961 resultados para Humid Tropics


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Mode of access: Internet.

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Mode of access: Internet.

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LC copy replaced by microfilm.

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Mode of access: Internet.

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Prepared in cooperation with Ohio Agricultural Research and Development Center.

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Includes bibliographical references (p. 126-129) and index.

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"This study has been made with the cooperation of the Secretariat of the Institute of Pacific relations and constitutes a report in its International research series."

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The landscape of the Australian Wet Tropics can be described as islands of montane rainforest Surrounded by warmer or more xeric habitats. Historical glaciation cycles have caused expansion and contraction of these rainforest islands leading to consistent patterns of genetic divergence within species of vertebrates. To explore whether this dynamic history has promoted speciation in endemic and diverse groups Of insects, we used a combination of mtDNA sequencing and morphological characters to estimate relationships and the tempo of divergence among Australian representatives of the dung beetle genus Temnoplectron. This phylogenetic hypothesis shares a number of well-supported clades with a previously published phylogenetic hypothesis based on morphological data. though statistical support for several nodes is weak. Sister species relationships well-supported in both tree topologies. and a tree obtained by combining the two data sets. suggest that speciation has mostly been allopatric. We identify a number of speciation barriers, which coincide with phylogeographic breaks found in vertebrate species. Large sequence divergences between species emphasize that speciation events are ancient (pre-Pleistocene). The flightless, rainforest species appear to have speciated rapidly. but also in the distant past. (C) 2003 Elsevier Inc. All rights reserved.

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In order to investigate population history and demography in skinks endemic to the wet tropics of Australia, multiple nuclear DNA markers were sought. The utility of 72 primers (including 63 published intron-spanning 'CATS' primers) was tested.. Seven loci were characterized and shown to be single copy by single-strand conformation polymorphism analysis. Primers to five nuclear loci were developed, four with utility in skinks and three with utility in frogs. These observations extend the available information on intron-spanning primers for amphibians and reptiles.

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Effects of water stress duration and intensity on gas exchange and leaf water potential were investigated in 7-month-old seedlings of a humid coastal provenance (Gympie) and a dry inland (Hungry Hills) provenance of E. cloeziana F. Muell. and in a dry inland (Chinchilla) provenance of E. argophloia Blakely supplied with 100% (T-100), 70% (T-70), 50% (T-50) of their water requirements, or were watered only after they were wilted at dawn (T-0). Seedlings of E. argophloia had the highest midday net photosynthetic rate (A), stomata] conductance (g(s)), stomatal density and predawn leaf water potential (Psi(pd)) in all treatments. The E. cloeziana provenances did not differ in these attributes. The T-70 and T-50 treatments caused reductions in A of 30% in E. argophloia, and 55% in the E. cloeziana provenances. Under the T-0 treatment, E. argophloia maintained higher rates of gas exchange at all levels of water stress than E. cloeziana provenances. The estimates of Psi(pd) and midday water potential (Psi(md)) at which plants remained wilted overnight were respectively: -2.7 and -4.1 MPa for E. cloeziana (humid), -2.8 and -4.0 MPa for E. cloeziana (dry) and, -3.7 and -4.9 MPa for E. argophloia. Following stress relief, both A and g(s) recovered more quickly in E. argophloia and in the dry provenance of E. cloeziana than in the humid provenance. We conclude that E. argophloia is more drought tolerant and has a potential for cultivation in the humid and semi humid climates, whilst E. cloeziana has greater potential in the humid subtropical climates.

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The proximity of the Great Barrier Reef (GBR) Marine Park to areas of intensive agriculture and increasing urbanisation places the park under potential threat of contamination by land-based pollutants. Passive samplers were deployed at inshore reef and river mouth sites in the Wet Tropics region of the GBR during a dry and a wet season to measure levels of land-based organic pollutants in this environment. Two types of passive sampling devices were deployed: (i) a polar sampler, which can be used to monitor polar herbicides and (ii) semipermeable membrane devices (SPMDs) which sequester more hydrophobic compounds (e.g. PAHs, chlorpyrifos). Herbicides (diuron, simazine, atrazine, hexazinone and/or flumeturon) were detected at low concentrations (ng L-1) at all sites sampled and in both seasons. Chlorpyrifos was not detected while PAHs were present in SPMDs at levels below limits of detection. The results show that the GBR environment does contain low levels of organic pollutants and that passive sampling provides a sensitive monitoring tool for measuring waterborne organic pollutants. (c) 2005 Elsevier Ltd. All rights reserved.

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The concentration of ammonium-nitrogen (NH4+-N) frequently exceeds that of nitrate-N (NO3--N) in Australian wet tropical sugarcane soils. The amount of mineral N in soil is the net result of complex processes in the field, so the objective of this experiment was to investigate nitrification and ammonification in these soils under laboratory conditions. Aerobic and saturated incubations were performed for 1 week on 2 wet tropical soils. Net NO3--N increased significantly in both soils during both types of incubation. A second series of aerobic incubations of these soils treated with NH4+-N and inoculated with subtropical nitrifying soils was conducted for 48 days. Nitrification in the wet tropical soils was not significantly affected by inoculation, and virtually all added N was nitrified during the incubation period. Mineral N behaviour of the 48-day incubations was captured with the APSIM-SoilN model. As nitrification proceeded under laboratory conditions and was able to be captured by the model, it was concluded that nitrification processes in the wet tropical soils studied were not different from those in the subtropical soils. Processes that remove NO3- from the soil, such as leaching and denitrification, may therefore be important factors affecting the proportions of NH4+-N and NO3--N measured under field conditions.