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351.
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Yang X Ongusaha PP Miles PD Havstad JC Zhang F So WV Kudlow JE Michell RH Olefsky JM Field SJ Evans RM 《Nature》2008,451(7181):964-969
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Philip N. Lehner 《西北部美国博物学家》2011,41(3)
Four observations made in Jackson Hole, Wyoming, indicate that coyote–badger associations are best considered as phoretic (accidental and nonobligatory) rather than a form of social symbiosis as has been previously suggested. 相似文献
355.
Understory vegetal response was found to significantly increase with the degree of thinning in an early regenerating, dense stand of lodgepole pine ( Pinus contorta ). The value of the increased vegetation for deer and elk was determined to be important through comparisons with known dietary and habitat preferences. 相似文献
356.
Reexamination of a semiarid foothill rangeland, first evaluated in 1948, indicated that secondary succession continues to shift toward a perennial grass-forb community formerly dominated by xeric shrubs, particularly big sagebrush ( Artemisia tridentata spp. vaseyana ). The direct role in livestock grazing in establishment and maintenance of shrub-dominant plant communities appears confirmed in the decline of shrubs upon cessation of livestock grazing in summer and continued browsing by mule deer in winter. The reduction of shrub forages on mule deer winter ranges is a major factor in population declines. 相似文献
357.
MB Gerstein A Kundaje M Hariharan SG Landt KK Yan C Cheng XJ Mu E Khurana J Rozowsky R Alexander R Min P Alves A Abyzov N Addleman N Bhardwaj AP Boyle P Cayting A Charos DZ Chen Y Cheng D Clarke C Eastman G Euskirchen S Frietze Y Fu J Gertz F Grubert A Harmanci P Jain M Kasowski P Lacroute J Leng J Lian H Monahan H O'Geen Z Ouyang EC Partridge D Patacsil F Pauli D Raha L Ramirez TE Reddy B Reed M Shi T Slifer J Wang L Wu X Yang KY Yip G Zilberman-Schapira S Batzoglou A Sidow PJ Farnham RM Myers 《Nature》2012,489(7414):91-100
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Buchhave LA Latham DW Johansen A Bizzarro M Torres G Rowe JF Batalha NM Borucki WJ Brugamyer E Caldwell C Bryson ST Ciardi DR Cochran WD Endl M Esquerdo GA Ford EB Geary JC Gilliland RL Hansen T Isaacson H Laird JB Lucas PW Marcy GW Morse JA Robertson P Shporer A Stefanik RP Still M Quinn SN 《Nature》2012,486(7403):375-377
The abundance of heavy elements (metallicity) in the photospheres of stars similar to the Sun provides a 'fossil' record of the chemical composition of the initial protoplanetary disk. Metal-rich stars are much more likely to harbour gas giant planets, supporting the model that planets form by accumulation of dust and ice particles. Recent ground-based surveys suggest that this correlation is weakened for Neptunian-sized planets. However, how the relationship between size and metallicity extends into the regime of terrestrial-sized exoplanets is unknown. Here we report spectroscopic metallicities of the host stars of 226 small exoplanet candidates discovered by NASA's Kepler mission, including objects that are comparable in size to the terrestrial planets in the Solar System. We find that planets with radii less than four Earth radii form around host stars with a wide range of metallicities (but on average a metallicity close to that of the Sun), whereas large planets preferentially form around stars with higher metallicities. This observation suggests that terrestrial planets may be widespread in the disk of the Galaxy, with no special requirement of enhanced metallicity for their formation. 相似文献
360.
Globemallows ( Sphaeralcea spp.) are arid land forbs suitable for seeding with crested wheatgrass ( Agropyron cristatum [L.] Geartner). However, little is known about the quantitative role of total nonstructural carbohydrates (TNC) in relation to globemallow tolerance of grazing, or about seasonal dynamics of mineral elements. The objectives of this study were to compare TNC and element pools (concentration x biomass) in the roots, crowns, and shoots of clipped versus unclipped S. munroana (Dogl.) Spach. Seedlings of S. munroana were transplanted to a northern Utah field site in 1985. Interplanted crested wheatgrass provided uniform competitive background. One-half of the globemallows were clipped to 5 cm on 10 May 1986 when stems were elongating the root and crown TNC pools were low. The remaining globemallows were not clipped. Root, crown and shoot pools of TNC and elements (N, P, K, Ca, and MG) were determined on 1 May, 20 May, 7 June, 11 July, 22 September, and 5 November 1986, and 29 May 1987. Defoliation did not affect shoot weights during a 1-year period. Experiment-long TNC and element pools also were not affected by clipping. Results indicate that S. munroana shoot recovery from a single spring grazing during a 1-year period would not be impaired by low root and crown TNC pools, and that TNC stored in the roots and crowns would account for only 7% of the regrowth produced. Furthermore, TNC and element pools of roots and crowns were generally constant from May to September but increased from September to November. TNC and element pools in shoots increased from May to September and then generally declined by November. TNC Pools of roots and crowns declined during winter. 相似文献