Catecholamine Response Curves of Male Hypertensives Identified by Lehmacher's Two Sample Configural Frequency Analysis

A new application of LEHMACHER'S (1980) marginal homogeneity sign tests is given by analysis of bivariate response curves (or response surfaces) in two unpaired samples of hypertensive versus normotensive patients. Rationale and computations are illustrated by empirical data from sympathomedullary stress research.     

Frost and forest stand effects on the population dynamics of Asplenium scolopendrium

Our objective was to analyze which factors are critical for the dynamics of terrestrial Asplenium scolopendrium populations at the northern edge of its distribution. Therefore, a long-term study (1978–1999) on the performance and demography of this fern species has been carried out in three different forest stands (Picea sitchensis with Fagus sylvatica, P. sitchensis with thinning, and Fraxinus excelsior) in the Netherlands. We used the recorded demographic data to parameterize 37 transition matrices. The number of frost days in severe winters correlated closely with frond damage and resulted in increased mortality and retrogression. Landslip on the trench banks and intraspecific competition were also found to increase mortality. In the F. excelsior plot, plants grew faster and bigger, produced more fronds and formed a more closed fern cover than in the P. sitchensis stands, likely due to higher light levels. Life-table response experiments revealed that reproduction contributed greatly to the differences in projected population growth rates: reproduction was importantly higher in the F. excelsior and in the thinned P. sitchensis plots than in the P. sitchensis–F. sylvatica plot. These differences can be attributed to an initial difference in light climate and to the accumulation of F. sylvatica litter which reduced recruitment. Recruitment occurred on bare soil but also in open moss carpets. We expect that the fern Asplenium scolopendrium will profit at its northern distribution edge when severe winters will occur less frequently, which is one of the expectations for global climate change.     

Convergence of carbon sink magnitude and water table depth in global wetlands

Wetlands are strategic areas for carbon uptake, but accurate assessments of their sequestration ability are limited by the uncertainty and variability in their carbon balances. Based on 2385 observations of annual net ecosystem production from global wetlands, we show that the mean net carbon sinks of inland wetlands, peatlands and coastal wetlands are 0.57, 0.29 and 1.88 tons of carbon per hectare per year, respectively, with a mean value of 0.57 tons of carbon per hectare per year weighted by the distribution area of different wetland types. Carbon sinks are mainly in Asia and North America. Within and across wetland types, we find that water table depth (WTD) exerts greater control than climate- and ecosystem-related variables, and an increase in WTD results in a stronger carbon sink. Our results highlight an urgent need to sustain wetland hydrology under global change; otherwise, wetlands are at high risk of becoming carbon sources to the atmosphere.     

Ecological genetics of the rotifer Brachionus plicatilis in Soda Lake,Nevada, USA

In an earlier study we found that the rotifer Brachionus plicatilis in Soda Lake, Nevada (USA) maintains extensive genetic variation for three isozymes. This variation was present both within and between different collections. No evidence was found that there was a seasonal succession of distinct electromorphs. In this paper we ask: is the genetic variation maintained by selective neutrality among electromorphs? Parthenogenetic females from ten clones representing seven different composite electromorphs were selected for life table analysis. Substantial main effects of genotype or interactions of genotype with experimental food quantities and temperatures, were found for the intrinsic rates of increase, net reproductive rates, and mean life spans of these clones. We conclude that these fitness differences permit us to reject the hypothesis that genetic variation is maintained because of selective neutrality among clones. Instead, it seems likely that directional selectional may be either too weak or of too brief a duration in Soda Lake for clonal exclusion to occur.     

The Exact Evaluation of 2-way Cross-classifications: An Algorithmic Solution

An algorithm is presented which permits the exact evaluation of sparse cross-classifications and contingency tables. It may be used to compute the exact point and cumulative probabilities of observed values of the X²-like test statistic, or even of the observed tables themselves. For sparser cases, it may also be used to generate part or all of the exact distributions. As a corollary, an operational solution is presented to the enumeration problem of rectangular integer matrices with arbitrarily fixed row and column sums. Exact results obtained with the algorithm accompany this presentation, giving, further support to the recommendation that the Gamma distribution be preferred to the Chi-square in sparse cases.     

Effects of water level and temperature on performance of four <Emphasis Type="Italic">Sphagnum</Emphasis> mosses

To evaluate the effects of changes in water level and temperatures on performance of four Sphagnum mosses, S. magellanicum, S. rubellum, S. imbricatum and S. fuscum were grown at two water levels, −5 cm and −15 cm, and at two temperatures, 15°C and 20°C. These species differ in their position along the microtopographical gradient and in their geographical distribution. Height increment, subcapitulum bulk density, biomass production, capitulum water content and cumulative evaporation were measured. Height increment and biomass production of S. magellanicum was lower at low water table than at high water table, whereas height increment and biomass production of S. rubellum, S. imbricatum and S. fuscum were unaffected. Height increment of S. magellanicum, S. rubellum and S. imbricatum was higher at high temperature than at low temperature. Biomass production of only S. magellanicum and S. rubellum was higher at high temperature than at low temperature, corresponding with their more southern distribution. Cumulative evaporation of S. magellanicum and S. rubellum was lower at low water table and could be explained by hampered water transport towards the capitula. We conclude that changes in water table and temperature may alter the Sphagnum composition on raised bogs, which may result in changes to important ecosystem processes. Therefore, it is important that species composition and changes therein are taken into account when evaluating global change effects on raised bog ecosystems.     

The effects of Nosema algerae on the horizontal life table attributes of Anopheles stephensi under laboratory conditions

Under controlled insectary conditions, infection with Nosema algerae (Cnidospora: Microsporidia) was found to significantly alter the life table characteristics of Anopheles stephensi (Diptera: Culicidae) as follows: immature to adult survivorship decreased and developmental time was slightly delayed, female and male life expectancy at emergence decreased, fecundity, and thus the net reproductive rate, decreased, and the instantaneous rate of increase and the instantaneous birth and death rates decreased. The time in life of female reproduction and generation time were not significantly altered. Results are discussed in the context of vectorial capacity for malaria.     

Comparing two independent binomial proportions by a modified chi square test

When using the chi square test to compare the proportions of successes in two independent binomial samples, a new continuity correction is proposed, which equals half the size of the smaller sample. Exact computations of unconditional tail-probabilities, together with a theoretical argument, show that this correction is more appropriate than the YATES correction. This version of the chi square test is still conservative, but less so, and as a consequence more powerful, than the YATES corrected test.