The Chilean Intermediate Depression to the north of Santiago has experienced a physiognomical transformation from a Prosopis chilensis woodland to an Acacia caven savanna. Today P. chilensis trees are scarce and belong mostly to the larger size classes. By contrast A. caven seems to reproduce frequently and its populations consist of individuals of all size classes. In this paper we document these changes and report the results of tests aimed at determining the causes of these physiognomical changes. We found that livestock, leporids, introduced Mediterranean forbs and agriculture account for differences in seed dispersal and survival of A. caven and P. chilensis, which can explain the documented changes in the Chilean landscape. 相似文献
Single cells were mechanically isolated from leaf-derived callus of mature Juniperus oxycedrus L. These cells divided and gave rise to callus when plated on medium containing growth regulators. Best plating efficiency was obtained on a modified Schenk and Hildebrandt medium supplemented with 0.6 micro M 2,4-dichlorophenoxyacetic acid and 100 mg l(-1) casein hydrolyzate. Although single-cell-derived callus showed poor morphogenic potential, both adventitious shoots and embryogenic tissues differentiated from the callus. We also achieved induction of somatic embryogenesis in leaf explants of mature J. oxycedrus trees cultured in the presence of 6.0 or 10.0 micro M 2,4-dichlorophenoxyacetic acid or picloram. Frequency of embryogenic callus ranged from 6 to 18%; however, under the culture conditions tested, isolated embryos failed to develop into plants. 相似文献
Tropical Animal Health and Production - The objective of this study was to compare hoof anatomy, hoof growth pattern, and hoof weight-bearing surface of six different Iranian sheep breeds to... 相似文献
Infections caused by Streptococcus suis are considered a global problem in the swine industry. In this animal species, S. suis is associated with septicemia, meningitis, endocarditis, arthritis and, occasionally, other infections. Moreover, it is an agent of zoonosis that afflicts people in close contact with infected pigs or pork-derived products. Although sporadic cases of S. suis infection in humans have been reported, a large outbreak due to S. suis serotype 2 emerged in the summer of 2005 in Sichuan, China. A similar outbreak was observed in another Chinese province in 1998. Symptoms reported in these two outbreaks include high fever, malaise, nausea and vomiting, followed by nervous symptoms, subcutaneous hemorrhage, septic shock and coma in severe cases. The increased severity of S. suis infections in humans, such as a shorter incubation time, more rapid disease progression and higher rate of mortality, underscores the critical need to better understand the factors associated with pathogenesis of S. suis infection. From the 35 capsular serotypes currently known, serotype 2 is considered the most virulent and frequently isolated in both swine and humans. Here, we review the epidemiological, clinical and immunopathological features of S. suis infection in humans. 相似文献
It is known that land-use and land-cover (LULC) changes affect plant community assembly for decades. However, both the short- and the long-term effects of contrasting LULC change pathways on this assembly are seldom explored.
Objectives
To assess how LULC change pathways affect woody plant community parameters (i.e. species richness, diversity and evenness) and species’ presence and abundance, compared with environmental factors and neutral processes.
Methods
The study was performed in Mediterranean limestone scrublands in NE Spain. Cover of each woody species was recorded in 150 scrubland plots belonging to five LULC change pathways along the past century, identified using land-cover maps and fieldwork. For each plot, total woody and herbaceous vegetation cover, local environmental variables and geographical position were recorded. Effects of these pathways and factors on plant community parameters and on species presence and abundance were assessed, considering spatial effects potentially associated to neutral processes.
Results
Species richness and diversity were associated with LULC change pathways and elevation, while evenness was only associated with this last. Pathways and environmental variables explained similar variance in both species’ presence and cover. In general, while community parameters were affected by recent-past (1956) use, species presence and abundance were associated with far-past (pre-1900) cropping. No relevant spatial effect was detected for any studied factor.
Conclusions
Historical LULC changes and current environmental factors drive local-scale community assembly in Mediterranean scrublands to an equal extent, while contrasting time-scale effects are found at community and species level. Neutral, dispersal-based processes are found to be non-relevant.
The Peru‐Humboldt Current system (HCS) supports the world's largest pelagic fisheries. Among the world's eastern boundary current systems, it is the most exposed to high climatic stress and is directly affected by El Niño and La Niña events. In this volatile ecosystem, fish have been led to develop adaptive strategies in space and time. In this paper, we attempt to understand the mechanisms underlying such strategies, focusing on the El Niño 1997–98 in Peru from which an extensive set of hydrographic, capture and acoustic survey data are available. An integrated analysis of the data is crucial, as each has substantial shortcomings individually; for example, both catch data and acoustic surveys may easily lead to wrong conclusions. Existing hypotheses on anchovy and sardine alternations lead us to a ‘habitat‐based’ synthetic hypothesis. Using our data, an integrated approach evaluated how fish responded to habitat variation, and determined the consequences in terms of fish‐population variability. Various factors occurring at a range of different spatio‐temporal scales were considered: interdecadal regime (warm ‘El Viejo’/cool ‘La Vieja’ decadal scale); strength and the duration of the El Niño Southern Oscillation event (interannual scale); population condition before the event (interannual scale); fishing pressure and other predation (annual scale); changes in reproductive behaviour (intra‐annual scale); presence of local upwelling (local scale). During El Niño 1997–98, anchovy was able to exploit a small‐scale temporal and spatial ‘loophole’ inside the general unfavourable conditions. Moreover, sardine did not do better than anchovy during this El Niño and was not able to take advantage of the ‘loophole’ opened by this short‐term event. Our results question the traditional view that El Niño is bad for anchovy and good for sardine. 相似文献
Pneumatosis cystoides intestinalis (PCI) is an infrequent condition of animals characterized by the existence of numerous thin-walled, gas-filled cystic structures within the intestinal wall and adjacent lymph nodes. Microscopically, the cystic structures appear to be dilated lymphatics located in the lamina propria, submucosa, muscularis, subserosa, mesentery, and mesenteric lymph nodes. This report describes a case of pneumatosis cystoides intestinalis in a rabbit doe from an organic farm where 20 rabbit does were fed ad libitum with a natural diet consisting of whole barley, pea beans, alfalfa hay, and a pelleted vitamin-mineral blend. A combination of nutritional, bacterial, and other factors are hypothesized as possible predisposing factors in the development of PCI. 相似文献
Objective To characterize responses to different doses of propofol in horses pre‐medicated with xylazine. Animals Six adult horses (five females and one male). Methods Each horse was anaesthetized four times with either ketamine or propofol in random order at 1‐week intervals. Horses were pre‐medicated with xylazine (1.1 mg kg?1 IV over a minute), and 5 minutes later anaesthesia was induced with either ketamine (2.2 mg kg?1 IV) or propofol (1, 2 and 4 mg kg?1 IV; low, medium and high doses, respectively). Data were collected continuously (electrocardiogram) or after xylazine administration and at 5, 10 and 15 minutes after anaesthetic induction (arterial pressure, respiratory rate, pH, PaO2, PaCO2 and O2 saturation). Anaesthetic induction and recovery were qualitatively and quantitatively assessed. Results Differences in the quality of anaesthesia were observed; the low dose of propofol resulted in a poorer anaesthetic induction that was insufficient to allow intubation, whereas the high dose produced an excellent quality of induction, free of excitement. Recorded anaesthesia times were similar between propofol at 2 mg kg?1 and ketamine with prolonged and shorter recovery times after the high and low dose of propofol, respectively (p < 0.05; ketamine, 38 ± 7 minutes; propofol 1 mg kg?1, 29 ± 4 minutes; propofol 2 mg kg?1, 37 ± 5 minutes; propofol 4 mg kg?1, 50 ± 7 minutes). Times to regain sternal and standing position were longest with the highest dose of propofol (32 ± 5 and 39 ± 7 minutes, respectively). Both ketamine and propofol reversed bradycardia, sinoatrial, and atrioventricular blocks produced by xylazine. There were no significant alterations in blood pressure but respiratory rate, and PaO2 and O2 saturation were significantly decreased in all groups (p < 0.05). Conclusion The anaesthetic quality produced by the three propofol doses varied; the most desirable effects, which were comparable to those of ketamine, were produced by 2 mg kg?1 propofol. 相似文献
Information on 936 birth weights (BW), adjusted weaning weights (AWW) and average daily gains (ADG) from Brahman (B), Indubrazil
(I), Gyr (G) and commercial Zebu (C) cattle and their crosses were obtained from the records of a farm in the State of Yucatan,
Mexico. Two statistical models were used to analyse the data: the first included the effects of year and season of birth,
sex of the calf, cow's parity number and breed group. The other model included the same environmental effects as the previous
model and the genetic components of breed group (breed additive, breed maternal and heterosis effects). Additive and maternal
effects were expressed as deviations from those for the B breed. The means of BW, AWW and ADG for the B breed were 33.3 ±
0.64 kg, 204.0 ± 4.9 kg and 760.06 ± 19.24 g/day, respectively. Both models gave similar results in terms of the variance
explained. Additive effects were significant (p < 0.05) for AWW and ADG but not for BW. The minor additive effect was for the C breed (−10.75 kg and −40.77 g for WW and
ADG, respectively). Maternal and heterosis effects were not significant (p > 0.05) for any of the traits. The correlation between the breed group means and the means estimated by the prediction equation
was r = 0.88. Finally, there was no significant genetic effect on pre-weaning calf performance among the genotypes evaluated. The
genetic model can be used to predict the genotype means with a high degree of accuracy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献