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1.
中小尺度下西北太平洋柔鱼资源丰度的空间变异 总被引:4,自引:0,他引:4
西北太平洋柔鱼是我国最重要的远洋捕捞对象之一,掌握其资源分布在空间上的分布特征将可为资源的可持续开发和利用提供基础。本文采用2011年8-10月我国在北太平洋150?-160?E、38?-48?N海域的柔鱼生产统计数据,以单船日产量(CPUE)为资源丰度指标,分经纬度10′?10′、20′?20′、30′?30′、40′?40′、50′?50′、60′?60′和70′?70′等7个尺度,利用地统计学方法对柔鱼资源丰度的空间分布特征进行了分析,探讨柔鱼资源丰度的空间变异特性。结果显示,8-10月柔鱼资源丰度均以指数模型拟合产生的空间自相关异质性程度最好;小尺度下(10′?10′、20′?20′、30′?30′)柔鱼资源丰度空间结构表现出中等水平及其以上的空间自相关变异程度,中尺度下(40′?40′、50′?50′、60′?60′和70′?70′)则相对比较低,基本上为弱空间自相关变异程度;柔鱼资源丰度空间结构显示有各向异性,8月和9月的方向角分别为西北-东南走向和东北-西南走向,10月受柔鱼性成熟开始南向洄游以及海洋环境的影响,其方向角变化较大。此外,论文对柔鱼资源丰度的适宜尺度作了进一步探讨,综合分析认为CPUE空间变异的研究应以小尺度为适宜,其中30′?30′最为稳定。论文结合柔鱼的栖息环境等,分析了它们对资源丰度时空变异及其特征的影响。 相似文献
2.
The microstructure, morphology and ontogenetic development ofstatoliths and age and growth of 405 planktonic paralarvae and117 juveniles belonging to 10 species of gonatid squids (Cephalopoda,Oegopsida) were studied in the region of the continental slopein the western part of the Bering Sea (57°00'61°30'N,163°00'E179°20'W). The statolith microstructureof all species was characterized by the presence of a largedroplet-shaped nucleus and bipartite postnuclear zone dividedinto two by the first stress check, except for Berryteuthismagister which had only one stress check and an undivided postnuclearzone. In Gonatus spp., completion of development of the postnuclearzone coincided with full development of the central hook onthe tentacular club. Daily periodicity of statolith growth incrementswas validated by maintaining 13 paralarvae of the four mostabundant species in captivity. All species might be subdividedinto two groups based on statolith microstructure, i.e. specieswith a central position of the nucleus within the first statolithcheck (Gonatopsis spp., Egonatus tinro and B.magister) and specieswith the nucleus shifted to the inner side of the first statolithcheck (Gonatus spp.). Comparative analysis of statolith morphologyshowed that paralarval statoliths have species-specific charactersthat allowed the construction of keys to identify species ofgonatid paralarvae based on their statoliths. Analysis of paralarvalgrowth using statoliths revealed that these cold-water planktonicgonatid paralarvae have fast growth rates, attaining a mantlelength of 710 mm at 1520 days and 2025mm at 3570 days. 相似文献
3.
We examined deep-sea benthic data on polychaetes, isopods and bivalves from the Atlantic sector of the Southern Ocean. Samples
were taken during the expeditions EASIZ II (1998), ANDEEP I and II (2002) (depth: 742–6,348 m). The range between sites varies
from 3 to 1,900 km. Polychaetes (175 species in total) and isopods (383 species) had a high proportion of species restricted
to one or two sites (72 and 70%, respectively). Bivalves (46 species) had a higher proportion of species represented at more
sites. Beta diversity (Whittaker and Jaccard) was higher for polychaetes and isopods than for bivalves. The impact of depth
on species richness was not consistent among groups; polychaetes showed a negative relationship to depth, isopods displayed
highest richness in the middle depth range (2,000–4,000 m), whereas bivalves showed no clear relationship to depth. Species
richness was not related to latitude (58–74°S) or longitude (22–60°W) for any group. 相似文献
4.
The survivorships and growth rates ofPlanorbarius corneus andPlanorbis planorbis were measured during the whole life spanof the snails at constant temperatures of 5, 10, 15, 20 and25°C. Life expectancy tables were constructed. The maximumlongevities for P. corneus (231 weeks) and P. planorbis (175weeks) occurred at 15°C and 10°C respectively. The extremetemperatures were particularly unfavourable. Snail growth which was expressed logarithmically was most sensitiveto temperature during the exponential stage. However, if weconsider a given species duringjts entire life span, there wereno significant differences between temperature groups whichwere in order of decreasing suitability: P. corneus: 25, 20 and 15°C; 10°C; 5°C; P.planorbis: 20 and 15°C; 25 and 10°C; 5°C. Using the growth constants from the Von Berta-lanffy's modeladjusted to give a gaussian curve, it was calculated that theoptimum temperatures for the growth of P. planorbis and P. corneuswere 19 and 20.5°C respectively. A mathematical model basedon spline functions makes it possible to predict the growthof snails over a wide range of temperatures. (Received 2 June 1993; accepted 18 November 1993) 相似文献
5.
Daily vertical migration of dense deep scattering layers related to the shelf-break area along the northwest coast of Baja California, Mexico 总被引:1,自引:0,他引:1
Echo signals were collected with a Simrad 200 kHz transduceracross the shelf-break features off the northwest coast of BajaCalifornia (30°05'30°42'N, 115°50'116°26'W)during two diel cycles (July 1995) with the objective of describingvertical migrations of two dense deep scattering layers (DSL)found near the shelf break. DSL records were made within anarea ±50 m in the neritic zone, ±200 m at theshelf break and ±1000 m depth in the offshore station.Using an Isaacs-Kidd midwater net and Bongo nets, we inferredthat the DSL were composed mainly of juveniles and adults ofthe euphausiids Nyctiphanes simplex Hansen and Euphausia pacificaHansen. These aggregations have a close interaction with theocean bottom during the daytime and display a vertical migration,rising near to the surface at night where a progressive horizontaldispersion then occurs. The DSL measured 3.56.0 km horizontallyduring the night. The ascent and descent migrations of the DSLwere significantly fitted to a polynomial function of the secondorder, suggesting different swimming behavior during these twoprocesses. Vertical migrations of the DSL were between 60 and90 m. During the descent migration, maximum instantaneous speedsreached 0.7 cm s1, and during the ascent, maximum instantaneousspeeds were 0.3 cm s1. These coastal euphausiid species, alongwith other macrozooplankton and nektonic organisms, have a dailyclose interaction with the ocean bottom and also with the pelagicenvironment, suggesting that they play an important role providingfood for demersal and pelagic organisms on the slope and shelfbreak in the upwelling region off the northwest coast of BajaCalifornia. 相似文献
6.
Decadal change in zooplankton seasonal succession in the Bahia Blanca estuary, Argentina, following introduction of two zooplankton species 总被引:2,自引:0,他引:2
Seasonal zooplankton succession (mainly of the mesozooplankton)in the inner zone of Bahía Blanca estuary during theperiod 19901991 was compared to that from the period19791980 in order to detect changes having taken placein 10 years. Taxonomic composition, zooplankton abundance, speciesoccurrence and temperaturesalinity conditions were studiedwithin the two annual cycles. This estuarine ecosystem has beendeeply affected by a population increase and by the rapid growthof industrial activity and maritime traffic over the last twodecades. Several changes in the zooplankton assemblage compositionand structure were detected, probably due to temperaturesalinitygradient patterns, which showed discernible differences. Dominance,during winterspring, of two new invading species, namely,the cirriped Balanus glandula and the copepod Eurytemora americana,causing a decrease in the autochthonous key copepod Acartiatonsa, was one of the principal features of the period 19901991.Seasonal changes in diversity and species richness, as wellas differences in the multivariate general pattern of the zooplanktoncommunity structure with a consequent decrease in the communitystability during the second period, were also observed. 相似文献
7.
Zeng Zhigao Song Yanling Ma Yingtai Wang Xifeng Wu Xuntao Xie Zhenfeng Shao Jianbin Li Chunning 《Frontiers of Biology in China》2007,2(1):92-99
Niubeiliang National Nature Reserve (NNR, 108°45′–109°04′E, 33°47′–33°56′N) is located on the eastern range of the Qinling
Mountains in Shaanxi Province, China and spans the southern and northern slopes of Mt. Qinling. A transect survey and investigation
were carried out in NNR to determine the fauna characteristics and ecological distribution of carnivora and artiodactyla from
May 2003 to August 2004. The NNR has 18 mammals (carnivore and artiodactyl), two of which belong to the first class and seven
to the second class of state key protected wildlife in China. The results of this study indicated that ungulates were abundant
in the NNR, as all ungulates that were distributed within Mt. Qinling could be found within the reserve. However, only 45.5%
of the carnivores distributed within Mt. Qinling were detected within the NNR. Among the mammals, there were 12 oriental species
(66.7%), 1 palearctic specie (5.5%) and 5 widely-distributed species (27.8%). The NNR is a crossing area of palearctic species
and oriental species on the zoogeographical regions, and it is a transitional area from the oriental realm to the palearctic
realm. The results of the analysis on the ecological distribution of carnivore and artiodactyl in the area showed that their
elevation ranges had large differences. The species whose elevation ranges above 1 300 m, about 1 000 m, and in 450–700 m
occupied one third respectively. The results also indicated that species richness for the memals in the NNR peaked at a middle
elevation (rising at first, then descending with the increase in elevation). Not only on the southern slope, but also on the
northern slope of Mt. Qinling, the number of species distributed in the area at 1 800–2 200 m a.s.l. was the largest (more
than 80%), while the number of species distributed in the area above 2 600 m a.s.l. was the smallest (about 50%). Elevation
gradients of species richness for the mammals in the NNR also embodied the mammal distributions among the vegetation types.
The number of species distributed in the mixed coniferous and broadleaf deciduous forest at middle elevations was the largest,
while the number of species distributed in the broadleaf deciduous forest at middle and low elevations, subalpine coniferous
forest, subalpine shrubbery and meadow was relatively smaller.
Translated from Acta Ecologica Sinica, 2005, 25(9): 2249–2255 [译自: 生态学报] 相似文献
8.
Community analysis of Belarusian lakes: relationship of species diversity to morphology, hydrology and land use 总被引:1,自引:0,他引:1
Karatayev Alexander Y.; Burlakova Lyubov E.; Dodson Stanley I. 《Journal of plankton research》2005,27(10):1045-1053
In the glacial lake district of northern Belarus, limnologistscollected extensive biological, chemical and physical data on550 lakes (51% of all Belarusian glacial lakes). This largedata set provided a unique opportunity to examine subtle relationshipswith great statistical power. Our purpose was to use multivariateand correlation analyses to explore relationships of speciesrichness with morphological and hydrological parameters. A multivariateanalysis of the environmental data suggests that the Belarusianlakes can be separated along gradients of size, hydraulic residencetime and watershed development (land use). In most instances,species richness for major planktonic and benthic groups wascorrelated significantly with lake size and land use. Speciesrichness values were correlated less with watershed size orhydraulic residence time. In each community, there was a groupof species characterized by higher correlations with principalcomponent analysis (PCA) axes. These groups are as follows:for phytoplanktondiatoms, for zooplanktonrotifers,and for zoobenthosmolluscs. For lakes both in pristineand developed watersheds, we found small but significant negativespeciesarea correlations for littoral crustaceans. Asurvey of the relevant literature shows scale dependence forthe correlation between species richness and lake size. Forpelagic crustaceans, the speciesarea correlation wassignificant (and positive) for lakes with developed watershedsbut not for pristine watersheds. 相似文献
9.
Patterns in species richness,species density,and evenness in groundfish assemblages on the continental slope of the U.S. Pacific coast 总被引:1,自引:0,他引:1
Nick Tolimieri 《Environmental Biology of Fishes》2007,78(3):241-256
For many taxa, diversity, often measured as species richness, decreases with latitude. In this report patterns of diversity
(species richness, species diversity, and evenness) in groundfish assemblages were investigated in relation to depth (200–1200 m)
and latitude (33–47°N) on the continental slope of the U.S. Pacific coast. The data originated from the 1999–2002 upper continental
slope groundfish surveys conducted by the National Marine Fisheries Service. When the data were pooled across depths, species
density and evenness were found to decline with latitude. All three diversity measures declined with depth, with the lowest
overall diversity in the 600- to 900-m depth range where longspine thornyhead Sebastolobus altivelis constituted close to 70% of the catch. When latitudinal gradients were examined within four depth zones (200–300 m, 400–500 m,
600–900 m, and 1000–1200 m) more complex patterns emerged. At depth species richness and evenness were inversely correlated
with latitude as longspine thornyhead dominated catches to the north. However, in shallower areas of the slope, species richness
and evenness were positively correlated with latitude. Latitudinal patterns of diversity in the deeper zones and when pooled
across depths were positively correlated with temperature and broadly consistent with the Ambient Energy hypothesis discussed
by Willig et al. [Annu Rev Ecol System 34:273–309 (2003)]. 相似文献
10.
Effects of river level fluctuation on plant species richness, diversity, and distribution in a floodplain forest in Central Amazonia 总被引:6,自引:0,他引:6
River levels in Central Amazonia fluctuate up to 14 m annually, with the flooding period ranging from 50 to 270 days between
the rising and falling phases. Vast areas of forest along the rivers contain plant species that are well adapted to annual
flooding. We studied the effect of flooding level on tree species richness, diversity, density, and composition in lake, river,
and stream habitats in Jaú National Park, Brazil. 3051 trees >10 cm diameter (at 1.3 m diameter at breast height, dbh) were
measured and identified in 25 10 m × 40 m randomly selected plots in each habitat. Ordination methods and analysis of variance
results showed that forested areas near lakes had significantly lower species richness of trees than riverine and streamside
habitats. Plot species richness and diversity were strongly negatively correlated with the water level and duration of flooding.
The drier (stream) habitat had more total species (54 species of trees) and more unique species of trees (6 tree species)
than the riverine (52 tree species; 3 unique species) and lake (33 tree species; 3 unique species) habitats. Species composition
overlap among habitats was surprisingly high (42.6–60.6% overlap), almost one-third of the species were found in all three
habitat types, and few species were unique to each habitat. We conclude that: (1) duration of flooding has a strong impact
on species richness, diversity and plant distribution patterns; (2) most species are adapted to a wide range of habitats and
flood durations; and (3) while flood duration may decrease local diversity, it also creates and maintains high landscape-scale
diversity by increasing landscape heterogeneity.
Received: 20 April 1997 / Accepted: 14 January 1999 相似文献
11.
Effects of spatial heterogeneity on butterfly species richness in Rocky Mountain National Park, CO, USA 总被引:2,自引:0,他引:2
We investigated butterfly responses to plot-level characteristics (plant species richness, vegetation height, and range in
NDVI [normalized difference vegetation index]) and spatial heterogeneity in topography and landscape patterns (composition
and configuration) at multiple spatial scales. Stratified random sampling was used to collect data on butterfly species richness
from seventy-six 20 × 50 m plots. The plant species richness and average vegetation height data were collected from 76 modified-Whittaker
plots overlaid on 76 butterfly plots. Spatial heterogeneity around sample plots was quantified by measuring topographic variables
and landscape metrics at eight spatial extents (radii of 300, 600 to 2,400 m). The number of butterfly species recorded was
strongly positively correlated with plant species richness, proportion of shrubland and mean patch size of shrubland. Patterns
in butterfly species richness were negatively correlated with other variables including mean patch size, average vegetation
height, elevation, and range in NDVI. The best predictive model selected using Akaike’s Information Criterion corrected for
small sample size (AICc), explained 62% of the variation in butterfly species richness at the 2,100 m spatial extent. Average vegetation height and
mean patch size were among the best predictors of butterfly species richness. The models that included plot-level information
and topographic variables explained relatively less variation in butterfly species richness, and were improved significantly
after including landscape metrics. Our results suggest that spatial heterogeneity greatly influences patterns in butterfly
species richness, and that it should be explicitly considered in conservation and management actions. 相似文献
12.
Intermediary disturbance increases tree diversity in riverine forest of southern Brazil 总被引:1,自引:0,他引:1
Jean Carlos Budke João André Jarenkow Ary Teixeira de Oliveira-Filho 《Biodiversity and Conservation》2010,19(8):2371-2387
Floods are frequently associated with disturbance in structuring riverine forests and they lead to environmental heterogeneity
over space and time. We evaluated the distribution of tree species, ecological groups, species richness and diversity from
the point bar to the slope of a riverside forest in southern Brazil (Lat. 30°01′S, Long. 52°47′W) to analyze the effects of
flooding on soil properties and forest structure. A plot of 50 × 200 m divided in five contiguous transects of 10 × 200 m
parallel to the river was installed, where we measured all the individual trees with pbh ≥ 15 cm. A detailed topographical
and soil survey was carried out across the plot and indicated significant differences in organic matter and most mineral nutrients
through the topographical gradient. The 1,229 surveyed individuals belonged to 72 species and 35 families. We used Partial
CCA and Species Indicator Analysis to observe the spatial distribution of species. Both analyses showed that species distribution
was strongly related to the flooding gradient, soil properties and also by space and pure spatial structuring of species and
environmental variables (spatial autocorrelation), although a large part of variation remains unexplained. The ecological
groups of forest stratification, plant dispersal and requirements for germination indicated slight differences among frequently,
occasional and non-flooded transects. Species richness and diversity were higher at intermediate elevations and were associated
to the increased spatial–temporal environmental heterogeneity. Across the plot, the direct influence of flooding on tree species
distribution created a vegetation zonation that is determined by predicted ecological traits. 相似文献
13.
Dormancy in Rice Seed: III. THE INFLUENCE OF TEMPERATURE, MOISTURE, AND GASEOUS ENVIRONMENT 总被引:1,自引:0,他引:1
The influence of storage conditionstemperature, moisturecontent, oxygen, nitrogen, and carbon dioxideon dormancyin rice seed has been investigated. The effects of temperatureand oxygen when the seeds have been set to germinate have alsobeen studied. Storage in oxygen accelerates the breaking of dormancy; at lowertemperatures, the effect of oxygen is more noticeable. Carbondioxide and nitrogen have little or no effect except in so faras they exclude oxygen. It is shown that there is a negativelinear relationship between storage temperature and log. meandormancy period of intact seeds over the range 27°C. to47°C. In the variety tested, the Q10 for the rate of breakingdormancy is 3.38. Variation of moisture content over the range12.014.5 per cent, has little effect at 27°C. andno detectable effect at higher temperatures. When dormant seeds are soaked in water, they attain a moisturecontent close to 30 per cent. Pre-soaking seeds to achieve moisturecontents in this region can stimulate the breaking of dormancywhen compared with dry storage. At laboratory temperature (meanabout 27°C.) the stimulation caused by pre-soaking intactseeds is usually small and sometimes non-existent, but at alow temperature (3°C.) the stimulation is increased; butdry storage at 3°C. markedly delays the breaking of dormancy.When seeds are dehusked, a large proportion lose their dormancy.Much of the residual dormancy of dehusked seeds can be brokenby soaking at laboratory temperature. But in the sample of dehuskedseeds used, low temperature did not increase the effect of thepre-soaking, but slightly decreased the stimulation caused bythe soaking treatment in this case. The effect of temperature on wet seed has also been investigatedwhen the seed has been set to germinate. Maximum germinationof a partially dormant population of seed is achieved at anoptimum temperature which is near or somewhat below 27°C.In the sample tested, no germination occurred at 42°C.,although in populations which have completely broken dormancyfull germination will occur at this temperature. Non-dormantpopulations of rice seed can germinate at very low oxygen tensionsor probably even in the absence of oxygen, but germination ofa partially dormant sample is reduced under these circumstances.When oxygen tension is very low there is less germination at27°C. than at 37°C. In some varieties, at least, there is evidence that the seedsgo through a stage when they will germinate in daylight butnot in the dark. A simple practical method for rapidly breakingthe dormancy of intact seeds is described. The significanceof these results is discussed in relation to the published workon seeds of other species. 相似文献
14.
Knee, M. 1987. Development of ethylene biosynthesis in pearfruits at 1 °C.J. exp. Bot. 38: 17241733. The regulation of ethylene synthesis in pear fruits was investigated.During storage for 60 d at 1 °C the rate of ethylenesynthesis increased 100-fold but the concentration of 1-aminocyclopropane-l-carboxylicacid (ACC) increased only 2-fold and ACC synthase activity waslow. On transfer to 15 °C after storage at 1 °Cethylene synthesis increased 10-fold within 10 h but ACC synthaseactivity only increased rapidly after 24 h; the decline in ACClevels during the first 16 h at 15 °C was insufficient tosustain ethylene synthesis. Ethylene synthesis was further investigatedusing discs cut from the mid cortex of pear fruits. Synthesiswas inhibited by aminoethoxyvinylglycine (AVG) and amino-oxyaceticacid at all stages of ripening. The rate of synthesis and ACCsynthase activity increased rapidly after slicing of pears heldat 1 °C but more slowly in discs cut from pearsimmediately after harvest. Cycloheximide (CHI) inhibited theseincreases and reversed increases resulting from pre-incubationof discs. A combination of CHI and AVG abolished the capacityof discs to synthesize ACC and ethylene production was curtailed.Cordycepin and actinomycin-D were less effective as inhibitorsof the development of ethylene synthesis and ACC synthase activitythan as inhibitors of incorporation of 5-[3H] uridine into totalRNA or poly A rich RNA. The ability of discs to develop ethylenesynthesis and ACC synthase activity in the presence and absenceof cordycepin increased concurrently during storage of wholefruits at 1 °C. This suggested that mRNA for ACCsynthase was formed at 1 °C. Key words: 1-Aminocyclopropane-l-carboxylic acid, ethylene, fruit ripening, Pyrus communis L. (fruit ripening) 相似文献
15.
Rajeev Raghavan G. Prasad P. H. Anvar Ali Benno Pereira 《Biodiversity and Conservation》2008,17(13):3119-3131
Seventy one fish species belonging to 27 families and 50 genera were collected from various sampling sites spread along the
upstream and downstream parts of the Chalakudy river, in the Western Ghats biodiversity hotspot in Kerala, South India. Cyprinids
were the most dominant group represented by 24 species belonging to 13 genera, followed by the catfishes of the family Bagridae
(7 species from 2 genera) and loaches belonging to the family Balitoridae (5 species from 5 genera). Of the 71 species, 4
belong to the ‘critically endangered’ (CR) and 16 to the ‘endangered’ (EN) category. 3 of the critically endangered species
are strictly endemic to the Chalakudy river system. We also collected 5 exotic species several of them categorized as potential
pest. Fish species richness (FSR) showed a direct relationship with increasing stream order with maximum values observed in
the downstream/low elevation regions. Considerable differences were observed in the FSR between different microhabitats with
maximum values observed in bed rock and pool riffle and the lowest in regimes followed by step pools. Diversity and species
richness decreased with increasing altitude and higher diversity and species richness were observed in sampling sites located
between 0–200 m above sea level. A definite temporal partitioning was also observed with regard to FSR with higher richness
during the day time and the lowest observed at dawn. Indiscriminate collection of endemic and threatened ornamental fish species
for export, exploitation of endangered food fishes by forest-dwelling communities and local fisher folk, pollution, loss of
riparian cover, damming and exotic species threaten the rich ichthyofaunal diversity of Chalakudy River. An urgent need exists
for studying the life history traits and demography of the most important endemic and threatened fishes, as lack of information
on these aspects have significantly affected conservation efforts. The implementation of strong management strategies like
fixing total allowable catch (TAC), and the use of quotas are needed to reduce the overall collection pressure with regard
to the trade in native ornamental species from the river. 相似文献
16.
Lisi Dámaris Pereira Alvarenga Kátia Cavalcanti Pôrto Juliana Rosa do Pará Marques de Oliveira 《Biodiversity and Conservation》2010,19(3):619-635
The vertical distribution of the richness, abundance, and composition of epiphytic bryophytes was studied in a matrix of fragmented
habitats in the Brazilian Atlantic rainforest of the Murici Ecological Station (9°11′05″–9°16′48″ S, 35°45′20″–35°55′12″ W),
northeastern Brazil. The aim was to compare the horizontal (between sites) and vertical (between phorophyte heights) turnover
to test a hypothesis based on niche width vulnerability. There was a highly significant decreasing of richness accompanying
the loss of habitat, and the most conserved fragment housed a total richness more than 10 times higher than the less conserved
fragment. Epiphytes failed to colonize lower trunks (2.1–10 m) and higher zones in most of the non-conserved fragments; they
were restricted to the base (0–2 m) and displayed a clear altered floristic composition. The species with restricted ecological
amplitudes such as sun and shade tolerant taxa were more negatively affected by habitat loss than generalists. Although the
mean richness of generalists decreased in non conserved fragments, the proportional contribution of this guild increased,
proving that these taxa are the ones which persist in disturbed sites. The forest fragments capable of harboring rich epiphyte
flora in the area studied are over 300 ha in size, which is far from being a common size among Brazilian Atlantic rainforest
fragments. Hence, our results highlight the need of conserving the few large remnants in this ecosystem. 相似文献
17.
Maelstrom (MAEL) plays a crucial role in a recently-discovered piRNA pathway; however its specific function remains unknown. Here a novel MAEL-specific domain characterized by a set of conserved residues (Glu-His-His-Cys-His-Cys, EHHCHC) was identified in a broad range of species including vertebrates, sea squirts, insects, nematodes, and protists. It exhibits ancient lineage-specific expansions in several species, however, appears to be lost in all examined teleost fish species. Functional involvement of MAEL domains in DNA- and RNA-related processes was further revealed by its association with HMG, SR-25-like and HDAC_interact domains. A distant similarity to the DnaQ-H 3'–5' exonuclease family with the RNase H fold was discovered based on the evidence that all MAEL domains adopt the canonical RNase H fold; and several protist MAEL domains contain the conserved 3'–5' exonuclease active site residues (Asp-Glu-Asp-His-Asp, DEDHD). This evolutionary link together with structural examinations leads to a hypothesis that MAEL domains may have a potential nuclease activity or RNA-binding ability that may be implicated in piRNA biogenesis. The observed transition of two sets of characteristic residues between the ancestral DnaQ-H and the descendent MAEL domains may suggest a new mode for protein function evolution called "active site switch", in which the protist MAEL homologues are the likely evolutionary intermediates due to harboring the specific characteristics of both 3'–5' exonuclease and MAEL domains. 相似文献
18.
Response of seedling communities to mammalian pest eradication on Ulva Island, Rakiura National Park, New Zealand 下载免费PDF全文
《新西兰生态学杂志》2011,32(1):103-107
Norway rats (Rattus norvegicus) were eradicated from Ulva Island, Rakiura National Park, in 1996. The aim of our work was to determine if seedlings and saplings increased in density and/or species richness following this eradication. In 2003, we took advantage of eight permanent plots (5 × 5 m) that had been established on Ulva Island in 1991, by counting seedlings and saplings of woody species, including tree ferns. Over this period, total numbers of woody seedlings (< 30 cm tall), and saplings (30 cm – 2 m tall) did not increase significantly (P > 0.05). However, seedlings of two species, Dicksonia squarrosa and Pittosporum colensoi, and saplings of one species, Coprosma colensoi, did increase in numbers significantly. Little change in the species richness of seedlings or saplings was recorded. The removal of Norway rats may have been partly responsible for the recorded increases in density, though the eradication of white-tailed deer (Odocoileus virginianus borealis) from Ulva Island approximately two decades prior to this work is an important confounding factor. 相似文献
19.
Aquatic invertebrates of Lake Gregory,northwestern Australia,in relation to salinity and ionic composition 总被引:2,自引:2,他引:0
Lake Gregory is a large semi-permanent lake system in arid north-western Australia. Its catchment extends into humid areas
and as a result the lake has dried only twice in the last 25 years. Although the system is mostly fresh, parts of it become
saline as they dry. We identified aquatic invertebrates and undertook chemical analysis of water samples from several sites
at Lake Gregory in 1989, when the main water-body was saline, and in 1991 and 1993, after the system had flooded and was fresh.
During the period 1989–1993, salinities varied from 0.1‰ to 82‰, and ionic composition ranged from strong sodium chloride
dominance, in saline water and fresh water of the eastern part of the system, to bicarbonate dominance in fresh water of the
western area. At least 174 invertebrate species were recorded, including two mollusc species that were never collected live.
This species richness is much higher than that recorded from other Australian arid zone lakes, probably owing to long periods
of inundation with fresh water. The fauna was dominated by insects (42 per cent of total species richness), crustaceans (27
per cent) and rotifers (22 per cent). Most species (160) were restricted to fresh water; only 12 species were found in saline
water. Only one ostracod occurred in saline conditions, although ostracods are a dominant group in Australian saline lakes.
Among species restricted to fresh water, the proportion of rotifer and protozoan fauna that occurred in bicarbonate-dominated
water was greater than the proportion of insect, crustacean and hydracarine fauna that did so.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Macrobenthic species composition and diversity in the Godthaabsfjord system, SW Greenland 总被引:1,自引:0,他引:1
Mikael K. Sejr Maria Włodarska-Kowalczuk Joanna Legeżyńska Martin E. Blicher 《Polar Biology》2010,33(4):421-431
The southwest Greenland coast is made up of large and deep sill fjords. On the shelf, a number of shallow banks separated
by deep troughs are located 20–50 km from the coast. We collected three 0.1-m2 van Veen grabs at nine stations along a transect spanning from the inner Godthaabsfjord influenced by glaciers, across the
shallow Fyllas Bank and out to the slope of the continental shelf at approximately 1,000 m depth. Along this transect, we
explored patterns of macrobenthic diversity, species composition, abundance and biomass. The sampled stations were very different
in terms of environmental variables, resulting in large differences in species composition primarily related to differences
in depth, silt–clay fraction and chl a content of the sediment (BIO-ENV analysis). Habitat differences also reduced species spatial ranges and the majority of species
were found at only one (49%) or two (20%) stations and, consequently, species turnover or beta diversity was high and correlated
to differences in depth, silt–clay fraction and median sediment grain size. Species richness and diversity were lowest in
sites exposed to sediment disturbance: near the glaciers in the inner fjord (physical disturbance by mineral sedimentation)
and at selected stations on the shelf (bioturbation by burrowing sand eel). Alpha diversity and richness were only weakly
correlated to environmental parameters, indicating that alpha richness and diversity are influenced by several factors or
that relationships are non-linear as was found for species richness and silt–clay fraction. 相似文献