality affects N cycling in WbP stands may be critical to understanding the trajectory of ecosystem recovery. Thus, we measured above- and belowground N pools and fluxes for trees representing three different times since beetle attack, including unattacked trees. Litterfall N inputs were more than ten times higher under recently attacked trees compared to unattacked trees. Soil inorganic N concentrations also increased following beetle attack, potentially driven by a more than two-fold increase in ammonium (NH₄⁺) concentrations in the surface soil organic horizon. However, there were no significant differences in mineral soil inorganic N or soil microbial biomass N concentrations between attacked and unattacked trees, implying that short-term changes in N cycling in response to the initial stages of WbP attack were restricted to the organic horizon. Our results suggest that while mountain pine beetle attack drives a pulse of N from the canopy to the forest floor, changes in litterfall quality and quantity do not have profound effects on soil biogeochemical cycling, at least in the short-term. However, continuous observation of these important ecosystems will be crucial to determining the long-term biogeochemical effects of mountain pine beetle outbreaks.     

Macroinvertebrate drift in a Rocky Mountain stream

An extensive series of drift collections from a Rocky Mountain stream was used to investigate quantitative patterns in the taxonomic composition of drift throughout spring, summer and fall for 1975–1978. Drift was estimated by drift rate, the number of organisms drifting past a point per 24 h; and by drift density, the numbers of organisms collected per 100 m³ of water sampled.Drift densities were up to ten times greater by night than by day, and 24 h drift densities for the total fauna approached 2000 per 100 m³ in June–July, declining to <500 by autumn. Ephemeroptera, and especially Baetis, dominated the drift. Drift rates were greatest in late spring, around 10⁶ per 24 h, which are among the highest values reported for small trout streams. Drift rates declined to <10⁵ during the summer, and shifts in the taxonomic composition are described.Multiple regression analysis of the relationship between drift rate and density, and the independent variables discharge, benthic density and temperature, showed that discharge typically was a significant predictor of 24 h drift rate, usually the best single predictor. In contrast, 24 h drift density most frequently was independent of discharge, indicating that this measure tends to correct for seasonal variation in discharge, as suggested in the literature. However, this was not invariably true. Drift density significantly correlated with benthic density in five of eight taxa inspected, thus seasonal declines in the benthos probably accounted for parallel declines in drift density.     

Using High-Resolution Future Climate Scenarios to Forecast Bromus tectorum Invasion in Rocky Mountain National Park

National Parks are hallmarks of ecosystem preservation in the United States. The introduction of alien invasive plant species threatens protection of these areas. Bromus tectorum L. (commonly called downy brome or cheatgrass), which is found in Rocky Mountain National Park (hereafter, the Park), Colorado, USA, has been implicated in early spring competition with native grasses, decreased soil nitrogen, altered nutrient and hydrologic regimes, and increased fire intensity. We estimated the potential distribution of B. tectorum in the Park based on occurrence records (n = 211), current and future climate, and distance to roads and trails. An ensemble of six future climate scenarios indicated the habitable area of B. tectorum may increase from approximately 5.5% currently to 20.4% of the Park by the year 2050. Using ordination methods we evaluated the climatic space occupied by B. tectorum in the Park and how this space may shift given future climate change. Modeling climate change at a small extent (1,076 km2) and at a fine spatial resolution (90 m) is a novel approach in species distribution modeling, and may provide inference for microclimates not captured in coarse-scale models. Maps from our models serve as high-resolution hypotheses that can be improved over time by land managers to set priorities for surveys and removal of invasive species such as B. tectorum.     

Interactions between Canopy Structure and Herbaceous Biomass along Environmental Gradients in Moist Forest and Dry Miombo Woodland of Tanzania

We have limited understanding of how tropical canopy foliage varies along environmental gradients, and how this may in turn affect forest processes and functions. Here, we analyse the relationships between canopy leaf area index (LAI) and above ground herbaceous biomass (AGB_H) along environmental gradients in a moist forest and miombo woodland in Tanzania. We recorded canopy structure and herbaceous biomass in 100 permanent vegetation plots (20 m × 40 m), stratified by elevation. We quantified tree species richness, evenness, Shannon diversity and predominant height as measures of structural variability, and disturbance (tree stumps), soil nutrients and elevation as indicators of environmental variability. Moist forest and miombo woodland differed substantially with respect to nearly all variables tested. Both structural and environmental variables were found to affect LAI and AGB_H, the latter being additionally dependent on LAI in moist forest but not in miombo, where other factors are limiting. Combining structural and environmental predictors yielded the most powerful models. In moist forest, they explained 76% and 25% of deviance in LAI and AGB_H, respectively. In miombo woodland, they explained 82% and 45% of deviance in LAI and AGB_H. In moist forest, LAI increased non-linearly with predominant height and linearly with tree richness, and decreased with soil nitrogen except under high disturbance. Miombo woodland LAI increased linearly with stem density, soil phosphorous and nitrogen, and decreased linearly with tree species evenness. AGB_H in moist forest decreased with LAI at lower elevations whilst increasing slightly at higher elevations. AGB_H in miombo woodland increased linearly with soil nitrogen and soil pH. Overall, moist forest plots had denser canopies and lower AGB_H compared with miombo plots. Further field studies are encouraged, to disentangle the direct influence of LAI on AGB_H from complex interrelationships between stand structure, environmental gradients and disturbance in African forests and woodlands.     

Exotic Herbivores as Drivers of Plant Invasion and Switch to Ecosystem Alternative States

This paper discusses the evidence of the way in which coupled herbivore and plant invasions altered the structure and functioning of ecosystems in central Chile, and compares these patterns to results from other Mediterranean ecosystems around the world. In pre-Columbian times, sclerophyllous matorral forests largely covered mediterranean Chile. Remnants of the original, continuous matorral can now be found only on relatively humid slopes of the Coastal Range. In the Intermediate Depression, a long central valley, it has been replaced by extensive savannas dominated by the exotic Acacia caven, whereas the matorral remains on dry slopes as isolated shrub clumps. Experimental work suggests that introduced cattle have played a major role in promoting the shift to Acacia savanna, whereas introduced European rabbits prevent the recolonization of clearings by matorral on the slopes. As in other regions of the world, the loss of woodlands in Chile is likely to have resulted in reduced carbon storage capacity and nutrient recycling, and in increased erosion and climatic aridity within the region. Numerous exotic herbs and grasses now dominate the open areas, and experiments indicate that the dry conditions in the absence of woodland cover in combination with loss of soil fertility and severe grazing by introduced mammals has pushed the competitive balance from native to exotic species. These changes are probably very difficult to reverse. Even if grazing is drastically reduced, drought may prevent the recovery of matorral species in much of the region. However, recent theoretical work suggests that if such grazer reduction is timed to coincide with wet El Niño episodes, recovery of the original woodlands may be triggered.     

Ant Diversity and Distribution along Elevation Gradients in the Australian Wet Tropics: The Importance of Seasonal Moisture Stability

The threat of anthropogenic climate change has seen a renewed focus on understanding contemporary patterns of species distribution. This is especially the case for the biota of tropical mountains, because tropical species often have particularly narrow elevational ranges and there are high levels of short-range endemism. Here we describe geographic patterns of ant diversity and distribution in the World Heritage-listed rainforests of the Australian Wet Tropics (AWT), revealing seasonal moisture stability to be an important environmental correlate of elevational patterns of species composition. We sampled ants in leaf litter, on the litter surface and on tree trunks at 26 sites from six subregions spanning five degrees of latitude and elevation ranges from 100–1,300 m. A total of 296 species from 63 genera were recorded. Species richness showed a slight peak at mid elevations, and did not vary significantly with latitude. Species composition varied substantially between subregions, and many species have highly localised distributions. There was very marked species turnover with elevation, with a particularly striking compositional disjunction between 600 m and 800 m at each subregion. This disjunction coincides with a strong environmental threshold of seasonal stability in moisture associated with cloud ‘stripping’. Our study therefore provides further support for climatic stability as a potential mechanism underlying patterns of diversity. The average height of orographic cloud layers is predicted to rise under global warming, and associated shifts in seasonal moisture stability may exacerbate biotic change caused by rising temperature alone.     

Life histories and production of three Rocky Mountain aquatic insects along an elevation-driven temperature gradient

Hydrobiologia - Although temperature is known to influence individual traits such as growth, body size, and fecundity, few studies have examined how these relationships influence population-level...     

Variability and convergence in benthic communities along the longitudinal gradients of four physically similar Rocky Mountain streams

1. High‐gradient mountain streams are ideal for studying longitudinal biological patterns, although the degree of similarity in the biological gradient among physically similar streams in a region is poorly known. Our first objective was to evaluate variability in benthic communities along four streams in the central Rocky Mountains of Colorado. We analysed the relative influence of longitudinal position versus reach‐scale physical variables on community structure and measured community similarity at comparable longitudinal positions on the four streams. 2. Our second objective was to evaluate the relative utility of taxonomically versus functionally defined communities to characterise assemblage structure: are taxonomic patterns more predictable along the gradient than are patterns of ecologically important species traits? 3. Redundancy analyses (RDA), including measures of both reach‐scale environmental variables (substratum properties, periphytic cover, local channel slope) and longitudinal position (altitude, stream size), confirmed that the longitudinal position of a site was most important in determining taxonomic composition. Functional community structure was also influenced by longitudinal position, but reach‐scale variables (especially periphyton and median particle size) were of greater importance. 4. Redundancy analyses explained 29.3% of total taxonomic variance and 26.0% of functional variance, indicating that defining assemblages functionally provides no greater understanding of community patterns given several known environmental variables. Strict longitudinal limits of taxa, the presumably identical regional species pool across our sites, and/or trade‐offs among different types of species traits probably explain this result. 5. Redundancy analyses did suggest, however, that traits related to longer life (semivoltinism, long‐lived adults, and slow larval development) were more common downstream, while long‐distance dispersal ability and high fecundity were associated with higher altitude and its associated harsher conditions. 6. When sampling sites were grouped into three ecological zones defined by altitude, mean community similarity (measured both taxonomically and functionally) was lowest across streams at the highest altitude. This pattern could be driven by increased insularity of alpine‐zone streams, resulting from a combination of harsh terrestrial environment, lack of hydrological connectivity, and limited species ranges along the longitudinal continuum.     

贵州北盘江不同强度石漠化区木本植物多样性及生态功能群研究

该研究通过典型群落抽样和聚类分析方法,分析贵州北盘江不同石漠化强度等级的木本植物多样性变化特征,以明确不同石漠化强度等级上的适应性功能群树种组成。结果表明:(1)随着石漠化强度的增大,木本植物的科、属、种数皆呈下降趋势,适生树种数减少;落叶型植物种类相对增加,常绿型植物种类相对减少;矮、小高位芽植物的适应种类相对增加,中、高位芽植物的适应种类相对减少。(2)欧氏距离为6.5时,将46种优势种划分为8个功能群,其中,轻度石漠化型有3个功能群共21个树种;中度石漠化型有3个功能群共14个树种;强度石漠化型有2个功能群共10个树种。     

Positive Effects of Non-Native Grasses on the Growth of a Native Annual in a Southern California Ecosystem

Fire disturbance is considered a major factor in the promotion of non-native plant species. Non-native grasses are adapted to fire and can alter environmental conditions and reduce resource availability in native coastal sage scrub and chaparral communities of southern California. In these communities persistence of non-native grasses following fire can inhibit establishment and growth of woody species. This may allow certain native herbaceous species to colonize and persist beneath gaps in the canopy. A field manipulative experiment with control, litter, and bare ground treatments was used to examine the impact of non-native grasses on growth and establishment of a native herbaceous species, Cryptantha muricata. C. muricata seedling survival, growth, and reproduction were greatest in the control treatment where non-native grasses were present. C. muricata plants growing in the presence of non-native grasses produced more than twice the number of flowers and more than twice the reproductive biomass of plants growing in the treatments where non-native grasses were removed. Total biomass and number of fruits were also greater in the plants growing in the presence of non-native grasses. Total biomass and reproductive biomass was also greater in late germinants than early germinants growing in the presence of non-native grasses. This study suggests a potential positive effect of non-native grasses on the performance of a particular native annual in a southern California ecosystem.     

Habitat Selection of Rocky Mountain Elk in a Nonforested Environment

Abstract: Recent expansions by Rocky Mountain elk (Cervus elaphus) into nonforested habitats across the Intermountain West have required managers to reconsider the traditional paradigms of forage and cover as they relate to managing elk and their habitats. We examined seasonal habitat selection patterns of a hunted elk population in a nonforested high-desert region of southwestern Wyoming, USA. We used 35,246 global positioning system locations collected from 33 adult female elk to model probability of use as a function of 6 habitat variables: slope, aspect, elevation, habitat diversity, distance to shrub cover, and distance to road. We developed resource selection probability functions for individual elk, and then we averaged the coefficients to estimate population-level models for summer and winter periods. We used the population-level models to generate predictive maps by assigning pixels across the study area to 1 of 4 use categories (i.e., high, medium-high, medium-low, or low), based on quartiles of the predictions. Model coefficients and predictive maps indicated that elk selected for summer habitats characterized by higher elevations in areas of high vegetative diversity, close to shrub cover, northerly aspects, moderate slopes, and away from roads. Winter habitat selection patterns were similar, except elk shifted to areas with lower elevations and southerly aspects. We validated predictive maps by using 528 locations collected from an independent sample of radiomarked elk (n = 55) and calculating the proportion of locations that occurred in each of the 4 use categories. Together, the high- and medium-high use categories of the summer and winter predictive maps contained 92% and 74% of summer and winter elk locations, respectively. Our population-level models and associated predictive maps were successful in predicting winter and summer habitat use by elk in a nonforested environment. In the absence of forest cover, elk seemed to rely on a combination of shrubs, topography, and low human disturbance to meet their thermal and hiding cover requirements.     

珠穆朗玛峰自然保护区小叶金露梅灌丛群落数量分类和排序及其多样性垂直格局

根据野外样方调查数据,采用双向种指示分析(TWINSPAN)和典范对应分析(CCA),对珠穆朗玛峰国家级自然保护区小叶金露梅灌丛群落进行分类和排序,并分析物种多样性沿海拔梯度的分布格局。结果表明:(1)该区域24个样地中,记载的维管束植物共有23科45属80种,出现频度较高的种有小叶金露梅(Potentilla parvifolia)、高山嵩草(Kobresia pygmaea)、木根香青(Anaphalis xylorhiza)、垫状点地梅(Androsace tapete)、藏沙蒿(Artemisia wellbyi)、垫状雪灵芝(Arenaria pulvinata)和柴胡红景天(Rhodiola bupleuroides)等。(2)经TWINSPAN等级分类将该区域小叶金露梅灌丛24个样地划分为10个群丛类型。(3)样地和物种CCA二维排序结果表明,海拔和坡位是影响该区域小叶金露梅灌丛群落和物种分布格局的主要环境因子。(4)该区域小叶金露梅灌丛群落物种丰富度、Shannon-Wiener指数和Simpson指数均随海拔升高呈下降的趋势,而Pielou指数呈上升的趋势。(5)样地中优势种小叶金露梅的盖度和高度沿海拔梯度呈显著下降趋势。     

Upstream-downstream movements of aquatic invertebrates in a Rocky Mountain stream

Simultaneous collections of drift and organisms moving either upstream or downstream in association with the substrate were made using a specially designed sampler. Samples were taken in a diel series along a transect across the study riffle of a Colorado foothills stream on six dates over an annual cycle. In addition to longitudinal movements, taxonomic composition and diel periodicity were evaluated. The insect-dominated fauna showed a net downstream displacement. Only the caddisflies Helicopsyche borealis and Hesperophylax occidentalis exhibited net upstream movement, primarily a result of low drift frequencies. The taxonomic composition of moving invertebrates differed from that of the benthos. Drift resembled downstream moving substrate-associated invertebrates in composition, but differed from that of the upstream directed fauna. Taxa collectively exhibited four types of diel patterns: 1) similar downstream (drift and substrate-associated movements) patterns, which generally differed from the upstream pattern; 2) similar benthic (upstream and downstream) patterns, which differed from that of drift; 3) aperiodic patterns; and 4) independent patterns for each type of directional movement. Analysis of size classes based on head capsule width for the mayfly Baetis tricaudatus showed significantly smaller size in stationary individuals compared with moving individuals in the population and revealed that nymphs moving during the day were smaller than those moving at night.     

锡林河流域草原群落植物多样性和初级生产力沿水热梯度变化的样带研究

用样带法研究了草原群落植物多样性和初级生产力沿海拔和水分梯度的变化,结果表明;在样带梯度上,物种丰富度、多样性和群落初级生产力与海拔高度、年降水量和土壤有机C及全N含量呈正相关,而与年平均气温和干燥度呈负相关。随着海拔高度的降低,降水量的减少,热量和干燥度的增加,以及土壤有机C和全N含量的降低,草原群落的物种丰富度、多样性和初级生产力逐渐降低。典型相关分析的结果揭示出,土壤有机C含量和干燥度是对草原群落物种丰富度和初级生产力具有更大的影响。同时,草地的利用方式和强度对群落植物多样性和生产力也具有较强的影响。     

退化植物群落结构及其物种组成在人为干扰梯度上的响应

在岷江上游大沟流域,沿着人为干扰梯度,调查了退化榛栎群落的结构及其物种组成变化。结果表明：（１）除密度外,群落木本层的结构特性（密度、高度、生物量、基径面积和物种多样性）与干扰强度的增加呈负相关,而其草本物种多样性、生态优势度呈正反应,但地上生物量变化呈现相反的趋势;（２）根据群落内植物种群密度（或盖度）在干扰梯度上的响应变化,群人４７个种可基本上分成３个反应种组：１６个为扩展种（ｉｎｖａｓｉｖｅ     

The Middle Asian Element in the Southern Rocky Mountain Flora of the western United States: a critical biogeographical review

Aim Presentation of an hypothesis suggesting that the extraordinarily similarity of the Russian Altai and the American Southern Rocky Mountain Flora represents an Oroboreal Flora; that had to have had an essential continuity across the northern part of the world in the Tertiary period, constituting a highland and steppe component of the better‐known Arcto‐Tertiary Flora of eastern and far‐western North America and eastern Asia. Location North America and Middle (Altai) Asia. Methods Summarization of the author's field and herbarium studies of whole floras over a period of over 60 years, consisting of successive specializations in vascular plants, lichens, and bryophytes. Main conclusions (1) The modern alpine and associated marginal steppe and montane floras contain taxa of Tertiary age. (2) The floras of the southern mountains antedate those of the present‐day Arctic. (3) The Middle Asiatic and the North American floras once enjoyed a contiguous existence over a broad area involving connections between North America and Asia across the North Pole by way of Greenland. Their present disjunctions are products of extinction and attrition of ranges, not of long‐distance migration or dispersal mechanisms. (4) North‐eastern North American disjunctions of so‐called Cordilleran species (the Nunatak hypothesis) need not require explanations involving long‐distance dispersal or migration, but represent relictual populations of the once widely distributed Oroboreal flora.     

Toxoplasmic encephalitis in a free-ranging Rocky Mountain bighorn sheep from Washington

A 4-mo-old free-ranging Rocky Mountain bighorn sheep (Ovis canadensis canadensis) from the Hells Canyon area (Washington, USA) was diagnosed with encephalitis associated with Toxoplasma gondii infection. The sheep had concurrent pneumonic pasteurellosis and resided in a geographic area with endemic Pasteurella-associated pneumonia and mortality in bighorn sheep. The brain had multifocal necrotizing and nonsuppurative encephalitis with intralesional protozoa. The protozoa were identified as T. gondii by immunohistochemistry. To our knowledge, this is the first report of T. gondii infection in a Rocky Mountain bighorn sheep.     

The Importance of Detritivore Species Diversity for Maintaining Stream Ecosystem Functioning Following the Invasion of a Riparian Plant

The strength of linkages between riparian plants and stream communities can be expected to be influenced by invading plants. While most studies so far have been focussed on the effects of the leaf litter quality of the invader, this study addresses the impact of detritivores on the pool of detritus. In a natural setting, we found that species richness of shredding macroinvertebrates significantly influenced the breakdown rate of an invasive weed species, the Japanese knotweed (Fallopia japonica), which has become a major plant invader along streams and rivers in Europe and North America. Our findings imply that a reduction of the diversity of shredder species, which may be the result of disturbances, could negatively influence stream ecosystems' capacity of processing knotweed leaves. Although the knotweed showed breakdown rates similar to those of common native tree and shrub species, other exotic leaf species might show considerably slower rates and hence have greater consequences for the ecosystems. We have, in this study, indicated a technique by which the effects of other non-indigenous plants on ecosystem functioning might be considered.     

Gradients in nucleotide and codon usage along Escherichia coli genes

The usage of codons and nucleotide combinations varies along genes and systematic variation causes gradients in usage. We have studied such gradients of nucleotides and nucleotide combinations and their immediate context in Escherichia coli. To distinguish mutational and selectional effects, the genes were subdivided into three groups with different codon usage bias and the gradients of nucleotide usage were studied in each group. Some combinations that can be associated with a propensity for processivity errors show strong negative gradients that become weaker in genes with low codon bias, consistent with a selection on translational efficiency. One of the strongest gradients is for third position G, which shows a pervasive positive gradient in usage in most contexts of surrounding bases.