High Product Variability Research Articles

Variability of chlorophyll and primary production in the Eastern North Atlantic Subtropical Gyre: potential factors affecting phytoplankton activity

Size-fractionated chlorophyll- a and carbon incorporation rates were determined on a series of 13 cruises carried out from 1992 to 2001with the aim of investigating the patterns and causes of variability in phytoplankton chlorophyll and production in the Eastern North Atlantic Subtropical Gyral Province (NASE). Averaged (±SE) integrated chlorophyll- a concentration and primary production rate were 17±1 mg m −2 and 253±22 mg C m −2 d −1. Small-sized cells (<2 μm) formed the bulk of phytoplankton biomass (71%) and accounted for 54% of total primary production. A clear latitudinal gradient in these variables was not detected. By contrast, large seasonal variability was detected in terms of primary production, although integrated phytoplankton biomass, as estimated from chlorophyll- a concentration, remained rather constant and did not display significant changes with time. Variability in primary production (PP) was related mainly to variability in surface temperature and surface chlorophyll- a concentration. The control exerted by surface temperature was related to nutrient availability. By contrary, euphotic-zone depth, depth of maximum concentration of chlorophyll- a and integrated chlorophyll- a did not contribute significantly to the high variability in primary production observed in this oligotrophic region.

Primary production of Inner Mongolia, China, between 1982 and 1999 estimated by a satellite data-driven light use efficiency model

Declining biological production as a part of an ongoing land degradation process is considered a severe environmental problem in the dry northern and northwestern regions of China. The aim of this study is to develop and adapt a satellite data-driven gross primary production model called Lund University light use efficiency model (LULUE) to temperate conditions in order to map gross primary production (GPP) for the Grasslands of Inner Mongolia Autonomous Region (IMAR), China, from 1982 to 1999. The water stress factor included in the original model has been complemented with two temperature stress factors. In addition, algorithms that allocate the proportions of C3/C4 photosynthetic pathways used by plants and that compute temperature-based C3 maximum efficiency values have been incorporated in the model. The applied light use efficiency (LUE) model is using time series of the Normalized Difference Vegetation Index (NDVI), CLouds from AVHRR (CLAVR) from the 8-km resolution NOAA Pathfinder Land Data Set (PAL). Quasi-daily rainfall and monthly minimum and maximum temperatures, together with soil texture information, are used to compute water limitations to plant growth. The model treats bare soil evaporation and actual transpiration separately, a refinement that is more biophysically realistic, and leads to enhanced precision in our water stress term, especially across vegetation gradients. Based on ground measurements of net primary production (NPP) at one site, the LULUE reproduces the variability of primary production better than CENTURY or NDVI alone. Mean annual GPP between 1982 and 1999 range from about 100 g/m 2 in desert regions in the west to about 4000 g/m 2 in the northeast of IMAR, and the coefficient of variation for GPP is highest near the margins of the deserts in the west where rainfall is erratic. Linear trends fitted through the 18-year time series reveal that the western regions have encountered no change, while a large area in the center of the IMAR shows marked increases in GPP. In the northeast, negative trends in GPP are noted and coincide with rainfall trends. Though the high inter-annual variability in primary production undermines the identification of significant trends, we could not isolate any general decline in grassland primary production.

MODEL PROJECTIONS OF THE FISHERY IMPLICATIONS OF THE ALLEE EFFECT IN BROADCAST SPAWNERS

There has been widespread concern that reduction in density of broadcast spawners by a fishery can have severe effects on reproduction. As fishing decreases density, fertilization efficiency declines, so that reproduction declines more rapidly than indicated by density, producing an Allee effect. However, this potentially precipitous decline in reproduction with declining density or stock size is not well understood at the population level. We used a simple deterministic model of the reproductive dynamics of a broadcast spawning invertebrate to show that the abrupt threshold often proposed as the form of this Allee effect is possible only when individuals are evenly spaced, and when sperm dispersal distribution is a constant out to a specified distance. When the spatial distribution is random and the sperm dispersal distribution is either Gaussian or exponential, fertilization success is linear up to 100%; thus, zygote production is quadratic up to this density. As the width of the dispersal function decreases, fertilization reaches 100% at higher densities, so that it may be beyond the highest density experienced by the population. In that case, zygote production is functionally linear. We then used a simulation model to assess the effects of aggregative behavior and stochastic variability in spatial patterns. We compared narrow and broad sperm dispersal distributions that were based on empirically determined fertilization of the green sea urchin, Strongylocentrotus droebachiensis, under two flow regimes. Zygote production exhibited a gradual nonlinear Allee effect as density decreased for the broader gamete dispersal distribution, but a functionally linear relationship with a much lower slope for the narrower sperm dispersal distributions. Increasing aggregation increased the slope of both fertilization and zygote production vs. density at the origin, but they remained linear for the narrower distribution. High interannual variability in zygote production due to different spatial configurations suggested that the geometric mean of recruitment is a better indicator of population consequences than the arithmetic mean, and it displays a sharper threshold than the arithmetic mean. Our results imply that potential Allee effects at low density in broadcast spawning populations rarely exhibit threshold behavior, and that these Allee effects may be too weak to be detected in stock–recruitment relationships.

Uremia-associated immune defect: The IL-10–CRP axis

Unstable atherosclerotic disease is related to systemic inflammation. While this inflammation remains at a subclinical level in otherwise healthy individuals, chronic elevation of pro-inflammatory cytokines is a common feature in patients with end-stage renal disease (ESRD). Current hypotheses on the pathogenetic links between inflammation and atherosclerosis emphasize that cytokine-producing monocytes/macrophages can actively infiltrate atherosclerotic plaques. A high activation level of this cell type may contribute to plaque growth. In the healthy, some 15% to 20% of circulating monocytes may be activated for cytokine production. This percentage is much higher in dialysis patients (50%), which may contribute to the rapid progression of atherosclerosis. Anti-inflammatory mechanisms such as interleukin-10 (IL-10) limit the production of a broad range of pro-inflammatory factors. Animal models, as well as clinical findings, suggest an involvement of this cytokine in the pathogenesis of vascular lesions. In hemodialysis (HD) patients, a protective role of IL-10 against systemic inflammation could be proven. A high interindividual variability in IL-10 production leads to distinct patient groups who can or cannot effectively limit the uremia- and dialysis-induced inflammation. Single nucleotide polymorphisms (SNPs) in the promotor of the IL-10 gene may genetically explain this heterogeneity. The IL-10 genotype strongly influences the range of variation of C-reactive protein (CRP), the most widely used marker of inflammation in dialysis patients. By limiting the inflammatory activation in ESRD patients, the IL-10 genotype is predictive for the risk of cardiovascular disease, meaning that the IL-10 "high-producer" genotype is associated with a lower event rate, and even mortality, than the IL-10 "low-producer" genotype.

The faint promise of a distant market: a survey of Belem’s trade in non-timber forest products

Increased trade in non-timber forest products (NTFPs) has been promoted as one possible means to slow tropical deforestation by increasing the economic value of intact forest. A market survey of NTFPs occurring in the Capim River basin in eastern Amazonia, Brazil demonstrated that the reality for many smallholder communities in frontier and remote regions includes chronic transportation difficulties, high variability in fruit production, perishable products and lack of market expertise. In some communities, declining abundance of NTFPs due to logging and fire has resulted in a lack of forest products to even meet subsistence needs. In areas close to cities where transportation is assured and where forest clearing has eroded the natural occurrence of some valuable native NTFPs, smallholders who manage and successfully market native fruit and medicinal species are overcoming these obstacles. In frontier regions undergoing rapid transformation, however, decline in locally used and regionally marketed NTFPs currently pose detrimental consequences for communities. Findings suggest that an overemphasis on NTFP marketing has diverted attention from local livelihood, resource access and subsistence issues.

Speech patterns in kabuki make-up syndrome: A case report

The case of a girl aged 3 years and 8 months with Kabuki make-up syndrome is reported. At presentation, she had normal cognitive functioning, and she also had a history of otitis media, a submucous cleft palate, and some hypotonia. Language testing showed normal receptive skills and good expressive vocabulary but poor morphosyntactic abilities. Speech analysis showed that she was capable of producing most of the sounds of her native language but demonstrated high variability in production of the sounds. In addition, she inconsistently simplified words by application of several phonologic processes. Possible explanations for the communication problems demonstrated are discussed.

Prosodic disambiguation of syntactic ambiguity in discourse context

A cooperative boardgame task was used to examine how native speakers use prosodic structure to resolve syntactic ambiguity in discourse context. The game task required two speakers to use utterances from a predetermined set to negotiate the movement of gamepieces to goal locations. In one condition, the discourse contained two situations that had to be described using the same syntactically ambiguous word sequence. In the other condition, an identical syntactically ambiguous structure was used to describe only one situation. Sentences that could describe two situations had an ambiguous prepositional phrase attachment as in ‘‘I want to move the square with the triangle,’’ in which the move involved either a combined square-and-triangle piece or a triangle pushing a square to another position. Sentences describing only one situation involved only a cylinder pushing the square as in ‘‘I want to move the square with the cylinder.’’ Phonological analyses and phonetic analyses of duration and fundamental frequency were compared. Results indicate that speakers used prosodic phrasing to reflect situational syntactic ambiguity. Examples of relatively high and low variability in production will be discussed. [Work supported by NIH grant MH-51768, NZ/USA Cooperative Science Programme grant CSP95/01, Marsden Fund grant VUW604, and NIH research DC-00029.]

Progressive Hand Assembly of Circuit Packs in a Small-Lot, High-Mix Environment

Progressive assembly is widely used to hand-assemble components on circuit packs. However, this method is normally used whenever lot sizes are large and the production volume is high enough to justify the effort required to set up the operation. When the manufacturing environment consists of small lot sizes and many circuit pack codes, progressive assembly is usually not the method of choice. It is a manufacturing truism that the benefits of progressive hand assembly do not extend to small-lot production where many code changeovers and setups are required. The prevailing view is that the benefits derived do not exceed the effort required to prepare and update the manufacturing information for each circuit pack type. This paper describes the application of progressive hand assembly to a manufacturing shop that typifies small-lot production and high product variability. It shows that the benefits from a high-volume operation can be achieved in a small-lot operation when component preforming, kitting, and setup issues are appropriately addressed.

Bacterial biomass and production rates in the Gulf Stream front regions

3H-Thymidine incorporation rate, bacterial total count and mean bacterial cell volume were measured at eight depths throughout the euphotic zone at 10 stations in Gulf Stream water and front regions in October 1985. Highest rates of bacterial biomass and production were found in the surface layers of entrained shelf water and in the mixing zones between shelf water and Gulf Stream water. High variability in bacterial production and in biomass related to layers of different water masses was observed in the front regions. Thymidine incorporation rate varied between 3 and 300 pmol l −1 day −1 (mean = 30, S. D. = 50, N = 76). Bacterial total count varied between 3.6 × 10 7 and 2.3 × 10 9 cells l −1 (mean = 6.8 × 10 8, S. D. = 4.4 × 10 Su8, N =76). Bacterial mean cell volume varied between 0.01 and 0.11 μm 3 (mean 0.056, S. D. = 0.024, N = 75). Thymidine incorporation rate was positively correlated with bacterial total count, but not correlated with temperature and mean bacterial cell volume.

Seasonal Variation of Nutrient Concentrations in a Semi-Arid Savanna Ecosystem in Botswana

(1) Seasonal changes of nutrient concentrations in the leaves of the main tree and grass species of a semi-arid savanna in Botswana have been analysed. (2) The nitrogen concentration in the leaves of shallow-rooted Acacia species is higher than in deep-rooted ones. The higher nitrogen status of the shallow-rooted Acacia species could be the cause for their encroachment into overgrazed areas. (3) Substantial quantities of nitrogen and phosphorus are translocated from the deciduous leaves to perennial organs long before leaf abscission; sodium, calcium and iron are accumulated in older leaves. (4) A comparison of the nutrient budgets of inflorescences and infructescences in trees shows a strong nutrient demand for the developing infructescence. It is suggested that the high variability in fruit production between and within trees is caused by the high phosphorus demand of the developing fruit.

Faecal egg counts and nematode fecundity: Heligmosomoides polygyrus and laboratory mice.

The results are presented of an experimental investigation of the relationship between faecal egg counts and worm burden in outbred MF1 mice infected with Heligmosomoides polygyrus (Nematoda). The sex-ratio of the adult parasites was found to be significantly female biased, but independent of parasite burden. Evidence was also found to suggest a significant association between parasite density and mating success. The linear logarithmic relationship (gradient of approximately 2) between the variance and mean of repeated egg counts from individual mice could not be disrupted by controlled experimental conditions, and is therefore concluded to be an inherent feature of the biology of helminth-host interactions. A significant positive association was detected between host faecal output and parasite fecundity; further investigation of the cause of this association is now required. Average faecal production was found to be inversely related to worm burden. In combination, the above two factors account partly, but not completely, for the observed density dependence in the absolute rate of parasite egg production. Two epidemiological consequences of the relationship between faecal production and parasite fecundity are discussed. First, absolute rates of egg production can only be estimated by temporal egg counts (epd). Secondly, measurements of egg production/g of faecal material (epg) are more reliable indicators of worm burden than measurements of epd. Both faecal output and worm fecundity respond as might be predicted to a period of host food deprivation; faecal egestion and measurements of epd are significantly depressed, and measurements of epg are significantly increased. The data are consistent with the hypothesis that egg production and faecal output are causally associated, but that other factors relating to parasite density also influence egg production. Of the possible causes for the high variability in parasite egg production between mice harbouring low number of worms, the most likely explanation seems to be host heterogeneity (possible genetic in origin). This is discussed in relation to similar patterns observed in data collected from human populations in areas of endemic helminth infection.

Erosion and Sediment Control At Road-Stream Crossings

The effectiveness of a "brush mulch" to control erosion and sediment at road-stream crossings was evaluated by measurement and comparison of upstream and downstream suspended sediment. The brush mulch consisted of logging debris, such as branches, tree tops and logs 2-15 cm in diameter, laid on the ground to intercept and to slow overland flow and to trap sediment. Two treatments were defined and tested. Treatment no. 1 was a brush mulch and grass-fertilizer mixture applied by hydroseeding to three bare soil road-stream crossings. Treatment no. 2 was a grass-fertilizer mixture applied by hydroseeding to another three road-stream crossings.Total seasonal and storm sediment production for mulched and unmulched crossings averaged 31 and 37, and 566 and 2297 kg/day/ha, respectively. Tests showed significant differences between treatments for both seasonal and storm sediment production. The levels of significance were low because of high variability in sediment production among treatments and road crossings. Frequent onsite inspections during storm and nonstorm conditions, however, identified sources of variability and supported a final conclusion that the brush mulch was effective for erosion and sediment control at road-stream crossings.

Potential Soil Erosion of Selected Habitat Types in the High Desert Region of Central Oregon

During the summers of 1975 and 1976, an infiltration/sedimentation study was conducted in the Bear Creek watershed of central Oregon. A Rocky Mountain infiltrometer was used to simulate high intensity rainfall over 468 sediment plots. The Bear Creek watershed was divided into seven ecological land units which were further refined into ten tentative habitat types based upon an associated table developed from vegetation and soils field data. Tractor logging in the mixed forest caused a signiflcant increase in soil loss. In nonforested units, a high natural variability in sediment production within sites tended to mask any differences that may have resulted from a management treatment. Significant differences that did occur appeared to be closely related to differences in soils and ecological condition. Beyond the identiflcation of specific sediment production potentials, this work investigated the value of the habitat type level of ecological refinement in relation to hydrologic response. Management of semiarid range watersheds is based primarily upon the harvest of natural resources and the realization of nontangible benefits from the land and its vegetation. Watershed concerns on these rangelands deal with soil stability and protection and the quantity and quality of water that is produced. Management, therefore, requires the maintenance of a vegetation and soil cover that is able to utilize and store precipitation at its maximum effectiveness. The purpose of this study was to investigate ecological land units within the Bear Creek watershed, 65 km east of Bend, Oregon, in terms of their susceptibility to surface