Consequences of defaunation for a tropical tree community

Hunting affects a considerably greater area of the tropical forest biome than deforestation and logging combined. Often even large remote protected areas are depleted of a substantial proportion of their vertebrate fauna. However, understanding of the long‐term ecological consequences of defaunation in tropical forests remains poor. Using tree census data from a large‐scale plot monitored over a 15‐year period since the approximate onset of intense hunting, we provide a comprehensive assessment of the immediate consequences of defaunation for a tropical tree community. Our data strongly suggest that over‐hunting has engendered pervasive changes in tree population spatial structure and dynamics, leading to a consistent decline in local tree diversity over time. However, we do not find any support for suggestions that over‐hunting reduces above‐ground biomass or biomass accumulation rate in this forest. To maintain critical ecosystem processes in tropical forests increased efforts are required to protect and restore wildlife populations.     

The binding of lipopolysaccharide from Escherichia coli to mammalian cell membranes and its effect on liposomes

The kinetics of the absorption of ³²P- or ¹⁴C-labelled lipopolysaccharide from Escherichia coli NCTC 8623, serotype 0 125, chemotype XII, to erythrocytes, leukocytes, peritoneal macrophages and peritoneal lymphocytes was examined. Under variable conditions maximal levels of binding were found due to saturation of receptor sites on the cell membrane or steric hindrance by bound lipopolysaccharide. During adsorption slight leakage of haemoglobin was found but complete lysis of erythrocytes was ruled out after noting the effect of lipopolysaccharide on artificial lipid bilayers.The affinity of lipopolysaccharide to cell membranes revealed a consistent pattern of cyclic fluctuation between adsorption and desorption. A model was proposed to explain this cyclic fluctuation in binding based on membrane reorganization. It was significant that the cycle of lipopolysaccharide adsorption-desorption proceeded to completion even if the process was interrupted. The indication was that, once triggered, membrane reorganization occurred independently without influence from the test environment.     

An analysis of the association of collagen based on structural models.

The existence and distribution of vertical, interacting edges on cylindrical surfaces, which were derived from the basic structural features of the collagen molecule, have been examined as a function of the angle θ of the superhelix. Over the range θ = 26°–33° and near θ = 36°, the strongest intermolecular association was detected at 29.95°. This model exhibited three similar, self-interacting edges, separated by approximately 120°. The potential for three similar but nonidentical edges lies in the geometry of the collagen molecule, but the existence of such edges and their ability to self-associate is dependent upon the unique amino acid sequence. The relative strengths of association of each edge with itself and with the other edges are not identical, but the present analysis does not permit a judgment as to whether this variation could result in functional specificity in such interactions. All three chains participate in each edge though their contribution to the relative interaction strength is not identical. These edges showed distinct maxima when displaced past one another by integral intervals of D, where D = 233 residue positions (quarter-stagger). The strongest relative interaction occurs at a displacement of 1D.     

Factors affecting the colonisation of a root system by fluorescent Pseudomonads: The effects of water,temperature and soil microflora

The colonisation of a radish root system by strains ofPseudomonas fluorescens, selected for their ability to promote potato and radish growth under different environmental conditions is reported. In pot experiments colonisation of different parts of the root system was measured at different temperatures, in different watering regimes and in sterile and recropped soil. Root colonisation was extensive but populations were highest on the upper root system and their distribution throughout the root system was greatly affected by environmental factors. percolation of water through the soil and partial soil sterilisation enhanced colonisation but the effects of temperature and recropping were complex. Growth promotion was unpredictable and there was no simple relationship between PGPR colonisation and stimulation of plant growth.