Submerged vascular plants and water chemistry in the coastal marsh Albufera de Mallorca (Balearic Islands)

Ten species of aquatic macrophytes have been analyzed for seven environmental variables by means of a significance test. A synthetic view has been obtained through a cluster analysis for species and a principal component analysis for 17 variables which form the multidimensional space where we project the species habitats. Myriophyllum spicatum L., Najas marina L., Potamogeton crispus L., Potamogeton pectinatus L. and Zannichellia pedunculata Reichenb. are widely distributed in the Albufera. Ceratophyllum submersum L. and Ruppia maritima L. var. brevirostris Ag. are considered stenoic. The tolerance of Ceratophyllum submersum to salts is significantly low and that of Ruppia cirrhosa (Petagna) Grande and Ruppia maritima var. brevirostris significantly high. Ceratophyllum submersum has a significantly negative distribution with regard to chlorophyll a and phosphate concentrations. Ceratophyllum demersum L. and C. submersum primarily occur in nitrate-rich waters whereas Ruppia cirrhosa primarily occurs in low nitrate waters.     

Effective population size,genetic diversity,and coalescence time in subdivided populations

A formula for the effective population size for the finite island model of subdivided populations is derived. The formula indicates that the effective size can be substantially greater than the actual number of individuals in the entire population when the migration rate among subpopulations is small. It is shown that the mean nucleotide diversity, coalescence time, and heterozygosity for genes sampled from the entire population can be predicted fairly well from the theory for randomly mating populations if the effective population size for the finite island model is used.     

Effect of Watering Regimen on Injury to Corn and Grain Sorghum by Pratylenchus Species

The effect of simulated rainfall frequency on the pathogenicity of Pratylenchus zeae and P. brachyurus was studied in four greenhouse experiments. Corn and grain sorghum were watered at different intervals during predetermined cycles to create a gradient of water-stressed plants. Each experiment included nematode and uninoculated treatments. Growth reaction of plants to different frequencies of watering was significant but was not affected by the presence of nematodes. Pratylenchus zeae numbers differed among watering regimens on corn but not on sorghum. Numbers of P. brachyurus did not differ among watering regimens on corn or sorghum. Both lesion nematode species were harmful to corn, but sorghum increased plant growth in response to P. brachyurus. It is concluded that water stress is not the only environmental factor that influences the pathogenicity of these two species on corn and sorghum.     

Genetic studies of water buffalo blood markers. I. Red cell acid phosphatase,albumin, catalase,red cell α-esterase-3, group-specific component,and protease inhibitor

We have developed the methodologies for typing and family studies to establish the modes of inheritance of water buffalo red cell acid phosphatase (Acp), protease inhibitor (Pi), and group-specific component (Gc) on isoelectric focusing and albumin (Alb), red cell -esterase-3 (Est-3), and catalase (Cat) on polyacrylamide gel electrophoresis. Family studies showed that Pi, Gc, Alb, and Cat are coded by autosomal genes with two codominant alleles, while Est-3 is autosomal with two codominant alleles and a recessive null allele and Acp exhibits three codominant alleles.This project was funded by the Australian Centre for International Agricultural Research through Grant PN 8364 and the Malaysian programme for Intensification of Research in Priority Areas through Grant IRPA 1-07-05-057.     

Partitioning behavior and enrichment of proteins with reversed micellar extraction: I. forward extraction of proteins from aqueous to reversed micellar phase

Protein extractions using aerosol OT (AOT)-isooctane reverse micelle solutions have been studied to explore the potential for separating and enriching proteins with the reversed micellar extraction. The effects of pH, ionic strength, and different cations of chlorides in a bulk aqueous phase and of AOT concentration in an organic phase on the partitioning of lysozyme and myoglobin and the solubilization of water are presented in detail. The extraction of lysozyme was affected by the concentration of potassium or barium but was almost independent of that of sodium or calcium, whose ionic diameter is smaller than that of potassium and barium. For the extraction of myoglobin, however, the effect of barium concentration was not appreciable. Lysozyme could be enriched into the reversed micellar phase up to 30 times the aqueous feed concentration. (c) 1993 John Wiley & Sons, Inc.     

An ecosystems approach to base-rich freshwater wetlands,with special reference to fenlands

A survey of base-rich wetlands in The Netherlands is presented. The main area of their occurrence is the low-lying Holocene part of the country, until some thousand years ago a large and coherent wetland landscape: the Holland wetland. The development of various parts of the Holland wetland into marshes, fens and bogs can be understood from hydrological relations in mire basins, as recognized in the distinction of primary, secondary and tertiary mire basin stages. Presently, the remnants of the Holland wetland are separate base-rich wetlands. The succession of their vegetation reflects various abiotic conditions and human influences. Three main developmental periods are distinguished as regards these factors. The first, geological period of mire development is seen as a post-glacial relaxation, with the inertia due to the considerable mass of wetland as a stabilizing factor. Biological “grazing” influences, as an aspect of utilization by humans, converted base-rich wetlands to whole new types in the second, historical period. Presently, mass and harvesting have decreased in importance, and actual successions in terrestrializing turbaries seem to reflect rapidly changing environmental conditions. Human control could well become the most important factor in the future development of wetland nature. The present value of open fen vegetation strongly depends on the continuation of the historical harvesting. The development of wooded fen may help to increase the mass of wetland in the future. Best results in terms of biodiversity are expected when their base state is maintained through water management. The vegetation and hydrology of floating fens in terrestrializing turbaries is treated in some more detail. Various lines and phases in the succession are distinguished. Open fen vegetation at base-rich, yet nutrient-poor sites is very rich in species threatened elsewhere. The fast acidification of certain such fens is attributed to hydrological and management factors. This acidification is illustrated in the profile of a floating raft sample. At the scale of these small fens, the elemental structure comprising base-rich fen, transitional fen and bog vegetation, is not as stable as it was in the large Holland wetland. A critical role seems to be played by the supply of bases with the water influx. The changing base state is supposed to change the nutrient cycling to such an extent that it would be correct to call this trophic excitation of the ecosystem, rather than just eutrophication. Eutrophication indicates a quantitative reaction to an increased nutrient supply, the internal system being unaltered. The drainage of fens, resulting in an increased productivity of the vegetation, provides another example of excitation, to the effect that the functional system is dramatically changed internally.     

Variable generation times and Darwinian fitness measures

Summary Reproductive value (RV) and net reproductive output (R _o) are frequently used fitness measures. We argue that they are only appropriate when intervals between reproductive events are fixed, as they are dimensionless generation-to-generation scalings with units offspring per parent. A fitness measure should account for two different effects of a decrease in generation time: (1) increased survival due to shorter exposure to mortality agents and (2) increased frequency of reproduction.R _o andRV deal with the first of these two effects, while a measure with a physical dimensionper time [T^–1] is needed to account for the second. The Malthusian growth parameter,r, meets this requirement and in situations where time to reproduction is variable, we propose, the instantaneous rate of spread of descendants (from an individual) be used instead ofR _o. As an alternative toRV, we suggest using the instantaneous difference = –r, wherer is the population rate of increase. WhileRV andR _o are dimensionless ratios, , and areper time rates which are appropriate in accounting for alterations in generation time.     

The ecosystem wilting point defines drought response and recovery of a Quercus-Carya forest

Soil and atmospheric droughts increasingly threaten plant survival and productivity around the world. Yet, conceptual gaps constrain our ability to predict ecosystem-scale drought impacts under climate change. Here, we introduce the ecosystem wilting point (Ψ_EWP), a property that integrates the drought response of an ecosystem's plant community across the soil–plant–atmosphere continuum. Specifically, Ψ_EWP defines a threshold below which the capacity of the root system to extract soil water and the ability of the leaves to maintain stomatal function are strongly diminished. We combined ecosystem flux and leaf water potential measurements to derive the Ψ_EWP of a Quercus-Carya forest from an “ecosystem pressure–volume (PV) curve,” which is analogous to the tissue-level technique. When community predawn leaf water potential (Ψ_pd) was above Ψ_EWP (=−2.0 MPa), the forest was highly responsive to environmental dynamics. When Ψ_pd fell below Ψ_EWP, the forest became insensitive to environmental variation and was a net source of carbon dioxide for nearly 2 months. Thus, Ψ_EWP is a threshold defining marked shifts in ecosystem functional state. Though there was rainfall-induced recovery of ecosystem gas exchange following soaking rains, a legacy of structural and physiological damage inhibited canopy photosynthetic capacity. Although over 16 growing seasons, only 10% of Ψ_pd observations fell below Ψ_EWP, the forest is commonly only 2–4 weeks of intense drought away from reaching Ψ_EWP, and thus highly reliant on frequent rainfall to replenish the soil water supply. We propose, based on a bottom-up analysis of root density profiles and soil moisture characteristic curves, that soil water acquisition capacity is the major determinant of Ψ_EWP, and species in an ecosystem require compatible leaf-level traits such as turgor loss point so that leaf wilting is coordinated with the inability to extract further water from the soil.     

Ranking species based on sensitivity to perturbations under non-equilibrium community dynamics

Managing ecological communities requires fast detection of species that are sensitive to perturbations. Yet, the focus on recovery to equilibrium has prevented us from assessing species responses to perturbations when abundances fluctuate over time. Here, we introduce two data-driven approaches (expected sensitivity and eigenvector rankings) based on the time-varying Jacobian matrix to rank species over time according to their sensitivity to perturbations on abundances. Using several population dynamics models, we demonstrate that we can infer these rankings from time-series data to predict the order of species sensitivities. We find that the most sensitive species are not always the ones with the most rapidly changing or lowest abundance, which are typical criteria used to monitor populations. Finally, using two empirical time series, we show that sensitive species tend to be harder to forecast. Our results suggest that incorporating information on species interactions can improve how we manage communities out of equilibrium.     

Hydrodynamics in early animal evolution

Choanoflagellates and sponges feed by filtering microscopic particles from water currents created by the flagella of microvillar collar complexes situated on the cell bodies of the solitary or colonial choanoflagellates and on the choanocytes in sponges. The filtering mechanism has been known for more than a century, but only recently has the filtering process been studied in detail and also modelled, so that a detailed picture of the water currents has been obtained. In the solitary and most of the colonial choanoflagellates, the water flows freely around the cells, but in some forms, the cells are arranged in an open meshwork through which the water can be pumped. In the sponges, the choanocytes are located in choanocyte chambers (or choanocyte areas) with separate incurrent and excurrent canals/pores located in a larger body, which enables a fixed pattern of water currents through the collar complexes. Previous theories for the origin of sponges show evolutionary stages with choanocyte chambers without any opening or with only one opening, which makes separation of incurrent and excurrent impossible, and such stages must have been unable to feed. Therefore a new theory is proposed, which shows a continuous evolutionary lineage in which all stages are able to feed by means of the collar complexes.