Biomass: Is it a useful tool in paleocommunity reconstruction?

In general, more of the biomass of the community is preserved than is its numerical abundance. Thus, the paleontologist, on the average, works with more of the community when biomass is used. Community characteristics such as taxon dominance and habitat proportions are at least as accurately derived from biomass as numerical abundance. The use of biomass is clearly more appropriate in describing energy flow and trophic proportions. Whenever possible, biomass should be used as a complement to numerical abundance in future paleoecologic reconstructions.     

A multivariate study of resource partitioning in soft bottom lotic Chironomidae

For two years a community of larval chironomid midges was studied in a sandy-run portion of a fourth order natural stream in SE Ohio, U.S.A. in order to determine if the species partitioned the spatial resources. The habitat structure was simplified from ten habitat variables to three significant principal components. The three eigenvectors were easily interpreted as sediment size, sediment heterogeneity, and organic deposition. Species abundances were loaded on these axes and niche metrics examined. Strong differences in habitat preference were demonstrated for midge species on each component. Also, there were no differences in distributions for the intraspecific instars for each species tested at a given time, but for each of the instars tested, their distributions were found to change from time to time. Apparently, individuals of a species, regardless of instar, simultaneously choose the same habitat, however, the preferred habitat may shift temporally due to change in resource availability, or niche expansion or compression due to competition.     

金沙江河谷苏铁天然植物群落的研究

近年在金沙江干热河谷及其邻近地区陆续发现的苏铁天然植物群落,为本属植物在欧亚大陆内陆分布的最北边缘。其中,面积最大和保存较好的是渡口市攀枝花苏铁(Cycas panzhihuaensis)植物群落。本文研究了这个群落的分布与生境、生长状况、外貌、种类组成以及群落的综合特征等。认为具有稀树草原的特点,而这里的稀树草原是次生性质的,苏铁群落是其中幸存的残遗植被类型。这对研究我国植物地理有着重要意义。     

Floristic groups and plant communities of southeastern Santa Fe,Argentina

This paper is a survey of the vegetation of the southeastern departments in the Province of Santa Fe (Argentina). The vegetation was analyzed following Braun-Blanquet's approach modified by Mueller-Dombois & Ellenberg (1974). The most relevant species of the region were placed in 25 groups according to their requirements or general behaviour. Most of the communities are herbaceous, and apart from the woody and some other miscellaneous ones they were grouped into three ecologically and floristically defined sets. The first set, the Stipa grasslands and related communities, which are characterized by the more or less abundant presence of Stipa hyalina, Stipa neesiana and Stipa papposa, comprises five different communities. The second, the halophilous communities, comprises five communities, the two Spartina ssp. grasslands, the halophilous prairies of Distichlis spicata, the short sedge Scirpus americanus communities and the ‘pela-dales’. The third, the hygrophilous communities, comprises nine communities which are not so well defined as the ones in the other sets. Besides, two further communities have been included, the Paspalum quadrifarium and the Melica macra tall grasslands.     

Estimation of the size of freshwater ciliate populations by a sub-sampling technique

A technique is described for the estimation of the size of ciliate populations based on replicated counts. Sample drops were taken by automatic pipettes of different volume from activated sludge and from a small oligotrophic stream. Specific aims were: 1) the estimation of the number of species; 2) the estimation of the number of individual in each species; 3) the selection of a suitable sub-sample size and number of replicates. For each volume the cumulative increase in species taken in successive sub-samples was determined. For each species the minimum permissible sub-sample volume and the number of replicates required for an allowable error of 10% and 25% were determined. Lastly, the relationship between the mean number of individuals counted for each species and the relative coefficient of variation was visualized.     

Phytoplankton community structure and distribution in the nearshore zone of Lake Ontario

Spatial and temporal distributions of phytoplankton were studied during 1979 in the nearshore zone of Lake Ontario. Genera such as Dinobryon, Oscillatoria, and Gymnodinium tended to be found at discrete depths whereas other genera such as Cryptomonas and Rhodomonas tended to be more uniformly distributed throughout the water column. The discrete depth distribution of some of these genera compared with the weak thermal stabilization of the area suggests depth selection and habitat preference within the algal community.Physical processes probably played a major role in regulating the timing and duration of vertical diatom pulses, and resuspension from the sediment played a major role as to the timing of the autumn growth. Vertical mixing in the nearshore zone was sufficient for some diatom genera such as Tabellaria to maintain populations throughout the summer. These mixing processes, however, affect the stability of community structures and associations that develop within the water column. The role of physical processes and their potential effects on algal production in the Great Lakes is discussed.     

Effect of Folate Deficiency on Local Cerebral Glucose Utilization in the Rat

There is considerable debate on the role of folate in CNS function. Recent work indicates that folate deficiency may affect CNS serotonin metabolism, and clinical studies describe many consequences of such a deficiency. On the other hand some workers maintain that folate deficiency alone causes CNS abnormalities. We maintained rats, through dietary deprivation, at folate levels below 4 ng/ml for more than 6 weeks and showed that at that time both their liver and brain folate levels were significantly reduced. We then studied their local cerebral glucose utilization (LCGU) using the [14C]deoxyglucose technique. This method assesses cerebral function by measuring regional metabolic activity. We also determined LCGU in rats given the same diet but replenished with folate (folate control) and in others given free access to commercially available food (normal controls). Our results show that this degree of folate deficiency has no effect on cerebral function. This contrasts with the focal suppression of LCGU we previously reported in a model of vitamin B12 deficiency.     

贵州部分森林群落物种多样性初步研究

 本文根据贵州省178个森林群落样地的数据研究了群落物种的多样性。测定的指标有群 落物种丰富度,群落Simpson多样性指数和群落均匀度。测定结果表明;不同垂直带生物气 候条件下的森林群落有不同的多样性。相同垂直带生物气候条件下,基质生境相同时,不同森林植被亚型的群落的多样性近似,基质生境不同时,群落多样性则不同;同一群落类型的各个样地的多样性也有变化,结构不同的群落个体,其多样性指数不同,演替趋势也不同。乔木第二亚层的多样性普遍地高于乔木第一亚层。同一演替系列中,越接近顶极阶段多样性越高。多样性指数与群落物种丰富度,均匀度呈紧密的正相关,与群落个体总数没有相关。认为多样性测定在比较、说明群落的结构、类型、组织特征、生境、演替等方面有一定意义。     

Effects of stormwater sewer discharges on the aquatic community in urban canals in Lelystad

In urban areas with a separate sewerage system, the stormwater runoff is discharged into surface waters. A study on the effects of stormwater sewer discharges on the composition of the aquatic community in urban waters was carried out in two areas with a primarily residential use in the new town of Lelystad. The aquatic organisms considered included hydrophytes, epiphytic diatoms, filamentous algae and macroinvertebrates.The results indicate that the stormwater sewer discharges cause a slight change in the composition of the aquatic community. The water in the urban surface waters can be characterized as eutrophic and - toa-mesosaprobic. Near stormwater sewer outfalls the water tends to the more polluteda-mesosaprobic state. The shifts in the composition of the aquatic community could be traced primarily on the basis of a number of epiphytic diatoms and macroinvertebrates (in particular some Diptera and Trichoptera). Most hydrophytes, filamentous algae and the remaining epiphytic diatoms and macroinvertebrates (in particular water beetles and water mites) turned out to be of little or no use in this respect.Because the investigation was carried out in an unusually dry summer, the results probably underestimate the effects of stormwater discharges on the aquatic community.     

A mechanism of respiration-dependent water uptake enhanced by auxin

Summary There are many contradictory observations on the mechanohydraulic relation of growing higher plant cells and tissues. Graphical analysis of the simultaneous equations which govern irreversible wall yielding and water absorption has made more comprehensive the understanding of this relation when relative growth rate is plotted against turgor pressure. It suggests that some respiration-dependent and auxin sensitive process might regulate the difference of osmotic potential between cells and water source. Based on anatomical and electrophysiological knowledge of the pea stem xylem, we propose the wall canal system as the mechanism of respiration-dependent water uptake which is sensitive to auxin. This system consists of the xylem apoplastic walls, the xylem proton pumps, active solute uptake system and cell membranes. In the simplest case, third-order simultaneous differential equations are involved. Numerical analysis showed that net uptake of solutes enables water to be taken up against an opposing gradient of water potential. The behaviour of this wall canal system describes well the mechano-hydraulic relation of enlarging plant cells and tissues. Recent typical, but incompatible, interpretations of this relation are critically discussed based on our model.Abbreviations V the volume of enlarging symplast - the average extensibility of the wall - Pⁱ turgor pressure - Y the yield threshold of the wall - L the relative hydraulic conductance - the solute reflection coefficient of the plasmamembrane - Cⁱ the osmotic concentration of the symplast cells - C^x the osmotic concentration of the xylem vessels - P^x hydrostatic pressure in the xylem vessels - R the gas constant - T absolute temperature - ^o water potential of xylem fluid - ⁱ water potential of symplast cells