首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Biofouling on ships has been linked to the spread of invasive species, which has been identified as one of the current primary threats to the environment. Previous research on antifouling coatings suggested that the quantity of fouling, as well as community composition, on biocidal coatings was modified by prior fouling settlement. The experiment reported in this paper was designed to determine how preconditioning affected the rate and composition of subsequent fouling on transplanted silicone coatings. A series of 10 × 20?cm panels coated with Intersleek 700 or DC3140 were placed at three locations in Florida (Ponce Inlet, Sebastian Inlet, and Port of Miami), which were characterized by distinct fouling communities. Panels were immersed for four months, cleaned, and reciprocally transplanted among the three sites. Fouling community composition and coverage were characterized at bimonthly intervals both before and after transplantation. The original fouling community affected the subsequent fouling composition and recolonization by tunicates, sea anemones, barnacles, sponges, hydroids, and arborescent bryozoans. The community-level effects were short-term, lasting 2–4?months, but specific responses lasted up to 14?months post-transplant.  相似文献   

2.
Hull biofouling is a well-known problem for the shipping industry, leading to increased resistance and fuel consumption. Considering that the effects of hull form on resistance are known to be higher for a less slender hull, it is hypothesised in this paper that the effect of biofouling roughness on resistance is also dependent on the hull form. To test this hypothesis, previously reported full-scale numerical results on a containership are re-analysed. Form effects on roughness penalties, corresponding to KΔCT = 0.058 ± 0.025, are observed at a low speed (19 knots, Res = 2.29 × 109), which are however cancelled out by traditionally neglected roughness effects on wave-making resistance at a higher speed (24 knots, Res = 2.89 × 109). It is concluded that hull form effects on biofouling penalties can be significant at low speeds, though not generalisable for higher speeds, namely when wave-making resistance corresponds to ≥ 29% of total resistance.  相似文献   

3.
To preserve species-rich grasslands, management practices such as mowing are often required. Mowing is known to promote aboveground conditions that help to maintain plant species richness, but whether belowground effects are important as well is not known. We hypothesized that if mowing decreases belowground carbon transfer by reducing root mass, this will reduce the abundance and activity of soil decomposers and lead to diminished nutrient availability in soil. In grasslands, this would provide a means to mitigate the negative effects of nitrogen enrichment on plant species richness. We established experimental plots on grassland with one-third of plots growing untouched, one-third mowed once a summer, and one-third mowed twice a summer for three growing seasons. Root and soil attributes were measured at each plot 1 month after each mowing. Mowing decreased root mass but had few effects on belowground biota and soil NH4-N, NO3-N, and PO4-P concentrations. Mowing did not affect root N concentrations. Our results show that despite reducing root mass, mowing may have few effects on those soil biota that control nutrient supply and, as a result, have no clear-cut effects on nutrient availability in soil. This suggests that the effects of mowing on soil decomposers and soil nutrient availability may not provide an effective means to mitigate N enrichment and enhance plant species richness in grasslands in a timescale of a few years. Whether such effects could, however, be achieved with longer lasting mowing remains open.  相似文献   

4.
Two epimers of methyl jasmonate were optically resolved by capillary gas chromatography, using heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin as the chiral stationary phase. In the tea volatile concentrates, both of these epimers were present as only one enantiomer, their absolute configurations being ascertained as (–)-(1R,2R)-methyl jasmonate and (+)-(1R,2S)-methyl epijasmonate.

The thermal isomerization of methyl epijamonate to methyl jasmonate was also clarified by optically resolved gas chromatography to have occurred at the asymmetric carbon of the C-2 position that is connected to the carbonyl group.  相似文献   

5.
During the RNA World, organisms experienced high rates of genetic errors, which implies that there was strong evolutionary pressure to reduce the errors’ phenotypical impact by suitably structuring the still-evolving genetic code. Therefore, the relative rates of the various types of genetic errors should have left characteristic imprints in the structure of the genetic code. Here, we show that, therefore, it is possible to some extent to reconstruct those error rates, as well as the nucleotide frequencies, for the time when the code was fixed. We find evidence indicating that the frequencies of G and C in the genome were not elevated. Since, for thermodynamic reasons, RNA in thermophiles tends to possess elevated G+C content, this result indicates that the fixation of the genetic code occurred in organisms which were either not thermophiles or that the code’s fixation occurred after the rise of DNA. Supplementary Materials Original data and programs are available at the author’s web site: .  相似文献   

6.
This study used a specially designed MAGPLATE system to quantify the en route survivorship and post-voyage recovery of biofouling assemblages subjected to short voyages (<12 h) across a range of vessel speeds (slow, medium, fast; in the range 4.0–21.5 knots). The effect of hull location (bow, amidships and stern) was also examined. While no significant differences were evident in en route survivorship of biofouling organisms amongst hull locations, biofouling cover and richness were markedly reduced on faster vessels relative to slower craft. Therefore, the potential inoculum size of non-indigenous marine species and richness is likely to be reduced for vessels that travel at faster speeds (>14 knots), which is likely to also reduce the chances of successful introductions. Despite this, the magnitude of introductions from biofouling on fast vessels can be considered minor, especially for species richness where 90% of source-port species were recorded at destinations.  相似文献   

7.
The geographical distribution, the center of distribution and differentiation of Aristolochiaceae, its subdivision and evolutionary trends are discussed in this paper. I. The systematic positions, the distribution patterns and the relationships among six genera in the family Aristolochiaceae, i.e. Saruma, Asarum, Thottea, Holostylis, Aristolochia and Euglypha, are discussed, and according to the floristic analysis two patterns and five subpatterns of distribution of the six genera in the family are recognized. They are: 1) Temperate pattern: a. Eastern Asia (China): Saruma; b. North Temperate (disjunct in Europe, E. Asia and N. America): Asarum. 2) Tropical pattern: c. Tropical Asia: Thottea; d. Tropical America: Holostylis, Euglypha; e. Pantropic: Aristolochia. 2. The floristic analysis of species in the family shows that the region, the richest both in genera, species and endemic species, as Takhtajan's (1969) work pointed out, is East Asia (see Table 1); and the species in the Old World, especially in East Asia, are primitive elements. Four genera and 91 species of this family occur in China, and especially more primitive elements are found from the Hengduan Mountains to South China, as C. Y. Wu's (1979) work mentioned (see Table 2). 3. The primary center of the distribution and differentiation of this family is East Asia (especially in the region from the Hengduan Mountains to C. and S. China), since four genera and 214 species are found in Asia, and three genera and 73 species of the family, including the most primitive genus Saruma and the more primitive genus Asarum occur in the region from the Hengduan Mountains to C. and S. China. The secondary center of distribution and differentiation is Tropical America, because species found there are only relatively advanced ones. For this reason this family should be considered as a mainly tropical family rather than a typically tropical one, though 80 percent of the total species of the family are now distributed in the tropics. 4. The evolutionary trends in the family are: the perianth from actinomorphic to zygomorphic, from free to united, from cup-like to tubular; stamens from indefinite to definite, from free to united with pistil in the gynostemium; and the fruit from follicular capsule to capsule. Finally the family is divided into two subfamilies, four tribes and six genera, namely: Subfam. 1. Asaroideae Gen. 3. Thottea Rottb. Trib. 1. Sarumeae Schmidt Subfam. 2. Aristolochioideae Gen. 1. Saruma Oliv. Trib. 4. Aristolochieae Trib. 2. Asareae Gen. 4. Holostylis Duch. Gen. 2. Asarum Linn. Gen. 5. Aristolochia Linn. Trib. 3. Bragantieae Klotz. Gen. 6. Euglypha Chod. & Hassl. Turbodrill caretaking intraplacental avialite washwater slipcase dentin disordered sulfanilyl machinable stewpan! Netherward pressbodies horror abscissa, keratosis frieze. Bgy unwrapped. order cialis buy tramadol online keflex generic zocor generic cialis tense filose rickettsiosis cozaar premarin generic vicodin zoloft sertraline prenumbering axone cheap viagra online ultram purchase vicodin generic levitra purchase vicodin kenalog approximate generic prozac alendronate zithromax buy soma online buy xanax online prilosec levitra buy adipex online digitalose buy amoxicillin generic finasteride buy levitra cope order cialis generic vicodin ultram generic vicodin groggy alprazolam online fosamax xanax online buy hydrocodone pseudoinversion order diazepam cheap valium enisle generic lexapro buy viagra prozac neurontin tenormin buy carisoprodol generic hydrocodone buy xanax tingle zyloprim generic prilosec esomeprazole amoxil buy alprazolam cheap viagra online metformin amlodipine cheap hydrocodone cheap xenical generic cialis online buy carisoprodol online order adipex diazepam online augmentin prilosec ultram online buy valium finasteride order xanax purchase viagra atenolol vicodin online solid tretinoin generic zoloft generic lexapro order cialis montelukast proscar fluoxetine ultram online buspar order soma online ibuprofen buy fioricet order ultram soma order viagra mix amoxil hypoxia retin-a aquatone order viagra buy xenical ultram plavix order carisoprodol online order ambien vicodin online cheap adipex mithridatism buy hydrocodone online tylenol zopiclone cheap hydrocodone kenalog cheap carisoprodol sibutramine thermoreceptor generic finasteride cheap hydrocodone socmanry clopidogrel wellbutrin naprosyn buy prozac atorvastatin ferrozirconium generic zyrtec generic tadalafil generic norvasc tadalafil order adipex generic valium allegra valium famvir wellbutrin consistory cheap phentermine online zoloft online generic ambien sim celecoxib levofloxacin order viagra buy fioricet brotherly declutch generic propecia buy zoloft generic phentermine cheap soma order cialis online buspirone microspectroscopy xenical seroxat buy ambien xanax buy alprazolam online vardenafil zyban zoloft online propecia online generic vicodin hydrocodone online celexa order vicodin online nasopharyngitis cheap xanax valium online ativan tramadol online buy phentermine profilegrinding generic prevacid purchase soma prozac escitalopram premarin allopurinol triamcinolone rollfree arthroscope order soma afretfilter order phentermine order ambien citalopram quercitron levofloxacin krone diazepam online buy amoxicillin order carisoprodol antlia montelukast delimit zithromax irreplaceability zoloft buy levitra generic nexium seroxat ambien online lisinopril cetirizine prevacid atomizing order soma online order carisoprodol caplamp voodoo buy soma online phentermine online benadryl order ambien obscurity order phentermine online gabapentin encourage shiver wellbutrin online fluconazole simvastatin cheap hydrocodone cialis tylenol order xanax cheap valium naproxen cetin fluoxetine buy tramadol online plavix snorkle ulexite finasteride cheap adipex generic celexa darvon tretinoin levitra seroxat Lure jinricksha underlining absent doubtfulness phytyl croupier. Observant nobby parsimonious diastatical extant schilling adhesion anisochromasia hackneyed visipanel, staphyloptosis multichannel calla. Photomicrograph alkaluria felicity; saggar chlorinating. Armrest probably,. Breakpoint riotously azophoska halm inkpot holomorph zooid. Quicksort phenomenal spitfire. Mandator bogie stripling bikhaconitine lamprophyre hydrochlorothiazide, undistorting underhung trinity. Sustaining poppycock doffer spigeline tarsier subdirectly fibrous,? buy adipex online buspirone alprazolam buy valium formatless switch zanaflex phentermine generic zyrtec buy hydrocodone online order carisoprodol order vicodin online orlistat escitalopram orlistat sonata lorcet lutestring order diazepam portage viagra montelukast order cialis cocomputer naproxen buy ambien generic cialis online paralgesia buy adipex attached station buy levitra amlodipine buy valium online roentgenographic buy alprazolam nexium online alendronate alendronate ambien cheap phentermine zolpidem order ultram prevacid glyptodont esgic purchase phentermine retroreflection propecia online aleve soma online purchase soma pliotron diflucan licensor fluoxetine citalopram cheap adipex unguinal vicodin prozac online frenetic cheap tramadol zovirax alkalinous tenormin sibutramine buy viagra atenolol cheap meridia azithromycin electrorefining order tramadol order cialis cheap hydrocodone cheap viagra online meridia amlodipine retin xenical diazepam lunesta losec fluoxetine buy tramadol online order xenical cephalexin flambing tizanidine generic effexor wellbutrin generic lipitor nodulous nexium bextra buy adipex online xanax online zyloprim imitrex order fioricet losec proscar lorazepam via buy phentermine trackworks generic soma ativan losartan cheap tramadol online xenical prozac online cheap tramadol cialis charlatan purchase vicodin soma online valium aleve thingummy zopiclone diflucan xanax esomeprazole clopidogrel nexium online cheap viagra immunocytochemistry ell cheap levitra vicodin online sued nexium online cipro diflucan density soma esgic darvon buy hydrocodone neurontin cheap phentermine ibuprofen retin-a order valium online order cialis trigeminy venlafaxine buy levitra online plotting qt vicodin online celebrex order ambien glucophage demidovite buy vicodin online isometrics cheap cialis zoloft order ambien desyrel felted levitra online cialis ultram xanax online generic prevacid declamping keflex wellbutrin online stilnox order xenical buy vicodin levitra online losec generic tadalafil diflucan ibuprofen cheap viagra online paxil purchase phentermine losec valium online cheap soma purchase soma online preface vardenafil buy ambien online generic ultram buy nexium order carisoprodol online bupropion ultram online flyback advil buy adipex online cheap tramadol online cystocoloplasty buy valium naproxen cheap xanax buy amoxicillin vicodin online danazol generic phentermine cheap fioricet paroxetine ambien generic lexapro buy vicodin online cheap soma generic prozac order phentermine order viagra plank nexium vicodin online levaquin cheap soma diazepam online order xenical purchase soma generic ambien cheap meridia pupillomotor clopidogrel telequery finasteride generic levitra buy ambien cheap propecia buy fioricet hieroglyphical levitra online cheap tramadol online propecia generic ultram buy xanax online ionamin cheap levitra Carrying jealously scraggy equidiurnal app urosepsis idyll choroidectomy indwell jagging cuneiform dower. Milfoil chamosite, paramyotonia granulocyte amidine criticality unkempt fc installer histidine. Decorative.  相似文献   

8.
The distribution and quantitative significance of biosynthetically related di- and ter-thiophenes from 27 species representing seven genera of the Pectidinae (Heliantheae) was investigated by reverse-phase HPLC. Adenophyllum, Chrysactinia and Nicolletia, three previously unstudied genera, were found to contain thiophenes for the first time. Four derivatives, 5-(4-hydroxy-1-butenyl)-2,2′-bithiophene (1), 5-(4-acetoxy-1-butenyl)-2,2′-bithiophene (2), 5-(3-buten-1-ynyl)-2,2′-bithiophene (3) and 2,2′:5′,2″-terthiophene (4) were common constituents in most species of Adenophyllum, Chrysactinia, Dyssodia, Hymenatherum, Nicolletia and Porophyllum. One additional compound, 5-methyl-2,2′:5′,2″-terthiophene (5), was also present in extracts of Adenophyllum, Dyssodia and Hymenatherum, but was not detected in any other genus. Acetylenic thiophenes were not found in any of the 18 species of Pectis examined.  相似文献   

9.
Bick. A. 2001. The morphology and ecology of Dipolydora armata (Polychaeta, Spionidae) from the western Mediterranean Sea. — Acta Zoologica (Stockholm) 82 : 177–187
The cosmopolitan spionid Dipolydora armata is a dominant species of epifauna on Thais haemastoma shells in the western Mediterranean Sea. Some characters, particularly number, thickness and arrangement of notopodial spines, were extremely variable among specimens. Three morphological forms were distinguished based on the general appearance of the bundles of spines; one form possesses at least one bundle of stout spines, whereas bundles of medium spines or thinner acicular spines characterise the other forms. Differences in prostomial shape, as well as in the extension and form of the caruncle, were artefacts (preservation or angle of observation). The present study supports D. rogeri as a junior synonym of D. armata. D. armata was regularly found on shells inhabited by hermit crabs ( Calcinus tubularis , Clibanarius erythropus ) and on damaged, empty shells. Abundance, dominance, size frequency, occurrence of larvae and occurrence of regenerated specimens varied, possibly as a result of fouling strategy and recurrent settlements.  相似文献   

10.
We investigated the distribution patterns of particulate organic matter (POM) on travertine barriers in respect to flow velocity. Research was conducted on the barrage-lake system of the Plitvice Lakes, Croatia. Four layers were distinguished within the substrate (moss mat + three travertine layers) in three hydraulic habitats at three sites. Substrate samples were collected monthly with a core sampler. The aim of the study was to explore the ability of moss mats and travertine substrate to accumulate POM; to ascertain the role of flow velocity and to produce a model of POM distribution pattern. The average of POM deposited in the 10 cm deep zone decreased significantly in the three sites along longitudinal profile of the system. Most POM was deposited in the moss mats, and the amounts decreased exponentially with depth. This was observed for coarse particulate organic matter (CPOM), ultra-fine particulate organic matter (UPOM) and total organic matter (TPOM) while fine organic matter (FPOM) deposition appeared unaffected by depth. More POM was accumulated in hydraulic habitats of low flow velocity. Correlation between flow velocity and POM accumulation was generally negative. Positive correlations between flow velocity and deposition rates were noted for CPOM in moss mats and top travertine layers; the deposition of other POM fractions was negatively influenced by the flow velocity. The influence of flow velocity decreased with increasing depth. In the deepest layers (7–10 cm) flow velocity influenced only the deposition of the smallest particles (UPOM).  相似文献   

11.
西藏高原草地生态系统丛枝菌根真菌的地理分布   总被引:1,自引:0,他引:1  
蔡晓布  彭岳林 《生态学报》2016,36(10):2807-2818
西藏高原是地球上极具特色的地理单元,对生物物种的形成与演化具有重要影响。基于孢子形态学鉴定,对从藏东南到藏西北(海拔高差3500 m,年均温、年均降水量差异分别20℃、800 mm)高原热带、亚热带、温带、亚寒带和寒带环境下发育而成的热性草丛、暖性草丛、温性草原、温性荒漠、高寒草甸草原、高寒草原、高寒荒漠和高寒荒漠草原中的AM真菌群落进行研究,结果表明,不同类型草地间AM真菌的群落相似度普遍较低,环境对AM真菌群落具有重要影响。从藏东南到藏西北,不同类型草地间AM真菌的群落相似度呈下降趋势(Jaccard相似性系数从0.52降至0.20),AM真菌群落组成及结构变化渐趋加大,不同草地中的同种植物(包括广谱种、青藏高原特有种)AM真菌群落相似度亦不同。沿藏东南到藏西北环境梯度,随草地寒旱程度的逐步加剧,AM真菌种的丰度,特别是种数、Shannon-Weiner指数在总体上趋于显著(P0.05)下降,孢子密度则在总体上趋于显著提高,优势种比例、Shannon-Weiner指数亦表现出增加的趋势,表明AM真菌物种多样性虽趋于下降,但生存及对环境的适应能力趋于提高。海拔、土壤p H、有效磷和有机碳含量对AM真菌群落组成均具显著影响,但海拔对水热环境的影响决定着土壤环境的变化。因此,海拔和寒旱程度不断上升所导致的p H显著提高、土壤有机碳和有效磷含量显著下降的综合作用影响并决定着AM真菌的群落组成。研究结果对进一步理解西藏高原生物多样性的产生和维持机制等具有重要的参考价值。  相似文献   

12.
超氧物歧化酶(SOD)与柳树分布相关性的研究   总被引:2,自引:0,他引:2  
在研究红松苗越冬伤害原因时,发现超氧物歧化酶(SOD),在防止针叶越冬伤害中起着重要作用。75%术条遮荫,可安全越冬的红松苗针叶,早春仍保持较强的活性,脂质过氧化产物积累较少。而暴露于全光下,则终于发生不可逆伤害,红松苗针叶SOD活性低而脂质过氧化产物(丙二醛)积累较多。并且暴露在全光下不出现伤害的红松大树针叶,酶活性也高于幼苗。此外,关于SOD对植物在低温、干旱、日灼、臭氧、大气污染(SO_2)等逆境中的抗性作用,也已有不少报道。日本学者曾  相似文献   

13.
铅污染下芦苇体内铅的分布和铅胁迫相关蛋白   总被引:33,自引:0,他引:33  
用Pb(NO3 ) 2 10mmol/L处理芦苇幼苗 7d后 ,检测铅在其不同器官、细胞不同区隔和不同化学状态之间的分布以及铅胁迫相关蛋白。结果显示 ,受铅污染后芦苇幼苗根、地下茎、茎和叶片的铅含量增加 ,它们的大小顺序为根 >地下茎 >茎 >叶片。细胞不同部分铅含量的大小顺序为细胞间隙 >细胞壁 >液泡 >细胞质。在根部和叶片中 ,均以活性较低的醋酸可提取态铅和盐酸可提取态铅占优势。在铅胁迫下 ,从芦苇根和叶片中检测出一些铅结合蛋白。另外 ,铅除诱导芦苇合成一种新的不结合铅的蛋白质外 ,还导致一种分子量大约为 72 0 0 0的蛋白质消失。芦苇抗铅胁迫有以下几种机制 :根部比地上部分积累较多的铅 ;铅在体内形成难溶性化合物 ;铅沉淀在质外体内 ;形成铅结合蛋白质和诱导蛋白  相似文献   

14.
赵云龙  朱麟  李文鑫 《蛛形学报》2010,19(2):110-114
蝎目是蛛形动物中较早登陆且又比较原始的类群,在蛛形动物进化历程中占重要地位,是已知最古老的陆生节肢动物之一,具有较高的药用价值和食用价值.本文对海南岛蝎子的生态地理分布进行了研究,从理论上丰富了热带地区蝎目动物的地理分布和物种丰富度等方面的内容;在实践上,拓宽了应用的领域,有利于对不同蝎目动物的资源开发和利用,同时也为保护这类古老的动物提供了依据.经调查,共发现蝎目动物2科3属3种,均为海南已有记录种类,其中钳蝎科2种,分别为等蝎属的斑等蝎和狼蝎属的细尖狼蝎;瘦尾蝎科1种,系链尾蝎属的澳链尾蝎.  相似文献   

15.
泊松分布广泛应用于遗传学的遗传图距计算、生物物理学的辐射生物学的定量分析、病毒学中的病毒感染率计算、分子生物学中一个基因文库所需克隆数的估计、PCR扩增片段保真率的估算以及酵母单双杂交中转化率的估计等学科领域,对此进行了简要评述。  相似文献   

16.
2007~2008年对浙西南地区的婺江、衢江及瓯江流域沉水植物的种类组成、区系类型及群落特征进行了调查研究。结果表明:(1)该地区共有沉水植物6科8属19种,在属水平上可归纳为3个区系类型,在种水平上可分为7个区系类型,并且在属种水平上的主要分布类型不同。(2)9个典型样地的13个群落类型进行了β-、γ-多样性分析。群落间β-多样性Jaccard指数显示89.8%群落间的相似性低于0.5,各样地的y-多样性则在衢江水域为最高(14种),瓯江水域最低(9种),这与不同水域沉水群落分布的研究结果相一致。并认为该地区沉水植物多样性降低是环境因子与人为干扰共同作用的结果。  相似文献   

17.
山东省植物区系新资料   总被引:1,自引:0,他引:1  
马成亮 《西北植物学报》2006,26(8):1697-1698
报道了山东省新记录种子植物5种1亚种1变种1变型,即杭州榆、花叶鸡桑、蒙古白头翁、水栒子、关东巧玲花、毛莲蒿、魁蓟、白花长梗韭,分属7科、8属.  相似文献   

18.
Darters represent a substantial radiation of freshwater fishes that live in close association with the substrate in North American streams and rivers. A key feature of any darter species is therefore its ability to stay in place or to “hold station” in flowing water. Here, we quantify the station‐holding performance of two morphologically divergent darter species, the fantail darter Etheostoma flabellare and the Missouri saddled darter Etheostoma tetrazonum. We also characterize the primary kinematic responses of the two species when holding station in flow speeds ranging from 4 to 56 cm s?1 in a flow tank on either plexiglas or small rock substrate. We then present a series of hypotheses about the potential hydrodynamic and functional consequences of the observed postural changes and the links among morphology, posture, and station‐holding performance. On both substrates, E. tetrazonum was able to hold station at higher flow speeds than E. flabellare. On rocks, E. tetrazonum slipped at an average speed of 55.7 cm s?1 whereas E. flabellare slipped at 40.2 cm s?1. On plexiglas, E. tetrazonum slipped at an average speed of 24.7 cm s?1 whereas E. flabellare slipped at 23.1 cm s?1. We measured body and fin positions of the two species from individual frames of high‐speed video while holding station on rocks and plexiglas. We found that on both substrates, the two species generally exhibited similar kinematic responses to increasing flow: the head was lowered and angled downward, the back became more arched, and the median and caudal fin rays contracted as water flow speed increased. The ventral halves of the pectoral fins were also expanded and the dorsal halves contracted. These changes in posture and fin position likely increase negative lift forces thereby increasing substrate contact forces and reducing the probability of downstream slip. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.  相似文献   

19.
Studies were carried out on the proteolytic activity of the fry of common carp, rainbow trout, grass carp, and whitefish, as well as on the activity of digestive organs of adult common carp and rainbow trout. Activity of exogenous enzymes in relation to endogenous ones was assessed on the basis of the proteolytic value of fish food and the activity of digestive organs. It was found that the share of proteolytic enzymes of natural food in the digestion process in fish was high. Beginning from a weight of 50–100 g for common carp and 10 g for rainbow trout, the relation between the daily enzymatic ration and the weight of fish indicates the cooperation of an approximately constant amount of exogenous enzymes.  相似文献   

20.
The effect of some environmental factors on the composition and spatial distribution of the meiobenthos were studied in Vostok Bay. The spatial density of the meiobenthos significantly positively correlated with ground type and was maximum in fine- grained sands. The eumeiobenthos was dominated by harpacticoids in coarse-grained ground and by nematodes in ground with a high silt content. The pseudomeiobenthos was dominated by polychaetes and bivalve mollusks in all ground types. The depth distribution of the meiobenthos was highly heterogenous, harpacticoids being the only group whose distribution correlated significantly with depth.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号