Generation of internal waves by sheared turbulence: experiments

A series of experiments is presented that model the generation of internal gravity waves in the ocean by the forcing of turbulent eddies in the surface mixed layer.The experimental setup consists of a shallow mixed upper layer and a deep continuously stratified lower layer. A source of turbulence is dragged through the upper layer. Internal waves can freely propagate in the lower layer. The internal waves are measured using synthetic schlieren to determine the frequencies of the generated waves. Consistent with other studies, it is found that the characteristic frequencies of internal waves generated by turbulence are an approximate constant fraction of the buoyancy frequency.     

Mineral licks: motivational factors for visitation and accompanying disease risk at communal use sites of elk and deer

Free-ranging cervids acquire most of their essential minerals through forage consumption, though occasionally seek other sources to account for seasonal mineral deficiencies. Mineral sources occur as natural geological deposits (i.e., licks) or as anthropogenic mineral supplements. In both scenarios, these sources commonly serve as focal sites for visitation. We monitored 11 licks in Rocky Mountain National Park, north-central Colorado, using trail cameras to quantify daily visitation indices (DVI) and soil consumption indices (SCI) for Rocky Mountain elk (Cervus elaphus) and mule deer (Odocoileus hemionus) during summer 2006 and documented elk, mule deer, and moose (Alces alces) visiting licks. Additionally, soil samples were collected, and mineral concentrations were compared to discern levels that explain rates of visitation. Relationships between response variables; DVI and SCI, and explanatory variables; elevation class, moisture class, period of study, and concentrations of minerals were examined. We found that DVI and SCI were greatest at two wet, low-elevation licks exhibiting relatively high concentrations of manganese and sodium. Because cervids are known to seek Na from soils, we suggest our observed association of Mn with DVI and SCI was a likely consequence of deer and elk seeking supplemental dietary Na. Additionally, highly utilized licks such as these provide an area of concentrated cervid occupation and interaction, thus increasing risk for environmental transmission of infectious pathogens such as chronic wasting disease, which has been shown to be shed in the saliva, urine, and feces of infected cervids.     

将高纬度地区生态系统的反馈与恢复力引入公司决策

本文讨论了在高纬度地区公司所起的作用,它被概念化为以社会和经济为媒介的生态系统,同时指出了商业环境里其他的一些重要的社会参与者.我们列举了高纬地区企业行为的三个案例并对其中各种共性进行了讨论.特别的,我们认为有必要对商业理论和实践进行革新,以使其不只是停留在社会与经济概念的组织恢复力上,而要把高纬地区的生态恢复力也包括到商业管理的目标之中.同时我们也认为区域生态系统的恢复力应该成为衡量企业可持续管理的一个有意义的指标,企业高层可以据此制定和修改企业的管理策略.最后,文章在结尾处呼吁对高纬地区内的跨国公司和国内公司的作用制定更为详细的研究议程.     

Hotspots of Epiphytic Lichen Diversity in Two Young Managed Forests

Understanding within-stand variation in diversity of epiphytes will provide an improved basis for producing timber while conserving biological diversity. Two 80-ha, 50–year–old managed stands of conifers were surveyed to locate 0.4 ha putative "diversity" plots, the areas appearing most diverse in lichen epiphytes. These plots were generally located in areas made heterogeneous by canopy gaps, wolf trees (trees with large-diameter lower branches), and old-growth remnant trees. "Matrix" plots, in contrast, were chosen at random from the remaining, more homogenous forest. Diversity plots hosted from 25% to 40% more epiphytic lichen species than matrix plots in both stands. The strongest within-stand gradients in species composition were correlated with percentage of plot occupied by gaps and wolf trees. Percentage of the plot in gaps was correlated with species richness (r = 0.79). In the more structurally diverse stand, diversity and abundance of nitrogen-fixing "cyanolichens" were correlated with percentage of the plot occupied by gaps (0.5 < r < 0.9), and alectorioid lichens were correlated with percentage of the plot occupied by old-growth remnant trees (0.5 < r < 0.6). In the stand with more homogenous structure, percentage of the plot under gaps was correlated with regionally common species that were otherwise absent or sparse in the matrix. Protecting gaps, hardwoods, wolf trees, and old-growth remnant trees during thinning or other partial cutting is likely to promote the majority of epiphytic macrolichens in young conifer forests. Because these features are easily recognized on aerial photos and on the ground by land managers, it is practical to manage for forest structures that would promote lichen diversity.     

Age-specific survivorship in relation to clutch size and fledging success in California gulls

Summary Data from a natural population of California gulls (Larus californicus) demonstrated that increasing reproductive effort with age was associated with reduced survivorship. Number of offspring fledged but not clutch size was inversely related to adult survivorhip indicating that reproductively induced mortality resulted from the cumulative effects of the entire breeding season. Agerelated increases in fledging success were correlated with increased adult mortality. Young gulls fledged few offspring and had high survival rates. Old gulls tended to fledge more offspring and had low survival rates. However, those old gulls fledging few offspring survived as well as young gulls. Data also invalidate the assumption that survivorship is age-constant in this species.