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231.
Fertilized ova of razorback sucker, Xyrauchen texanus, were adhesive for 3 to 4 hours after fertilization. Cleavage was completed at 24 hours, gastrulation occurred at 34 hours, and blood circulation was established at 117 hours. Hatching occurred from 5.2 to 5.5 days after fertilization. Larvae were from 6.8 to 7.3 mm TL at hatching. Yolk was assimilated at 13 days (10 mm TL). All fins were formed and had ossified rays at 64 days (27 mm TL). The unique nuchal keel appeared about 200 days after fertilization. 相似文献
232.
Vegetation characteristics of 15 sagebrush community types identified on the Humboldt National Forest, northeastern Nevada, are described. A total of 218 plant species were found over the 372 relatively undisturbed rangeland communities sampled. The dominant plant families encountered were the Asteraceae (45 taxa), Poaceae (32 taxa), Scrophulariaceae (14 taxa), and the Fabaceae (12 taxa). Average annual dry weight production of the community types ranged from about 400 kg/ha/yr on types with Artemisia nova as the dominant sagebrush species to 1,200 kg/ha/yr on some A. tridentata ssp. vaseyana community types. A general increase in species richness and vegetation plus litter ground cover was observed within community types as the dominant sagebrush species changed from A. nova to A. arbuscula to A. longiloba to A. tridentata spp. tridentata to A. tridentata ssp. vaseyana . Major differences in plant species production and constancy exist between the sagebrush community types studied. 相似文献
233.
Christopher W. Hoagstrom Steven S. Wall Jason G. Kral Brian G. Blackwell Charles R. Berry Jr. 《西北部美国博物学家》2011,67(2)
We summarized historic and recent fish distributions in South Dakota and analyzed fish faunal similarity at 2 spatial scales (geomorphic province and river drainage) for both historic (native) and recent (post-1990) faunas. We quantified zoogeographic patterns between geomorphic provinces and among neighboring river drainages for historic and recent faunas. We also quantified faunal change (species losses and additions) between provinces and among drainages. Ninety-seven fishes were native to South Dakota, but 111 fishes were present in recent collections because 8 native species were missing, and 22 nonnatives were present. There was high β diversity among historic and recent river drainage fish faunas, but there was between 22% and 56% faunal change between periods. Recent faunas were homogenized compared to historic faunas at both provincial and river drainage spatial scales. Patterns of nonnative species establishment were geographically distinct from patterns of native species loss. Most nonnative species additions were in cold-water or human-made habitats of the Great Plains. Most native species declines stemmed from warm water streams of the Central Lowlands and Missouri River valley. Conservation of rare and declining native species and containment of nonnatives are both necessary to preserve historical patterns of fish biodiversity in South Dakota. 相似文献
234.
Cover types and vegetative characteristics (e.g., grasses, forbs, shrubs) used by female Sage Grouse ( Centrocercus urophasianus ) during summer were compared with available habitat on two study areas in southeastern Oregon. Broodless hens, which constituted 114 of the 125 (91%) radio-marked hens studied, selected big ( Artemisia tridentata ) subspp.) and low sagebrush ( A. arbuscular ) cover types at both study areas. At Hart Mountain, broodless hens did not select specific vegetative characteristics within cover types. However, at Jackass Creek, forb cover was greater ( P = .004) at broodless hen sites than at random locations. Differences in habitat use by broodless hens between study areas were associated with differences in forb availability. Broodless hens used a greater diversity of cover types than hens with broods. Broodless hens gathered in flocks and remained separate from but near hens with broods during early summer. By early July broodless hens moved to meadows while hens with broods remained in upland habitats. 相似文献
235.
In a greenhouse experiment, effects of nitrogen form and concentration on productivity and dry matter allocation differed between two species native to semiarid ecosystems of the Great Basin. Aboveground production of green surface area and of dry matter were consistently enhanced by increased nitrogen for the rhizomatous grass Elymus lanceolatus , but not for the bunchgrass Oryzopsis hymenoides . These differences were likely due to inherently low growth rates of O. hymenoides . Aboveground dry matter allocation also differed between the two species. O. hymenoides had more leaves per tiller with increased nitrogen, whereas leaf size but not number increased for E. lanceolatus . Furthermore, increases in tiller density with increased nitrogen for E. lanceolatus were almost three times greater than those for O. hymenoides . E. lanceolatus , but not O. hymenoides , was sensitive to the form of nitrogen supplied to the plants. When NH 4 -N was the only form of nitrogen supplied, high concentrations of NH 4 -N inhibited aboveground production of E. lanceolatus . 相似文献
236.
William S. Longland 《西北部美国博物学家》2011,67(3)
Heteromyid rodents in the deserts of North America have been shown to harvest large quantities of seeds of both native and introduced plants from soil seed banks, but rarely has the impact of this seed removal been demonstrated experimentally. I used a series of fenced plots (some of which excluded rodents) to demonstrate that heteromyids at a western Nevada study site can measurably reduce seed banks and subsequent seedling establishment of Salsola paulsenii , an introduced invasive weed that has become a significant problem over much of the desert Southwest. The frequency of S. paulsenii seedlings in both 2004 and 2005 was significantly greater around the interior perimeters of plots that permitted access by rodents than in plots that excluded rodents. Density of S. paulsenii seedlings was significantly greater inside than outside rodent exclusion plots, but there was no such difference in seedling density inside versus outside plots that permitted rodent access. Salsola paulsenii has such a conspicuous presence in many desert environments that the effect of rodents in reducing its abundance may not be visually apparent; however, rodents may still ameliorate competitive effects of this weed on coexisting plants. Heteromyid rodents disperse seeds through caching, and they also consume them. Caching may enhance establishment of native plant seedlings, but is unlikely to benefit exotics such as S. paulsenii . 相似文献
237.
The early fall diet of Oregon blue grouse ( Dendragapus obscurus pallidus ) from Wallowa County, Oregon, was determined from 145 crops obtained during 1981 and 1982. Of more than 50 plant and animal foods in the diet, short-horned grasshoppers ( Acrididae ), prickly lettuce ( Lactuca serriola ), yellow salsify ( Tragopogon dubius ), wild buck-wheat ( Eriogonum spp.), and snowberry ( Symphoricarpos albus ) occurred in 30% or more of the crops and collectively amounted to 68% of the diet by weight. Seven of the 12 most common foods were consumed differentially by the four sex and age classes of birds. Results indicated that blue grouse foraged in forest and grassland habitats. 相似文献
238.
Ponderosa pine cones from 10 areas in Arizona were collected prior to natural seed dispersal and dissected to determine the number of sound, hollow, and insect-damaged seeds in each cone. Total and sound seed yields per cone did not vary significantly among areas but did vary significantly among trees within each area. Numbers of hollow and Megastigmus -infested (Hymenoptera: Torymidae) seeds varied significantly among areas and trees within areas. Numbers of sound seed increased significantly with increasing cone length but did not change with increasing numbers of cones per cluster. The percentages of Megastigmus -infested seed did not change significantly with increasing cone length or number of cones per cluster. 相似文献
239.
The reproductive cycle in Belding ground squirrels was studied in the Sierra Nevada Mountains at two locations, one at 2,100 m elevation, the other at 3,000 m. Adults emerged from hibernation completely prepared physiologically for reproduction. Males tended to emerge slightly ahead of females and yearlings tended to emerge later than adults. Yearling females were fertile but produced smaller litters than adults, 4.48 vs. 6.31. Yearling males were infertile. They exhibited a slight seasonal cycle in testicular growth but did not reach sexual maturity. Testicular growth and spermatogenesis were incipient in many adults and in yearlings prior to hibernation. 相似文献
240.
Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Sixty-four cougar ( Felis concolor ) stomachs and 41 intestinal tracts were examined for food items in northeastern Oregon from 1976 through 1979. Food items, in order of decreasing frequency, were mule deer ( Odocoileus hemionus ), North American elk ( Cervus elaphus ), porcupine ( Erethizon dorsatum ), snowshoe hare ( Lepus americanus ), and deer mouse ( Peromyscus maniculatus ). 相似文献