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461.
A system of primary wildland reserves may be required to ensure a diversity of plant and animal species in the future. A strategy for locating such reserves involves considerations of their location, number, size, and linkage. The equilibrium theory of island biogeography is a useful analytical tool for predicting future biogeographies according to the dynamics of present plant and animal distributions. Existing reserves in the United States are inadequate in size and number and are clumped in one geographic region. In a planned network there might be several levels of reserves, starting with first- and second-order watersheds of large enough size to support a stable population of large carnivores. Reserves should be distributed so that they include a maximum of the world's biological diversity. Lower-order reserves might serve as stepping-stones among which a supply of species might move as a kind of distributed storage and reintroduce themsleves when local instabilities occur. This would maintain a high immigration rate to balance an extinction rate which can only increase as human settlements expand.  相似文献   
462.
The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface.  相似文献   
463.
The alpha subunits of Gs and Gi link different sets of hormone receptors to stimulation and inhibition, respectively, of adenylyl cyclase. A chimeric alpha i/alpha s cDNA was constructed that encodes a polypeptide composed of the amino terminal 60% of an alpha i chain and the carboxyl terminal 40% of alpha s. The cDNA was introduced via a retroviral vector into S49 cyc- cells, which lack endogenous alpha s. Although less than half of the hybrid alpha chain is derived from alpha s, its ability to mediate beta-adrenoceptor stimulation of adenylyl cyclase matched that of the normal alpha s polypeptide expressed from the same retroviral vector in cyc- cells. This result indicates that carboxyl terminal amino acid sequences of alpha s contain the structural features that are required for specificity of interactions with the effector enzyme, adenylyl cyclase, as well as with the hormone receptor.  相似文献   
464.
The incidence and severity of injection-site lesions has decreased since the development of the Beef Quality Assurance program. The objective was to evaluate the route of administration and the pharmaceutical product on the impact on tenderness, collagen concentration, and lesion occurrence in muscles of chucks and rounds. A total of 144 yearling steers (initial BW = 383 +/- 29.4 kg) were selected and transported to Oklahoma State University. Steers were blocked into 2 groups of 72 based on initial BW and were randomly allocated, within block, into pens of 6 head per pen (12 pens per block). Each pen was randomly assigned an injection protocol. On May 19, 2006 (d 0), steers were administered one of the following treatment injections: a standard Biobullet containing 100 mg of ceftiofur sodium (Naxel, Pfizer Inc., New York, NY); a traditional needle and syringe dose of ceftiofur sodium; a standard Biobullet containing BallistiVac infectious bovine rhinotracheitis (IBR; Titanium 5, SolidTech Animal Health, Newcastle, OK); a traditional needle and syringe dose of IBR; a traditional needle and syringe dose of Vira Shield 5 (Grand Laboratories Inc., Freeman, SD); a standard placebo Biobullet; or a traditional needle and syringe dose of sterile water. Percentage of samples with an identifiable lesion did not differ by drug administered or injection method. Warner-Bratzler shear force values of lesion center cores in chucks tended to be different (P = 0.07) from cores from the control steaks and at 2.54 and 5.08 cm away from the lesion center. Lesion centers from the Biobullet-BallistiVac IBR had a Warner-Bratzler shear force value of 7.01 kg, which was greater (P < 0.05) than values for lesion centers from chucks injected with a Biobullet-placebo (6.27 kg) or needle-ceftiofur sodium (5.08 kg). No significant differences (P > 0.10) were observed in the total collagenous connective tissue in samples extracted from the chuck or round. The comparison of lesion site and control (nonlesion site) samples for lipid concentration showed no significant difference (P > 0.10) among treatments in the round. It was concluded the Biobullet did not create a greater occurrence of lesions in the muscles of the chuck and round. The Biobullet is not an appropriate injection method for the round of beef cattle because it caused tissue damage similar to a needle injection. However, the Biobullet can be used effectively in neck (chuck) applications without additional negative effects on tenderness.  相似文献   
465.
OBJECTIVE: To evaluate the clinical signs, results of clinical pathology and serology tests, and treatment outcome of clinical leptospirosis in 40 dogs from North Queensland. DESIGN: Retrospective study from January 1995 to August 1999. PROCEDURE: Case records were reviewed for age, breed, sex, month of submission, geographical location and presenting clinical signs in 40 dogs with titres of > or = 200 for leptospirosis by the microscopic agglutination test. A biochemistry panel and complete blood count were performed on 18 dogs. RESULTS: Canine leptospirosis occurred most frequently during the summer and autumn particularly in the 'wet' tropical coastal areas of Mackay and Cairns. Fewer cases were seen in the Atherton Tablelands and 'dry' tropics around Townsville. Young and male dogs were more commonly affected. Most cases were caused by L australis (80%) and L zanoni (15%) with individual cases of L hardjo and L copenhageni. All dogs showed a distinctive multiorgan disease pattern including renal failure and cholestatic hepatopathy. Presenting clinical signs were related to these disease syndromes and included jaundice, vomiting, lethargy, inappetence, dehydration, pyrexia, abdominal pain and diarrhoea. Just over 50% of the dogs in the present study failed to recover. Clinical biochemical changes indicative of renal failure and cholestasis were significantly less severe in dogs that recovered compared with dogs that did not survive. CONCLUSIONS: Clinical pathology testing should be performed on all dogs presented for illness in the endemic areas so as to help make a presumptive diagnosis and assist in determining the prognosis as soon as possible. The presumptive diagnosis should be confirmed serologically.  相似文献   
466.
Scalded lands are common in acid sulphate soil areas on the New South Wales coast, Australia. In this work, chemical characteristics of the scalded acid sulphate soils at nine sites along this coast were investigated. The investigated acid sulphate scalds are characterized by an extremely acidified topsoil layer (0–0.6 m) although they derive from the sediments of varying salinity and the metal sulphides contained in the soils have experienced different degrees of oxidation. Almost all of the investigated scalds occur in the areas that have a lower surface elevation than the surrounding areas. These hollows may act as sinks for acid sulphate materials and salts that are transported from the surrounding areas and the shallower watertables in such locations may enhance upward transport of acid and salt materials from the underlying oxidized sulphidic sediments. In general, the scalded acid sulphate soils have less organic matter and soluble phosphorus, and a greater salinity, soluble acidity, soluble Al, Mn and Zn concentrations, compared to the adjacent non‐scalded acid sulphate soils. These are most likely soil constraints for revegetation of the scalded lands and treatment will need to involve acid neutralization (e.g. application of lime) and addition of P fertilizers to reduce the soluble acidity, immobilize soluble Al, Mn and Zn, and increase P availability. The evidence also shows that the higher soluble Al concentration in the scalded soils, relative to the non‐scalded soils, is related to their lower organic matter content. Hence, rehabilitation of these scalded lands should involve the addition of organic matter to reduce soluble Al concentrations; it may also help reduce Mn and Zn toxicity, and salinity. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
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