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401.
Meiofauna on the seagrass Thalassia testudinum: population characteristics of harpacticoid copepods and associations with algal epiphytes 总被引:1,自引:0,他引:1
The composition and abundance of bladedwelling meiofauna was determined over a 15 mo period (1983–1984) from a Thalassia testudinum Banks ex König meadow near Egmont Key, Florida, USA. Harpacticoid copepods, copepod nauplii, and nematodes were the most abundant meiofaunal taxa on T. testudinum blades. Temporal patterns in species composition and population life-history stages were determined for harpacticoid copepods, the numerically predominant taxon. Sixteen species or species complexes of harpacticoid copepods were identified. Harpacticus sp., the most abundant harpacticoid, comprised 47.8% of the total copepods collected, and was present throughout the study. Copepodites dominated the population structures of the blade-dwelling harpacticoid species on most collection dates. Ovigerous females and/or copepodites were always present, indicating continuous reproductive activity. Results suggest that epiphytic algae influence meiofaunal abundance on seagrass blades, as densities of most meiofaunal taxa at Egmont Key were positively associated with percent cover of epiphytic algae throughout the study. The majority of significant correlations between meiofaunal density and cover of epiphytic algae involved filamentous algae, although encrusting algae dominated the epiphytic community. It appears that resources provided by epiphytic algae to seagrass meiofauna (additional food, habitat, and/or shelter from predation) may be associated with algal morphology. 相似文献
402.
403.
Geographic populations of the anemonefish Amphiprion clarkii (Bennett) from 6 widely separated locations off the coast of southern Japan are morphologically different, exhibiting (1) latitudinal clinal patterns in color pattern and meristics and (2) degrees of genetic differentiation. Electrophoretic examination of 7 polymorphic loci (95% level) among 6 populations collected between July 1979 and January 1980 revealed an average genetic distance value of 0.008. Significance was demonstrated for 39 out of 105 (37%) tests of heterogeneity. Averaged over the 6 populations, the percentage of polymorphic loci (
0.95) was 24.6% and the proportion of heterozygous loci per individual (
) was 0.0613. The results indicate that genetic clines are absent and suggest that the morphological variation may not be genetic. Relative isolation of genetic populations may be maintained by (1) localized larval dispersal resulting from a relatively short larval stage, and (2) current gyres tending to trap larvae, increasing the return of juveniles to their adult coastal habitat. Morphological clines may be due to clines in ecological parameters related to latitude.Contribution No. 39 of the Tatsuo Tanaka Memorial Biological Station 相似文献
404.
对溧水神仙洞的发掘和进行地质、地貌、孢粉、古脊椎动物与古人类、C14 年代及考古等多学科综合研究结果表明 :该洞是石炭系石灰岩沿层面裂隙经地下水溶蚀而成 ;洞穴堆积物的时代应属全新世早期 ,或新石器时代早期 ,绝对年代距今约为 1.1万年。其中发现的动物群为我国南方晚更新世动物群向现代动物群过渡的类型 ,而代表中 -晚更新世的最后鬣狗与代表新石器时代文化标志的陶片共生 ,为我国第四纪时代的划分 ,或新、旧石器时代文化的划分提供了重要依据。陶片则迄今为止是我国具有完整地层层位记录的最古陶片。它的发现 ,不仅将我国新石器时代文化大大推前 ,更为重写中华古史 ,校正“中华五千年文明”的提法 ,将中华文明追溯到一万年前并重排世界古文明位次增加了依据。同时 ,智人颞骨的发现 ,对长江中、下游古人类的研究 ,也提供了新的资料 相似文献
405.
406.
Orientation of female lesser wax moths (Achroia grisella) to male calling song was tested on a locomotion-compensator device that withheld all inter-aural acoustic differences from the insect. Under these circumstances, females remained longer in the vicinity of the sound source if they experienced a variable sound level that increased when approaching the source rather than a level that remained constant at all times. Analyses of orientation paths revealed that greater retention near the source was achieved by enhanced turning when the perceived sound level remained unchanged or decreased but retaining the previous heading when the level increased. These findings suggest that acoustic orientation can be supplemented by mechanisms based on sequential, as opposed to instantaneous, comparison of auditory input. Such mechanisms may be valuable when binaural hearing is impaired or asymmetric or in environments where acoustic differences at the two ears are unreliable indications of direction to the sound source. 相似文献
407.
The effects of exposing plants of Dryopteris filix-mas (L.) Schott, Phyllitis scolopendrium (L.) Newman and Polypodium vulgare L. to 60 nl litre(-1) (122 microg m(-3)) NO(2) for 37 weeks were investigated in a closed chamber fumigation system. There was no effect of NO(2) on the numbers of fronds produced for any species at any time during the exposure period. However, at the end of the study, there was a lower dry weight yield of green shoots of D. filix-mas and P. scolopendrium and a higher yield of green shoots of P. vulgare for plants in the NO(2) treatment as compared to control plants. These differences in shoot dry weights were not accompanied by an effect of NO(2) exposure on total plant dry weights. 相似文献
408.
Effect of air pollution on peri-urban agriculture: a case study 总被引:10,自引:0,他引:10
Agrawal M Singh B Rajput M Marshall F Bell JN 《Environmental pollution (Barking, Essex : 1987)》2003,126(3):323-329
Peri-urban agriculture is vital for the urban populations of many developing countries. Increases in both industrialization and urbanization, and associated air pollution threaten urban food production and its quality. Six hour mean concentrations were monitored for SO(2), NO(2) and O(3) and plant responses were measured in terms of physiological characteristics, pigment, biomass and yield. Parameter reductions in mung bean (Vigna radiata), palak (Beta vulgaris), wheat (Triticum aestivum) and mustard (Brassica compestris) grown within the urban fringes of Varanasi, India correlated directly with the gaseous pollutants levels. The magnitude of response involved all three gaseous pollutants at peri-urban sites; O(3) had more influence at a rural site. The study concluded that air pollution in Varanasi could negatively influence crop yield. 相似文献
409.
The abundances of epiphytes on free-standing oaks (Quercus robur) along a transect extending approximately 70 km SSW from Central London were redetermined annually from 1979 to 1990. During this period SO(2) levels in inner London fell to between one-quarter and one-seventh of levels occurring in the 1960s. The sample trees were also scored annually using Hawksworth and Rose's (1970) scale for predicting SO(2) levels from the epiphytes present. Little evidence was obtained for epiphyte recolinization of oaks at sites within the built-up area. At Epsom Common, on the urban fringe, cover of the pollution-tolerant lichen Lecanora conizaeoides fell, and in the inner suburbs, at Putney Heath, L. conizaeoides and Lepraria incana increased, while the alga Desmococcus viridis declined at this site. These changes might be due to a contraction inwards of zones of peak abundance of L. conizaeoides and D. viridis with decreasing SO(2) levels. However, it is also possible that the changes at Putney Heath resulted from scrub clearance activities and alteration to the microclimate. The cover of the moderately SO(2) tolerant foliose lichen Hypogymnia physodes remained low and static at Putney Heath during the 12-year period. Possible reasons for the poor recolinization of London's oaks by epiphytes are discussed. Particular emphasis is given to the highly acidic bark of oak in the London area (pH2.9-4.0) in comparison with other tree species and with oaks in unpolluted regions. 相似文献
410.
Kinnersley RP Shaw G Bell JN Minski MJ Goddard AJ 《Environmental pollution (Barking, Essex : 1987)》1996,91(2):227-235
There is a requirement for data describing the loss with time of particulate contamination from plant canopies. Measurements were made of the loss rates of monodispersed silica spheres (three sizes, with Mass Median Aerodynamic Diameters (MMADs) 1.9, 5.3 and 8.4 microm) from wheat (Triticum aestivum) and broad bean (Vicia faba) canopies. The spheres were labelled with tracers detectable by Instrumental Neutron Activation Analysis (INAA). Canopies were contaminated under realistic turbulence conditions in a wind tunnel, then removed to sheltered and exposed field sites or to a glasshouse containing a rain simulator. Samples were taken periodically, and the level of contamination per plant determined by INAA. Statistical analysis of the resulting data suggested an offset exponential loss model, with a residue of deposit that is not lost over time. Loss half-lives in the order of 1-2 days were obtained for an exposed wheat crop and 3-4 days for a partially sheltered wheat crop, with permanent residues of initial deposit for the exposed crop of 4-8%, and for the partially sheltered crop of 22-52%. A broad bean crop under glasshouse conditions showed loss half-lives of 0.5-1.5 days with residues of 22-26% initial contamination. A double exponential loss model also fitted the data well in some cases, and it is possible that a slow loss of the residual deposit occurs, being masked by noise in the current data set. 相似文献