Biotic filtering and mass effects in small shrub patches: is arthropod community structure predictable based on the quality of the vegetation?

1. Community assembly is affected by four processes: dispersal, filtering effects (selection), ecological drift and evolution. The role of filtering relative to dispersal and drift should decline with patch size, hampering possibilities to predict which organisms will be observed within small‐sized patches. However, vegetation structure is known to have a marked impact on species assemblages, and plant quality may act as a biotic filter. This challenges the assumption of unpredictable species assemblages in small‐sized vegetation patches. 2. Using 32 stands of five shrub species in south‐west Finland, this study investigated whether biotic filtering effects caused by patch‐forming plants are strong enough to overcome the mixing of mobile arthropod assemblages across small patches. 3. Stochastic variation did not hide the signals of biotic filtering and dispersal in the small shrub patches. Habitat richness around the patches explained a three times larger share of variation in the species composition than did the identity of the patch‐forming plant, but it had less effect on the abundance of arthropods. A radius of 50–100 m around a patch explained the species composition best. 4. Abundance patterns varied between the feeding guilds; the patch‐forming shrub influenced the abundances of detritivores and leaf‐feeding herbivores, whereas the abundances of flower‐visiting herbivores appeared to track the flowering phenology of the plants. Shrub identity had little effect on omnivores or predators. Predator abundances were correlated with the abundance of potential prey. 5. The results of this study suggest that community composition within a vegetation patch may be predictable even if dispersal overrides local filtering effects, as suggested by the mass‐effects paradigm.     

Visual responses of flying aphids and their chemical modification

Abstract. Five winged forms of the black bean aphid, Aphis fabae, were subjected to 30 min of free flight in a recently designed, automated wind tunnel (David & Hardie, 1988). A circular green target, on the side of the chamber, was illuminated for 2.5 s of each minute of flight. Half of the fundatrigeniae ('spring migrants') and all of the virginoparous 'summer migrants' responded by flying towards the illuminated target while gynoparae ('autumn migrants') induced by short days over two generations in uncrowded conditions were unresponsive. 27% of generation 1 gynoparae, induced by crowded conditions and short days over one generation, responded to the target as did 50% of males.
Anaesthetization of adult gynoparae with nitrogen and carbon dioxide, but not ether, induced targeted flights. However, the effect of carbon dioxide was transient over the first 10 min whereas the effect of nitrogen continued throughout the 30-min experimental period. In addition, treatment of late fourth instar larvae, but not young adults, with Juvenile Hormone I provoked target responses. The results are discussed with reference to settling behaviour and the endocrine control of polyphenism.     

INTER‐ETHICS: TOWARDS AN INTERACTIVE AND INTERDEPENDENT BIOETHICS

Since its origin bioethics has been a specialized, academic discipline, focussing on moral issues, using a vast set of globalized principles and rational techniques to evaluate and guide healthcare practices. With the emergence of a plural society, the loss of faith in experts and authorities and the decline of overarching grand narratives and shared moralities, a new approach to bioethics is needed. This approach implies a shift from an external critique of practices towards embedded ethics and interactive practice improvement, and from a legal defence of rights towards fostering interdependent practices of responsibility. This article describes these transitions within bioethics in relation to the broader societal and cultural dynamics within Western societies, and traces the implications for the methodologies and changing roles of the bioethicist. The bioethicist we foresee is not just a clever expert but also a relationally sensitive person who engages stakeholders in reciprocal dialogues about their practice of responsibility and helps to integrate various sorts of knowledge (embodied, experiential, visual, and cognitive‐scientific). In order to illustrate this new approach, we present a case study. It concerns a project focusing on an innovation in elderly care, based on the participation of various stakeholders, especially older people themselves.     

Assessment of female gamete quality in the Pacific oyster Crassostrea gigas

Summary

The possible relationship between certain oocyte and embryo characteristics and larvae viability was investigated with reference to the following aspects: (1) morphological—oocyte diameter and shape; (2) cytological—overall ultrastructure and membrane integrity; (3) biochemical—content of lipids, proteins and carbohydrates; and (4) physiological—respiration. The rate of survival and incidence of abnormality were estimated 24 h after fertilization. The first results showed that 80–90% of oocytes were cytologically viable before fertilization. Eighty to 90% of oocytes are apparently viable before fertilization on the basis of staining with Trypan blue, but this parameter shows little correlation with larval viability. However, Trypan blue staining is of value in allowing the recognition of oocytes with damaged membranes. Respiration was measured for unfertilized oocytes 5 min after stripping, after 6 h, and for 3-h embryos. Positive correlations were found between the O₂-consumption of embryos and both the rate of fertilization and the hatching rate of 24-h larvae. In contrast, no correlation was found between hatching parameters and the O₂-consumption of unfertilized oocytes. These results suggest that embryos possess quality indicators, relating to metabolic characteristics, which can be quantified more easily than those of oocytes.     

Studies of Membrane Formation in Tetrahymena pyriformis. VIII. On the Origin of Membranes Surrounding Food Vacuoles*†

SYNOPSIS. A procedure was devised for the isolation of purified food vacuoles from Tetrahymena pyriformis fed particles of ferric oxide. Phospholipids extracted from vacuolar membranes were more similar in composition to the lipids of microsomes than to lipids of whole cells, cilia or post-microsomal supernatant. Fractionation of cells grown in the presence of [¹⁴C]palmitic acid or [³²P]inorganic phosphate also revealed similarities in the specific radioactivities of microsomes and vacuolar membranes. The data suggested that vacuolar membranes arise from a pool of cytoplasmic membranes.     

Growth responses of African savanna trees implicate atmospheric [CO2] as a driver of past and current changes in savanna tree cover

Atmospheric CO₂ has more than doubled since the last glacial maximum (LGM) and could double again within this century, largely due to anthropogenic activity. It has been suggested that low [CO₂] contributed to reduced tree cover in savanna and grassland biomes at LGM, and that increasing [CO₂] over the last century promoted increases in woody plants in these ecosystems over the past few decades. Despite the implications of this idea for understanding global carbon cycle dynamics and key global role of the savanna biome, there are still very few experimental studies quantifying the effects of CO₂ on tree growth and demography in savannas and grasslands. In this paper we present photosynthetic, growth and carbon allocation responses of African savanna trees (Acacia karroo and Acacia nilotica) and a C₄ grass, Themeda triandra, exposed to a gradient of CO₂ concentrations from 180 (typical of LGM) to 1000 µmol mol^?1 in open‐top chambers in a glasshouse as a first empirical test of this idea. Photosynthesis, total stem length, total stem diameter, shoot dry weight and root dry weight of the acacias increased significantly across the CO₂ gradient, saturating at higher CO₂ concentrations. After clipping to simulate fire, plants showed an even greater response in total stem length, total stem diameter and shoot dry weight, signalling the importance of re‐sprouting following disturbances such as fire or herbivory in savanna systems. Root starch (per unit root mass and total root starch per plant) increased steeply along the CO₂ gradient, explaining the re‐sprouting response. In contrast to the strong response of tree seedlings to the CO₂ gradient, grass productivity showed little variation, even at low CO₂ concentrations. These results suggest that CO₂ has significant direct effects on tree recruitment in grassy ecosystems, influencing the ability of trees to recover from fire damage and herbivory. Fire and herbivore regimes that were effective in controlling tree increases in grassy ecosystems could thus be much less effective in a CO₂‐rich world, but field‐based tests are needed to confirm this suggestion.     

Inter-Strain Variability of Insertion/Deletion Events in the Encephalitozoon cuniculi Genome: A Comparative KARD-PFGE Analysis

ABSTRACT. We applied a two-dimensional pulsed-field gel electrophoresis procedure to the genomes of two karyotype variants assigned to two different strains of the microsporidian Encephalitozoon cuniculi , termed D (strain III) and F (strain II). Data obtained for Bss HII and Mlul restriction fragment length polymorphisms in each chromosome are compiled and compared to the reference strain I variant A. Six Insertion/Deletion (InDels) are found in subterminal position, some of these being characteristic of either D or F. Like in strain I, the terminal fragments extending between each telomere and rDNA locus are conserved in length for each chromosome. They are however smaller than in reference variant. This size reduction is estimated to be 2.5 kbp for the strain III isolate and 3.5 kbp for the strain II isolate. We hypothesize that for the three E. cuniculi strains, all chromosome extremities are prone to a constant process of sequence homogenization through mitolic recombination between conserved regions.