bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of urbanization on direct and indirect interactions in a tri‐trophic system
Authors: Turrini Tabea , Sanders Dirk , Knop Eva
Published: May 2016

While effects of urbanization on species assemblages are receiving increasing attention, effects on ecological interactions remain largely unexplored. We investigated how urbanization influences the strength of direct and indirect trophic interactions in a tri‐trophic system. In a field experiment including five cities and nearby farmed areas, we used potted Vicia faba plants and manipulated the presence of Megoura viciae aphids and that of naturally occurring aphid predators. When predators could access aphids, they reduced their abundance less in the urban than in the agricultural ecosystem. Compared to aphid abundance on plants without predator access, abundance on plants with predator access was 2.58 times lower in urban and 5.27 times lower in agricultural areas. This indicates that urbanization limited top‐down control of aphids by predators. In both ecosystems, plant biomass was negatively affected by herbivores and positively affected by predators, but the positive indirect predator effect was weaker in cities. Compared to aphid‐infested plants without predator access, plants with predator access were 1.89 times heavier in urban and 2.12 times heavier in agricultural areas. Surprisingly, differences between ecosystems regarding the indirect predator effect on plants were not explained by the differentially strong herbivore suppression. Instead, the urban environment limited plant biomass per se, thereby mitigating the scope of a positive predator effect. Our results show that urbanization can influence direct and indirect trophic interactions through effects on biotic top‐down forces and on plant growth. In order to understand how urbanization affects biodiversity and ecosystem functioning, it is fundamental to not only consider species assemblages, but also species interactions.
Space‐time investigation of the effects of fishing on fish populations
Authors: Ono Kotaro , Shelton Andrew O. , Ward Eric J. , Thorson James T. , Feist Blake E. , Hilborn Ray
Published: May 2016

Species distribution models (SDMs) are important statistical tools for obtaining ecological insight into species–habitat relationships and providing advice for natural resource management. ManySDMs have been developed over the past decades, with a focus on space‐ and more recently, time‐dependence. However, most of these studies have been on terrestrial species and applications to marine species have been limited. In this study, we used three large spatio‐temporal data sources (habitat maps, survey‐based fish density estimates, and fishery catch data) and a novel space‐time model to study how the distribution of fishing may affect the seasonal dynamics of a commercially important fish species (Pacific Dover sole,Microstomus pacificus) off the west coast of theUSA. Dover sole showed a large scale change in seasonal and annual distribution of biomass, and its distribution shifted from mid‐depth zones to inshore or deeper waters during late summer/early fall. In many cases, the scale of fishery removal was small compared to these broader changes in biomass, suggesting that seasonal dynamics were primarily driven by movement and not by fishing. The increasing availability of appropriate data and space‐time modeling software should facilitate extending this work to many other species, particularly those in marine ecosystems, and help tease apart the role of growth, natural mortality, recruitment, movement, and fishing on spatial patterns of species distribution in marine systems.
Spatial patterns of plant litter in a tidal freshwater marsh and implications for marsh persistence
Authors: Elmore Andrew J. , Engelhardt Katharina A. M. , Cadol Daniel , Palinkas Cindy M.
Published: May 2016

The maintenance of marsh platform elevation under conditions of sea level rise is dependent on mineral sediment supply to marsh surfaces and conversion of above‐and belowground plant biomass to soil organic material. These physical and biological processes interact within the tidal zone, resulting in elevation‐dependent processes contributing to marsh accretion. Here, we explore spatial pattern in a variable related to aboveground biomass, plant litter, to reveal its role in the maintenance of marsh surfaces. Plant litter persisting through the dormant season represents the more recalcitrant portion of plant biomass, and as such has an extended period of influence on ecosystem processes. We conducted a field and remote sensing analysis of plant litter height, aboveground biomass, vertical cover, and stem density (collectively termed plant litter structure) at a tidal freshwater marsh located within the Potomac River estuary, USA. LiDAR and field observations show that plant litter structure becomes more prominent with increasing elevation. Spatial patterns in litter structure exhibit stability from year to year and correlate with patterns in soil organic matter content, revealed by measuring the loss on ignition of surface sediments. The amount of mineral material embedded within plant litter decreases with increasing elevation, representing an important tradeoff with litter structure. Therefore, at low elevations where litter structure is short and sparse, the role of plant litter is to capture sediment; at high elevations where litter structure is tall and dense, aboveground litter contributes organic matter to soil development. This organic matter contribution has the potential to eclipse that of belowground biomass as the root : shoot ratio of dominant species at high elevations is low compared to that of dominant species at low elevations. Because of these tradeoffs in mineral and organic matter incorporation into soil across elevation gradients, the rate of marsh surface elevation change is remarkably consistent across elevation. Because of the role of plant litter in marsh ecosystem processes, monitoring and assessment of these dynamic geomorphic marsh landscapes might be streamlined through the measurement of plant litter structure, either via LiDAR technologies or field observation.
Do biomass harvesting guidelines influence herpetofauna following harvests of logging residues for renewable energy?
Authors: Fritts Sarah , Moorman Christopher , Grodsky Steven , Hazel Dennis , Homyack Jessica , Farrell Chris , Castleberry Steven
Published: May 2016

Forests are a major supplier of renewable energy; however, gleaning logging residues for use as woody biomass feedstock could negatively alter habitat for species dependent on downed wood. Biomass Harvesting Guidelines (BHGs) recommend retaining a portion of woody biomass on the forest floor following harvest. DespiteBHGs being developed to help ensure ecological sustainability, their contribution to biodiversity has not been evaluated experimentally at operational scales. We compared herpetofauanal evenness, diversity, and richness and abundance ofAnaxyrus terrestrisandGastrophryne carolinensisamong six treatments that varied in volume and spatial arrangement of woody biomass retained after clearcutting loblolly pine (Pinus taeda) plantations in North Carolina,USA(n = 4), 2011–2014 and Georgia (n = 4),USA2011–2013. Treatments were: (1) biomass harvest with noBHGs, (2) 15% retention with biomass clustered, (3) 15% retention with biomass dispersed, (4) 30% retention with biomass clustered, (5) 30% retention with biomass dispersed, and (6) no biomass harvest. We captured individuals with drift fence arrays and compared evenness, diversity, and richness metrics among treatments with repeated‐measure, linear mixed‐effects models. We determined predictors ofA. terrestrisandG. carolinensisabundances using a priori candidateN‐mixture models with woody biomass volume, vegetation structure, and groundcover composition as covariates. We had 206 captures of 25 reptile species and 8710 captures of 17 amphibian species during 53 690 trap nights. Herpetofauna diversity, evenness, and richness were similar among treatments.A. terrestrisabundance was negatively related to volume of retained woody biomass in treatment units in North Carolina in 2013.G. carolinensisabundance was positively related with volume of retained woody debris in treatment units in Georgia in 2012. Other relationships betweenA. terrestrisandG. carolinensisabundances and habitat metrics were weak or absent. The lack of consistent community or population responses suggests the addition of a woody biomass harvest to a clearcut in pine plantations does not impact herpetofauna use of Coastal Plain loblolly plantations in the southeastern United States. We recommend additional research to examine relationships between woody biomass harvesting and rarer species or amphibians with high desiccation risk, particularly in other regions and harvesting systems.
Learning about colonization when managing metapopulations under an adaptive management framework
Authors: Southwell Darren M. , Hauser Cindy E. , McCarthy Michael A.
Published: May 2016

Adaptive management is a framework for resolving key uncertainties while managing complex ecological systems. Its use has been prominent in fisheries research and wildlife harvesting; however, its application to other areas of environmental management remains somewhat limited. Indeed, adaptive management has not been used to guide and inform metapopulation restoration, despite considerable uncertainty surrounding such actions. In this study, we determined how best to learn about the colonization rate when managing metapopulations under an adaptive management framework. We developed a mainland–island metapopulation model based on the threatened bay checkerspot butterfly (Euphydryas editha bayensis) and assessed three management approaches: adding new patches, adding area to existing patches, and doing nothing. Using stochastic dynamic programming, we found the optimal passive and active adaptive management strategies by monitoring colonization of vacant patches. Under a passive adaptive strategy, increasing patch area was best when the expected colonization rate was below a threshold; otherwise, adding new patches was optimal. Under an active adaptive strategy, it was best to add patches only when we were reasonably confident that the colonization rate was high. This research provides a framework for managing mainland–island metapopulations in the face of uncertainty while learning about the dynamics of these complex systems.
Cascade of ecological consequences for West Nile virus transmission when aquatic macrophytes invade stormwater habitats
Authors: Mackay Andrew J. , Muturi Ephantus J. , Ward Michael P. , Allan Brian F.
Published: May 2016

Artificial aquatic habitats are ubiquitous in anthropogenic landscapes and highly susceptible to colonization by invasive plant species. Recent research into the ecology of infectious diseases indicates that the establishment of invasive plant species can trigger ecological cascades which alter the transmission dynamics of vector‐borne pathogens that imperil human health. Here, we examined whether the presence or management of two invasive, emergent plants, cattails (Typha spp.) and phragmites (Phragmites australis), in stormwater dry detention basins (DDBs) alter the local distribution of vectors, avian hosts, or West Nile virus (WNV) transmission risk in an urban residential setting. Mosquitoes and birds were surveyed at 14 DDBs and paired adjacent residential sites. During the study period, emergent vegetation was mowed by site managers in three DDBs. In the absence of vegetation management, the overall abundance and species composition of both adult vectors and avian hosts differed between residential and DDB habitats; however, WNV entomological risk indices were equivalent. Communal bird roosts composed primarily of three species, European Starlings (Sturnus vulgaris), Red‐winged Blackbirds (Agelaius phoeniceus), and Common Grackles (Quiscalus quiscula), representing a broad range of WNV reservoir competence, were observed at half (three out of six) of the DDBs containing unmanaged stands of phragmites; however, their presence was associated with a lower seasonal increase in vector infection rate. Conversely, mowing of emergent vegetation resulted in a significant and sustained increase in the abundance of WNV‐infected vectors in DDBs and the increase in risk extended to adjacent residential sites. These findings indicate that management of invasive plants in DDBs during the growing season can increase, while presence of communal bird roosts can decrease, WNV transmission risk.
Shrubland resilience varies across soil types: implications for operationalizing resilience in ecological restoration
Authors: Wonkka Carissa L. , Twidwell Dirac , West Jason B. , Rogers William E.
Published: May 2016

In ecosystems with alternative stable states, restoration success can be thought of as overcoming the resilience of an undesirable state to promote an alternative state that yields greater ecosystem services. Since greater resilience of undesirable states translates into reduced restoration potential, quantifying differences in resilience can enhance restoration planning. In the context of shrub‐encroached rangeland restoration, shrubland resilience is the capacity of a woody vegetated state to absorb management interventions designed to produce a more desirable grass‐dominated state, and remain within its current regime. Therefore, differences in the resilience of a state can be quantified in a relative sense by measuring whether a state switches to an alternate state following perturbation or remains in its current stability domain. Here we designed an experimental manipulation to assess the contribution of soils to differences in the relative resilience of a shrub‐invaded state. In this large‐scale experiment, we repeated perturbations across a gradient of soil textures to inform restoration practitioners of differences in the relative resilience of shrubland occurring on different soil types to common rangeland restoration practices. On each soil type, we compared the relative ability of the shrubland state to withstand chemical and mechanical brush control treatments, commonly employed in this study region, to untreated controls. While the shrubland community composition did not differ prior to the study, its capacity to absorb and recover from brush removal treatments depended on soil type. Shrubland resilience to chemical and mechanical brush removal was highest on coarse soils. On these soils, brush removal temporarily restored grassland dominance, but woody plants quickly regained pretreatment levels of dominance. However, shrublands on fine soils did not recover following treatments, continuing to be grass‐dominated for the duration of the study. This study highlights a simple approach for prioritizing restoration actions by mapping the locations of different soil attributes that support shrub‐dominated states with differing levels of resilience to brush control. This experimental approach provides a basis for operationalizing resilience in restoration and prioritizing management actions across a range of environmental conditions, which is critical given the economic constraints associated with broad‐scale mechanical and chemical interventions for rangeland restoration.
Moderation is best: effects of grazing intensity on plant–flower visitor networks in Mediterranean communities
Authors: Lázaro Amparo , Tscheulin Thomas , Devalez Jelle , Nakas Georgios , Stefanaki Anastasia , Hanlidou Effie , Petanidou Theodora
Published: May 2016

The structure of pollination networks is an important indicator of ecosystem stability and functioning. Livestock grazing is a frequent land use practice that directly affects the abundance and diversity of flowers and pollinators and, therefore, may indirectly affect the structure of pollination networks. We studied how grazing intensity affected the structure of plant–flower visitor networks along a wide range of grazing intensities by sheep and goats, using data from 11 Mediterranean plant–flower visitor communities from Lesvos Island, Greece. We hypothesized that intermediate grazing might result in higher diversity as predicted by the Intermediate Disturbance Hypothesis, which could in turn confer more stability to the networks. Indeed, we found that networks at intermediate grazing intensities were larger, more generalized, more modular, and contained more diverse and even interactions. Despite general responses at the network level, the number of interactions and selectiveness of particular flower visitor and plant taxa in the networks responded differently to grazing intensity, presumably as a consequence of variation in the abundance of different taxa with grazing. Our results highlight the benefit of maintaining moderate levels of livestock grazing by sheep and goats to preserve the complexity and biodiversity of the rich Mediterranean communities, which have a long history of grazing by these domestic animals.
Optimal management of a stochastically varying population when policy adjustment is costly
Authors: Boettiger Carl , Bode Michael , Sanchirico James N. , LaRiviere Jacob , Hastings Alan , Armsworth Paul R.
Published: May 2016

Ecological systems are dynamic and policies to manage them need to respond to that variation. However, policy adjustments will sometimes be costly, which means that fine‐tuning a policy to track variability in the environment very tightly will only sometimes be worthwhile. We use a classic fisheries management problem, how to manage a stochastically varying population using annually varying quotas in order to maximize profit, to examine how costs of policy adjustment change optimal management recommendations. Costs of policy adjustment (changes in fishing quotas through time) could take different forms. For example, these costs may respond to the size of the change being implemented, or there could be a fixed cost any time a quota change is made. We show how different forms of policy costs have contrasting implications for optimal policies. Though it is frequently assumed that costs to adjusting policies will dampen variation in the policy, we show that certain cost structures can actually increase variation through time. We further show that failing to account for adjustment costs has a consistently worse economic impact than would assuming these costs are present when they are not.
Synthetic predator cues impair immune function and make the biological pesticide Bti more lethal for vector mosquitoes
Authors: Op de Beeck Lin , Janssens Lizanne , Stoks Robby
Published: May 2016

The control of vector mosquitoes is one of the biggest challenges facing humankind with the use of chemical pesticides often leading to environmental impact and the evolution of resistance. Although to a lesser extent, this also holds for Bacillus thuringiensis israelensis (Bti), the most widely used biological pesticide to control mosquito populations. This raises the need for the development of integrated pest management strategies that allow the reduction of Bti concentrations without loss of the mosquito control efficiency. To this end, we tested in a laboratory experiment the combined effects of larval exposure to a sublethal Bti concentration and predation risk cues on life history and physiology of larval and adult Culex pipiens mosquitoes. Besides natural predator kairomones and prey alarm cues, we also tested synthetic kairomones of Notonecta predators. Neither Bti nor predation risk cues affected mortality, yet when both stressors were combined mortality increased on average by 133% compared to the treatment with only predation risk cues. This synergistic interaction was also present when Bti was combined with synthetic kairomones. This was further reflected in changes of the composite index of population performance, which suggested lowered per capita growth rates in mosquitoes exposed to Bti but only when Bti was combined with synthetic kairomones. Furthermore, predation risk cues shortened larval development time, reduced mass at metamorphosis in males, and had an immunosuppressive effect in larval and adult mosquitoes which may affect the mosquito vector competence. We provide the first demonstration that synthetic kairomones may generate similar effects on prey as natural kairomones. The identified immunosuppressive effect of synthetic kairomones and the novel lethal synergism type between a biological pesticide and synthetic predator kairomones provide an important proof of principle illustrating the potential of this combination for integrated mosquito control and should in a next step be evaluated under more natural conditions. It may guide novel integrated pest management programs with Bti that incorporate synthetic kairomones and thereby can reduce environmental impact and evolution of resistance creating more efficient and sustainable mosquito control.
Using counterfactuals to evaluate the cost‐effectiveness of controlling biological invasions
Authors: McConnachie Matthew M. , van Wilgen Brian W. , Ferraro Paul J. , Forsyth Aurelia T. , Richardson David M. , Gaertner Mirijam , Cowling Richard M.
Published: May 2016

Prioritizing limited conservation funds for controlling biological invasions requires accurate estimates of the effectiveness of interventions to remove invasive species and their cost‐effectiveness (cost per unit area or individual). Despite billions of dollars spent controlling biological invasions worldwide, it is unclear whether those efforts are effective, and cost‐effective. The paucity of evidence results from the difficulty in measuring the effect of invasive species removal: a researcher must estimate the difference in outcomes (e.g. invasive species cover) between where the removal program intervened and what might have been observed if the program had not intervened. In the program evaluation literature, this is called a counterfactual analysis, which formally compares what actually happened and what would have happened in the absence of an intervention When program implementation is not randomized, estimating counterfactual outcomes is especially difficult. We show how a thorough understanding of program implementation, combined with a matching empirical design can improve the way counterfactual outcomes are estimated in nonexperimental contexts. As a practical demonstration, we estimated the cost‐effectiveness of South Africa's Working for Water program, arguably the world's most ambitious invasive species control program, in removing invasive alien trees from different land use types, across a large area in the Cape Floristic Region. We estimated that the proportion of the treatment area covered by invasive trees would have been 49% higher (5.5% instead of 2.7% of the grid cells occupied) had the program not intervened. Our estimates of cost per hectare to remove invasive species, however, are three to five times higher than the predictions made when the program was initiated. Had there been no control (counterfactual), invasive trees would have spread on untransformed land, but not on land parcels containing plantations or land transformed by agriculture or human settlements. This implies that the program might have prevented a larger area from being invaded if it had focused all of its clearing effort on untransformed land. Our results show that, with appropriate empirical designs, it is possible to better evaluate the impacts of invasive species removal and therefore to learn from past experiences.
Scale‐dependent effects of landscape composition and configuration on natural enemy diversity, crop herbivory, and yields
Authors: Martin Emily A. , Seo Bumsuk , Park Chan‐Ryul , Reineking Björn , Steffan‐Dewenter Ingolf
Published: May 2016

(1) Land‐use intensification in agricultural landscapes has led to changes in the way habitats and resources are distributed in space. Pests and their natural enemies are influenced by these changes, and by the farming intensity of crop fields. However, it is unknown whether the composition of landscapes (amount and diversity of land cover types) or their configuration (spatial arrangement of cover types) are more important for natural enemy diversity, and how they impact crop damage and yields. In addition, effects of interactions between local farming practices (organic vs. conventional) and landscape variables are unclear. (2) Here, we make use of a data set where landscape composition and configuration were uncorrelated across multiple spatial scales. Natural enemies, crop damage, and yields were sampled in 35 organic and conventional crop fields. Out of seven broad natural enemy taxa, five were positively affected by a complex landscape configuration. In contrast, only carabids were positively affected by the amount of seminatural habitat around fields. Increasing diversity of land cover types had positive effects on some, but negative effects on other taxa. Effect sizes varied among taxa but increased with increasing spatial scale, defined by circular areas of increasing radius around fields. (3) The diversity of aerial, but not of ground‐dwelling enemies was higher in fields under organic than conventional management. Interactions of local and landscape variables were important for birds, but not other enemies. Bird richness was higher in organic fields in simple landscapes, but not in landscapes with complex configuration or high land cover diversity. (4) Crop damage decreased with landscape diversity, but increased in conventional fields with complex configuration. Yields increased with both parameters in conventional fields only, and were higher on average in organic compared to conventional fields. Enemy diversity was positively related to crop damage, indicating positive density‐dependence of enemies on pests. However, the diversity of aerial enemies was also positively related to yields. (5) Our results suggest that the effectiveness of agri‐environmental schemes for managing natural enemy diversity, crop damage and yields could be enhanced by optimizing the effects of distinct landscape parameters, particularly landscape configuration and diversity, across scales.
Consequences for conservation: population density and genetic effects on reproduction of an endangered lagomorph
Authors: DeMay Stephanie M. , Becker Penny A. , Waits Lisette P. , Johnson Timothy R. , Rachlow Janet L.
Published: May 2016

Understanding reproduction and mating systems is important for managers tasked with conserving vulnerable species. Genetic tools allow biologists to investigate reproduction and mating systems with high resolution and are particularly useful for species that are otherwise difficult to study in their natural environments. We conducted parentage analyses using 19 nuclear DNA microsatellite loci to assess the influence of population density, genetic diversity, and ancestry on reproduction, and to examine the mating system of pygmy rabbits (Brachylagus idahoensis) bred in large naturalized enclosures for the reintroduction and recovery of the endangered distinct population in central Washington, USA. Reproductive output for females and males decreased as population density and individual homozygosity increased. We identified an interaction indicating that male reproductive output decreased as genetic diversity declined at high population densities, but there was no effect at low densities. Males with high amounts (>50%) of Washington ancestry had higher reproductive output than the other ancestry groups, while reproductive output was decreased for males with high northern Utah/Wyoming ancestry and females with high Oregon/Nevada ancestry. Females and males bred with an average of 3.8 and 3.6 mates per year, respectively, and we found no evidence of positive or negative assortative mating with regards to ancestry. Multiple paternity was confirmed in 81% of litters, and we report the first documented cases of juvenile breeding by pygmy rabbits. This study demonstrates how variation in population density, genetic diversity, and ancestry impact fitness for an endangered species being bred for conservation. Our results advance understanding of basic life history characteristics for a cryptic species that is difficult to study in the wild and provide lessons for managing populations of vulnerable species in captive and free‐ranging populations.
In‐Season and Carry‐Over Effects of Cover Crops on Productivity and Weed Suppression
Authors: Hodgdon Elisabeth A. , Warren Nicholas D. , Smith Richard G. , Sideman Rebecca G.
Published: May 2016

Data necessary to evaluate cover crop multifunctionality are lacking, particularly for cool, short‐season cropping niches typical of northern New England. We quantified cover crop biomass, weed suppression, and carry‐over effects on subsequent crop and weed growth in 12 winter cover crop treatments {monocrops and mixtures of annual ryegrass [Lolium multiflorum Lam.], winter rye [Secale cereale L.], alfalfa [Medicago sativa L.], crimson clover [Trifolium incarnatum L.], white clover [T. repens L.], hairy vetch [Vicia villosa Roth], soybean [Glycine max (L.) Merr.], and forage radish [Raphanus sativus L.], and a weedy fallow [control] treatment}. The forage radish treatments (11 and 28 kg ha−1 seeding rates) were among the highest producers of fall cover crop biomass in all 4 site‐years. The forage radish treatments were also among the most weed‐suppressive in the fall, reducing weed biomass relative to the weedy fallow treatment by 89 to 97% in each of the 4 site‐years. In the spring, annual ryegrass was among the highest (ranging from 349–571 g m−2 across site‐years) and alfalfa was among the lowest (39–287 g m−2) biomass‐producing treatments in 3 out of 4 site‐years. Weed biomass in the spring was 73 to 99% lower in annual ryegrass, hairy vetch, and hairy vetch–winter rye mixture treatments than in the weedy fallow treatment. Biomass of the sorghum [Sorghum bicolor (L.) Moench]–sudangrass [S. sudanense (Piper) Stapf] phytometer was higher following white clover, hairy vetch, the hairy vetch–rye mixture, and both forage radish treatments compared to following annual ryegrass.

Core Ideas

Cover crops differ in their ability to provide multiple ecosystem services.

This study quantified weed suppression services in 12 cover crop treatments.

Weed suppression in fall, spring, and a subsequent phytometer differed among the treatments.

Phytometer biomass was higher following forage radish and several legume cover crops compared to annual ryegrass.

Cover crop multi‐functionality and tradeoffs were assessed with spider plots.
Wheat Yield Gap in the Pampas: Modeling the Impact of Environmental Factors
Authors: De Paepe Josefina L. , Álvarez Roberto
Published: May 2016

As global grain demand is expected to keep on rising, productive but underachieving regions like the Argentine Pampas play a key role. Reduction of yield gaps in these regions would allow an increase in global food production. The objectives were to model the spatial patterns of the wheat (Triticum aestivum L.) yield gap in the Pampas and relate it to environmental factors. The study comprised an area of approximately 45 Mha during a 40‐yr interval. Attainable yield was estimated by a stochastic frontier production function adjusted on statistical data generated at county scale. Yield gap was calculated for each combination of climate and soil variables as the difference between attainable yield and the average yield estimated using an artificial neural network (ANN) model. Yield gap was then modeled by another ANN using as inputs climate and soil factors. Average yield gap was 865 kg ha−1 (25% of average attainable yield), ranging from 740 kg ha−1 (26%) in humid environments to 1140 kg ha−1 (42%) under semiarid ones during the last 5 yr. Yield gap could be adequately modeled with an ANN (R2 = 0.745, RMSE = 144 kg ha−1). The model showed that soil factors deeply impacted yield gap and minimum values were obtained in soils with medium to high organic C contents and available water storage capacity. Yield gap and a soil productivity index developed locally were negatively correlated. The methodology developed for yield gap analysis can be used for other crops and regions.

Core Ideas

Yield gap calculation combined two modeled yield levels, applying a frontier production function and an artificial neural network.

Climate partially defined yield gaps; in semiarid environments these were largest.

Soil properties explained 50% of yield gap variability at regional scale.

Soil organic carbon and available water holding capacity interacted positively defining a minimum yield gap.

Yield gap reducing efforts should be focused in low productivity soils.
Trace Elements in Dominant Species of the Fenghe River, China: Their Relations to Environmental Factors
Authors: Yang Yang , Zhou Zhengchao , Bai Yanying , Jiao Wentao , Chen Weiping
Published: May 2016

The distribution of trace elements (TEs) in water, sediment, riparian soil and dominant plants was investigated in the Fenghe River, Northwestern China. The Fenghe River ecosystem was polluted with Cd, Cr, Hg and Pb. There was a high pollution risk in the midstream and downstream regions and the risk level for Cd was much higher than that of the other elements. The average values of bioconcentration coefficient for Cd and Zn were 2.21 and 1.75, respectively, indicating a large accumulation of Cd and Zn in the studied species. With broad ecological amplitudes, Portulaca oleracea L., Artemisia argyi Levl. et Vant., Phragmites communis Trin., and Polygonum hydropiper L. had the greatest TE concentrations in aboveground and belowground biomass of the studied species and were potential biomonitors or phytoremediators for the study area. Multivariate techniques including cluster analysis, correlation analysis, principal component analysis, and canonical correspondence analysis were used to analyze the relations between TE concentrations in plants and various environmental factors. The soil element concentration is the main factor determining the accumulation of TEs in plants. The co‐release behavior of common pollutants and TEs drove the accumulation of Hg, Cd, and As in the studied plants. Significant enrichment of some elements in the Fenghe River has led to a decline in the biodiversity of plants.

Core Ideas

Trace elements posed high ecological risk in the Fenghe River system.

Four native species could be used for phytoremediation.

Dissolved NH3–N, NO3–N, TN, and TP drove elemental uptake by plants.

Soil elements and soil pH had major effect on plants uptake of elements.

Plant diversity was sensitive to the high level trace elements in the water habitats.
Illinois River Nitrate‐Nitrogen Concentrations and Loads: Long‐term Variation and Association with Watershed Nitrogen Inputs
Authors: McIsaac Gregory F. , David Mark B. , Gertner George Z.
Published: May 2016

The Illinois River is a major contributor of nitrate‐N to the Mississippi River and the Gulf of Mexico, where nitrate is a leading cause of summertime benthic hypoxia. Corn–soybean production on tile‐drained land is a leading source of nitrate‐N in this river system, in addition to municipal wastewater discharge. We calculated annual nitrate‐N loads in the Illinois River at Valley City from 1976 to 2014 by linear interpolation. Although there was not a significant trend in annual loads during the entire study period, there was a significant downward trend in flow‐weighted nitrate‐N concentration after 1990 despite high concentrations in 2013 after the 2012 drought. Multivariate regression analysis revealed a statistically significant association between annual flow‐weighted nitrate‐N concentration and cumulative residual agricultural N inputs to the watershed during a 6‐yr window. This suggests that declines in flow‐weighted nitrate‐N concentration may reflect increasing N use efficiency in agriculture and a depletion of legacy N stored in the watershed. The watershed appears to have transitioned from a state of stationarity in nitrate concentration to nonstationarity. The average annual nitrate‐N load at Valley City from 2010 to 2014 was 10% less than the 1980–1996 average load, indicating recent progress toward Illinois’ nutrient loss reduction milestone of 15% reduction by 2025 and ultimate target of 45% reduction.

Core Ideas

Downward trend in annual flow‐weighted nitrate‐N concentrations since 1990.

Nitrate‐N concentrations correlated with residual agricultural N during the previous 6 yr.

Nitrate‐N concentrations correlated with current year Chicago wastewater discharge.

Nitrate‐N load highly variable due to variation in precipitation and water discharge.

Average nitrate‐N load during 2010–2014 was 10% less than the 1980–1996 baseline period.
Riverine Response of Sulfate to Declining Atmospheric Sulfur Deposition in Agricultural Watersheds
Authors: David Mark B. , Gentry Lowell E. , Mitchell Corey A.
Published: May 2016

Sulfur received extensive study as an input to terrestrial ecosystems from acidic deposition during the 1980s. With declining S deposition inputs across the eastern United States, there have been many studies evaluating ecosystem response, with the exception of agricultural watersheds. We used long‐term (22 and 18 yr) sulfate concentration data from two rivers and recent (6 yr) data from a third river to better understand cycling and transport of S in agricultural, tile‐drained watersheds. Sulfate concentrations and yields steadily declined in the Embarras (from ∼10 to 6 mg S L−1) and Kaskaskia rivers (from 7 to 3.5 mg S L−1) during the sampling period, with an overall −23.1 and −12.8 kg S ha−1 yr−1 balance for the two watersheds. There was evidence of deep groundwater inputs of sulfate in the Salt Fork watershed, with a much smaller input to the Embarras and none to the Kaskaskia. Tiles in the watersheds had low sulfate concentrations (<10 mg S L−1), similar to the Kaskaskia River, unless the field had received some form of S fertilizer. A multiple regression model of runoff (cm) and S deposition explained much of the variation in Embarras River sulfate (R2 = 0.86 and 0.80 for concentrations and yields; n = 46). Although atmospheric deposition was much less than outputs (grain harvest + stream export of sulfate), riverine transport of sulfate reflected the decline in inputs. Watershed S balances suggest a small annual depletion of soil organic S pools, and S fertilization will likely be needed at some future date to maintain crop yields.

Core Ideas

Riverine sulfate in agricultural watersheds responds to atmospheric deposition inputs.

Agricultural sulfur budgets suggest annual depletion of organic S pools.

Tile drains respond quickly to agricultural sulfate inputs.
Influence of Surface Crusting on Infiltration of a Loess Plateau Soil
Authors: Wang Jian , Watts Dexter B. , Meng Qinqian , Zhang Qingfeng , Way Thomas R.
Published: May 2016

Core Ideas

Soil crusting and surface sealing often adversely affect agricultural yields.

A modified Green–Ampt model was evaluated for predicting infiltration of crusted soil.

The model provided a good estimate of soil crusting's influence on infiltration.

Crusting frequently occurs on farmland soil of the Loess Plateau in China and often adversely affects agricultural yields. Therefore, a study was conducted to evaluate the occurrence of soil crusting and its influence on infiltration in a Loess Plateau silt loam soil. Simulated rainfall events were conducted at two intensities (0.67 and 1.33 mm min−1) on four slopes (5, 9, 18, and 29%) under two soil conditions (crusted and uncrusted). Infiltration was evaluated as the difference between precipitation applied and water lost to runoff. A modified Green–Ampt model adjusted to account for soil crusting was also evaluated for predicting infiltration of crusted soil. Mean soil crust thickness was 3.33 and 3.94 mm under rainfall intensities of 0.67 and 1.33 mm min−1, respectively. Slope had no effect on crust formation. In all instances, cumulative infiltration was lower in crusted soil than in uncrusted soil. The time to runoff decreased from 17.98 min in uncrusted soil to 4.64 min in crusted soil under a rainfall intensity of 0.67 mm min−1. Time to runoff also decreased from 16.25 min in uncrusted soil to 4.54 min in crusted soil at a rainfall intensity of 1.33 mm min−1. The modified Green–Ampt model provided a good estimate of soil crusting's influence on infiltration (coefficient of determination range 0.85–0.97). This suggests that the Green–Ampt model could be used as a tool for predicting soil crusting's influence on infiltration and runoff from soils of the Loess Plateau.
Application of machine learning techniques to predict anomalies in water supply networks
Authors: Vries D. , van den Akker B. , Vonk E. , de Jong W. , van Summeren J.
Published: May 2016

Methods to improve the operational efficiency of a water supply network by early detection of anomalies are investigated by making use of the data streams from multiple sensor locations within the network. The water supply network is a demonstration site of Vitens, a Dutch water company that has several district metering areas where flow, pressure, electrical conductance and temperature are measured and logged online. Three different machine learning approaches are tested for their feasibility to detect anomalies. In the first approach, day-dependent support vector regression (SVR) models are trained for predicting the measurement signals and compared to straightforward models using mean and median estimates, respectively. Using SVRs or the averaged data as real-time pattern recognizers on all available signals, large leakages can be detected. The second approach utilizes adaptive orthogonal projections and reports an event when the number of hidden variables required to describe the streaming data to a user-defined degree (energy-level threshold) increases. As a third approach, (unsupervised) clustering techniques are applied to detect anomalies and underlying patterns from the raw data streams. Preliminary results indicate that the current dataset is too limited in the amount of events and patterns to harness the potential of these techniques.
Finding the “Right-Size” Physical Therapy Workforce: International Perspective Across 4 Countries
Authors: Jesus Tiago S. , Koh Gerald , Landry Michel , Ong Peck-Hoon , Lopes António M.F. , Green Peter L. , Hoenig Helen
Published: May 2016

Finding the “right-size” physical therapy workforce is an increasingly important issue, but it has had limited study, particularly across nations. This perspective article provides a comprehensive examination of physical therapy workforce issues across 4 countries (United States, Singapore, Portugal, and Bangladesh), which were deliberately selected to allow consideration of key contextual factors. This investigation provides a theoretical model uniquely adapted to focus on variables most likely to affect physical therapy workforce needs. This theoretical model was used to guide acquisition of public domain data across the respective countries. The data then were used to provide a contextualized interpretation about the physical therapy workforce supply (ie, physical therapists per capita) across the 4 countries in light of the following factors: indicators of physical therapy need, financial and administrative barriers affecting physical therapy access and demand, the proportion of physical therapy graduates (with varying trends over time across the countries), and the role of emigration/immigration in supply inequalities among countries of lower and higher income. In addition, both the physical therapy workforce supply and scope of practice were analyzed in the context of other related professions across the 4 countries. This international comparison indicated that there may not be a “one-size-fits-all” recommendation for physical therapy workforce supply across countries or an ideal formula for its determination. The optimal, country-specific physical therapy workforce supply appears to be affected by discipline-specific health care and contextual factors that may vary across countries, and even within the same country. This article provides a conceptual framework and basis for such contextualized evaluations of the physical therapy workforce.
Career Preferences and Opinions on Animal Welfare and Ethics: A Survey of Veterinary Students in Australia and New Zealand
Authors: Cornish Amelia R. , Caspar Georgina L. , Collins Teresa , Degeling Christopher , Fawcett Anne , Fisher Andrew D. , Freire Rafael , Hazel Susan J. , Hood Jennifer , Johnson A. Jane , Lloyd Janice , Phillips Clive J.C. , Stafford Kevin , Tzioumis Vicky , McGreevy Paul D.
Published: May 2016

Historically, the veterinary profession has understood animal welfare primarily in terms of animal health and productivity, with less recognition of animals' feelings and mental state. Veterinary students' career preferences and attitudes to animal welfare have been the focus of several international studies. As part of a survey in Australia and New Zealand, this study reports on whether veterinary students prioritize animal welfare topics or professional conduct on the first day of practice and examines links between students' career preferences and their institution, gender, and year of study. The questionnaire was designed to explore the importance that students assign to topics in animal welfare and ethics. Of the 3,320 students invited to participate in the online survey, a total of 851 students participated, representing a response rate of 25.5%. Students' preferences increased for companion-animal practice and decreased for production-animal practice as they progressed through their studies. Females ranked the importance of animal welfare topics higher than males, but the perceived importance declined for both genders in their senior years. In line with previous studies, this report highlighted two concerns: (1) the importance assigned to animal welfare declined as students progressed through their studies, and (2) males placed less importance overall on animal welfare than females. Given that veterinarians have a strong social influence on animal issues, there is an opportunity, through enhanced education in animal welfare, to improve student concern for animal welfare and in turn improve animal care and policy making by future veterinarians.