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21.
Relict sites are geographically isolated areas that are undisturbed by direct and indirect human influences. These sites facilitate long-term ecological monitoring by providing a reference for gauging impacts occurring elsewhere. Knowledge gained through comparing vegetation change on matched relict and proximal disturbed areas can help partition the causes of change into natural and human-produced components. Fishtail Mesa in Grand Canyon National Park is a 439-ha relict site that is inaccessible to domestic livestock. Human visitation is infrequent and irregular, and fires have never been suppressed or managed. In 1958, U.S. Forest Service range scientists conducted a survey of Fishtail Mesa to gather reference data on vegetation, wildlife, and soils. Vegetation sampling was conducted using a method called the ";";elb.";"; We returned to Fishtail Mesa in May 1996 to perform a general vegetation and floristic survey, assess the extent of vegetation change after 38 years, and evaluate the suitability of the site as a location for long-term surveillance of ecological change. Fishtail Mesas vegetation consists primarily of a Pinus edulis (pinyon) and Juniperus osteosperma (Utah juniper) woodland with an Artemisia tridentata (sagebrush) understory, or tree-type (310.9 ha), and an Artemisia and Poa fendleriana (mutton grass) steppe, or shrub-type (127.5 ha). Since 1958 vegetation changes in both shrub- and tree-types have been limited to only a few species. In the shrub-type we detected slight increases from 1958 to 1996 in both Pinus and Juniperus , and reexamination of 1958 photo sites confirmed that Pinus and Juniperus are reoccupying the shrub-type. Artemisia cover declined from 1958 to 1996, whereas Poa increased from near trace amounts in 1958 to moderate cover in 1996. In the tree-type, Poa has increased from 1958 to 1996, while Artemisia , Juniperus , and Pinus showed no apparent change. Other species such as Ephedra torreyana (Torrey joint-fir), Opuntia polyacantha (prickly pear), and Gutierrezia sarothrae (snakeweed) have decreased. Vegetation analysis aided by TWINSPAN revealed that the shrub-type is defined more on the basis of absence of Pinus and Juniperus rather than any special association of differential species with a high preference for this type. We interpret the ";";invasion";"; of the shrub-type by Pinus and Juniperus as a ";";reoccupation.";"; Indirect ordination using DECORANA inferred 2 environmental gradients, a moisture gradient and perhaps a substrate texture gradient, that appeared to influence vegetation distribution on Fishtail Mesa. Fishtail Mesa is a valuable relict area for studying the effects of livestock grazing and prescribed fire. It should be designated a Federal Research Natural Area based on its vegetation communities, size, and protection afforded by its location in Grand Canyon National Park. 相似文献
22.
The distribution and breeding habitats of the Great Basin spadefoot toad ( Scaphiopus intermontanus ) were investigated in the Bonneville Basin of western Utah. The permanent springs and man-made reservoirs used for breeding were largely found below the 1600 m elevation. The pH's ranged between 7.2 and 10.4 and the total dissolved solids between 170 and 4800 mg/l. The springs were less alkaline than the rain-filled reservoirs. The lack of aquatic vegetation was a common feature of the reservoirs and most of the springs. Observations of breeding without rain are noted as well as the lack of breeding with rain. The snout – vent lengths of adult spadefoots are greater in the Bonneville Basin than in other parts of the Great Basin. Utilization of permanent water sources and stimuli for emergence and breeding, as well as the larger adult size of S. intermontanus in the Bonneville Basin, are discussed in relation to the diverse precipitation patterns, the sparseness of the water sources, and the Holocene history of the Great Basin. 相似文献
23.
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;} A program to control hydatid disease in central Utah was evaluated by: (1) surveillance of infection in dogs and sheep, (2) questioning adult residents of two Sanpete County communities (Fountain Green and Spring City) about their knowledge of hydatid disease and their attitudes toward preventive measures, (3) interviewing local officials to evaluate the proposed implementation of proper community-wide measures, (4) analyzing records of prophylactic treatment of dogs with praziquantel, and (5) comparing scores of tests given to third and fourth grade students before and after they colored an educational pamphlet about hydatid disease. Infection rates of Echinococcus granulosus in dogs brought to volunteer diagnostic clinics dropped from 28.3 percent in 1972 to 1.0 percent in 1979, but increased to 9.8 percent in 1981. This last rise was due mainly to the fact that some dogs were examined that belonged to range sheepmen who had either not attended a field clinic recently or had never attended at all. Prevalence of the parasite in slaughtered sheep decreased steadily from 13.2 percent in 1972 to 2.8 percent in 1981. With regard to the questionnaire phase of the project, 87.3 percent and 84.3 percent of the respondents understood the role of dogs in the life cycle of E. granulosus in Fountain Green and Spring City, respectively. Over 50 percent of the respondents of these two communities had worked directly with sheep sometime in their life. In general, residents were more willing to practice preventive measures involving sheep than they were to implement measures involving dogs alone. However, many of the recommended community-wide preventive measures were not implemented. With the coloring book, students answered an average of 62.5 percent of the questions correctly before they colored the pamphlet and 83.3 percent afterward. Overall, our results suggest that residents of Sanpete County are knowledgeable about hydatid disease and its mode of transmission, and that, in general, progress has been made in control of hydatid disease in central Utah. 相似文献
24.
Thirteen Speyeria nokomis apacheana (Edwards) (Nymphalidae) populations from the western Great Basin were assayed for isozyme variability using starch-gel electrophoresis. Eight of the 25 presumptive isozyme loci analyzed were found to be polymorphic. Collections made in 1991and 1992 allowed for between-year comparisons of heterozygosity and the estimation of effective population size for five of the sampled populations. Speyeria nokomis apacheana populations exhibit lower mean heterozygosity levels than other nymphalids. This may be attributed to genetic drift in apparently isolated populations with small effective sizes. 相似文献
25.
Jean-Pierre Vilardaga Guillermo Romero Peter A. Friedman Thomas J. Gardella 《Cellular and molecular life sciences : CMLS》2011,68(1):1-13
The parathyroid hormone (PTH) receptor type 1 (PTHR), a G protein-coupled receptor (GPCR), transmits signals to two hormone
systems—PTH, endocrine and homeostatic, and PTH-related peptide (PTHrP), paracrine—to regulate different biological processes.
PTHR responds to these hormonal stimuli by activating heterotrimeric G proteins, such as GS that stimulates cAMP production. It was thought that the PTHR, as for all other GPCRs, is only active and signals through
G proteins on the cell membrane, and internalizes into a cell to be desensitized and eventually degraded or recycled. Recent
studies with cultured cell and animal models reveal a new pathway that involves sustained cAMP signaling from intracellular
domains. Not only do these studies challenge the paradigm that cAMP production triggered by activated GPCRs originates exclusively
at the cell membrane but they also advance a comprehensive model to account for the functional differences between PTH and
PTHrP acting through the same receptor. 相似文献
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28.
J. H. van 't Hoff's 1874 Dutch pamphlet, in which he proposed the spatial arrangement of atoms in a molecule, is one of the most significant documents in the history of chemistry. This essay presents a new narrative of Van 't Hoff's early life and places the appearance of the pamphlet within the context of the 'second golden age' of Dutch science. We argue that the combination of the reformed educational system in The Netherlands, the emergence of graphical molecular modelling within the theoretical and practical culture of chemistry during the 1860s and 1870s, as well as Van 't Hoff's own personal research trajectory, formed the background to his unprecedented attribution of spatial meaning to the traditional concept of atomic 'arrangement'. We also present a new English translation of the pamphlet, for we have found that the existing translation, published by G. M. Richardson in 1901, contains many errors, changes and omissions. The new version offers a more accurate rendition in English of Van 't Hoff's style and argument. 相似文献
29.
John T. Heiker Nora Klöting Peter Kovacs E. Bartholomeus Kuettner Norbert Sträter Stephan Schultz Matthias Kern Michael Stumvoll Matthias Blüher Annette G. Beck-Sickinger 《Cellular and molecular life sciences : CMLS》2013,70(14):2569-2583
The molecular target of the adipokine vaspin (visceral adipose tissue-derived serpin; serpinA12) and its mode of action are unknown. Here, we provide the vaspin crystal structure and identify human kallikrein 7 (hK7) as a first protease target of vaspin inhibited by classical serpin mechanism with high specificity in vitro. We detect vaspin–hK7 complexes in human plasma and find co-expression of both proteins in murine pancreatic β-cells. We further demonstrate that hK7 cleaves human insulin in the A- and B-chain. Vaspin treatment of isolated pancreatic islets leads to increased insulin concentration in the media upon glucose stimulation without influencing insulin secretion. By application of vaspin and generated inactive mutants, we find the significantly improved glucose tolerance in C57BL/6NTac and db/db mice treated with recombinant vaspin fully dependent on the vaspin serpin activity and not related to vaspin-mediated changes in insulin sensitivity as determined by euglycemic-hyperinsulinemic clamp studies. Improved glucose metabolism could be mediated by increased insulin plasma concentrations 150 min after a glucose challenge in db/db mice, supporting the hypothesis that vaspin may inhibit insulin degradation by hK7 in the circulation. In conclusion, we demonstrate the inhibitory serpin nature and the first protease target of the adipose tissue-derived serpin vaspin, and our findings suggest hK7 inhibition by vaspin as an underlying physiological mechanism for its compensatory actions on obesity-induced insulin resistance. 相似文献
30.
Benjamin Förthmann Hella Brinkmann Andreas Ratzka Michal K. Stachowiak Claudia Grothe Peter Claus 《Cellular and molecular life sciences : CMLS》2013,70(14):2555-2568
Reduced levels of survival of motoneuron (SMN) protein lead to spinal muscular atrophy, but it is still unknown how SMN protects motoneurons in the spinal cord against degeneration. In the nucleus, SMN is associated with two types of nuclear bodies denoted as gems and Cajal bodies (CBs). The 23 kDa isoform of fibroblast growth factor-2 (FGF-223) is a nuclear protein that binds to SMN and destabilizes the SMN-Gemin2 complex. In the present study, we show that FGF-223 depletes SMN from CBs without affecting their general structure. FRAP analysis of SMN-EGFP in CBs demonstrated that the majority of SMN in CBs remained mobile and allowed quantification of fast, slow and immobile nuclear SMN populations. The potential for SMN release was confirmed by in vivo photoconversion of SMN-Dendra2, indicating that CBs concentrate immobile SMN that could have a specialized function in CBs. FGF-223 accelerated SMN release from CBs, accompanied by a conversion of immobile SMN into a mobile population. Furthermore, FGF-223 caused snRNP accumulation in CBs. We propose a model in which Cajal bodies store immobile SMN that can be mobilized by its nuclear interaction partner FGF-223, leading to U4 snRNP accumulation in CBs, indicating a role for immobile SMN in tri-snRNP assembly. 相似文献