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1.
Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration 总被引:1,自引:0,他引:1
D. Y. HOLLINGER S. V. OLLINGER A. D. RICHARDSON T. P. MEYERS D. B. DAIL M. E. MARTIN N. A. SCOTT T. J. ARKEBAUER D. D. BALDOCCHI K. L. CLARK P. S. CURTIS K. J. DAVIS A. R. DESAI D. DRAGONI M. L. GOULDEN L. GU G. G. KATUL S. G. PALLARDY K. T. PAW U H. P. SCHMID P. C. STOY A. E. SUYKER S. B. VERMA 《Global Change Biology》2010,16(2):696-710
Vegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site‐years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two‐stream albedo submodel provided accurate predictions of boreal needle‐leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two‐stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r2=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r2=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two‐stream albedo model and foliage nitrogen concentration. These nitrogen‐based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes. 相似文献
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Our purpose was to identify the effect of diminished plantar cutaneous sensation on time-to-boundary (TTB) measures of postural control during double and single limb quiet standing. Thirty-two healthy young adults underwent 10 min of ice immersion of the plantar aspect of the feet prior to balance testing. On a different day, the subjects did not receive this intervention prior to testing. A 2 × 2 vision (eyes open, eyes closed) by sensation (control, hypoesthesia) repeated measures design was used to analyze the TTB measures. In double limb stance, there were significant interactions between sensation and vision for the absolute TTB minimum and the mean of TTB minima in the anteroposterior (AP) direction. There was a significant increase in both measures after sensation was diminished with eyes closed compared to the control, but not with eyes open. In single limb stance, the TTB absolute minimum, the mean of TTB minima in the AP direction, and the standard deviation of TTB minima significantly increased with hypoesthesia regardless of vision. No significant differences were found in the medial–lateral (ML) direction for any of the TTB measures in double or single limb stance. Sensory information from the plantar cutaneous receptors appears to be most important in the maintenance of AP postural control. 相似文献
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1. Human activities affect fish assemblages in a variety of ways. Large‐scale and long‐term disturbances such as in‐stream dredging and mining alter habitat and hydrodynamic characteristics within rivers which can, in turn, alter fish distribution. Habitat heterogeneity is decreased as the natural riffle–pool–run sequences are lost to continuous pools and, as a consequence, lotic species are displaced by lentic species, while generalist and invasive species displace native habitat specialists. Sediment and organic detritus accumulate in deep, dredged reaches and behind dams, disrupting nutrient flow and destroying critical habitat for habitat specialist species. 2. We used standard ecological metrics such as species richness and diversity, as well as stable isotope analysis of δ13C and δ15N, to quantify the differences in fish assemblages sampled by benthic trawls among dredged and undredged sites in the Allegheny River, Pennsylvania, U.S.A. 3. Using mixed‐effects models, we found that total catch, species richness and diversity were negatively correlated with depth (P < 0.05), while species richness, diversity and proportion of species in lithophilic (‘rock‐loving’) reproductive guilds were lower at dredged than at undredged sites (P < 0.05). 4. Principal components analysis and manova revealed that taxa such as darters in brood hider and substratum chooser reproductive guilds were predominantly associated with undredged sites along principal component axis 1 (PC1 and manova P < 0.05), while nest spawners such as catfish and open substratum spawners including suckers were more associated with dredged sites along PC2 (P < 0.05). 5. Stable isotope analysis of δ13C and δ15N revealed shifts from reliance on shallow water and benthic‐derived nutrients at undredged sites to reliance on phytoplankton and terrestrial detritus at deep‐water dredged sites. Relative trophic positions were also lower at dredged sites for many species; loss of benthic nutrient pathways associated with depth and dredging history is hypothesised. 6. The combination of ecological metrics and stable isotope analysis thus shows how anthropogenic habitat loss caused by gravel dredging can decrease benthic fish abundance and diversity, and that species in substratum‐specific reproductive guilds are at particular risk. The effects of dredging also manifest by altering resource use and nutrient pathways within food webs. Management and conservation decisions should therefore consider the protection of relatively shallow areas with suitable substratum for spawning for the protection of native fishes. 相似文献
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JAY A. KOLBE JOHN R. SQUIRES DANIEL H. PLETSCHER LEONARD F. RUGGIERO 《The Journal of wildlife management》2007,71(5):1409-1418
Abstract: Coyotes (Canis latrans) and Canada lynx (Lynx canadensis) are sympatric throughout much of the lynx's southern range. Researchers and managers have suggested that the presence of compacted snowmobile trails may allow coyotes to access lynx habitat from which they were previously excluded by deep, unconsolidated snow. This could then allow coyotes to more effectively compete with lynx for snowshoe hares (Lepus americanus), the lynx's primary prey. We investigated how coyotes interacted with compacted snowmobile trails by conducting carnivore track surveys and by snow tracking adult coyotes (4 M, 8 F) in areas of western Montana, USA, with both documented lynx presence and recreational snowmobile use. Coyotes remained in lynx habitat having deep snow throughout the winter months. They used compacted snowmobile trails for 7.69% of their travel distance and traveled on them for a median distance of 124 m. Coyotes used compacted forest roads (5.66% of total travel) and uncompacted forest roads (4.62% of total travel) similarly. Coyotes did not travel closer to compacted snowmobile trails than random expectation (coyote x̄ distance from compacted trails = 368 m, random expectation = 339 m) and the distance they traveled from these trails did not vary with daily, monthly, or yearly changes in snow supportiveness or depth. However, they strongly selected for naturally shallower and more supportive snow surfaces when traveling off compacted snowmobile trails. Coyotes were primarily scavengers in winter (snowshoe hare kills composed 3% of coyote feed sites) and did not forage closer to compacted snowmobile trails than random expectation. The overall influence of snowmobile trails on coyote movements and foraging success during winter appeared to be minimal on our study area. The results of this study will allow land managers to better assess the effects of snow-compacting activities on coyotes and lynx. 相似文献
5.
目的研究亚甲基蓝/光化学法辅助治疗慢性牙周炎对牙龈卟啉单胞菌(Porphyromonas gingivalis,Pg)检出率的变化。方法经伦理委员会同意后,本研究拟筛选出45例慢性牙周炎患者(每位患者经过详细牙周检查及X线检查后确认为牙周炎,有4个以上≥5 mm的牙周袋并分布在2个以上口腔区域),随机分3组:其中A组在SRP之后接受1次PERIOWAVE光化学治疗,B组在SRP后接受1次PERIOWAVE治疗以及在6周后再一次接受光化学治疗,而SRP组仅接受SRP治疗,各组患者取治疗前后相同4个位点龈下菌斑,聚合酶链式反应(Poly-merase chain reaction,PCR)检测Pg,观察Pg菌的检出率,采用卡方检验,并计算χ2值。结果 SRP组、A组、B组3组各组治疗后均较治疗前检出率降低(P<0.001),A组与SRP组治疗后比较差异无统计学意义[A组:40%(24/60),SRP组:45%(27/60),χ2=1.4815,P>0.05],B组与SRP治疗后比较检出率降低[SRP组:45%(27/60),B组:20%(12/60)χ2=8.547,P<0.01];B组与A组治疗后比较检出率降低[A组:40%(24/60),B组:20%(12/60),χ2=5.7143,P<0.05]。结论亚甲基蓝/光化学法辅助治疗慢性牙周炎后牙龈卟啉单胞菌的检出率较治疗前降低;结合临床试验结果,尚可认为2次激光疗效较1次激光好。 相似文献
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STEPHEN JAY GOULD 《Biological journal of the Linnean Society. Linnean Society of London》1992,47(4):407-437
Two major developmental constraints, identified and assessed by the covariance structure of ontogenetic measures, strongly influence the form and variation of Cerion in every study I have ever undertaken on this protean genus: the jigsaw constraint of large-and few vs small-and-many whorls for shells reaching a similar final size; and the compensatory constraint of later heights balancing juvenile widths to bring adult shells into a limited range of final proportions.
This study explores a set of taxa (the Cerion dimidiatum complex of eastern Cuba) growing at one extreme of the compensatory constraint–maximally flat juvenile shells followed by abrupt allometric transition to orthogonal adult whorls. I show that the most curious of all Cerion taxa, the teratologously uncoiling C. disforme , owes its unique and distinctive form to growth at an extreme of the compensatory constraint: the juvenile cross-section goes beyond mere flatness to actual concavity; and the adult shell, after maximally abrupt allometric transition to downward growth, loses contact with the juvenile whorls and begins to unwind in teratologic fashion. I present several categories of evidence to demonstrate that C. disforme is the extreme in a morphocline of taxa, whose correlated features express increasing discordance (and correlated sequelae of size and shape) under the compensatory constraint: C. geophilus – C. dimidiatum – C. alberli – C.disforme. I provide data for clines in morphology, in amount and character of variation, and in mode of growth. This genre of constraint–Darwin's old "correlations of growth"–must be given equal weight with immediate adaptation in a unified explanation of growth and form. 相似文献
This study explores a set of taxa (the Cerion dimidiatum complex of eastern Cuba) growing at one extreme of the compensatory constraint–maximally flat juvenile shells followed by abrupt allometric transition to orthogonal adult whorls. I show that the most curious of all Cerion taxa, the teratologously uncoiling C. disforme , owes its unique and distinctive form to growth at an extreme of the compensatory constraint: the juvenile cross-section goes beyond mere flatness to actual concavity; and the adult shell, after maximally abrupt allometric transition to downward growth, loses contact with the juvenile whorls and begins to unwind in teratologic fashion. I present several categories of evidence to demonstrate that C. disforme is the extreme in a morphocline of taxa, whose correlated features express increasing discordance (and correlated sequelae of size and shape) under the compensatory constraint: C. geophilus – C. dimidiatum – C. alberli – C.disforme. I provide data for clines in morphology, in amount and character of variation, and in mode of growth. This genre of constraint–Darwin's old "correlations of growth"–must be given equal weight with immediate adaptation in a unified explanation of growth and form. 相似文献
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