The air-borne distribution of zoonotic agents from livestock waste spreading and microbiological risk to fresh produce from contaminated irrigation sources

Aims:  To assess the risks of zoonotic agents in dissemination of livestock wastes into the environment by airborne distribution. To subsequently assess the survival time of zoonotic agents, introduced in irrigation water, on the phylloplane of produce.
Methods and Results:  An Escherichia coli marker was introduced into pig slurry which was spread using a rain gun sprayer. Air sampling was undertaken to determine the distance reached by the marker. No recoveries were observed at a distance of 250 m. Borehole water, contaminated with zoonotic agents, was used to irrigate field plots sown with lettuce and spinach. Decline in bacterial numbers on the phylloplane was observed with time. After initial rapid decreases, we were unable to detect any pathogen from the phylloplane, 1 month after contamination.
Conclusions:  These preliminary results suggest that the risks to public health from the aerosolized spread of bacteria during slurry spreading by rain gun are low. Although, zoonotic agents on crop phylloplanes perish quickly, the risks of overhead irrigation of fresh produce 3 weeks before harvest should still be considered.
Significance and Impact of the Study:  These preliminary results improve our understanding on the fate of zoonotic agents in the environment. Spreading liquid livestock wastes by an airborne mechanism may not pose a significant public health risk. Detection of zoonotic agents 3 weeks after contamination of lettuce and spinach means that consideration should be given by the farmers until the time of harvest, when irrigating fresh produce with water that may have been directly or indirectly contaminated by livestock wastes.     

外来植物肿柄菊(Tithonia diversifolia)的繁殖特性及其地理扩散

肿柄菊 Tithonia diversifolia (Hemsl.) A.Gray 原产墨西哥及中美洲,被作为观赏及绿肥植物引入我国各地栽培.引入云南栽培的肿柄菊于20世纪30年代在云南南部逃逸生长,现在云南的热带、南亚热带和中亚热带地区形成危害.为了查明肿柄菊的扩散特点和入侵潜能,对选取的5个不同地理气候条件下的肿柄菊居群的果序直径、每序结实量、结籽率、千粒重、种子大小(长和宽)等6个指标进行统计分析.结果表明,6个生物学指标在5个居群间都具有极显著差异(p＜0.01),并随着居群间地理气候条件差异的增大,这6个指标值在居群间的差异也有增大趋势.对新鲜采集的不同居群种子在15、20、25、30、35℃下做萌发实验,结果显示在前4种温度条件下5个居群间的种子萌发率有极显著差异(p＜0.01),在35℃下萌发率有显著差异(p＜0.05),并且5个居群的种子最高萌发率不相同且差异极显著(p＜0.01).分析对比作者以往对肿柄菊群落特征和克隆繁殖特性的研究结果认为,虽然肿柄菊在不同的地理气候条件下有性繁殖特性有较大差异,但群落结构差异不大,危害程度表现相似;由于肿柄菊有性繁殖和克隆繁殖的协同作用,使其通过人为引种、道路交通、水流等传播到新的地域后,极易建立新种群,并形成单优种群落而不断侵占和统治新的领地.     

The habitat and conduit functions of roads in the spread of three invasive plant species

Nonnative plant species commonly occur along roadsides, and populations are often assumed to invade by spread along the road axis. To distinguish between the function of roadsides as movement corridors and as habitat, nonnative plant species were surveyed along roads in deciduous forest sites in southeastern Ohio, USA. The importance of road proximity was tested by comparing nonnative species abundance in 100 m transects along roads with transects in undisturbed forest. Nonnative species were most abundant and most frequently observed in roadside sites in valleys. Three common species were chosen for closer scrutiny. In a seed sowing experiment roads and open sites proved to be better locations for the germination and growth of Microstegium vimineum than non-roadside and closed-canopy sites. Tussilago farfara and Rosa multiflora occurred in a small number of disjunct patches suggesting infrequent arrival in the sampled transects. Both species were strongly clustered at scales consistent with diffusive spread by vegetative growth and short-range seed dispersal. Comparisons of distributions parallel and perpendicular to roads showed no evidence for enhanced dispersal along the road axis. Microstegium distributions were correlated with local light availability implying site saturation. Microstegium micro-distributions suggested that spread along the road axis was facilitated by movement of dormant seeds in road maintenance. Thus, roadsides appear to function as both habitat and a conduit for population expansion, with the rate of spread dependent on the life history of the individual species. These results suggest a hierarchical process of regional invasion, with different dispersal mechanisms functioning at different spatial scales.     

Restoration of a species‐rich meadow on arable land by transferring meadow blocks

Question: Does transplantation of small blocks of turfs contribute to restoration of species‐rich meadows on fallow land? What is the role of vegetative spread and seedling establishment of meadow plants in the neighbourhood of the transplanted turfs? Location: Bílé Karpaty Mountains, SE Czech Republic. Methods: Twenty‐five meadow blocks, 0.4 m × 0.4 m in size, were transplanted to fallow land (unfertile and dry) and species composition was monitored in the source area, in the transferred turfs and in their neighbourhood for 3 yr. Multivariate analyses were used to assess successional trends. Results: The transferred meadow blocks served as a source of diaspores for the seed‐limited fallow land. Out of 80 transplanted species 17 species spread to adjacent plots within 3 yr. The frequency of plants expanding from the transferred turfs, either vegetatively or by seeds, was relatively low and from 2002 to 2004 a total of 22 species declined in the transferred turfs before expanding to the neighbourhood. Successional trends in species composition of the plots adjacent to the transferred blocks were strongly significant compared with the vegetation of the source area despite the short‐term data used for the evaluation. The role of the seed bank in restoration was negligible. Conclusions: In infertile and dry environments, transplanted turfs may significantly speed up restoration, especially if natural sources of target plant seeds are not available in the neighbourhood. However, the restoration process is long‐term and not all transferred plants can be expected to establish in the fallow land.     

The intermediate distance hypothesis of biological invasions

Biological invasions are a worldwide phenomenon, but the global flows between native and alien regions have rarely been investigated in a cross‐taxonomic study. We therefore lack a thorough understanding of the global patterns of alien species spread. Using native and alien ranges of 1380 alien species, we show that the number of alien species follows a hump‐shaped function of geographic distance. We observe distinct variations in the relationship between alien species exchanges and distance among taxonomic groups, which relate to the taxa‐specific dispersal modes and their pathways of introduction. We formulate a simple statistical model, combining trade volume and biogeographic dissimilarity, which reproduces the observed pattern in good agreement with reported data and even captures variations among taxonomic groups. This study demonstrates the universality of the intermediate distance hypothesis of alien species spread across taxonomic groups, which will help to improve the predictability of new alien species arrivals.     

When is it socially acceptable to feel sick?

Disease is a ubiquitous and powerful evolutionary force. Hosts have evolved behavioural and physiological responses to disease that are associated with increased survival. Behavioural modifications, known as ‘sickness behaviours’, frequently involve symptoms such as lethargy, somnolence and anorexia. Current research has demonstrated that the social environment is a potent modulator of these behaviours: when conflicting social opportunities arise, animals can decrease or entirely forgo experiencing sickness symptoms. Here, I review how different social contexts, such as the presence of mates, caring for offspring, competing for territories or maintaining social status, affect the expression of sickness behaviours. Exploiting the circumstances that promote this behavioural plasticity will provide new insights into the evolutionary ecology of social behaviours. A deeper understanding of when and how this modulation takes place may lead to better tools to treat symptoms of infection and be relevant for the development of more efficient disease control programmes.     

The potential and realized spread of wildfires across Canada

Given that they can burn for weeks or months, wildfires in temperate and boreal forests may become immense (eg., 10⁰ – 10⁴ km²). However, during the period within which a large fire is ‘active’, not all days experience weather that is conducive to fire spread; indeed most of the spread occurs on a small proportion (e.g., 1 – 15 days) of not necessarily consecutive days during the active period. This study examines and compares the Canada‐wide patterns in fire‐conducive weather (‘potential’ spread) and the spread that occurs on the ground (‘realized’ spread). Results show substantial variability in distributions of potential and realized spread days across Canada. Both potential and realized spread are higher in western than in eastern Canada; however, whereas potential spread generally decreases from south to north, there is no such pattern with realized spread. The realized‐to‐potential fire‐spread ratio is considerably higher in northern Canada than in the south, indicating that proportionally more fire‐conducive days translate into fire progression. An exploration of environmental correlates to spread show that there may be a few factors compensating for the lower potential spread in northern Canada: a greater proportion of coniferous (i.e., more flammable) vegetation, lesser human impacts (i.e., less fragmented landscapes), sufficient fire ignitions, and intense droughts. Because a linear relationship exists between the frequency distributions of potential spread days and realized spread days in a fire zone, it is possible to obtain one from the other using a simple conversion factor. Our methodology thus provides a means to estimate realized fire spread from weather‐based data in regions where fire databases are poor, which may improve our ability to predict future fire activity.