Direct and interactive effects of enemies and mutualists on plant performance: a meta-analysis

Plants engage in multiple, simultaneous interactions with other species; some (enemies) reduce and others (mutualists) enhance plant performance. Moreover, effects of different species may not be independent of one another; for example, enemies may compete, reducing their negative impact on a plant. The magnitudes of positive and negative effects, as well as the frequency of interactive effects and whether they tend to enhance or depress plant performance, have never been comprehensively assessed across the many published studies on plant-enemy and plant-mutualist interactions. We performed a meta-analysis of experiments in which two enemies, two mutualists, or an enemy and a mutualist were manipulated factorially. Specifically, we performed a factorial meta-analysis using the log response ratio. We found that the magnitude of (negative) enemy effects was greater than that of (positive) mutualist effects in isolation, but in the presence of other species, the two effects were of comparable magnitude. Hence studies evaluating single-species effects of mutualists may underestimate the true effects found in natural settings, where multiple interactions are the norm and indirect effects are possible. Enemies did not on average influence the effects on plant performance of other enemies, nor did mutualists influence the effects of mutualists. However, these averages mask significant and large, but positive or negative, interactions in individual studies. In contrast, mutualists ameliorated the negative effects of enemies in a manner that benefited plants; this overall effect was driven by interactions between pathogens and belowground mutualists (bacteria and mycorrhizal fungi). The high frequency of significant interactive effects suggests a widespread potential for diffuse rather than pairwise coevolutionary interactions between plants and their enemies and mutualists. Pollinators and mycorrhizal fungi enhanced plant performance more than did bacterial mutualists. In the greenhouse (but not the field), pathogens reduced plant performance more than did herbivores, pathogens were more damaging to herbaceous than to woody plants, and herbivores were more damaging to crop than to non-crop plants (suggesting evolutionary change in plants or herbivores following crop domestication). We discuss how observed differences in effect size might be confounded with methodological differences among studies.     

Grazer traits, competition, and carbon sources to a headwater-stream food web

We investigated the effect of grazing by a dominant invertebrate grazer (the caddisfly Glossosoma penitum) on the energy sources used by other consumers in a headwater-stream food web. Stable isotope studies in small, forested streams in northern California have shown that G. penitum larvae derive most of their carbon from algae, despite low algal standing crops. We hypothesized that the caddisfly competes with other primary consumers (including mayflies) for algal food and increases their reliance on terrestrial detritus. Because Glossosoma are abundant and defended from predators by stone cases, their consumption of algal energy may reduce its transfer up the food chain. We removed Glossosoma (natural densities >1000 caddisflies/m2) from five approximately 4 m2) stream sections during the summer of 2000 and measured responses of algae, invertebrate primary consumers, and invertebrate predators. The treatment reduced Glossosoma biomass by 80-90%. We observed a doubling in chlorophyll a per area in sections with reduced Glossosoma abundance and aggregative increases in the biomass of undefended primary consumers. Heptageniid mayfly larvae consumed more algae (as measured by stable carbon isotope ratios and gut content analysis) in caddisfly removal plots at the end of the 60-day experiment, although not after one month. We did not see isotopic evidence of increased algal carbon in invertebrate predators, however. Patterns of caddisfly and mayfly diets in the surrounding watershed suggested that mayfly diets are variable and include algae and detrital carbon in variable proportions, but scraping caddisflies consume primarily algae. Caddisfly and mayfly diets are more similar in larger, more productive streams where the mayflies assimilate more algae. Isotopic analysis, in combination with measurements of macroinvertebrate abundance and biomass in unmanipulated plots, suggested that a substantial portion of the invertebrate community (>50% of biomass) was supported, at least partially, by local algal carbon during midsummer. These data suggest that algae may be more important to community dynamics in headwater streams than their relatively low productivity would suggest. Through their high densities and relative invulnerability to predation, armored grazers may also affect community structure and flow of algal and detrital carbon in headwater streams.     

A preliminary ergonomic assessment of piloting a lifeboat in ice

This paper examines human factors associated with piloting a totally enclosed motor propelled survival craft (TEMPSC or lifeboat) in ice. The first section of the paper describes the use of a usability assessment scale to evaluate the coxswain’s (TEMPSC captain) control panel. The second portion examines environmental conditions (habitability) inside the lifeboat during evacuation. All testing was completed in conditions that were consistent with those that might be experienced by ship or offshore oil and gas crewmembers in the event of abandonment due to an onboard emergency. Results indicated that the lifeboat test configuration presented considerable challenges to usability/functionality as well as habitability. These findings suggest that further research should be conducted to evaluate the safety of all existing lifeboat designs. Finally, it is recommended that the international maritime organization (IMO) and safety of life at sea (SOLAS) Convention should mandate user-centered design evaluations for future lifeboat manufacturing.     

Influence of weak electric and magnetic fields on turning behavior in elvers of the American eel Anguilla rostrata

The turning behavior of elvers of the American eel Anguilla rostrata was studied in an arena in which a horizontal electric or a vertical magnetic field could be manipulated. The objectives were to determine if the strength and polarity of a weak direct-current (dc) electric field influenced elver orientation, and to determine if any such influence was due to electric fields generated by the elvers' own swimming movements. As electric current density increased from 10^-2 A cm^-2 to 10² A cm^-2, elvers turned increasingly more toward the anode, regardless of whether the anode was on the left or right side of the arena. Elvers in the lowest field turned more toward the cathode than control elvers, and elvers in the highest field turned more toward the anode than controls. There were no differences in mean turning angles of groups of elvers swimming in four different vertical magnetic field conditions (0.54 gauss, <0.02 gauss, 0.52 gauss reversed direction, and 2.00 gauss), suggesting that elvers were not influenced by internally generated electric fields. However, swimming speeds were such that the generated fields would have been of the order of 10^-4 A cm^-2 or less. Elver orientation apparently could be influenced by electric fields of the magnitude generated in major ocean current systems, but probably are not influenced by electric fields generated by their own swimming in the geomagnetic field.     

Magneto-biomonitoring of intra-urban spatial variations of particulate matter using tree leaves

Preliminary mineral magnetic results from a pilot project investigating the suitability of roadside tree leaves as depositories of vehicular pollution are presented. Tree leaf surfaces (Lime: Tilia europaea; Sycamore: Acer pseudoplatanus) at four roadside and one woodland location in Wolverhampton, UK, have been monitored (July 2003 to November 2003). Mineral magnetic technologies have revealed spatial variations of particulate pollution concentration throughout the conurbation and data analysis indicates that magnetic concentration parameters are suitable proxies for fine particulate pollution, which are particularly hazardous to health. Site-specific traffic management and associated vehicle behaviour appear to be chiefly responsible for the magnetic concentration differences between sites. Magneto-biomonitoring in this way allows the high-resolution spatial mapping of particulate matter (PM) pollution, which may also benefit epidemiology in better assessing exposure to vehicular-derived particulates. Given the speed, measurement sensitivity and non-destructive nature of the technique, it is proposed that this low-cost approach offers some advantages over centralised monitoring stations to monitor urban roadside particulate pollution.     

车用三效催化转化器发展概况

从载体及三效催化剂角度论述了车用三效催化转化器的发展；指出了影响车用三效催化转化器性能的因素，这些因素的作用是协同的；为提高催化转化器的性能，必须采用系统的方法对其进行优化设计。     

Metabolic scaling,buoyancy, and growth in larval Atlantic menhaden,Brevoortia tyrannus

We measured growth of larval Atlantic menhaden, Brevoortia tyrannus in terms of mass, volume, and weight in water as well as the mass-specific activities of the metabolic enzymes citrate synthase, lactate dehydrogenase, and malate dehydrogenase. Weight in water, the force the fish must exert to maintain vertical position, increases by a factor of 18 in larvae growing from 10 to 15 mm. The weight increase coincides with the development of the larval swim bladder. The activities of all three enzymes per unit mass of fish tissue decline greatly over this time period, indicating that the fish does not further develop its aerobic and anaerobic metabolic capacity for swimming during this growth interval.     

Incorporating Social Context Variables Into Paired Watershed Designs to Test Nonpoint Source Program Effectiveness1

Prokopy, Linda Stalker, Z. Asligül Göçmen, Jing Gao, Shorna Broussard Allred, Joseph E. Bonnell, Kenneth Genskow, Alicia Molloy, and Rebecca Power, 2011. Incorporating Social Context Variables Into Paired Watershed Designs to Test Nonpoint Source Program Effectiveness. Journal of the American Water Resources Association (JAWRA) 47(1):196‐202. DOI: 10.1111/j.1752‐1688.2010.00508.x Abstract: In a traditional paired watershed study, watersheds are selected to be as similar as possible so that conclusions may be drawn about the performance of Best Management Practices. We have extended the paired watershed concept to examine the effectiveness of watershed management programs by adding comparative criteria for social characteristics. For four different 8 or 11/12 digit hydrologic unit code (HUC) watersheds in the Midwest, we have piloted a systematic method for selecting paired subwatersheds. First, we developed a list of 11 key variables. Next, a factor analysis was conducted to determine the underlying structure of the 11 input variables. Finally, in each of the four watersheds, potential paired subwatersheds (all 14 digit HUCs) were selected using the factors in a cluster analysis. Informal interviews were then held with key informants in each watershed to provide qualitative assessments of criteria that could impact the comparability of the subwatersheds. This method for selecting paired watersheds should be helpful for other researchers to test the effectiveness of watershed management programs focused on behavior change.     

Visitor impact on backcountry campsites in the Great Smoky Mountains

Over the last decade the Great Smoky Mountains National Park (GSMNP) has experienced a tremendous increase in visitation, especially in backcountry camping. In 1976 there were an estimated 117,500 backcountry visitor nights, with a peak of 16,865 visitor nights in April. The high use season extends from March to October. Visitation tends to be concentrated in certain sections of the park and at specific sites. The Appalachian Trail, which includes about 8 percent of the maintained trail mileage, carried 32 percent of the visitor nights in 1976.Campsite disturbance is also concentrated in specific sites and sections of the park. Maximum camping disturbance per km of maintained trail was 3,400 m² for the sites on the Appalachian Trail. Shelter sites have more visitation per site and more total disturbance per site than open campsites, but shelters tend to have less intensive disturbance, such as bare soil, because they concentrate trampling impacts. Visitation levels were strongly correlated with disturbances such as bare soil at open campsites. Visitation was significantly correlated to the number of firepits at shelter sites but not to other types of disturbance. Regressions indicate that for each additional visitor night at a site (annual average), one can expect an additional 9 m² of total disturbance and 1 m²of bare soil. The distance of a site from the nearest road was not significantly correlated with damage or visitation. Elevation was correlated to visitation levels, especially in the case of the shelters. More legal sites and large illegal sites are in mesic forest types. Illegal camping accounted for 10 percent of the total camping disturbance.The data imply that the suggested removal of shelters will require redistribution of visitor use or replacement developments, such as tent platforms, in order to mitigate damage. Zone camping is a possible alternative but presents difficulties because campers may concentrate in certain plant communities and topographic positions.