Ecosystem function and species loss – a microcosm study

There are too many kinds of organisms to be able to study and manage each, yet the loss of a single species can sometimes unravel an ecosystem. Such `fusewire species'– critical in the same sense that an electrical fuse can cut out a whole circuit – would be a rewarding focus for research and management effort. However, this approach can only be effective if these `fusewires' represent but a small proportion of the number of species in the system.  

Aim

To demonstrate methods for measuring what proportion of the species in a system are critical to ecosystem function.  

Methods

The prevalence of fusewire species was measured in manipulative experiments on an aquatic microcosm.  

Results

No single genus deletion caused changes in key characteristics of the system.  

Main conclusions

Comparison of these results with other published studies shows that the proportion of critical fusewire species varies amongst different ecosystems. The oxidation pond microcosms were shown to contain no single species indispensable to system function. They appear to be ill-suited to a management strategy which focuses on priority eukaryote species. However, a single study provides no evidence that this result is general or even typical of other kinds of ecosystems; it is presented here as an empirical model. Other methods of investigation are available; they are less experimentally rigorous but more practical. These could provide important guidance in planning an approach to management in a particular ecosystem.     

Distribution of Adult Male and Female Baccharis concinna (Asteraceae) in the Rupestrian Fields of Serra Do Cipó, Brazil

Abstract: This study focuses on the sex ratio and spatial distribution of males and females in three populations of the endemic and restricted tropical dioecious shrub, Baccharis concinna (Asteraceae) in the mountainous region of Serra do Cipó, southeastern Brazil. The proportion of female plants in the population at lower elevation (1000 m a.s.l.) was significantly greater than of male plants. At this elevation of P/N and Ca/Al ratios in the soil were also greater indicating better nutritional status of the soils. The concentration of aluminium increased significantly with the elevation ( p < 0.001), perhaps rendering soils less conducive to female plants at higher elevations. Female plants are possibly adversely affected to a greater extent by soil quality than male plants. The spatial distribution of the populations within habitat was tested by the K(t) function, where the neighbourhood of a given individual was defined by a circle with a radius (t) up to 3 m. Despite the strong tendency for aggregation, the distribution of the sexes within habitats was random and the hypothesis was not supported. The independent distribution of the sexes within habitats may be explained by nutrient homogeneity of the soils, as well as by an absence of antagonism between the sexes. Nevertheless, we found a trend for males and females to be aggregated according to their gender.     

Bacterial ecology, antibiotics and selection for virulence

The evolution of antibiotic resistance in bacteria is well known. Here I describe possible mechanisms by which an increased rate of re-colonization of vertebrate guts by microbes caused by antibiotic use could lead to selection for increased virulence in currently mutualistic or benign microbes. The importance of understanding both the source and the frequency of colonization in such mutualisms is stressed and the possible importance of pseudo-vertical transmission in the evolution of these systems is discussed. A number of areas requiring experimental investigation are identified.     

Bayesian Estimation of the Distribution Function of the Poisson Model

This paper presents the Bayes estimators of the Poisson distribution function based on complete and truncated data under a natural conjugate prior. Laplace transform of the incomplete gamma function and the Gauss hypergeometric function have been employed in order to overcome the intractability of the integrals. Numerical examples from biosciences are given to illustrate the results. A Monte Carlo study has been carried out to compare Bayes estimators under complete data with the corresponding maximum liklihood estimators.     

Developmental studies on the loricate choanoflagellateStephanoeca diplocostata Ellis. V. The cytoskeleton and the effects of microtubule poisons

Summary InStephanoeca diplocostata microtubules are located in four positions namely: within the flagellar axoneme; just beneath the plasmalemma; associated with the silica deposition vesicles (SDVs) during early stages of costal strip deposition; and in the mitotic spindle. At the anterior end of the cell the 50–60 peripheral microtubules, which are organized more or less parallel to the long axis of the cell, converge around the base of the emergent flagellum. A short second flagellar base is positioned between the nucleus and the base of the emergent flagellum. Developing costal strips are located individually within SDVs in the peripheral cytoplasm. During the early stages of silica deposition each SDV is curved and subtended longitudinally on its concave side by two microtubules. When a costal strip has achieved sufficient rigidity to withstand bending the SDV-associated microtubules are depolymerized. Treatment of exponentially growing cells with sublethal concentrations of microtubule poisons, such as colchicine, podophyllotoxin, griseofulvin andVinca alkaloids depresses growth. Treatment with these drugs also affects the length and morphology of developing costal strips perhaps by interfering with the shaping and supporting functions of SDV-associated microtubules. Instead of being long and crescentic with a standard radius of curvature, costal strips of treated cells are usually short and misshapen, with irregular bends. After drug treatment, juveniles produced as a result of cell division do not develop flagella but can still assemble a lorica although it is usually misshapen. The role of microtubules and microfilaments in lorica production is discussed.     

Response of Soybean to Heterodera glycines Races 1 and 2 in Different Soil Types

Experiments were conducted for 3 years at four locations and 1 year with six soil types at a common location in North Carolina to determine damage and control-cost functions for Heterodera glycines races 1 and 2 on soybean. In the experiments on native loamy sand and sandy soils, tolerance limits for initial population densities were 0 or very low, whereas in a muck, the tolerance limit was 315 eggs/500 cm³ soil. The aggressive race 2 was more damaging than race 1 in Lakeland sand and Norfolk loamy sand. The crop response was not different between races in the Appling sandy clay loam and Belhaven muck. Soybean yield responses to H. glycines were linear in six soil types in microplots at a common site. The amount of damage varied among these soil types, with lowest yields in the muck because of severe drought stress in this soil. An exponential function adequately described soybean yield response relative to nematode control with increasing rates of aldicarb in Norfolk loamy sand. Treatment with aldicarb in the Lakeland sand decreased the effective egg population of H. glycines but had only a minor effect in the muck.     

Comparative gastrointestinal morphology of the Kori bustard and secretary bird

Two secretary birds and three Kori bustards were studied to determine differences between their body size and gastrointestinal morphology. Body measurements were made on captive, live birds and gastrointestinal measurements on fresh postmortem specimens. For predator species, such as the Kori bustard and secretary bird, body size is a function of their ability to capture and destroy prey. While the secretary bird was clearly the taller of the two species, superior body weight, wing length, and therefore body size was noted for the Kori bustard. The size and length of the gastrointestinal tract varied between species. The secretary bird had the shorter, less complex digestive tract, with a foregut well adapted for consumption of large quantities of flesh. The large intestine was devoid of ceca. The gastrointestinal tract of the Kori bustard was markedly different from that of the secretary bird. The foregut was less complex and the large intestine possessed large, voluminous ceca.     

Involvement in DNA repair of the ruvA gene of Escherichia coli

Summary The ruv operon of Escherichia coli consists of two genes, orfl1 and ruv, which encode 22 and 37 kilodalton proteins, respectively, and are regulated by the SOS system. Although the distal gene, ruv, is known to be involved in DNA repair, the function of orf1 has not been studied. To examine whether orf1 is also involved in DNA repair, we constructed a strain with a deletion of the entire ruv operon. The strain was sensitive to UV even after introduction of low copy number plasmids carrying either orf1 or ruv, but UV resistance was restored by introduction of a plasmid carrying both orfl and ruv. These results suggest that orf1 as well as ruv is involved in DNA repair. Therefore, orf1 and ruv should be renamed ruvA and ruvB, respectively.