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Analysis of a large sample of well-dated fossil mammals from localities in the Turkana Basin of Kenya and Ethiopia revealed sampling biases that affect patterns of faunal turnover during the late Pliocene. When these biases were accounted for, results indicated that 58 to 77 percent of the mammal species were replaced between 3.0 and 1.8 million years ago (Ma). Overall diversity increased from 3.0 to 2.0 Ma but then declined. No distinct turnover pulse is seen between 2.8 and 2.5 Ma; instead, the most significant period of faunal change began after 2.5 Ma and continued through 1.8 Ma.  相似文献   
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Modulation of diversity by grazing and mowing in native tallgrass prairie   总被引:4,自引:0,他引:4  
Species diversity has declined in ecosystems worldwide as a result of habitat fragmentation, eutrophication, and land-use change. If such decline is to be halted ecological mechanisms that restore or maintain biodiversity are needed. Two long-term field experiments were performed in native grassland to assess the effects of fire, nitrogen addition, and grazing or mowing on plant species diversity. In one experiment, richness declined on burned and fertilized treatments, whereas mowing maintained diversity under these conditions. In the second experiment, loss of species diversity due to frequent burning was reversed by bison, a keystone herbivore in North American grasslands. Thus, mowing or the reestablishment of grazing in anthropogenically stressed grasslands enhanced biodiversity.  相似文献   
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Bovine viral diarrhoea virus (BVDV) is an economically significant disease affecting the Australian cattle industry, with losses stemming from decreased production and reproductive performance and control costs. However, these losses can be difficult to appreciate, particularly in endemic regions. Overall, there is a variable but high herd-level seroprevalence in Australia. Despite a potentially high financial burden of the disease, the onus for control ultimately falls on producers and strategies employed will vary between regions. A cross-sectional study, using a postal survey, was conducted in 2013 to evaluate the BVDV knowledge, attitudes and management practices utilised by Australian cattle producers. A total of 192 producers participated in the study, and results indicate that knowledge and attitudes towards disease risk are variable and can be improved. Producer knowledge of how persistently infected (PI) animals are produced was higher than that of disease outcomes or transmission pathways. Implementation of biosecurity practices was limited, with approximately half of respondents employing quarantine procedures for introduced stock and only 2% indicating they would antigen test introduced stock for BVDV. Approximately a third (36%) of producers reported engaging in BVDV control, with the majority of these using vaccination strategies over deliberate exposure to a PI. Knowledge of and engagement with BVDV control was positively influenced by the producer relationships with veterinarians. Findings from this study suggest that building on education and delivering a consistent message among stakeholders would likely improve producer awareness and understanding in relation to BVDV and support decision making in BVDV management.  相似文献   
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A sequential fractionation scheme, based on a soil phosphorous fractionation, was developed to assess the chemical nature, and thus the potential bioavailability and mobility of As, at the sites. Soil As was separated into five fractions with (i) anion exchange resin, (ii) NaHCO3, (iii) NaOH, (iv) HCl, (v) residual. Most sites contained relatively low concentrations of As in the two most labile fractions. The bulk of the contaminant As at the sites seemed to be associated with soil amorphous Fe and Al minerals and the dominant clay minerals which help in As sorption are montmorillonite and mica. Resin-extractable As in particular might provide a good index of potential As bioavailability and mobility.  相似文献   
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This study was conducted on summer anoestrous buffalo heifers to monitor the efficacy of melatonin for induction of ovulation and ovarian cyclicity. During pre‐treatment period of 24 days, the ovarian dynamics of five cycling and 10 summer anoestrous heifers was monitored on each alternate day using a transrectal ultrasound scanner. Thereafter, during treatment period, these 10 anoestrous heifers along with additional seven anoestrous heifers were randomly allocated into non‐implanted (n = 5) and implanted (n = 12, one melatonin implant/50 kg, 18 mg melatonin/implant) group. Non‐implanted heifers were monitored on each alternate day till the confirmation of second‐ovulation in implanted heifers. Pre‐treatment period revealed the presence of dominant follicles in anoestrous heifers which attained the diameter comparable with ovulatory follicles of cycling heifers but failed to ovulate and regressed. Between 6 and 36 days (15.3 ± 2.9 days) post‐treatment, all the implanted heifers (p < 0.05) exhibited ovulation of dominant follicles; however none of the non‐implanted heifers ovulated during the corresponding period. The first‐interovulatory period in implanted heifers ranged between 8 and 28 days (18.0 ± 1.8 days). The implanted heifers with short (≤16 days) interovulatory period had short‐lived corpus luteum (CL) that had smaller diameter and secreted less progesterone (p < 0.05). The diameter of CL was large (p < 0.05) and plasma progesterone was high (p < 0.05) following second‐ovulation compared with first‐ovulation in implanted heifers. In conclusion, using melatonin implants, ovulatory size nonovulatory follicles observed in summer anoestrous buffalo heifers can be successfully ovulated to initiate ovarian cyclicity.  相似文献   
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Objectives Evaluate current disease surveillance activities at saleyards and abattoirs in New South Wales (NSW) in order to establish the prevalence of clinical anomalies in pigs at different sites and to compare the sensitivity of detecting anomalies inside versus outside of pens. Procedure Routine inspections of pigs by staff and government inspectors were observed at two saleyards and two abattoirs in NSW during three visits over a 2-month period (January 2008–March 2008). All pigs presented for sale or slaughter were examined for 19 clinical anomalies from either the side of the pen or while animals were moving outside the pen, with data being combined to give an assumed ‘gold standard’. We compared the prevalence of anomalies among animals at the four sites using logistic regression, as well as the sensitivity of detection of the two inspection methods. Results Frequency and methodology of routine inspection varied among sites. Of the 7747 pigs inspected, 822 (10.6%) showed at least one clinical anomaly. There was moderate agreement between detecting anomalies in penned pigs versus while being moved. Pigs at one abattoir exhibited significantly fewer anomalies than pigs at the other sites. Conclusion The prevalence of anomalies among pigs at saleyards and abattoirs in NSW was relatively high (≈10%). Weaknesses in current disease surveillance activities for pigs post-farmgate have been identified. Increased regulation, surveillance training and modification of standard operational procedures for inspection have the potential to improve the current system.  相似文献   
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