Controlled Field Experiment Research Articles

Tori lines mitigate seabird bycatch in a pelagic longline fishery

Albatross bycatch has been increasing over the past decade in the US tuna longline fishery of the central North Pacific. A controlled field experiment was used to assess the efficacy of bird scaring or tori lines as a seabird bycatch mitigation measure for this fishery in a 3-factor sampling design with other mitigation methods (blue-dyed bait, offal discharge). A multilevel geoadditive Bayesian regression modeling approach was used to assess 3 albatross-gear interaction metrics (attempted contacts, contacts, captures) recorded for each longline set using an electronic monitoring system. We found albatross contacts with baited hooks were ca. 3 times (95% highest posterior density interval [HDI] 1–7) less likely for sets equipped with tori lines rather than without tori lines. Attempts to contact baited hooks were ca. 2 times (95% HDI 1–4) less likely for tori line-equipped sets. Albatrosses were also less likely to be captured in tori line sets but captures were too few to support strong inference compared with the contact rates. Tori lines were therefore found to be an effective management measure to mitigate albatross interactions in this fishery. Offal discharge during setting, however, was associated with higher seabird interactions—but that inference was not strong since offal discharge and blue-dyed bait were confounded treatments in some sets. Nonetheless, it was apparent that neither offal discharge nor blue-dyed bait was helpful in reducing albatross interactions in this trial and so the efficacy of those measures warrants further experimental investigation.

Social Media, Influencers, and Adoption of an Eco-Friendly Product: Field Experiment Evidence from Rural China

Can low-cost marketing tools that are used to enhance business performance also contribute to creating a better world? The authors investigate the role of online social media tools in alleviating customer (farmer) uncertainty and promoting the adoption of a new eco-friendly pesticide in rural China via a randomized controlled field experiment. The key finding is that even for a new product such as a pesticide, a low-cost social media support platform can effectively promote adoption. A combination of information from peers and from the firm on the platform facilitates learning about product features and alleviates uncertainty associated with product quality and appropriate product usage. Nevertheless, at the trial stage of the funnel, the platform underperforms the firm’s customized one-on-one support because available information does not resolve uncertainty in supplier credibility and product authenticity. Having an influencer on the platform, albeit not an expert on this product, vouching for its credibility helps resolve this funnel-holdup problem. From a theoretical perspective, this paper provides suggestive evidence for referent influence and credibility signaling on social media platforms and consequences for new product trial. The authors also provide direct empirical evidence on how information facilitates learning, a phenomenon typically assumed to be present in studies estimating learning models.

Stemphylium blight reduces milling qualities of lentil

AbstractStemphylium blight (SB) (Stemphylium botryosum) is a major disease of lentil (Lens culinaris Medik.) in many global production regions. In Canada, SB typically occurs after canopy closure in the second half of the growing season when weather conditions become warm and humid. Experiments were carried out to assess the impact of SB disease on milling qualities of lentil. In 2014, milling qualities of red lentils were compared between seed obtained from an uninfected site and those produced at a naturally SB‐infected site. In 2016 and 2017, controlled field experiments were conducted by artificially inoculating the plots with SB conidia at the early flowering stage. Seed yield in the infected plots was reduced by 52, 22, and 30% compared with control plots in 2014, 2016, and 2017, respectively. The percentages of stained and deformed seeds were increased in infected plots in 2016 and 2017. Seeds infected with SB have reduced milling qualities. Dehulling efficiency was reduced by 25.3, 23.0, and 15.9%, and milling recovery was reduced by 23.7, 25.4, and 15.1% compared with the uninfected control plots, respectively, in 2014, 2016, and 2017. Stemphylium blight had minimal impact on football lentil recovery. These results suggest that SB is potentially the leading cause of the reported poor milling quality of Canadian red lentils that reduces the economic value in years when the growing season is favorable for development of SB. These results have major implications for agronomy, pathology, and breeding strategies of the lentil crop in temperate production regions.

Optimal fishing effort benefits fisheries and conservation

The ecosystem effects of all commercial fishing methods need to be fully understood in order to manage our marine environments more effectively. The impacts associated with the most damaging mobile fishing methods are well documented leading to such methods being removed from some partially protected areas. In contrast, the impacts on the ecosystem from static fishing methods, such as pot fishing, are less well understood. Despite commercial pot fishing increasing within the UK, there are very few long term studies (> 1 year) that consider the effects of commercial pot fishing on temperate marine ecosystems. Here we present the results from a controlled field experiment where areas of temperate reef were exposed to a pot fishing density gradient over 4 years within a Marine Protected Area (MPA), simulating scenarios both above and below current levels of pot fishing effort. After 4 years we demonstrate for the first time negative effects associated with high levels of pot fishing effort both on reef building epibiota and commercially targeted species, contrary to existing evidence. Based on this new evidence we quantify a threshold for sustainable pot fishing demonstrating a significant step towards developing well-managed pot fisheries within partially protected temperate MPAs.

Disaggregating the effects of nitrogen addition on gross primary production in a boreal Scots pine forest

Adding nitrogen to boreal forest ecosystems commonly increases gross primary production (GPP). The effect of nitrogen addition on ecosystem GPP is convoluted due to the impacts of and interactions among leaf scale photosynthetic productivity, canopy structure, site fertility, and environmental constraints. We used a unique controlled nitrogen fertilisation experiment combined with eddy covariance measurements and the calibration of a LUE-based (light use efficiency) photosynthetic production model in order to reveal differences in photosynthetic capacity due to nitrogen addition.A systematically designed soil moisture survey was conducted to characterise the within-site spatial heterogeneity and validate the difference of water stress between fertilised and control sites. The canopy photosynthetic light responses and environmental constraints were evaluated using an inverse modelling approach. We found that nitrogen fertilisation elevated ecosystem GPP by 24% according to model simulations. This was caused by increases in ecosystem light interception (through an increase in leaf area index (LAI)) and LUE by 7% and 17%, respectively. Nitrogen addition increased canopy potential LUE for both low and high photosynthetic photon flux density (PPFD) conditions. The calculations of leaf area and light interception indicated that the understorey vegetation contributed 9% of ecosystem GPP in the fertilised site and 7% in the control site when assuming a same LUE for trees and shrubs. The constraint arising from atmospheric water demand, rather than soil water stress, was the dominating control of the intra- and inter-annual GPP variations. The uncertainty propagated from soil moisture data is negligible for GPP predictions, but influential in the inference on the severity of the drought. This study demonstrates the combination of the controlled field experiment with the inverse modelling approach provides a powerful tool to quantitatively describe and disaggregate N addition effects on forest ecosystem GPP.

EXPERIMENTALLY INDUCED PORCINE COCCIDIOSIS

Two controlled field experiments in which the performance of groups of pigs were studied following daily exposures to large numbers of mixed sporulated coccidial oocysts are reported. Comparisons between control and principal groups were made on the basis of faecal oocyst counts (OPG) and body weight gains. On the basis of oocyst counts, experimentally in fected principals in both experiments developed substantial oocyst populations which reached a peak on the 9th day of infection and declined steadily. Therefore, environmental controls did not develop oocysts. Controls gained more weight on the average than the infected principals during the experiments. Microscopic examination of intestinal tissue sections from an infected principal that died on day 22 revealed the presence of several large cystic bodies in the mucosa of the caecum and large colon. It is suggested that these structures could be schizonts.

Do Arabian babblers play mixed strategies in a “volunteer’s dilemma”?

When group-living Arabian babbler songbirds hear a sentinel alarm call that indicates a raptor approach, they should instantaneously choose whether to flee to shelter, or rather to expose themselves while calling towards the raptor to communicate to it its detection. If enough group members thus signal to the raptor their vigilance, the raptor is likely to be dissuaded from attacking the group. Groupmates thus engage in a variant of the “volunteer’s dilemma” game (Diekmann, 1985), whose symmetric equilibrium is in mixed strategies.We check whether in nature Arabian babblers indeed make independent randomized choices upon hearing alarm calls, in natural conditions as well as in a controlled field experiment in which recorded alarm calls were broadcast to group members. We use a resampling method to check for independence across group members in their reactions to sentinel alarm calls.In natural conditions independent mixed-strategy behaviour was refuted, and not refuted in the artificial conditions of the experiment. This is the first real-world test of mixed-strategy behaviour in games with more than two players.

Turning the tide: a quasi-experimental study on a coaching intervention to reduce burn-out symptoms and foster personal resources among medical residents and specialists in the Netherlands

ObjectivesPhysician burn-out is increasing, starting already among residents. The consequences of burn-out are not limited to physicians’ well-being, they also pose a threat to patient care and safety. This study...

Mandatory Integration Agreements for Unemployed Job Seekers: A Randomized Controlled Field Experiment in Germany

In the German unemployment insurance system, Integration Agreements (IA) are mandatory contracts between the employment agency and the unemployed, jointly signed by the latter and the caseworker. IAs stipulate rights and obligations but are generally perceived as instruments to control search behavior. We designed and implemented a Randomized Controlled Trial involving thousands of newly unemployed workers, where we randomize the timing of the IA as well as the extent to which this timing is announced prior to the meeting. Randomization is at the individual level. We use administrative registers to observe outcomes. A theoretical analysis of anticipation of prior announcements provides suggestions to empirically detect this. The results show that IAs early in the spell have on average a small positive effect on entering employment within a year. When classifying individuals using an employability indicator, we find that this result is driven by individuals with adverse prospects. Among them, being assigned to an early IA increases the probability of re-employment within a year from 45% to 53%.

Recommender Systems: Friend (of Choice) or Foe? A Large-scale Field Experiment in Online Shopping Platforms

Recommender System (RS) algorithms are increasingly involved in online decision-making, helping consumers quickly screen large assortments by presenting the most appealing products first. However, while purporting to facilitate choice, RS algorithms might be inadvertently hindering it due to the highly attractive choice-sets they produce which might contribute to choice overload. I conduct the first randomized controlled field experiment examining the effect of a RS algorithm on choice overload in an online shopping context. In this experiment with 23,165 consumers in two online retailers, I find that a considerably altered RS algorithm that presented consumers with only the most appealing product results followed by results of diminished attractiveness did not affect various measures of consumer choice. The revised algorithm neither mitigated nor aggravated choice overload, as measured by likelihood of purchase/add-to-cart, number of products viewed and session time, suggesting that such algorithms could be designed more effectively. This article proposes that studying consumer psychology phenomena in the unique setting provided by RS algorithms can result in both rich scientific insights and more helpful algorithms.

Friday Morning Fever. Evidence from a Randomized Experiment on Sick Leave Monitoring in the Public Sector

This paper provides the first analysis of a population-wide controlled field experiment for home visits checking on sick leave in the public sector. The experiment was carried out in Italy, a country with large absenteeism in the public sector, and it concerned the universe of public employees. We exploit unique administrative data from the Italian social security administration (INPS) on sick leave and work histories. We find that receiving a home visit reduces the number of days on sick leave in the following 16 months by about 12% (5.5 days). The effect is stronger for workers who are found irregularly on sick leave (-10.2 days). We interpret our findings as a deterrence effect of home visits: workers being found irregularly on sick leave experience a decline of about 2% of their wage in the following 12 months. Uncertainty aversion (there is no automatism in these sanctions) can play a role in these results. Our estimates suggest that home visits are cost-effective: every Euro spent for the visits involves up to 10 Euros reductions in sick benefits outlays. We estimate the marginal value of public funds (MVPF) spent on home visits at about 1.13, which is significantly lower than estimates of MVPF of income taxes in the US.

Harvester Ants Reduce Seed Survivorship in Slickspot Peppergrass, a Rare Mustard Endemic to Idaho

Seed predation can significantly reduce the reproductive success of individual plants and their populations. The consequences of seed predation often are most pronounced for rare plant species, in which loss of seeds can have a disproportionate effect on populations. The present study examined the effects of seed predation by Owyhee harvester ants (Pogonomyrmex salinus) on seed survivorship in slickspot peppergrass (Lepidium papilliferum), a rare mustard endemic to sagebrush-steppe habitat in southwestern Idaho. Within sagebrush-steppe, L. papilliferum is restricted to microsites known as “slick spots”—shallow depressions of soil characterized by distinct clay layers and surface water retention that is higher than that of surrounding areas. Harvester ants frequently nest in L. papilliferum habitat and readily consume the plant's seeds. We conducted a controlled field experiment at a population of L. papilliferum in 2012 to quantify seed loss to individual plants as a result of seed predation by harvester ants. Across 20 slick spots, plants exposed to harvester ants experienced a median reduction in seed survivorship of 89.2% (interquartile range, 69.3% to 93.9%) relative to plants in the same slick spot that were matched for size and shielded from ants. The proportion of seeds that plants lost to seed predation was more variable and significantly lower in slick spots with >150 plants than in those with fewer plants, suggesting that a threshold to the number of seeds that can be collected and consumed by ants may occur within the natural range of plant densities found in slick spots. Our results suggest that slick spots supporting large numbers of L. papilliferum in a given year may be buffered from the effects of predation, whereas those with relatively few plants are particularly vulnerable to high levels of seed loss to harvester ants.

The geomagnetic field does not appear to influence navigation in Eastern painted turtles

AbstractGeomagnetic cues provide important information to guide aspects of migration, from the general direction of movement to informing an animal's specific location on the planet. Although such cues are used by many long‐distant migrants, its use for short‐ and moderate‐distance migrations is less clear. We have been studying overland migratory movements in a population of Eastern painted turtles where animals use one of four precise, highly predictable routes to locate water sources during migration. Our previous work suggests a strong role of learning and spatial memory in this precise navigation, but the cues used and the context for their use are unknown. Here, we present a series of controlled field experiments in which we test the hypothesis that geomagnetic cues are utilized when Chrysemys picta engage in these intricate, overland movements. We fitted turtles with 3,309 Gauss magnets (n = 10) or aluminum disk controls (n = 5) and surveyed their ability to locate and navigate their routes during migration; turtles were similarly tested for these abilities outside of the context of migration (magnets, n = 30; control, n = 30). Strong magnets (3,309 Gauss) on their carapaces did not disrupt turtles’ ability to locate the paths or the precision with which they navigated them. Turtles, irrespective of treatment, found their paths and/or navigated their paths with the same high precision that we observed in controls and our previous work, both within and outside of the context of migration. Thus, alternative types of cues must be in use that explain the high precision and high reliability of path location over time. Future studies should examine alternative cues used in migratory navigation and the creation of complex and specific paths.

Forage yield gap analysis for tall fescue pastures in Argentina: A modelling approach

AbstractA large gap between actual and potential herbage production of tall fescue is a major limitation for livestock production systems in Argentina. The objectives of this work were to (a) calibrate and test the ability of a published pasture–soil water model to represent herbage growth dynamics of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] under different growing conditions, using data from controlled field experiments; (a) use the evaluated model to predict the magnitude and time of the year that N or soil water would constrain tall fescue from attaining its potential growth rate in the south‐eastern Pampas of Argentina; and (c) quantify herbage production gains and temporal variability for a proposed improved management practice (IMP) of N fertilizer under different meteorological and soils scenarios. After tall fescue‐specific calibration, the model accurately represented the response of tall fescue herbage mass to irrigation and N fertilization (root mean square error of prediction <550 kg DM ha−1, R2 > .70) observed in thirteen single‐season, controlled, field experiments. Results from a 40‐year simulation show that the gap between fertilized and unfertilized tall fescue pastures in Argentina can exceed 14 t DM ha−1 year−1. The proposed IMP maximized responses to N in autumn and early spring, reducing the annual herbage production gaps by 38%. The effect of IMP on annual herbage production was larger (4–5 t DM ha−1 year−1) than the effect due to variability in soils’ ability to store water (2–4 t DM ha−1 year−1) or annual variability in meteorological conditions (±1–2 t DM ha−1 year−1). This work provides a sound modelling approach to identify, for a particular forage species and site, most of the main gaps of herbage production; and to quantify, without the need of long‐term, expensive field studies, some of the potential gains (and risks associated with temporal variability), that could be achieved by producers. In addition, our results clearly indicate that site‐specific calibration is required for the model to provide accurate predictions and sound management advice to farmers.

Faunal responses to fire in Australian tropical savannas: Insights from field experiments and their lessons for conservation management

AbstractAimFire is particularly frequent, complex and contentious in the vast tropical savannas of northern Australia, where declines in many threatened species are associated with fire, and substantial areas are under fire management for greenhouse gas abatement. Controlled field experiments are crucial for understanding biodiversity responses, and here I present key insights into faunal responses to fire that have been revealed by them, along with their lessons for fire management.LocationAustralian monsoonal tropics.MethodsResults are synthesized from six replicated fire experiments that have been conducted in Australian savannas and include multispecies assessments of fauna. The synthesis also draws on other fire studies and is presented in the form of five key insights into faunal responses.ResultsThe key insights are as follows: (a) most faunal groups are extremely resilient to fire, with highly contrasting fire regimes often having little or no detectable impact on species abundances, at least in the medium term; (b) the most important effects of fire are typically indirect through habitat modification, even when there is substantial direct mortality; (c) fire intensity is not as important a factor as is widely thought; rather, fire frequency is particularly important; (d) there will always be winners and losers with any fire; and (e) fire is required for the maintenance of diversity.Main conclusionsThese insights have important implications for conservation management in Australian savannas: management needs to focus on fire‐induced changes to habitat suitability, and to consider faunal outcomes at the landscape scale; a combination of frequently (every 2–3 years) and less frequently (every ≥5 years) burned habitat may adequately conserve the great majority of animal species without a need for complex fire mosaics; special management attention is required for frequent‐fire losers because of an extremely low representation of longer‐unburnt habitat; and fire needs to be actively managed to promote diversity, not excluded. The insights are widely applicable to tropical grassy ecosystems more generally, and some appear to be universal to fire‐prone biomes.

The Effectiveness of the Effectuation Approach on Opportunity Identification and Pursuit: Evidence From a Randomized Controlled Field Experiment

Identifying and pursuing opportunities for new business are crucial capabilities of successful entrepreneurs; as such, opportunity identification and pursuit have emerged as important areas of entr...

Plant-mycorrhiza association in urban forests: Effects of the degree of urbanisation and forest size on the performance of sycamore (Acer pseudoplatanus) saplings

Environmental change as result of urbanisation can influence soil microbial communities in green areas. In cities, forests are among the most frequent types of green areas and provide a wide variety of ecosystem services for the residents, such as air cleaning, nutrient cycling and area for recreational activities. Mycorrhizal fungi play an important role for the establishment of trees and therefore for the natural regeneration of forests. We examined the effect of urbanisation on the arbuscular mycorrhizal (AM) fungal symbiosis and performance of Acer pseudoplatanus saplings in a controlled field experiment in forests situated in the city of Basel and its suburbs in Switzerland. A total of 660 one-year-old A. pseudoplatanus saplings were planted in plots in 11 forests, which differed in degree of urbanisation in the surroundings and size. Saplings including their full root systems were harvested after 4, 6 and 13 months. AM fungal colonisation was 15–45 % lower on roots of saplings growing in forests located in areas with a high degree of urbanisation than that on sapling roots in forests in less urbanised areas. Furthermore, AM fungal colonisation of saplings decreased with decreasing forest size. Sapling survival was not influenced by urbanisation, but by forest size. In particular, sapling survival was reduced in small and medium-sized forests. Sapling survival also increased with increasing percentage of AM fungal colonisation after 13 months. These urbanisation- and forest-size induced changes became more pronounced with the time elapsed since the saplings were planted. Our findings demonstrate the negative impact of urbanisation on AM fungal symbiosis and the performance of A. pseudoplatanus saplings and indicate that urbanisation is a threat for the long-term maintenance of intact small urban forests.

Underwater acoustic characterisation of unexploded ordnance disposal using deflagration

The seabed off North West Europe contains much unexploded ordnance (UXO), posing a hazard to offshore developments such as windfarms. The typical removal method is through high-order detonation of a donor charge placed adjacent to the UXO. This method poses a risk of injury or death to marine mammals and other fauna from the high sound levels produced. This paper describes a controlled field experiment to compare the sound produced by high-order detonations with a low-order disposal method called deflagration, which uses a shaped charge of modest size, is less energetic, and offers reduced environmental impact from lower acoustic output. The results demonstrate a substantial reduction over high order detonation, with the peak sound pressure level and sound exposure level being more than 20 dB lower for the deflagration, and with the acoustic output depending only on the size of the shaped charge (rather than the size of the UXO).

Effects of cassava allelochemicals on rubber tree pathogens, soil microorganisms, and soil fertility in a rubber tree–cassava intercropping system

The rubber tree (Hevea brasiliensis)–cassava (Manihot esculenta) intercropping system is one of the most popular intercropping patterns for small-holder rubber planters. However, this practice is not recommended in some rubber-producing countries, since it is believed that the rubber tree and cassava share some identical pathogens and that the intercropping system will deplete soil fertility. The effects of cassava allelochemicals on rubber tree pathogens have never been reported. Using controlled plate tests, pot tests, and field experiments, this study aimed to assess the possible adverse effects that cassavas may impart to rubber plantations. The results showed: (1) although the leaf extract, decomposed leaf extract and root exudates of cassava inhibited or had no effect on the mycelial growth of the rubber tree pathogen Corynespora cassiicola, 10 mg mL−1 and 100 mg mL−1 cassava leaf water extracts and testing concentrations of cassava root extraction significantly promoted the mycelial growth of the rubber tree pathogen Rigidoporus lignosus, which increased the risk of rubber tree white root disease; (2) the overall soil fertility was increased significantly in the rubber tree–cassava intercropping system. However, the soil phosphorus content was reduced significantly in the field experiment; (3) the average girth of rubber trees was significantly reduced, and the girth uniformity was decreased in the intercropping system. Based on the experiment results, we suggested that an optimised fertiliser recommendation, particularly on the phosphorus amount, should be developed and implemented for the rubber tree–cassava intercropping system. In addition, since the intercropping of cassava will increase the risk of R. lignosus-induced rubber tree white root disease, which is very hard to prevent and eradicate once rubber trees are infected, the intercropping of cassava in rubber plantation rows should not be recommended in the R. lignosus prevailing areas.

Benthic Suffocation of Invasive Lake Trout Embryos by Fish Carcasses and Sedimentation in Yellowstone Lake

AbstractIntroduced Lake Trout Salvelinus namaycush threaten native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Yellowstone Lake, Yellowstone National Park, where gill nets have been used to suppress subadult and adult Lake Trout since 1995. However, survival of embryonic and larval life history stages can have profound effects on the population dynamics of Lake Trout. Inducing additional mortality at those stages, especially if used in concert with intensive gillnetting of older fish, could enhance overall suppression efforts. Therefore, we conducted controlled field experiments at Yellowstone Lake to systematically evaluate the effects of sediment deposition and ground Lake Trout carcass deposition on Lake Trout embryos in pre‐positioned incubators. Sediment deposition caused dissolved oxygen concentrations to decline below lethal levels for a prolonged overwinter period (92 d). Embryo mortality among overwintering incubators varied from 97.0 ± 5.3% (mean ± SE) at the substrate surface to 100.0 ± 0.0% at 20 cm below the substrate surface. Decomposition of ground carcass material on spawning sites caused dissolved oxygen concentrations to decline to lethal levels (<3.4 mg/L) for about 9 d after biomass application rates of 14 and 28 kg/m2 in treatment plots. Exposure to ground carcass material resulted in 100.0 ± 0.0% embryo mortality at the substrate surface and within interstices 20 cm below the surface in 14‐ and 28‐kg/m2 biomass treatments. Embryo mortality was probably caused by hypoxic conditions within substrates in both experiments. The deposition of sediment and ground Lake Trout carcass material on Lake Trout spawning sites in Yellowstone Lake could provide an additional source of mortality in ongoing Lake Trout suppression efforts. These methods may also be beneficial in other systems when incorporated in an integrated pest management approach targeting multiple life history stages of invasive freshwater fish.