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261.
Control of landscape diversity by catastrophic disturbance: A theory and a case study of fire in a Canadian boreal forest 总被引:3,自引:0,他引:3
A landscape may be envisioned as a space partitioned by a number of ecosystem types, and so it conforms to a neo-Clementsian model of succession. A corollary is that intermediate disturbance rates should maximize landscape (beta) diversity. This was confirmed using eight boreal forest landscapes in northwestern Ontario, Canada, where intermediate rates of forest fire were associated with highest landscape diversity. Because current measures of evenness subsume a richness measure, it is not, as yet, feasible to assess the relative contributions of evenness and richness to biological diversity, and thus it was not possible to determine the roles of numbers of habitat types and relative amounts of habitat types in the above situation. Both theory and observations suggest that forest fire control in fire-prone landscapes increases landscape diversity, but that it is lowered by fire control in landscapes of intermediate to low diversity. 相似文献
262.
Robert L. Edmonds Ted B. Thomas Roger D. Blew 《Journal of the American Water Resources Association》1995,31(3):409-419
ABSTRACT: The biogeochemistry of a coastal old-growth forested watershed in Olympic National Park, Washington, was examined. Objectives were to determine: (1) concentrations of major cations and anions and dissolved organic C (DOC) in precipitation, throughfall, stemflow, soil solution and the stream; (2) nutrient input/output budgets; and (3) nutrient retention mechanisms in the watershed. Stemilow was more acidic (pH 4.0–4.5) than throughfall (pH 5.1) and precipitation (pH 5.3). Organic acids were important contributors to acidity in throughfall and stemflow and tree species influenced pH. Soil solution pH averaged 6.2 at 40 cm depth. Stream pH was higher (7.6). Sodium (54.0 μeq L-1) and Cl (57.6 μeq L?1) were the dominant ions in precipitation, reflecting the close proximity to the ocean. Throughfall and stemflow were generally enriched in cations, especially K. Cation concentrations in soil solutions were generally less than those in stemilow. Ion concentrations increased in the stream. Dominant ions were Ca (759.7 μeq L?1), Na (174.4 μeq L?1), HCO3 (592.0 μeq L?1), and SO4 (331.5 μeq L?1) with seasonal peaks in the fall. Bedrock weathering strongly influenced stream chemistry. Highest average NO3 concentrations were in the stream (5.2 μeq L?1) with seasonal peaks in the fall and lowest concentrations in the growing season. Nitrogen losses were similar to inputs; annual inputs were 4.8 kg/ha (not including fixation) and stream losses were 7.1 kg/ha. Despite the age and successional status of the forest, plant uptake is an important N retention mechanism in this watershed. 相似文献
263.
Roger Reynolds 《The Environmentalist》1983,3(2):131-136
Summary This paper describes some of today's important information handling products and attempts to predict tomorrows devices in the light of convergence and greater flexibility offered through the use of microchip technology.The main contention of this paper is that Information Technology and its impact on privacy depends, as ever, on the way in which Information Systems are used. It is argued that the privacy issue is more to do with moral and physiological attitudes within society than the technicalities of implementation.As a conclusion, the paper asks that we should define standards and exercise vigilance in the maintenance of those standards. In addition, it recognises that attitudes to privacy will almost certainly change with time and that this should be regarded as a healthy and natural occurrence.Roger Reynolds has worked in the computer industry for 18 years and has experience in both hardware design and systems development. He has been employed in ICL for the last 5 years and has been deeply involved with the development of communications and Information Technology within this company.Previously he worked on a project designed to integrate various activities in the health service. This involved the development of computer based systems connected together by telecommunications.This article represents a personal view by Mr Reynolds and it is hoped that it will stimulate further thought and understanding in the development of future technologies. 相似文献
264.
Roger D. Hansen 《Journal of the American Water Resources Association》1983,19(2):263-269
ABSTRACT: Rome is noted for its water and waste water systems which were constructed during ancient times. This paper is a discussion of the impact these systems had on living conditions in the imperial city. Rome's water system provided a constant supply to centrally located areas in contrast to modern systems which deliver water on demand to individual connections. For both water and waste water systems, access points were generally outside the household. Because of this lack of individual connections, Romans were forced to spend much of their time outside their tenements in the baths, latrines, arenas, streets, and shops of the imperial city. 相似文献
265.
266.
Genetic variability among males is a necessary precondition for the evolution of female choice based on indirect genetic benefits.
In addition to mutations and host–parasite cycles, migration of locally adapted individuals offers an explanation for the
maintenance of genetic variability. In a previous study, conducting a reciprocal transplant experiment on a grasshopper, Chorthippus biguttulus, we found that environmental conditions significantly influenced not only body condition but also an important trait of male
calling song, the amplitude of song. Although not significant, all other analysed physical and courtship song traits and attractiveness
were superior in native than in transferred males. Thus, we concluded that local adaptation has a slight but consistent influence
on a range of traits in our study populations, including male acoustic attractiveness. In our present study, we scanned male
grasshoppers from the same two populations for amplification fragment length polymorphism (AFLP) loci connected with acoustic
attractiveness to conspecific females. We found greater differences in allele frequencies between the two populations, for
some loci, than are expected from a balance between drift and gene flow. These loci are potentially connected with locally
adapted traits. We examined whether these alleles show the proposed genotype environment interaction by having different associations
with attractiveness in the two populations. One locus was significantly related to sexual attractiveness; however, this was
independent of the males’ population affiliation. Future research on the evolution of female choice will benefit from knowledge
of the underlying genetic architecture of male traits under intraspecific sexual selection, and the ‘population genomics’
approach can be a powerful tool for revealing this structure. 相似文献
267.
Post‐catastrophe recovery and financial liquidity have long challenged small Caribbean islands. These states are vulnerable to multifarious natural hazards that often cause considerable socioeconomic dislocation. Such events inflict heavy losses on businesses and households, and significantly disrupt all aspects of government operations. After Hurricane Ivan devastated the economies of some islands in September 2004—with estimated losses of as much as 200 per cent of gross domestic product in some cases—regional governments, aided by the World Bank and international donors, approved the creation of a regional catastrophe insurance scheme. This parametric‐based mechanism is underpinned by derivatives‐based catastrophe modelling whose outputs determine policy triggers and pay outs. Hazard models, particularly catastrophe models, are not widely accepted as yet. Despite recent advancements, major concerns have rendered them peripheral tools for many establishments. This paper reviews the region's vulnerabilities and examines constraints on the application of these models and suggests a means of improving their efficacy and acceptability. 相似文献
268.
269.
The catalytic activity of Pd catalysts supported on Ce0.73Tb0.27Ox/SiO2, Ce0.6Zr0.4Ox/SiO2, Ce0.73Tb0.27Ox/La2O3-Al2O3 and Ce0.6Zr0.4Ox/La2O3-Al2O3 was studied using the reduction of NO by CO. The catalysts were characterized by X-ray fluorescence, surface area, X-ray diffraction, temperature-programmed reduction, CO chemisorption and oxygen storage capacity. Temperature-programmed reduction results indicated that Tb or Zr incorporation improves the reducibility and oxygen storage capacity. CO chemisorption data suggested the presence of large PdO particles due to the low CO/Pd ratio. No significant differences were obtained in light off temperatures (TLight off) for all Pd catalysts and the most active was 1.5%Pd/Ce0.6Zr0.4Ox/SiO2. 相似文献
270.
Effects of Landscape Disturbance on Animal Communities in Lake Tanganyika, East Africa 总被引:1,自引:0,他引:1