Latitudinal pattern in plant composition along the Peruvian and Chilean fog oases

Fog oases in western South America (locally named lomas) are distributed in a kind of fragmented or patchy way into the coastal desert. Their origin, as well as their current ecological connections in terms of species' dispersal capability, remains an open question. We analyzed the latitudinal pattern in plant species and phylogenetic similarities of 13 lomas, which cover the latitudinal extent of these habitats, from 7°58′ to 26°15′ S. A data-set of 1004 species from available checklists was considered. Plant species composition and phylogenetic relationships among lomas were analyzed by non-metric multidimensional scaling. Our results show three main groups of lomas (northern Peruvian, southern Peruvian, and North-Central Chilean lomas) that are aligned along a complex, nonlinear north–south gradient in ordination space. The weak species overlap between Peruvian and Chilean lomas, together with the higher content in endemic species of the Chilean communities, supports the hypothesis that, at least recently, species composition of the three main groups of lomas has been shaped by desert barriers limiting plant dispersal.     

Seasonal variation in the composition and rate of change of the phytoplankton community in a deep subalpine lake (Lake Garda, Northern Italy). An application of nonmetric multidimensional scaling and cluster analysis

Seasonal variations and spatial homogeneity of the phytoplankton community were followed, from spring 1991 to spring 1992, in four pelagic stations of a large deep subalpine lake (Lake Garda, Northern Italy). Both cluster analysis and nonmetric multidimensional scaling (NMDS) applied to Bray & Curtis' dissimilarity matrices computed on density and biovolume data were employed; the Bray & Curtis index, calculated between pairs of chronologically contiguous samples, was also used as a measure of the community change rate over the temporal succession. In the tree diagrams obtained both from density and biovolume data, six groups of different size have been identified, with ordered sequences of samples within them. Superimposition of the results of cluster analysis on the NMDS configurations has allowed interpretations of the trajectories of the samples as a chronological and cyclical succession of compositionally homogeneous groups. A clear relationship between the community change rate and stability of the water column has been assessed. The specific composition of the six groups has been discussed in relation to environmental variables and in terms of adaptive strategies. During winter (winter-spring group) the turbulence of the water and the availability of nutrients favour the development of colonial Bacillariophyceae (Fragilaria crotonensis Kitton, Tabellaria fenestrata (Lyngb.) Kütz., Aulacoseira spp.), Cyanophyceae (Planktothrix agardhii (Gom.) Anagn. et Kom. and Planktolyngbya limnetica (Lemur.) Kom.-Legn. et Cronb.) and Cryptophyceae. In late spring group, with the stabilisation of the water column and silicon depletion, the diatoms give way to small, opportunistic species (Ankyra judayi (G. M. Smith) Fott, Cyclotella spp., Chroomonas acuta Utermhöl) and larger species (Ceratium hirundinella (O. F. Müll.) Dujardin). The three summer groups are characterised by a development of Chlorophyceae (chiefly Chlorococcales), Cyanophyceae (mainly Chroococcales), Cyclotella spp. and Dinophyceae. With the autumn destratification the summer community undergoes a rearrangement principally in favour of Cyanophyceae and Cryptophyceae.     

Are we close enough? Comparing prairie reconstruction chronosequences to remnants following two site preparation methods in Missouri,U.S.A.

Prairie reconstruction has become a common method for reestablishing tallgrass prairie communities in the central United States. With the objective of creating plant communities that approximate remnant (reference) prairies, managers are interested in identifying: (1) best methods for reconstructing reference community conditions; (2) the rate of change in plant communities through time following reconstruction; and (3) species present in remnant communities but missing from reconstructed communities. This information is important in the development of adaptive management strategies during active reconstruction. We used a chronosequence approach to assess the success of two reconstruction methods in emulating local, reference remnant prairie plant communities. We compared broadcast dormant seeding following two types of site preparation, agricultural cropping (Crop) or herbicide control in existing grass assemblages (Grass), and remnant communities. The Crop site preparation method resulted in a rapid increase in richness shortly following seeding. Although more similar to remnant assemblages initially, the Grass method took longer for mean coefficient of conservatism and floristic quality index to approach conditions of the reference communities. However, neither method resulted in plant community compositions that converged with the reference through time. Further, indicator species analysis identified a diverse assemblage of species lacking from the reconstructed prairies. These results suggest the need to develop management strategies for establishing the “missing” species during reconstruction and provide further support for protection and conservation of existing remnant prairies.     

Monitoring bacterial and archaeal community shifts in a mesophilic anaerobic batch reactor treating a high-strength organic wastewater

Shifts in bacterial and archaeal communities, associated with changes in chemical profiles, were investigated in an anaerobic batch reactor treating dairy-processing wastewater prepared with whey permeate powder. The dynamics of bacterial and archaeal populations were monitored by quantitative real-time PCR and showed good agreement with the process data. A rapid increase in bacterial populations and a high rate of substrate fermentation were observed during the initial period. Growth and regrowth of archaeal populations occurred with biphasic production of methane, corresponding to the diauxic consumption of acetate and propionate. Bacterial community structure was examined by denaturing gel gradient electrophoresis (DGGE) targeting 16S rRNA genes. An Aeromonas -like organism was suggested to be mainly responsible for the rapid fermentation of carbohydrate during the initial period. Several band sequences closely related to the Clostridium species, capable of carbohydrate fermentation, lactate or ethanol fermentation, and/or homoacetogenesis, were also detected. Statistical analyses of the DGGE profiles showed that the bacterial community structure, as well as the process performance, varied with the incubation time. Our results demonstrated that the bacterial community shifted, reflecting the performance changes and, particularly, that a significant community shift corresponded to a considerable process event. This suggested that the diagnosis of an anaerobic digestion process could be possible by monitoring bacterial community shifts.     

Diatom Assemblages and their Associations with Environmental Variables in Oregon Coast Range Streams, USA

The Oregon Coast Range, rich in natural resources, is under increasing pressure from rapid development. The purpose of this study was to examine diatom species patterns in relation to environmental variables in streams of this region. Diatoms, water quality, physical habitat and watershed characteristics were assessed for 33 randomly selected stream sites. Watershed size, elevation, geology, vegetation and stream morphology varied substantially among sites. Streams were characterized by dilute water chemistry and a low percent of fine substrate. A total of 80 diatom taxa were identified. Taxa richness was low throughout the region (median 15, range 10–26). Assemblages were dominated by two adnate species, Achnanthidium minutissimum and Achnanthes pyrenaicum. Diatoms sensitive to organic pollution dominated the assemblages at all sites (median 85%). Non-metric multidimensional scaling (NMDS) and correlational analysis showed quantitative relationships between diatom assemblages and environmental variables. NMDS axes were significantly correlated with watershed area, watershed geology, conductivity, total nitrogen, total solids and stream width. Diatom-based site classification (Two-way Indicators Species Analysis, (TWINSPAN)) yielded 4 discrete groups that displayed weak correlations with environmental variables. When stream sites were classified by dominant watershed geology, overall diatom assemblages between groups were significantly different (Analysis of Similarity (ANOSIM) global R = 0.19, p < 0.05). Our results suggest that streams in the coastal region are in relatively good condition. High natural variability in stream conditions in the Oregon Coast Range ecoregion may obscure quantitative relationships between environmental variables and diatom assemblages. A bioassessment protocol that classifies sites by major landscape variables and selects streams along the major human disturbance gradient might allow for detection of early signs of human disturbance in environmentally heterogeneous regions, such as the Pacific Northwest.     

Zooplankton responses to predation by larval bluegill: an enclosure experiment

SUMMARY 1. Larval fish are gape-limited predators that forage on prey of specific sizes, and thus may be expected to differentially affect members of a zooplankton community, possibly altering the size-structure or species composition.
2. I used an enclosure experiment to look at the effect of predation by larval bluegill on the dynamics of two zooplankton communities, one dominated by large-bodied individuals and the other by small-bodied individuals. Enclosures containing these zooplankton received a zero, low, medium, or high density of larval bluegill predators.
3. Increasing larval density had a negative effect on zooplankton abundance and abundance declined similarly in the large-bodied and small-bodied communities.
4. Zooplankton size-structure, as estimated by the length of the average zooplankton, increased and then decreased during the experiment, decreasing faster at higher larval fish densities. When zooplankton size-structure was estimated as the length of the average cladoceran, size-structure declined in the large-bodied but not in the small-bodied community and the greatest decline in size-structure was seen in the medium and high larval density treatments.
5. Ordination of each community using multidimensional scaling (MDS) indicated that the trajectory of change in species composition differed between the presence and absence of larval fish. In both communities, the degree of response by individual taxa depended on the density of bluegill larvae. This effect on zooplankton abundance, size-structure and community composition suggests that larval fish may make an important contribution to zooplankton dynamics in many lakes and ponds.     

Response of overstory and understory vegetation 37 years after prescribed burning in an aspen-dominated forest in northern Minnesota,USA – A case study

Many studies have examined short-term changes in understory vegetation following prescribed burning. However, knowledge concerning longer term effects on both forest understory and overstory vegetation is lacking. This investigation was initiated to examine changes in understory (herbaceous and shrub) and overstory species composition almost four decades after logging and prescribed burning at the Pike Bay Experimental Forest in Minnesota. The experiment was established in 1964 with a randomized block design with four treatments: control (c); burned in spring 1967 (S0); burned in spring 1967 + repeat burn spring 1969 (S2); and burned in spring 1967 + repeat burn fall 1970 (F4). Overstory and understory species diversity indices and richness varied within and among treatments but were not strongly or consistently affected by the treatments. Multivariate analyses (multi-response block permutation procedures and non-metric multidimensional scaling) reveal some lingering effects of burning intensity and seasonal variation as well as some compositional differentiation among treatments, but only in the herb layer. In this environment, the effects of two repeated burnings (fire) have essentially disappeared for overstory and understory species diversity and community composition and have failed to convert an aspen-dominated stand to a coniferous stand (an original goal of the study).     

The mitochondrial cytochrome c oxidase I gene reveals phylogeographic structure in the African Goshawk Accipiter tachiro (Accipitridae)

We used a 298?bp fragment of the mitochondrial cytochrome c oxidase subunit I gene (COI) to examine sequence variation in (mostly) museum specimens of the African Goshawk Accipiter tachiro. Our results showed two clades with high bootstrap support in a phylogenetic analysis and two groups in a nonmetric multidimensional scaling (NMDS) analysis. Each of the two phylogenetic clades corresponded to one of the NMDS groups. One clade comprised haplotypes of the subspecies A. t. lopezi, A. t. macroscelides, A. t. toussenelli and A. t. canescens and corresponded to the morphospecies A. toussenelii. This taxon has a more north-western distribution. The second clade comprised haplotypes of the subspecies A. t. sparsimfasciatus, A. t. pembaensis and A. t. tachiro and corresponded to the morphospecies A. tachiro, which has a more south-eastern distribution. Furthermore, one branch corresponded to the morphospecies A. t. unduliventer, which is confined to the Ethiopian highlands. The genetic divergence observed among the three A. tachiro morphospecies appeared concordant with the ecological and morphological divergence and suggests the existence of three putative species. Within A. tachiro and A. toussenelii there is substantial morphological, but very little genetic, differentiation among subspecies.     

Arbuscular mycorrhizal fungi associated with Populus-Salix stands in a semiarid riparian ecosystem

This study examined the activity, species richness, and species composition of the arbuscular mycorrhizal fungal (AMF) community of Populus-Salix stands on the Verde River (Arizona, USA), quantified patterns of AMF richness and colonization along complex floodplain gradients, and identified environmental variables responsible for structuring the AMF community. Samples from 61 Populus-Salix stands were analyzed for AMF and herbaceous composition, AMF colonization, gravimetric soil moisture, soil texture, per cent organic matter, pH, and concentrations of nitrate, bicarbonate phosphorus and exchangeable potassium. AMF species richness declined with stand age and distance from and elevation above the channel and was positively related to perennial species cover and richness and gravimetric soil moisture. Distance from and elevation above the active channel, forest age, annual species cover, perennial species richness, and exchangeable potassium concentration all played a role in structuring the AMF community in this riparian area. Most AMF species were found across a wide range of soil conditions, but a subset of species tended to occur more often in hydric areas. This group of riparian affiliate AMF species includes several not previously encountered in the surrounding Sonoran desert.     

Plant communities of mountain grasslands in a broad cross-section of the Eastern Alps

Apart from forests, the landscape of the Alps is dominated by grasslands, where they account for up to 40% of the agricultural area. This study focuses on the main man-made grassland plant communities of the Eastern Alps, shows their current spatial distribution and examines how strongly the influence of land use and site factors determines the communities. Discriminant analysis was used to harmonize the phytosociological classification of 1502 vegetation relevés from the literature and 375 own recorded inventories from Western Austria and Northern Italy. Land-use intensity, altitude, slope and pH were also recorded, in order to assess the impact of the factors to plant communities, as calculated in nonmetric multidimensional scaling. We identified 39 plant communities and generated a table with the main ecological and floristic parameters as well as a map showing their present spatial distribution. Contrary to the literature, the pasture communities Crepido-Festucetum commutatae, Deschampsio cespitosae-Poetum alpinae and Rumicetum alpini occur also in fertilized meadows. On the other hand we found meadow communities occurring in pastures, such as the Angelico-Cirsietum oleracei, the Pastinaco-Arrhenatheretum, the Ranunculo repentis-Alopecuretum pratensis and the Trisetetum flavescentis. The most species-rich communities - the Caricetum ferruginei and the Seslerio-Caricetum sempervirentis - occur in unfertilized meadows above calcareous bedrock. Further species-rich communities - the Campanulo scheuchzeri-Festucetum noricae, the Gentianello anisodontae-Festucetum variae, the Pulsatillo alpinae-Festucetum noricae, the Trifolio thallii-Festucetum nigricantis and the Hypochoerido uniflorae-Festucetum paniculatae - are endangered: they are regionally restricted and depend on the absence of fertilizer and on mowing once annually or every second or third year. Therefore agri-environmental measures should focus on unfertilized mountain meadows, in order to conserve these rare grassland communities.     

多元统计方法在节肢动物群落分析中的应用

近年来有关节肢动物群落的研究报道较多,而传统的、简单的多样性指数分析远远不能满足对高通量群落数据的挖掘。采用多元统计方法可以较好地分析群落数据。其中,在研究某一处理的长期效应时,主响应曲线是一种经典的多元分析方法;而非度量多维尺度分析具有能处理较大量的数据且常能以低维排序图反映结果的优点,是一种具有广泛应用前景的排序技术。本文以Bt棉与非Bt棉不同比例混作棉田的节肢动物群落为例,详尽地介绍了主响应曲线和非度量多维尺度在节肢动物群落分析中的应用。     

嘉兴石臼漾湿地冬季浮游植物群落结构特征

2010年冬季对嘉兴石臼漾饮用水水源人工湿地水体的浮游植物群落结构进行了调查,以探索湿地净化措施对浮游植物群落结构的影响.结果表明:在石臼漾湿地共发现浮游植物77种,隶属7门39属,其中硅藻门最多,为14属33种;优势种有变异直链藻、梅尼小环藻、菱形藻、色球藻、针晶蓝纤维藻、四尾栅藻、小型黄丝藻等,梅尼小环藻优势度最大,为0.144.石臼漾湿地冬季浮游植物平均密度为1.28×106 cell·L-1;出水口密度最低,为6.80×105cell·L-1,并且出水口蓝藻细胞的密度仅为进水口的14.9％(P＜0.05).各采样点Shannon多样性指数为0.94 ～1.27.经聚类和多维尺度分析,石臼漾湿地冬季浮游植物群落可分为根孔沿岸带群落、根孔植物床流水型群落(2种)、深度净化湖区静水型群落和湿地源水群落五大类;各采样点生态环境及水体流速的不同是五类群落产生的主要影响因素.