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1.
Aquatic plant communities in arid zone wetlands underpin diverse fauna populations and ecosystem functions yet are relatively
poorly known. Erratic flooding, drying, salinity and turbidity regimes contribute to habitat complexity, creating high spatial
and temporal variability that supports high biodiversity. We compared seed bank density, species richness and community composition
of aquatic plants (submergent, floating-leaved and emergent) among nine Australian arid zone wetlands. Germinable seed banks
from wetlands within the Paroo and Bulloo River catchments were examined at nested scales (site, wetland, wetland type) using
natural flooding and salinity regimes as factors with nondormant seed density and species richness as response variables.
Salinity explained most of the variance in seed density (95%) and species richness (68%), with flooding accounting for 5%
of variance in seed density and 32% in species richness. Salinity-flooding interactions were significant but explained only
a trivial portion of the variance (<1%). Mean seed densities in wetlands ranged from 40 to 18,760 m−2 and were highest in wetlands with intermediate levels of salinity and flooding. Variability of densities was high (CVs 0.61–2.66),
particularly in saline temporary and fresh permanent wetlands. Below salinities of c. 30 g l−1 TDS, seed density was negatively correlated to turbidity and connectivity. Total species richness of wetlands (6–27) was
negatively correlated to salinity, pH and riverine connectivity. A total of 40 species germinated, comprising submergent (15
species), floating-leaved or amphibious (17 species), emergent (6 species) and terrestrial (6 species) groups. Charophytes
were particularly important with 10 species (five Chara spp., four Nitella spp. and Lamprothamnium macropogon), accounting for 68% of total abundance. Saline temporary wetlands were dominated by Ruppia tuberosa, Lamprothamnium macropogon and Lepilaena preissii. Variable flooding and drying regimes profoundly altered water quality including salinity and turbidity, producing distinctive
aquatic plant communities as reflected by their seed banks. This reinforces the importance of hydrology in shaping aquatic
biological communities in arid systems. 相似文献
2.
Atti Tchabi Stefanie Burger Danny Coyne Fabien Hountondji Louis Lawouin Andres Wiemken Fritz Oehl 《Mycorrhiza》2009,19(6):375-392
Yam (Dioscorea spp.) is a tuberous staple food crop of major importance in the sub-Saharan savannas of West Africa. Optimal yields commonly
are obtained only in the first year following slash-and-burn in the shifting cultivation systems. It appears that the yield
decline in subsequent years is not merely caused by soil nutrient depletion but might be due to a loss of the beneficial soil
microflora, including arbuscular mycorrhizal fungi (AMF), associated with tropical “tree-aspect” savannas and dry forests
that are the natural habitats of the wild relatives of yam. Our objective was to study the AMF communities of natural savannas
and adjacent yam fields in the Southern Guinea savanna of Benin. AMF were identified by morphotyping spores in the soil from
the field sites and in AMF trap cultures with Sorghum bicolor and yam (Dioscorea rotundata and Dioscorea cayenensis) as bait plants. AMF species richness was higher in the savanna than in the yam-field soils (18–25 vs. 11–16 spp.), but similar
for both ecosystems (29–36 spp.) according to the observations in trap cultures. Inoculation of trap cultures with soil sampled
during the dry season led to high AMF root colonization, spore production, and species richness (overall 45 spp.) whereas
inoculation with wet-season soil was inefficient (two spp. only). The use of D. cayenensis and D. rotundata as baits yielded 28 and 29 AMF species, respectively, and S. bicolor 37 species. AMF root colonization, however, was higher in yam than in sorghum (70–95 vs. 11–20%). After 8 months of trap
culturing, the mycorrhizal yam had a higher tuber biomass than the nonmycorrhizal controls. The AMF actually colonizing D. rotundata roots in the field were also studied using a novel field sampling procedure for molecular analyses. Multiple phylotaxa were
detected that corresponded with the spore morphotypes observed. It is, therefore, likely that the legacy of indigenous AMF
from the natural savanna plays a crucial role for yam productivity, particularly in the low-input traditional farming systems
prevailing in West Africa. 相似文献
3.
Arturo A. Alvarado‐Segura Luz María Calvo‐Irabién Rodrigo Duno de Stefano Henrik Balslev 《Nordic Journal of Botany》2012,30(5):613-622
Species richness, abundance and diversity patterns in palm communities in the Yucatan Peninsula were compared at three sites with different forest types (semi‐deciduous, semi‐evergreen and evergreen), as well as different precipitation, geomorphology and soil depth. All individual palms, including seedlings, juveniles and adults, were identified and counted in forty‐five (0.25 ha) transects. A total of 46 000 individual palms belonging to 11 species from nine genera and two subfamilies were recorded. Palm richness, diversity and abundance were highest in the evergreen forest. Species from the subfamily Coryphoideae dominated the semi‐deciduous and semi‐evergreen forests while species from the subfamily Arecoideae dominated the evergreen forest. Seven species were found only in the evergreen forest. Chamaedorea seifrizii and Sabal yapa were found in all three forest types, while Thrinax radiata was found in the semi‐deciduous and semi‐ evergreen forests and Cocothrinax readii only in the semi‐evergreen forest. Compared to other neotropical palm communities, the richness and diversity in the Yucatan Peninsula are lower than in the western Amazon basin. Although palm richness and diversity on the Yucatan Peninsula were positively associated with precipitation, other variables, in particular soil depth and fertility as well as habitat heterogeneity (microtopography and canopy cover), need to be considered to better understand the observed patterns. 相似文献
4.
We used canopy fogging to study the high (20–26 m), intermediate (13–19 m) and low (5–6 m) strata in three European beech
patches (Fagus sylvatica) in nine months (2005–2007) and estimate species richness and diversity of arboreal spiders. Eight species (10%) were previously
unseen in European beech trees, and one of these is likely a new species. Moreover, two species are on the Bavarian red list.
Our results revealed that the high stratum of the old-growth trees provided unique resources and possessed the greatest diversity
and evenness, whereas intermediate and low strata had high similarity in respect to diversity, dominance, species, and family
composition. Since the majority of beech forests consists of mature and young trees in Central Europe, and old-growth forests
are rarely preserved, we recommend young beech be used in a sampling protocol for rapid biodiversity assessment. However,
adding samples from the two higher strata to the lowest stratum (55 species), almost doubled the estimated species richness
(102 species). This suggests that the lower stratum alone does not represent a true image of the total canopy fauna inventory
in this, and likely other, beech stands. To complete this comprehensive inventory in European beeches, the Chao1 predicted
that additional sampling would be needed in the highest stratum, where there is a high probability to find previously undetected
species in a next survey. Our study clearly shows that neglecting the crowns of the largest, tallest trees risks underestimating
the overall spider diversity in Central European forests. 相似文献
5.
Useful Species Richness, Proportion of Exotic Species, and Market Orientation on Amazonian Dark Earths and Oxisols Anthropogenic soils of Amazonia, known as Amazonian Dark Earths (ADE), are environments with elevated soil fertility that
can produce crops that otherwise yield poorly on the leached and highly acidic Oxisols that dominate much of the basin. While
ADE sites near urban centers often attract commercial horticultural production of nutrient–demanding exotics, these soils
are also considered possibly unique reservoirs of endemic agrobiodiversity because of their relationship to pre–Columbian
indigenous occupation. Through botanical surveys and interviews with smallholder farmers, this study compared useful species
richness, proportion of exotic species, and market orientation of farms situated on ADE and non–anthropogenic Oxisols in the
municipality of Borba in Central Brazilian Amazonia. Species richness was similar on Amazonian Dark Earth and Oxisol farms
(19.6 spp vs. 18.3 spp); however, ADE farms showed significantly higher proportions of exotic species (39% vs. 26%; p = 0.025). Furthermore, ADE farms in Borba demonstrated significantly higher market orientation (61.0% vs. 47.3%; p = 0.028), likely a result of the advantage of Amazonian Dark Earths for production of crops that are nutrient–demanding or
pH–sensitive crops that have higher values in the nearby regional market of Manaus. 相似文献
6.
Riparian forest communities dominated by Populus balsamifera ssp. trichocarpa L. (Torr. and Gray ex Hook.) Brayshaw are important contributors to biodiversity in terrestrial and aquatic ecosystems of the Western United States. Species composition along a successional gradient from stand initiation to late-succession of P. balsamifera-dominated riparian forests was investigated along 145 km of the Willamette River, Oregon. There were 151 total species encountered across 28 stands and a mean species richness of 33.3 species per stand. Young stands were dominated by P. balsamifera and Salix tree spp. and opportunistic herbaceous species. Understory trees, shrubs, and herbaceous species as well as late-successional tree species established 12–15 years after stand initiation. Fraxinus latifolia Benth. was the dominant late-successional tree species. Vertical structural diversity, P. balsamifera mean diameter at breast height, large tree biomass, and stand age were strongly correlated with understory species presence and abundance based on non-metric multidimensional scaling (NMS) ordination. There were no young stands on mid and high terraces and this was reflected in geomorphic position being strongly correlated with the stand age gradient. Abundance of Phalaris arundinacea L. an invasive grass species, was also significantly correlated with plant species composition and abundance. This study indicates that Willamette River riparian forests are diverse and therefore important to the biodiversity of the Willamette River valley and that their presence as a mosaic of communities of different successional stages may be threatened by human interventions, including influences exerted by introduced plant species. 相似文献
7.
Oisín F. McD. Sweeney Mark W. Wilson Sandra Irwin Thomas C. Kelly John O’Halloran 《Biodiversity and Conservation》2010,19(8):2329-2342
This study compared the bird assemblages of native semi-natural woodlands and non-native Sitka spruce (Picea sitchensis) plantations in Ireland to identify what vegetation variables most influenced birds and to identify management targets in
plantations to maximise future bird conservation. Point counts were conducted in 10 Oak (Quercus spp.) and 10 Ash (Fraxinus excelsior) native woodlands and in five Mid-rotation (20–30 years old) and five Mature (30–50 years old) Sitka spruce plantations.
Ordination was used to characterise woodland types according to their constituent bird species. Total bird density (calculated
using Distance software) and species richness were assessed for the different woodland types. Oak and Ash woodland bird assemblages were
separated from Mid-rotation and Mature plantations by the ordination. There was no difference in total bird density between
any of the woodland types. Oak woodlands had significantly higher species richness than either Mid-rotation or Mature Sitka
spruce plantations. Ash had higher species richness than Mature Sitka spruce plantations. Understorey vegetation was negatively
associated with total bird density, which also varied with survey year. Understorey vegetation was positively associated with
species richness. Reasons for the relationships between vegetation and bird assemblages are discussed. Management should seek
to increase shrub and understorey vegetation in the Mid-rotation phase to improve the contribution of plantations to bird
conservation. 相似文献
8.
Ma Wenhong 《Frontiers of Biology in China》2007,2(3):318-323
The relationship between plant species richness and primary productivity has long been a central topic in biodiversity research.
In this paper, we examine the relationship between species richness and productivity in four typical grasslands of Northern
China at different spatial scales. At the community scale, a positive correlation was found for six of seven communities.
A unimodal pattern was found only for one community (Stipa glareosa community), while at a large scale (vegetation type or landscape/region), the relationship was also found significantly positive.
Species richness ranged from 4 to 35 species, and community aboveground productivity from 13 to 368 g·m−2·a−1. The highest species richness and aboveground productivity were found in alpine meadow, followed by meadow steppe, typical
steppe and desert steppe.
Translated from Biodiversity Science, 2006, 14(1): 21–28 [译自: 生物多样性] 相似文献
9.
Microfungal diversity associated with Kindbergia oregana in successional forests of British Columbia
Species richness and species composition of microfungi associated with Oregon beaked moss (Kindbergia oregana) were studied at two forest chronosequences on southeast Vancouver Island, British Columbia, Canada. The purposes were to
investigate the effects of clear-cutting and the transformation of old-growth forests into secondary forests on microfungi
and the succession of microfungi in relation to long-term stand development. Green and brown parts of moss were collected
from the forest floor of Douglas-fir (Pseudotsuga menziesii) stands of four age classes: post-harvest regeneration (13–14 years), immature (50–51 years), and mature (85–101 years) stands,
and a control old-growth (296–324 years) stand, and used for the isolation of microfungi. A total of 49 microfungal species
were recorded. Study site, stand age, and moss parts significantly affected the species richness and species composition of
microfungi. The species richness of microfungi was significantly greater on brown than on green moss parts and lower in post-harvest
regenerations than in forest stands of the other age classes. The species composition of major microfungal species changed
gradually along the seral stages. Possible environmental and biological factors that could account for the succession of microfungi
were discussed. 相似文献
10.
J. E. García Raso M. J. Martín V. Díaz V. Cobos M. E. Manjón-Cabeza 《Hydrobiologia》2006,557(1):59-68
The study of a decapod community in a Cymodocea nodosa meadow from Southeastern Spain (Western Mediterranean Sea) showed a stable structure, in which the families Hippolytidae,
Processidae, Majidae and Portunidae were the most abundant and the species Hippolyte niezabitowskii dominated. The animal community was more numerous and diverse during the night, showing the existence of nychthemeral movements,
which are essentially related to the trophic behaviour and shelter. In this way, many species increased their abundance as
a result of an increasing activity and, also, of an influx of other species and specimens from adjacent sandy bottoms, such
as Processa spp. (mainly P. modica) Sicyonia carinata, Liocarcinus spp. (mainly juveniles) and several species of hermit crabs, which were rare or absent during the day. All these changes
produced modifications in the dominance curves and in the values of all ecological indices (richness, diversity and evenness).
Monthly samples were grouped and ordered (MDS) by the factor “day–night”, which showed slight qualitative and quantitative
differences (SIMPER, dissimilarity average of the factor day–night = 61.67). On the other hand, no global seasonal differences
have been found (one way ANOSIM), but there was a significant level of similarity between winter and spring, while the summer
samples were the most different. The differentiation of the summer 1999 can be attributed to a decrease in species abundance
and richness, probably due to the dynamics of the decapod populations and the balance with predators (fishes), while that
of the summer 2000, to an anomalous event: the massive proliferation of filamentous algae, mainly Ectocarpus s.l., which modified the environmental conditions. 相似文献
11.
Addisu Mekonnen Afework Bekele Peter J. Fashing Graham Hemson Anagaw Atickem 《International journal of primatology》2010,31(3):339-362
Bale monkeys (Chlorocebus djamdjamensis) are little-known primates endemic to the forests of the Bale Massif and Hagere Selam regions of Ethiopia. From August 2007
to May 2008, we conducted the first ever study of the species’ behavior and ecology, focusing in particular on its diet, activity
patterns, and ranging ecology in the Odobullu Forest. We studied 2 neighboring groups (group A: 55–60 members; group B: 46–50
members) and conducted behavioral scan samples on the first 2–5 individuals sighted at 15-min intervals. Feeding accounted
for 65.7% of the activity budget, followed by moving (14.4%), resting (10.7%), social (7.1%), and other behaviors (2.4%).
Overall diet during the study was dominated by young leaves (80.2%), though subjects also ate fruits (9.6%), flowers (3.1%),
animal prey (2.3%), shoots (1.5%), stems (1.4%), mature leaves (1.1%), and roots (0.9%). Bale monkeys consumed only 11 plant
species; of these, the top 5 species accounted for 94.3% of their diet. The top food item, bamboo (Arundinaria alpina), was responsible for a remarkable 76.7% of their diet, with most (95.2%) of the bamboo consumption consisting of young leaves.
Mean daily path length for the study groups was 928 m and mean (100% minimum convex polygon) home range size was 15.2 ha.
Though we are cautious in drawing conclusions from only 2 groups, the larger group traveled further per day and occupied a
larger home range, patterns suggesting scramble competition may be occurring in Bale monkey groups at Odobullu. The dietary
specialization of Bale monkeys on bamboo makes them unique among Chlorocebus spp. and suggests an intriguing ecological convergence with the golden monkeys (Cercopithecus mitis kandti) of Uganda and bamboo lemurs (Hapalemur spp.) of Madagascar. Their narrow ecological niche, limited geographic distribution, and bamboo harvesting by local people
for commercial purposes place Bale monkeys at risk of extinction. To ensure the long-term survival of Bale monkeys, appropriate
management action should be taken to conserve the species and the bamboo forests upon which it depends. 相似文献
12.
Green algal communities were investigated in clean and pollution-impacted tundra soils around the large coal mine industrial
complex of Vorkuta in the E. European Russian tundra. Samples were collected in three zones of open-cast coal mining with
different degrees of pollution-impacted soil transformation. A total of 42 species of algae were found in all zones. The species
richness decreased from 27 species in undisturbed zones to 19 species in polluted zones. Under open-cast coal mining impacts
the community structure simplified, and the dominant algae complexes changed. Algae that are typical for clean soils disappeared
from the communities. The total abundance of green algae (counted together with Xanthophyta) ranged between 100–120 × 103 (cells/g dry soils) in undisturbed zones and 0.5–50 × 103 in polluted zones. Soil algae appear to be better indicators of coal mine technogenic pollution than flowering plants and
mosses.
Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia. 相似文献
13.
There are only few studies on shallow Antarctic benthic communities associated with habitats affected by intense mineral sedimentation
inflow. The analysis of macrofaunal communities associated with two shallow, isolated glacial coves was performed in Admiralty
Bay (King George Island) and compared with non-disturbed sites. Multivariate analyses (hierarchical classification, nMDS)
clearly separated glacial cove communities (two assemblages) from the sites situated outside both basins (two assemblages).
The community influenced by the streamflow of glacial discharge of meltwater situated in the area with sandy–clay–silt sediments
had a very low species richness, diversity and abundance. It was dominated by eurytopic, motile deposit feeding polychaetes
such as Mesospio
moorei, Tharyx
cincinnatus and Leitoscoloplos
kerguelensis as well as the bivalve Yoldia
eightsi. The second glacial community of the area located at a grater distance from the outlet of the stream was characterized by
sandy–clay–silt and clay–silt deposits and showed also a low diversity and species richness. The most abundant here were peracarid
crustaceans, with the dominant opportunistic feeder Cheirimedon
femoratus. Community from the non-disturbed area with silty–clay–sand, and silty–sand sediments had higher species richness and diversity.
The assemblage of fauna from the sandy bottom has values of those two indexes similar to those found in the disturbed areas. 相似文献
14.
Paula J. Fornwalt Merrill R. Kaufmann Laurie S. Huckaby Thomas J. Stohlgren 《Plant Ecology》2009,203(1):99-109
Throughout Pinus ponderosa–Pseudotsuga menziesii forests of the southern Colorado Front Range, USA, intense logging and domestic grazing began at the time of Euro-American
settlement in the late 1800s and continued until the early 1900s. We investigated the long-term impacts of these settlement-era
activities on understory plant communities by comparing understory composition at a historically logged and grazed site to
that of an environmentally similar site which was protected from past use. We found that species richness and cover within
functional groups rarely differed between sites in either upland or riparian areas. Multivariate analyses revealed little
difference in species composition between sites on uplands, though compositional differences were apparent in riparian zones.
Our findings suggest that settlement-era logging and grazing have had only minor long-term impacts on understories of upland
Front Range P. ponderosa–P. menziesii forests, though they have had a greater long-term influence on riparian understories, where these activities were likely
the most intense.
This article was written and prepared by US Government employees on official time, and therefore it is in the public domain
and not subject to copyright. 相似文献
15.
Several previous studies have attempted to correlate habitat complexity and reef fish species diversity. These studies have mostly examined natural reef systems, but results differed. To examine this relation, we built 1 m2 habitats with 20 replicates of five complexity levels from July to August 2001 in the northeastern Gulf of Mexico (n=100). In June and July 2002, we built new habitats using the 2001 design, but also added a sixth complexity level (n=120). In order of increasing complexity these included: cage, shell, cage-shell, block-shell, cage-block-shell, and shell-block-pyramid habitats. Most fish in both years were juveniles and included species common to reef structures in the northeastern Gulf of Mexico. In 2001, we identified 26 fish species, and the dominant species was red snapper, Lutjanus campechanus (41%), followed by rock sea bass, Centropristis philadelphica (23%), and sand perch, Diplectrum spp. (14%). In 2002 we identified 36 species, and the dominant species was tomtate, Haemulon aurolineatum (36%), followed by Diplectrum spp. (19%), and L. campechanus (13%). In 2001, species diversity and richness were significantly (P<0.05) higher on more complex habitats (H′=1.7, S=11–12) compared to less complex habitats (H′=0.8–1.0, S=4–9). In 2002, patterns among diversity, richness and reef complexity were less apparent with only the least complex habitats shell and cage showing significantly lower values. In both years, multidimensional scaling grouped by complexity levels with cage and shell habitats showing the clearest separation from other habitat types. Also, with few exceptions (only 8%) analysis of similarities showed significant (P<0.05) differences in fish communities across complexity levels. Although community composition varied between years, this study provided evidence to support the hypothesis that habitat complexity increased reef fish species diversity. 相似文献
16.
The objective of this study was to assess freshwater mussel (Mollusca: Bivalvia: Unionoida) species distributions among the
freshwater ecoregions of Africa and Madagascar to discover areas of high richness and endemism. These are among the top criteria
for identifying biodiversity hotspots and establishing conservation priorities. Distributions were determined from museum
specimens in 17 collections. In total, 5,612 records for 87 unionoid species could each be assigned to one of 90 freshwater
ecoregions. The majority of species (55%) are known from only one (34 spp.) or two (14) ecoregions. Only three are known from
more than 20 ecoregions: Etheria elliptica (38 ecoregions), Chambardia wahlbergi (25), and Mutela rostrata (21). The most species-rich ecoregions are Lake Victoria Basin (17 spp.), Upper Nile (16), Upper Congo (14), Senegal–Gambia
(13), and Sudanic Congo–Oubangi (13). Those with the most endemic species are Lake Tanganyika (8 spp.), Lake Victoria Basin
(6), Bangweulu–Mweru (4), and Lake Malawi (3). Twenty-five ecoregions have no known freshwater mussels. These patterns are
significantly correlated with fish and general freshwater mollusk richness. Unionoid richness also varies significantly among
major habitat types. These patterns are relevant to biogeography and conservation and indicate areas in need of further research.
We argue that freshwater mussels are valuable as focal species for conservation assessments, and they themselves merit management
consideration for their ecosystem functions and distributions in imperiled habitats. It is recommended that field surveys
be conducted to determine the current status of species in all areas of Africa and Madagascar. 相似文献
17.
Mycorrhizal species richness and host ranges were investigated in mixed deciduous stands composed of Fagus sylvatica, Tilia spp., Carpinus betulus, Acer spp., and Fraxinus excelsior. Acer and Fraxinus were colonized by arbuscular mycorrhizas and contributed 5% to total stand mycorrhizal fungal species richness. Tilia hosted similar and Carpinus half the number of ectomycorrhizal (EM) fungal taxa compared with Fagus (75 putative taxa). The relative abundance of the host tree the EM fungal richness decreased in the order Fagus > Tilia >> Carpinus. After correction for similar sampling intensities, EM fungal species richness of Carpinus was still about 30–40% lower than that of Fagus and Tilia. About 10% of the mycorrhizal species were shared among the EM forming trees; 29% were associated with two host tree species
and 61% with only one of the hosts. The latter group consisted mainly of rare EM fungal species colonizing about 20% of the
root tips and included known specialists but also putative non-host associations such as conifer or shrub mycorrhizas. Our
data indicate that EM fungal species richness was associated with tree identity and suggest that Fagus secures EM fungal diversity in an ecosystem since it shared more common EM fungi with Tilia and Carpinus than the latter two among each other. 相似文献
18.
Gupta RS 《Photosynthesis research》2003,76(1-3):173-183
To understand the evolution of photosynthetic bacteria it is necessary to understand how the main groups within Bacteria have evolved from a common ancestor, a critical issue that has not been resolved in the past. Recent analysis of shared conserved
inserts or deletions (indels) in protein sequences has provided a powerful means to resolve this long-standing problem in
microbiology. Based on a set of 25 indels in highly conserved and widely distributed proteins, all main groups within bacteria
can now be defined in clear molecular terms and their relative branching orders logically deduced. For the 82 presently completed
bacterial genomes, the presence or absence of these signatures in various proteins was found to be almost exactly as predicted
by the indel model, with only 11 exceptions observed in 1842 observations. The branching order of different bacterial groups
as deduced using this approach is as follows: low G+C Gram-positive (Heliobacterium chlorum) ↔ high G+C Gram-positive ↔ Clostridium–Fusobacterium–Thermotoga ↔ Deinococcus–Thermus ↔ green nonsulfur bacteria (Chloroflexus aurantiacus) ↔ Cyanobacteria ↔ Spirochetes ↔ Chlamydia–Cytophaga–Flavobacteria–green sulfur bacteria (Chlorobium tepidum) ↔ Aquifex ↔ Proteobacteria (δ and ∈) ↔ Proteobacteria (α) ↔ Proteobacteria (β) and ↔ Proteobacteria (γ). The Heliobacterium species, which contain an Fe–S type of reaction center (RC 1) and represent the sole photosynthetic phylum from the Gram-positive
or monoderm bacteria (i.e., bounded by only a single membrane), is indicated to be the most ancestral of the photosynthetic
lineages. Among the Gram-negative or diderm bacteria (containing both inner and outer cell membranes) the green nonsulfur
bacteria, which contain a pheophytin-quinone type of reaction center (RC 2), are indicated to have evolved first. The later
emerging photosynthetic groups which contain either one or both of these reaction centers could have acquired such genes from
the earlier branching lineages by either direct descent or by means of lateral gene transfer.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
In 2003–2004, 102 species of five weevil families were found in the steppe and desert associations of the Caspian semi-desert
(Dzhanybek Station). Representatives of Curculionidae predominated (87 species). The majority of the commonest weevil species
(20) were most abundant in the steppe associations, only 6 species being found in the desert ones. The composition of the
weevil community changed abruptly from spring to summer. The greatest species richness (86 species) was observed in spring;
only in this period weevils living mostly on the soil surface had high densities. In the herbage, both in the steppe and desert
communities, detritophagous steppe species Archaeophloeus inermis and Trachyphloeus amplithorax were abundant; the habitats of the solonetz complex (on microelevations and in the depressions), the desert-steppe and steppe
species (Humeromima nitida, Mesagroicus poriventris, Temnorhinus strabus) associated with saline substrates were also present. The spring hortobiont assemblage was dominated by the polyphagous steppe
weevils, Euidosomus acuminatus, Phyllobius brevis and Omias spp. In summer, 53 species of weevils were recorded; their numbers on the soil surface sharply dropped, the core of the herbage
assemblage consisted of the weevils feeding on alfalfa (Stenopterapion tenue, Sitona spp., Tychius spp.) in the steppe associations, with the maximum abundance in the more humid depressions. The summer assemblage of the
desert herbage was poor and consisted of the species associated with wormwoods and chenopods (Ptochus porcellus, Phacephorus argyrostomus, Metadonus anceps). The autumn groupings with only 24 species were poor and had low population densities. 相似文献
20.
Limnological characteristics of the freshwater ecosystems of Byers Peninsula, Livingston Island, in maritime Antarctica 总被引:2,自引:0,他引:2
M. Toro A. Camacho C. Rochera E. Rico M. Bañón E. Fernández-Valiente E. Marco A. Justel M. C. Avendaño Y. Ariosa W. F. Vincent A. Quesada 《Polar Biology》2007,30(5):635-649
A limnological survey of 15 lakes and 6 streams was carried out on Byers Peninsula (Livingston Island, South Shetland Islands,
Antarctica) during austral summer 2001–2002. Most of the surface waters had low conductivities (20–105 μS cm−1) and nutrients (total phosphorus 0.01–0.24 μM), but some coastal lakes were enriched by nutrient inputs from seal colonies
and marine inputs. Plankton communities in the lakes contained picocyanobacteria (102–104 cells ml−1), diatoms, chrysophytes and chlorophytes, and a large fraction of the total biomass was bacterioplankton. Zooplankton communities
were dominated by Boeckella poppei and Branchinecta gainii; the benthic cladoceran Macrothrix ciliata was also recorded, for the first time in Antarctica. The chironomids Belgica antarctica and Parochlus steinenii, and the oligochaete Lumbricillus sp., occurred in stream and lake benthos. The phytobenthos included cyanobacterial mats, epilithic diatoms and the aquatic
moss Drepanocladus longifolius. These observations underscore the limnological richness of this seasonally ice-free region in maritime Antarctica and its
value as a long-term reference site for monitoring environmental change. 相似文献