排序方式： 共有20条查询结果，搜索用时 218 毫秒
1.
A multiple-batch study was conducted using stocker catfish (0.09 kg/fish) and carryover fish (0.39 kg/fish) to look at the effects of different stocker densities on fish production. Twelve 0.1-ha ponds were stocked with 7,400; 11,120; or 14,825 stockers/ha, and equal weights of carryover fish (2,268 kg/ha). Fish were fed once daily to apparent satiation with a 32% protein floating feed and aerated with a single 0.37-kW electric paddlewheel aerator. No significant differences were detected for gross, net, and net daily yields, growth (g/d), or survival. Sub-marketable yield (<0.57 kg) increased as stocking density increased. However, marketable yields (≥0.57 kg) were not affected by density. Carryover fish in high-density ponds had a significantly lower (P < 0.05) mean weight at harvest, but mean stocker weight was not different across densities. Economic analysis found breakeven prices increased and net returns decreased with increased stocking density when sub-marketable fish were not considered as revenue. The study indicated the possibility that stockers compete with large carryover fish, particularly at higher densities. 相似文献
2.
Tropical forests worldwide are undergoing rapid changes due to increasing human populations and varied land use practices. In an effort to protect these forests and their species, the number of protected areas has increased exponentially in recent decades. Clearly protected areas play a crucial role in conservation efforts and this strategy has been found to be successful in several studies. However, protected areas are often embedded within a matrix of other land cover types, including non-protected forests, agricultural fields, or urban areas. It is therefore critical for park management to think beyond the borders of their protected areas and work to maintain ecological integrity of the surrounding matrix and the connectivity between protected areas. This study integrates remote sensing, GIS and field observations to examine the effects of different management strategies on land cover changes. As a case study we examine a tiger reserve in Central India which is surrounded by commercially managed forests, representative of many protected areas throughout India. Findings of this study show that while protected areas play an important role in conservation, alternative approaches including favorable management policies could also be effective to extend conservation over larger areas. 相似文献
3.
The efficacy of a drench containing praziquantel in combination with levamisole was evaluated in four trials performed in the 1990-91 and 1992-93 seasons in the Waikato Region of New Zealand. The trials involved 93 naturally infected lambs and compared the efficacy of a 3.75 mg/kg praziquantel 7.5mg/kg levamisole drench against Moniezia expansa, with albendazole, an albendazole-levamisole combination and oxyclozanide-levamisole combination in controlled trials. There was no significant reduction in the number of Moniezia expansa scoleces or proglottids in the control, albendazole and albendazole-levamisole groups. Oxyclozanide gave a high clearance of proglottids, but a 28% reduction of scoleces. The praziquantel-levamisole combination demonstrated complete removal of segments in all trials, and of scoleces in two trials. One scolex was found in each of the two other trials. The combination was also tested for efficacy against nematode parasites. Total worm counts indicated that levamisole in the praziquantel-levamisole combination drench retained its efficacy. The economic benefits of the use of the praziquantel-levamisole drench were investigated. This trial compared the liveweight gains of three groups of 100 lambs treated twice 4 weeks apart with either levamisole or with the praziquantel-levamisole combination or acting as untreated control group. The group treated with the praziquantel-levamisole combination gained significantly more weight in both 4-week periods and overall, when compared with either the control or levamisole treated animals. 相似文献
4.
Derekas A Kiss LL Borkovits T Huber D Lehmann H Southworth J Bedding TR Balam D Hartmann M Hrudkova M Ireland MJ Kovács J Mezo G Moór A Niemczura E Sarty GE Szabó GM Szabó R Telting JH Tkachenko A Uytterhoeven K Benko JM Bryson ST Maestro V Simon AE Stello D Schaefer G Aerts C ten Brummelaar TA De Cat P McAlister HA Maceroni C Mérand A Still M Sturmann J Sturmann L Turner N Tuthill PG Christensen-Dalsgaard J Gilliland RL Kjeldsen H Quintana EV Tenenbaum P Twicken JD 《Science (New York, N.Y.)》2011,332(6026):216-218
Hierarchical triple systems comprise a close binary and a more distant component. They are important for testing theories of star formation and of stellar evolution in the presence of nearby companions. We obtained 218 days of Kepler photometry of HD 181068 (magnitude of 7.1), supplemented by ground-based spectroscopy and interferometry, which show it to be a hierarchical triple with two types of mutual eclipses. The primary is a red giant that is in a 45-day orbit with a pair of red dwarfs in a close 0.9-day orbit. The red giant shows evidence for tidally induced oscillations that are driven by the orbital motion of the close pair. HD 181068 is an ideal target for studies of dynamical evolution and testing tidal friction theories in hierarchical triple systems. 相似文献
5.
George R. Southworth Stephen E. Herbes Paul J. Franco Jeffrey M. Giddings 《Water, air, and soil pollution》1985,24(3):283-296
The environmental fate of constituent phenols of a coal-derived oil spilled intermittently on water was evaluated in aquatic microcosms. Phenols dissolved rapidly from the oil into the water, and initially accumulated with sequential oil additions. The major process removing phenols from the microcosms was microbial degradation-other processes were negligible in comparison. After phenols attained maximum concentrations in the first 28 days of the study, degradation rates exceeded input rates in all microcosms during the second 28 days the study and total phenol concentrations decreased. Significant differences were apparent in the rates of degradation of various alkylphenol isomers and isomer groups, but no compounds were observed to be refractory. Upon discontinuation of oil inputs at day 56, dissolved phenols disappeared within several weeks. Microcosm exposure history and the presence of other phenol isomers affected the rate of removal of individual isomers, complicating prediction of the rate of removal of individual toxicants. 相似文献
6.
Dwindling resources and fragmentation of landscapes around parks: wetlands and forest patches around Kibale National Park,Uganda 总被引：2，自引：0，他引：2
Landscapes surrounding parks in most of the developing world, while still containing considerable biodiversity, also have
rapidly growing human populations and associated agricultural development. Since the establishment of Kibale National Park
first as a Crown Forest Reserve in 1932 and later as a park in 1993 in western Uganda, most access and resource extraction
has been prohibited. The park has become nearly a complete island of forested land cover surrounded by intensive small-scale
agriculture and some large-scale tea plantations, along with a network of wetland and forest patches. As the population grows
outside the park and land becomes more scarce, remaining forests and wetlands are being used more intensively for material
resources (e.g., fuelwood, building poles) and converted to other land uses (e.g., pasture, agriculture). This study uses
both discrete and continuous data analyses of satellite imagery to examine these diminishing resource bases at the landscape
level placing the results within the social context of conservation and parks. Findings reveal that the park boundaries have
remained fairly intact whereas, the landscape surrounding the park has become increasingly fragmented. From a landscape perspective,
while the park has indeed maintained its forest cover, it has become increasingly islandized with wetland and forest patches
in the surrounding landscape becoming smaller in number and size. Those that have survived are now more isolated and even
lower productivity than in 1984, which may be a precursor to their eventual loss in this landscape. 相似文献
7.
Azaarenes are one of several classes of organic compounds which contain mutagenic and carcinogenic substances that are found in synthetic fuels effluents. This study investigated the potential for a mutagenic azaarene, acridine, to accumulate in freshwater fish (Pimephales promelas) via four possible pathways: (1) direct uptake from water, (2) uptake via interaction with contaminated sediments, (3) uptake via ingestion of contaminated zooplankton (Daphnia pulex), and (4) uptake via ingestion of benthic invertebrates (Chironomus tentans) living in contaminated sediments. The results showed that acridine was rapidly accumulated from water by fathead minnows. Equilibrium concentration was attained within 24 h at a concentration factor ([acridine]fish, wet wt/[acridine]water) of 125±10. Depuration was rapid and appeared to occur in two stages, with a net elimination rate of 0.23 h?1 [acridine]fish at equilibrium. Equilibrium concentration factors of 51±5, 30±2, and 874±275 were observed forChironomus, Daphnia, and sediment, respectively. The calculated rates of uptake of acridine via ingestion of contaminated invertebrates (0.02 μg g?1 h?1) and ingestion of sediment (0.01 μg g?1 h?1) were negligible compared with direct uptake from water (1.40 μg g?1 h?1) in a hypothetical system with all compartments in equilibrium. 相似文献
8.
The sorption of three groups of polar organic compounds capable of H bonding with inorganic soil surfaces (phenols, alcohols, and ketones) by three soils having different organic-carbon (OC) contents was compared with the sorption of nonpolar compounds by the same soils. Soil OC content and compound hydrophobicity were observed to be of value in predicting sorption coefficients for all groups of compounds except phenols. The higher OC soil (1.2% OC) exhibited a significant relationship between sorption coefficient and hydrophobicity for all compound classes; the very low OC soil (0.06% OC), however, exhibited a relatively weak relationship between sorption coefficient and hydrophobicity. The data support the application of hydrophobicity-based predictions of soil/sediment sorption coefficients to compounds capable of weak H-bond interactions with mineral surfaces and soils of ≥0.1% OC. 相似文献
9.
G. R. Southworth 《Water, air, and soil pollution》1990,51(3-4):287-296
Sunfish (Lepomis auritus and L. macrochirus) were used to monitor polychlorinated biphenyl (PCB) contamination in a group of small streams flowing into a larger stream/reservoir system. Mean PCB concentrations in sunfish appeared to reflect exposure conditions at the site of capture. Fish from uncontaminated sites 1 to 2 km distant from PCB-contaminated sites did not exhibit PCB contamination, and PCB concentrations in fish downstream from a discrete source decreased at a rate greater than or equal to downstream dilution of the point source. Mean PCB concentrations in fish near the source exhibited relatively large (-40%) fluctuations between semi-annual sampling periods, suggesting that PCB concentrations in sunfish populations may respond rapidly to changes in exposure. Sunfish were not sensitive enough indicators of contamination to use in assessing whether or not problematic levels of contamination may occur in other species. Although the presence of PCB contamination in sunfish can be used to infer that PCBs are elevated in other species, the absence of PCB contamination in sunfish cannot be used to infer that older, fattier fish higher up the food chain are uncontaminated. 相似文献
10.
Joel?HartterEmail author Sadie?J.?RyanEmail author Jane?Southworth Colin?A.?Chapman 《Landscape Ecology》2011,26(6):877-890
Kibale National Park, within the Albertine Rift, is known for its rich biodiversity. High human population density and agricultural
conversion in the surrounding landscape have created enormous resource pressure on forest fragments outside the park. Kibale
presents a complex protected forest landscape comprising intact forest inside the park, logged areas inside the park, a game
corridor with degraded forest, and forest fragments in the landscape surrounding the park. To explore the effect of these
different levels of forest management and protection over time, we assessed forest change over the previous three decades,
using both discrete and continuous data analyses of satellite imagery. Park boundaries have remained fairly intact and forest
cover has been maintained or increased inside the park, while there has been a high level of deforestation in the landscape
surrounding the park. While absolute changes in land cover are important changes in vegetation productivity, within land cover
classes are often more telling of longer term changes and future directions of change. The park has lower Normalized Difference
Vegetation Index (NDVI) values than the forest fragments outside the park and the formerly logged area—probably due to forest
regeneration and early succession stage. The corridor region has lower productivity, which is surprising given this is also
a newer regrowth region and so should be similar to the logged and forest fragments. Overall, concern can be raised for the
future trajectory of this park. Although forest cover has been maintained, forest health may be an issue, which for future
management, climate change, biodiversity, and increased human pressure may signify troubling signs. 相似文献