Abstract: Summary This study examines spatial and temporal variation in the forest structure of the Kibale National Park, Uganda by contrasting tree density, tree size, and forest composition among four areas each separated by less than 15 km, and by quantifying changes in the composition of one of these forests over a 20-year period Densities of some tree species diVered markedly between sites, and some species common at one location were absent at others Monthly phenological monitoring demonstrated that it was not uncommon for phenological patterns to diVer between the forests To examine temporal variation in the tree composition over a 20-year period, a sampling regime that was carried out in the early 1970s was replicated on the floristic composition of one of these sites, using identical methods in the same sampling areas While no form of human intervention occurred in this area between the early 1970s and 1992, there were marked changes in the densities of some tree species Twenty-seven percent of the identified species increased in abundance, 33% decreased, and 40% remained relatively unchanged The observed spatial and temporal variation in forest composition could be the result of abiotic factors, such as altitude or rainfall, or biotic factors such as elephant and/or human influences on ecosystem dynamics; the implications of this variation for frugivores are discussed

Abstract: The two main biotic factors affecting grassland plant species are herbivory and competition. We investigated the significance of both these factors in establishing grassland communities through manipulation experiments conducted in both winter and summer in glasshouse conditions. Manipulations consisted of addition of above-ground and below-ground herbivores, reduction of herbivory through use of an insecticide, and varying of competitive pressure by removing either dicotyledonous or monocotyledonous seedlings as they appeared. In the winter experiment, the total biomass of dicotyledonous plants was reduced by both above-ground and below-ground herbivory, while monocotyledonous plant biomass was unaffected. However, in the summer experiment, only those treatments in which competition was manipulated had any detectable effect. This suggests that the relative importance of competition and herbivory can vary considerably. The above-ground herbivory treatment sometimes stimulated and sometimes reduced plant species diversity, and sometimes also induced significantly higher dicotyledonous species diversity than the root herbivory treatment. Those treatments in which competitive pressure was manipulated had no detectable effects on diversity. There were many strong effects detected when plant species were considered individually, with different species responding to different treatments, and with all treatments affecting at least some species. Different species therefore respond quite differently to competition and herbivory. None of the treatments affected soil microbial activity or active soil microbial biomass in the winter experiment, although active biomass was significantly positively correlated with dicotyledonous plant biomass. In the summer experiment, soil activity was positively affected by monocotyledonous plants, while active biomass was the same in all treatments except for the treatment with all plants removed, where biomass was less. None of the soil biotic variables showed any relationship with plant species richness. Our study shows that competition and herbivory can both exert important influences at both the community and ecosystem levels of resolution.

Abstract: 1. We studied the life history responses of Daphnia pulex under different biotic conditions. In a factorially designed experiment, we tested the impacts of water conditioned by the invertebrate predator Chaoborus, low and high food level (10 000 and 100 000 Scenedesmus cells ml–1), and exposure to toxic Microcystis (5000 cells ml–1) on twelve D. pulex clones originating from different habitats. Our aim was to compare the phenotypic plasticity of different clones, and to study the interactions among biotic factors. 2. Individuals cultured in Chaoborus-conditioned water started to reproduce at a larger size than individuals cultured in water not conditioned by the predators. We found interactions between food level and Chaoborus-conditioned water on age at first reproduction and total offspring number. In addition, the impact of the Chaoborus treatment on the size at first reproduction was reduced by Microcystis exposure. 3. Clonal differences were found in the degree of phenotypic plasticity of different life history traits. However, there was no obvious connection between the original habitat of the clone and the degree of plasticity.

Abstract: 226 Ra for the biotic components ranged from ~ 10 1 to ~ 10 3 . The significance of 226 Ra activity in the abiotic and biotic components of Cauvery river are discussed.

Abstract: The Fallingsnow Ecosystem Project documents the ecological consequences of alternative conifer release treatments (motor-manual [clearing/brush saw], mechanical [Silvana Selective/Ford Versatile tractor], helicopter-applied herbicides Vision® [a.i. glyphosate], Release® [a.i. triclopyr], and control [no treatment] in young spruce (Picea spp.) plantations. Here a series of papers that quantify the effects of these alternative treatments on major environmental components, as well as their production rates and costs is introduced. In general, one growing season after treatment, untreated plots tended to have consistently larger, more diverse populations of the biotic components examined. Biotic and abiotic changes caused by the cutting treatments were more similar to each other than to those resulting from the herbicide treatments, but statistical differences among treatments were few. Herbicide treatments were the most productive and least costly, and about 60% of the active ingredient was deposited on the ...

Abstract: Plants defend themselves against herbivores directly in various ways. They may do so chemically by producing toxins, digestibility reducers, repellents, etc., or physically by constructing a hard structure or spines, secreting viscous materials, etc. (Schoonhoven 1981; Bernays and Chapman 1994). In addition to these various direct defenses, plants may defend themselves indirectly by promoting the effectiveness of the natural enemies of herbivores (Price et al. 1980).

Abstract: In northern boreal forests ground level species occur which may have the capacity to suppress tree seedling regeneration substantially, particularly in late successional stages. We investigated, through an experiment involving sequential manipulations, the effects of three biotic components operating at the ground layer, i.e. aboveground effects of the ericaceous shrub Empetrum hermaphroditum and of the feathermoss species Pleurozium schreberi and the below-ground effects of extramatrical mycorrhizal hyphae, on the seedling establishment, growth and nutrient acquisition of Pinus sylvestris during two growing seasons. Germination and seedling establishment of P. sylvestris were enhanced by reduction of the above ground components of E. hermaphroditum and P. schreberi but were not influenced by temporary disruption of mycorrhizal hyphae. Seedling growth and nitrogen content were, however, significantly increased when hyphal connections were disrupted and above ground influence of P. schreberi and E. hermaphroditum were reduced. Higher shoot:root ratios were also found in seedlings when hyphal connections were disrupted. Seedlings in treatments where P. schreberi was left intact and above ground interference by E. hermaphroditum was reduced had unusually low shoot:root ratios (1.6) after two growing seasons and significantly lower total amounts of nutrients after one growing season than were initially present in the seeds, indicative of a net nutrient drain during the early establishment phase. The experiment could not explain the mechanisms behind this unexpected nutrient drain. Possible rhizosphere interactions immobilizing nutrients and causing seedling nutrient losses are discussed. From the results of this study and other indirect evidence we hypothesize that the three biotic components we investigated could act together to immobilize nutrients and to inhibit tree seedling regeneration and growth in late successional stages of boreal forests.

Abstract: From May to September in 1990 and 1991, 24 coastal wetland and beach sites in Green Bay, Lake Michigan, were sampled to investigate abiotic and biotic factors influencing fish assemblages; half the sites were modified by human developments, and half were relatively undeveloped. The greatest assemblage differences were observed among regions, but there also were strong differences among assemblages from different habitats. Degree of development had less of an effect on site differences, although assemblages at undeveloped wetlands were unique, and those from developed and undeveloped sites in the upper bay were relatively distinct. The most influential abiotic factors were turbidity, reflecting the trophic gradient in the bay, and a suite of variables associated with macrophyte coverage and diversity, which were critical components of nursery habitats for the primarily immature fishes we captured. The volatile and unpredictable nature of shoreline habitats in the Great Lakes apparently precluded competitio...

Abstract: This paper presents the results of an investigation on the distribution of210Po in Mutharasanallur pond ecosystem. It has been demonstrated that210Po is non-uniformly distributed within the ecosystem. The results of the study show a dissolved210Po concentration in pond water of 1 4mBq 1−1. The sediment samplso recorded a210Po activity of 59 9 Bq kg−1. The aquatic organisms showed differential accumulation of the radionuclide with enhanced bioaccumulation in soft tissues and muscle. The210Po activity in the biota fell within the range of 1·2–53 3 Bq kg−1 (wet wt). The bivalve mussel,Lamellidens marginalis was identified to accumulate higher concentration of210Poin soft tissues, suggesting that these organisms could serve as a bio-monitor of210Po radionuclide in a freshwater system. The concentration factors of210Po for the biotic components ranged from ∼102–∼104. Analyses of the results indicate that prawn and fish represent an important source of supply of210Po to humans via dietary intake. Results of210Po activity in the abiotic and biotic components of the pond ecosystem were higher when compared with those of Cauvery river system, the primary water source of the pond.