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.
In desert and steppe habitats of the complex North Caspian semi-desert, more than twofold differences in the number of hortobiont Curculionoidea species (33 and 75 species, respectively) were observed between the “dry” (1972–1974) and “humid” (2003–2005) climatic phases. The abundance of most species changed. Polyphagous steppe weevils of the subfamily Entiminae (Otiorhynchus velutinus, Euidosomus acuminatus, Omias verruca, and O. rotundatus) with spring activity of adults were the most stable, representing the main dominants of the spring communities both in the 1970s and 2000s. Nearly all of the weevils that changed their abundance since the 1970s were specialized herbivores with summer adult activity. In the more humid 2000s, the abundance of some desert-steppe weevils dominating the desert communities (Phacephorus nebulosus, Metadonus anceps and especially Ptochus porcellus) dropped drastically. Most of the species whose abundance increased most strongly (Phyllobius brevis, Trachyphloeus amplithorax, Archaeophloeus inermis, Stenopterapion tenue, Sitona inops, S. longulus, Tychius spp.) are associated with Medicago romanica, the plant that considerably raised its density in the microdepressions during the “humid” phase. The data show an evident reduction of the most xerophilic (desertsteppe) components of the weevil community and an increase in the fraction of mesophilic species. These changes seem to follow a cyclic pattern.  相似文献   

2.
Objective: To examine temporal trends in stature, body mass, body mass index (BMI), and the prevalence of overweight and obesity in Canada. Research Methods and Procedures: Data for adults 20 to 64 years of age were compared across eight Canadian surveys conducted between 1953 and 1998. Temporal trends in stature and body mass were examined using regression, and changes in weight‐for‐height were expressed as changes from 1953. BMI data were available from 1970 to 1972 to examine changes in overweight and obesity. Qualitative changes in the BMI distribution were examined using Tukey mean‐difference plots. Results: Significant temporal trends in stature and body mass have occurred since 1953 in Canada. Median stature increased 1.4 cm/decade in men and 1.1 cm/decade in women, whereas median body mass increased 1.9 kg/decade in men and 0.8 kg/decade in women. Increases in the 75th percentile of body mass were larger than the median. The average weight‐for‐height increased 5.1% in men and 4.9% in women from 1953. Furthermore, the prevalences of overweight and obesity have increased from 40.0% and 9.7% in 1970–1972 to 50.7% and 14.9% in 1998, respectively. The entire BMI distribution has shifted to the right since 1970–1972 and has become more skewed to the right for men than for women. Discussion: There have been significant increases in stature and body mass in Canada over the last 45 years. Body mass has increased more than stature, particularly in the upper percentiles, which has resulted in the currently observed high prevalences of overweight and obesity.  相似文献   

3.
Zusammenfassung Die afghanischen Flamingobrutplätze am Ab-e-Istada und in der Dasht-e-Nawar wurden während der Jahre 1970–72 regelmäßig besucht. In diesen Zeitraum fiel eine extreme Dürre, in deren Folge beide Seen 1971 völlig austrockneten. In der Dasht-e-Nawar hatte sich der Wasserstand nach zwei Jahren noch nicht soweit normalisiert, daß eine erfolgreiche Flamingobrut stattfinden konnte.Am Ab-e-Istada begannen die Flamingos 1970 und 1972 zwar das Brutgeschäft, wurden aber durch Menschen vergrämt, denen niedriger Wasserstand Zutritt zur Brutinsel ermöglichte. Für diesen See konnteCharadrius leschenaultii als Brutvogel neu nachgewiesen werden.Weiterhin werden Beobachtungen zur Unterwasserfauna und Beobachtungen von Herbstdurchzüglern mitgeteilt.
Observations at breeding-places of Flamingoes in Afghanistan
Summary The Afghan breeding-places of the Greater Flamingo Ab-e-Istada and Dasht-e-Nawar were regularly visited during 1970–1972. An extreme drought evaporated both lakes in 1971. In the Dasht-e-Nawar the water-level had not normalized after two years to allow the flamingoes' breeding.On the Ab-e-Istada flamingoes attempted breeding in 1970 and 1972 but were disturbed by men, who were able to ford to the breeding-island.Charadrius leschenaultii could be shown to breed on this lake.Notes on the waterfauna and observations of migrating birds are given.


Herrn Prof. Dr.Günther Niethammer in dankbarer Erinnerung gewidmet.  相似文献   

4.
  • 1 Hickling Broad underwent major changes from a clear water, charophyte-dominated state in the decades previous to 1970 to a turbid, phytoplankton-dominated state by the mid 1970s. These changes were complexly linked with increasing eutrophication by black-headed gulls and increased salinity due to agricultural changes in the catchment.
  • 2 At the turn of the 1970s, the lake began to change again and during the 1980s a submerged plant community, of tall, vigorously growing species (e.g. Myriophyllum spicatum, Patamogeton pectinatus) had recovered, despite a major reduction in the roosting gull population, no change in salinity, and only small reductions in phytoplankton biomass and total phosphorus concentration.
  • 3 Recovery of the plants may be linked to grazing of periphyton on them by an increased population of a mysid Neomysis integer which had been suppressed by toxicity from an alga, Prymnesium parvum formerly stimulated by the ingress of gull guano.
  • 4 A cladoceran community present in the clear-water phase has not recovered and may be suppressed by continued high salinities. Further restoration of the lake requires displacement of the large phytoplankton biomass and this might best be contemplated by land use changes leading to lowered salinity and predicted recovery of grazing Cladocera.
  • 5 Models are given which summarize the likely workings of the system in the early twentieth century, the mid-twentieth century, the 1970s and the late 1980s.
  相似文献   

5.
Changes from the 1970s to 2000s in phosphorus and chlorophyll levels, water transparency, zooplankton, and benthic communities in the upper, International Section of the St. Lawrence River were evaluated using trend data from limnological surveys. The influence of Lake Ontario as a source for riverine production was evident in the upper river. Total phosphorus levels from 1976 to 1978 (average ~20 μg/l) sampled during a period of nutrient pollution declined (to 6–7 μg/l) following abatement. As expected, water transparency indicated by summer Secchi depths showed an opposite response increasing from ~3.5 m in the 1970s to >10 m by 2003 but declined to 6–7 m in more recent years. Zooplankton communities have experienced declines in overall densities, and the community has changed but its primary components, Bosmina and Diacyclops remain. Ceriodaphnia lacustris abundance declined substantially from the 1970s to the recent time period while Chydorus sphaericus increased and Eurytemora affinis and Cercopagis pengoi had first appearances. In contrast, benthic invertebrate biomass increased substantially between time periods. Increases in families and occurrence of gastropods were observed, but the primary components–chironomids, amphipods, and oligochaetes–were consistent between the periods with the exception of dreissenid mussels. Dreissena was dominated by D. bugensis, and both D. bugensis and D. polymorpha show evidence of recent declines. Conversely, high abundance of round goby (Apollonia melanostomus) has promoted new trophic pathways. Downstream attenuation in nutrients and chlorophyll, and increased transparency suggest continued strong effects of Lake Ontario on the downstream river environment, but increased energy in the benthos has likely promoted greater in situ production.  相似文献   

6.
AGE, EGG-SIZE AND BREEDING SUCCESS IN THE HERRING GULL LARUS ARGENTATUS   总被引:1,自引:0,他引:1  
J. W. F. Davis 《Ibis》1975,117(4):460-473
The breeding biology of the Herring Gull Larus argentatus was studied in 1969, 1970 and 1972 on Skokholm, Pembrokeshire. The distribution of laying dates in three years is given; median laying date was always about 10 May. Laying dates of individual pairs were fairly constant between two years, but females up to nine years of age apparently advanced their laying date in successive years. In 1969 there was a decline in clutch-volume index during the season but this was not found in 1970 or 1972. Females laid clutches of similar volume in successive years, although the volume did vary with age, increasing up to 7 or 8 years of age and then declining. Hatching success was highest in the earliest of four periods in 1970 (69%) and lowest in the last (51%); in 1972 the corresponding figures were 71% and 63% and the seasonal trend was not significant. Chick mortality was higher in 1970 (69%) than in 1972 (59%); in 1970 there was significant seasonal variation in chick survival but in 1972 there was not. In 1970 chick survival was positively correlated with hatching weight (and hence egg-size) and chick survival was also related to growth which was itself correlated with hatching weight. There were no such correlations in 1972. Mean chick production in 1970 was 0.60 per pair and in 1972 0.70. In both years later breeders were less successful, but the seasonal range of mean success was less in 1972. In the discussion it is shown that some of these differences between years could be due to changes in the age structure of the population and it is suggested that the correlation between egg-size and chick survival in 1970 may be an artefact of the age structure.  相似文献   

7.
施磷对干旱胁迫下箭竹根际土壤养分及微生物群落的影响   总被引:2,自引:0,他引:2  
以箭竹及其根际土壤作为研究对象,采用两因素随机区组实验,设置2种水分处理(正常浇水和干旱胁迫)和2种施磷量处理(施磷和不施磷),探究施磷对干旱胁迫下箭竹根际土壤养分及微生物群落结构和多样性的影响。结果表明:(1)干旱胁迫显著降低了箭竹根际土壤中微生物量碳、可溶性有机氮和有效磷的含量,虽对箭竹根际土壤微生物群落的多样性无显著影响,但显著降低了箭竹根际土壤中总PLFA(phospholipid fatty acid contents)的含量和真菌、细菌、革兰氏阳性菌与革兰氏阴性菌的PLFA含量以及革兰氏阳性菌/革兰氏阴性菌的PLFA比值,显著改变了箭竹根际土壤微生物群落结构,结果显著降低了箭竹的生物量。(2)施磷显著增加了受旱箭竹根际土壤中微生物量碳和有效磷的含量,虽大体上对受旱箭竹根际土壤微生物群落的多样性无显著影响,但显著增加了受旱箭竹根际土壤中总PLFA和真菌PLFA的含量,并在一定程度上增加了细菌、革兰氏阳性菌、革兰氏阴性菌和放线菌的PLFA含量以及革兰氏阳性菌/革兰氏阴性菌和真菌/细菌的PLFA比值,也在一定程度上改善了受旱箭竹根际土壤微生物群落结构,从而改善受旱箭竹的生长。(3)主成分分析表明,干旱对箭竹根际土壤微生物群落结构的影响显著,而施磷的影响不明显。(4)相关分析发现,箭竹根际土壤微生物群落结构与箭竹根际土壤微生物量碳、可溶性有机氮及箭竹生物量呈显著正相关。综上,干旱降低了箭竹根际土壤养分含量和微生物生物量,改变了箭竹根际土壤微生物群落结构,抑制了箭竹的生长;施磷能增加受旱箭竹根际土壤养分含量和微生物生物量,改善受旱箭竹根际土壤微生物群落结构,进而改善受旱箭竹的生长。  相似文献   

8.
The history of study of these dinoflagellates is reviewed and emended diagnoses are proposed for the genera Ctenidodinium and Dichadogonyaulax. A new species, Dichadogonyaulax sellwoodii, is described and illustrated from the Bathonian of the Isle of Skye, Scotland. The new combination Dichadogonyaulax norrisii (Pocock, 1972) is proposed and it is considered that forms described by Gocht (1970) as Ctenidodinium pachydermum (Deflandre, 1938) may in fact be'attributable to Pocock's species. The species Ctenidodinium continuum Gocht, 1970, is briefly discussed and other Jurassic species attributable to these two genera are listed.  相似文献   

9.
受人类活动干扰的增加,亚热带森林频繁转换为次生林和人工林,可能显著影响土壤无脊椎动物群落结构及其生态功能,但当前的认识并不一致。因此,于2022年7月调查了亚热带天然常绿阔叶林转换为次生林、米槠人工林、杉木人工林后土壤无脊椎动物群落结构特征。共捕获土壤无脊椎动物659只,丰度为26540只/m2,隶属1门6纲13目59科,其中蚁科和球角 虫 兆 科为优势类群。森林转换改变了土壤无脊椎动物群落组成和多样性。天然林向米槠人工林和杉木人工林转换后,土壤无脊椎动物丰度和类群均明显降低,其中大型土壤无脊椎动物丰度的响应更为敏感,在2种林型中分别显著降低了33.58%和36.53%。尽管林型转换对土壤无脊椎动物群落多样性指数无显著影响,但改变了土壤无脊椎动物群落组成,其中天然林与杉木人工林群落组成极不相似(J < 0.25),等节 虫 兆 科为杉木人工林优势类群,占比达到59.84%。冗余分析显示,土壤湿度、凋落物现存量和凋落物磷含量是影响土壤无脊椎动物群落的主要因子,对土壤无脊椎动物群落的解释率为69.30%。可见,林型转换可能通过改变土壤理化性质和凋落物质量,调控土壤无脊椎动物群落结构。  相似文献   

10.
Four experiments tested a range of doses of the growth-retardant glyphosine on sugar-beet crops between 1970 and 1972. The period of time between application and harvest was varied. One experiment (1972) in nutrient mist culture examined its effect on seedling root development. The growth-retardant decreased root, sugar and top yield of sugar beet at all doses in excess of 0·56 kg a.i. ha-1 at all treatment times. It increased the α-amino nitrogen content of beet roots significantly (P < 0·05) with doses in excess of 1·12 kg a.i. ha-1. When applied to the leaves of seedlings with their roots in nutrient mist culture, glyphosine at 500 ppm and 2000 ppm of a.i. in aqueous solution slowed or stopped root elongation.  相似文献   

11.
Background: Tropical rainforests represent the most species-rich and at the same time the most fragmented terrestrial biome on Earth. Fragmentation of tropical rainforests is having wide-ranging consequences for the maintenance of local species diversity and community assembly patterns.

Aims: To examine floristic changes and changes in community phylogenetic structure in the forest fragment over the past five decades.

Methods: A new taxonomic diversity algorithm (within-family diversity) was developed to assess floristic changes in the forest fragment. Community phylogenetic structure was then compared before and after fragmentation.

Results: Taxonomic diversity changed greatly among families, with changes occurring randomly across the phylogeny. The forest fragment had higher phylogenetic diversity, higher mean pair-wise phylogenetic distance, but lower mean nearest-neighbour distance. The community phylogenetic structure has changed significantly from clustering to dispersion.

Conclusions: High species turnover occurred in the forest fragment. While shade-tolerant species have been lost, and ruderal and alien species have been added, overall phylogenetic diversity has increased with species being more phylogenetically distant. Competitive exclusion, which was related to the relatively drier conditions in the forest after fragmentation, led the plant community phylogenetic structure to be more dispersed.  相似文献   

12.
Uncertainty about predicted effects of global warming on freshwater ecosystems led us to manipulate the thermal regime of a shallow groundwater ecosystem. The study area was separated into a control and treatment block using a sheet-metal groundwater divide to a depth of 1 m. Temperatures were increased according to General Circulation Model (GCM) projections for Southern Ontario, Canada. We examined the response of the groundwater chironomid community during pre-manipulation, manipulation and recovery periods. We found that warming decreased the total abundance of chironomids whereas no significant change in taxonomic richness was apparent. Interestingly, taxon composition changed markedly during both the manipulation and the recovery period. Whereas Heterotrissocladius disappeared during the manipulation in the treatment block, other coldstenothermal taxa such as Micropsectra, Parametriocnemus and Heleniella remained unaffected. Conversely, Corynoneura, Polypedilum and Thienemannia gracilis disappeared but were not reported as coldstenothermal. The chironomid community composition in the system changed from a Heterotrissocladius, Brillia, and Tanytarsini-dominated community during the pre-manipulation towards one dominated by Parametriocnemus, Polypedilum, Orthocladius/Cricotopus and Corynoneura during the recovery. Although increased temperature had a strong effect, chironomid occurrence was also influenced by a number of other abiotic variables, such as dissolved oxygen, depth, ammonia concentration and TDS (Total dissolved solids). Handling editor: S. Stendera  相似文献   

13.
EARLY work on the effects of inorganic ions on the activity of acetylcholine acetyl-hydrolase (EC 3.1.1.7; AChE) from various sources has been summarized by COHEN and OOSTERBAAN (1963) and many other reports have been published subsequently (CHANGEUX, 1966; CRONE, 1973; HELLER and HANAHAN, 1972; IVANOVA, 1967; KITZ, BRASWELL and GINSBURG, 1970; ROUF-CALIS and QUIST, 1972; ROUFOGALIS and THOMAS, 1968; WINS, SCHOFFENIELS and FOIDART, 1970). Despite this work, no comprehensive study has yet been made to determine whether the observed effects are specific to particular ions or dependent only on the ionic strength of the medium (CHANGEUX, 1966). In some cases, specific ion effects have been observed (CHANGEUX, 1966; HELLER and HANAHAN, 1972; ROUFOGALIS and QUIST, 1972; ROUFOGALIS and THOMAS, 1968) at salt concentrations from 600 mM to below 1 mM, but the studies were not detailed enough and in some cases the total ionic strength was not rigidly controlled, so that no general deductions can be drawn. We have studied the hydrolysis of acetylcholine (ACh) by bovine erythrocyte AChE at subinhibitory substrate concentrations, and now present our results on the effect of inorganic salts at varying ionic strength on the kinetic parameters Km, and Vmax. The present work shows that this hydrolysis follows simple Michaelis kinetics very closely, and therefore these two constants suffice to define the complete pattern of initial reaction velocity as a function of substrate concentration (ATKINSON, 1966).  相似文献   

14.
武夷山保存了典型的中亚热带原生性森林生态系统。加强武夷山常绿阔叶林研究,对支撑武夷山生态保护实践具有重要意义。2016年,对按照美国史密森热带研究所热带森林研究中心调查技术规范建立的甜槠常绿阔叶林样地进行了首轮复查,并从物种组成、群落多样性、重要值、死亡率、补员率、胸径等方面分析了其群落动态。结果表明:2016年的乔木个体为25科44属88种,较2011年增加了2科2属7种。群落的优势种组成及其优势程度变化不大,在重要值大于1的21个常见树种中,10个树种的重要值增高,11个降低。甜槠仍为建群种,其重要值略下降。乔木个体增加到3888个,年死亡率为1.31%,年补员率为2.98%。43个树种出现死亡,46个出现补员。4个常见树种的种群数量下降,16个上升。群落的平均胸径从4.82 cm增大为4.89 cm,5个常见树种的平均胸径下降,16个上升。死亡个体的平均胸径为4.47 cm,补员个体为1.67 cm。甜槠仍然将在乔木层,马银花和鹿角杜鹃在亚乔木层保持优势地位。在短期内群落结构不会出现较大的变化,但黄绒润楠、厚皮香等阴生树种和中性树种优势度的增加可能预示群落将向中生群落(顶级群落)演替。  相似文献   

15.
土壤是植物定居的场所,也是植物-微生物互作的重要界面。古菌是土壤微生物重要组份,在碳、氮、硫、铁等元素的生物地球化学循环和植物的生长发育、适应生境中发挥重要作用。植物定居对土壤古菌群落的影响研究鲜有开展,孑遗植物在研究植物-微生物-环境互作中具有独特的优势。采用扩增子高通量测序技术,研究以荒漠孑遗植物四合木为建群种或优势种的四合木-红砂-珍珠-针茅群落、四合木-针茅群落和四合木群落等三种荒漠植物群落类型中,四合木根区土壤和光板地土体土壤古菌群落特征,揭示四合木定居对土壤古菌物种数量、多样性、群落组成及功能的影响。结果表明,荒漠孑遗植物四合木定居不仅增加了根区土壤古菌的物种数量,提高了根区土壤古菌群落多样性,而且改变了土壤古菌群落组成,减少了奇古菌门Nitrososphaeraceae科未分类的属氨氧化古菌(unclassified_f_Nitrososphaeraceae)和暂定Nitrososphaera属氨氧化古菌(Candidatus Nitrososphaera)相对丰度,增加了Nitrososphaeraceae科暂定Nitrocosmicus属氨氧化古菌(Candidatus Nitrocosmicus)和广古菌门海洋古菌类群Ⅱ中未分类的属(norank_o_Marine_Group_II)相对丰度,广古菌门热原体纲未分类的属(unclassified_c__Thermoplasmata)相对丰度变化显著。植物群落演替对四合木根区土壤和光板地土体土壤古菌群落均无显著影响。Nitrososphaeraceae科氨氧化古菌是三种不同荒漠植物群落类型中土壤古菌的核心微生物组。四合木定居也显著改变土壤古菌群落的功能,减弱了高丰度功能,增强了低丰度功能,对有氧呼吸、核苷酸合成、氨基酸合成等途径影响显著。荒漠孑遗植物四合木定居改变了土壤古菌群落物种数量、多样性、组成、功能等特征。  相似文献   

16.
Summary Part of a salt-marsh (32 ha), ungrazed from 1958 until 1971, was grazed again from 1972 onwards with young cattle (1.3–1.7 per ha, May–October). In five vegetation types management experiments, including doing nothing (control). June mowing, August mowing, June and August mowing, all in combination or not in combination with grazing have been started with the objective to compare annually their effects on the vegetational structure and composition by means of permanent plots (2×2 m).Thirteen years (1958–1971) after the grazing had ceased the vegetation types of Festuca rubra/Armeria maritima, Artemisia maritima, Juncus maritimus and Elytrigia pungens hardly changed anymore. The vegetation type of Festuca rubra/Limonium vulgare, changed considerably. The experiments showed rather specific effects during the period 1971–1975 for each type of vegetation. Changes in the Festuca rubra/Armeria maritima vegetation were small and gradually under all treatments. Changes in The Artemisia maritima, Festuca rubra/Limonium vulgare and Juncus maritimus vegetation types were rather great under the different grazing treatments, the changes being abrupt and especially taking place in the third and fourth year of the experiments. The Elytrigia pungens vegetation showed large changes under all treatments, except the control plot, whereas these changes were abrupt, particularly occurring in the first and second year of the experiments. The study is continued.Nomenclature of taxa follows Heukels & van Ooststroom (1970), that of syntaxa Westhoff & den Held (1969).Contribution to the Symposium of the Working Group for Succession research on permanent plots of the International Society for Vegetation Science, held at Yerseke, the Netherlands, October 1975.Thanks are due to Prof. Dr. D. Bakker for his interest in the present study and his critical reading of the text, and to Drs D.C.P. Thalen for critical reading and correction of the English text. Thanks are also due to the students who analyzed the permanent plots: M. van der Duim and F. Prins (1971), M. van der Duim (1972), R. Schwab and T. Schwab-Vos (1973), and G. Allersma (1974, 1975).  相似文献   

17.
为了解羊肚菌(Morel)烂柄病的发生对土壤真菌群落结构的影响,采用Illumina MiSeq高通量测序技术,对健康羊肚菌根际土、烂柄病发病子实体根际土及相同环境下未栽培羊肚菌土壤的真菌群落结构进行研究。结果表明,测序样品共获得344 163条序列,归为7个真菌门。各样品真菌多样性分析结果表明,未栽培土壤真菌群落多样性较高,栽培羊肚菌根际土壤真菌多样性显著降低,烂柄病发生后土壤真菌多样性增加。群落结构分析表明,烂柄病根际优势真菌类群为拟青霉属(Paecilomyces)、木霉属(Trichoderma)、葡萄穗霉属(Stachybotrys)、枝顶孢属(Acremonium)、Paratritirachium、Zopfiella、被孢霉属(Mortierella)和柄孢壳属(Podospora)。烂柄病的发生改变了土壤真菌群落结构,促进了根际真菌的繁殖。为了解羊肚菌烂柄病的发生、传播机理及防治提供了参考。  相似文献   

18.
Besprechungen     
Book reviewed in this article: Baumann , Peter (1972): Tiere in geplanter Wildbahn. Grüsser, O.-J. , und R. Klinke ed. (1971): Zeichenerkennung durch biologische und technische Systeme (Pattern Recognition in Biological and Technical Systems). Tagungsbericht des 4. Kongresses der Deutschen Gesellschaft für Kybernetik in Berlin vom 6.–9. April 1970. Hooff , J. A. R. A. M. van (1971): Aspecten van het sociale gedrag en de communicatie bij humane en hogere niet-humane Primaten (Von Sozialverhalten und Mitteilungsweisen bei Menschen und Menschenaffen). Pagès, E. (1972): Comportement aggressif et sexuel chez les Pangolins arboricoles (Manis tricuspis et M. longicaudata). (Kampf- und Fortpflanzungs-verhalten der baumbewohnenden Schuppentiere M. tricuspis und M. longicaudata). Dies. (1972): Comportement maternel et développement chez un Pangolin arboricole, M. tricuspis. (Mutterverhalten und Jugendentwicklung des Schuppentieres M. tricuspis). Papi , F., L. Fiore, V. Fiaschi und S. Benvenuti (1972): Olfaction and Homing in Pigeons (Geruchsinn und Heimfinden bei Tauben). Rowe-Rowe , D. T. (1972): The African Weasel, Poecilogale albinucha Gray. Observations on behaviour and general biology. (Beobachtungen zu Biologie und Verhalten des Weißnacken-Streifenwiesels).  相似文献   

19.
Fish introduction, eutrophication and disappearance of aquatic vegetation are important disturbances of aquatic ecosystems, especially in plateau lakes, which are generally considered to be very vulnerable. Fish were introduced to Lake Dianchi, a eutrophic plateau lake in southwest China, in the late 1950s and 1970s. After the introduction, invasive fish became the dominant species, and the total fish yield increased. Meanwhile, the trophic level of Lake Dianchi had a tendency to increase in the past decades because of the increases in human activities in the watershed area. In addition, the area of aquatic vegetation decreased from more than 90 to 1.8% of the lake area from the 1950s to 2000. This study investigated the effects of fish introduction, eutrophication and aquatic vegetation on the diatom community of Lake Dianchi by examining the changes of microfossil diatom assemblage and abundance. Results showed that the absolute abundance and diatom assemblages changed after fish were introduced. The endemic species, Cyclotella rohomboideo-elliptica, disappeared with the introduction of fish and increasing trophic levels after 1958. Fragilaria crotonensis entered into the lake with the introduction of fish and gradually thrived in the lake after 1958. Diatom species numbers also decreased gradually from 21 to 9 from the past to present. Epiphytic diatoms disappeared with the decrease of aquatic vegetation after 1985. Our study indicated that eutrophication was the most important process determining diatom abundance, and fish introduction was a secondary process determining diatom abundance, while aquatic vegetation had a more important role in structuring the diatom community in this eutrophic plateau lake.  相似文献   

20.
青藏高原气候变暖幅度显著高于全球其他区域,深刻影响着该地区植物群落的结构和稳定性。选择西藏念青唐古拉山的三种典型植物群落(高寒草原、高寒草甸和流石滩)作为研究对象,采用开顶式增温箱(OTC)模拟增温,研究了短期增温对植物群落结构和稳定性的影响。结果表明:(1)增温改变了群落的优势物种,影响其结构组成,而对物种多样性无显著影响;(2)增温显著降低了高寒草甸的地上生物量(P < 0.05),增加地下生物量(P < 0.01),从而导致了群落地下地上生物量分配策略的改变;(3)增温降低群落中部分物种的生态位宽度,进而影响群落稳定性,其中高寒草甸变化最大,达到-66.8%。研究结果可为青藏高原高寒草地生态系统应对和适应未来气候变化提供一定科学依据。  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