The landscape epidemiology of foot-and-mouth disease in South Africa: A spatially explicit multi-agent simulation

This study aimed at understanding how landscape heterogeneity influences outbreaks of contagious diseases in southern Africa. Landscape attributes influence patterns of movement and behaviour of animal hosts, virus spread and survival, as well as land use practices. A multi-agent simulation was developed to represent the spatial and temporal dynamics of pathogens between human-livestock and wildlife interfaces at the fringe of large wildlife conservation areas. The model represents the three main elements associated with epidemics - populations, space, and time - to simulate direct contacts between wildlife and livestock. The dynamics of these populations emerge from interactions between agents and the landscape. The model was calibrated to represent the transmission of foot-and-mouth disease through direct contact at the border of the Kruger National Park in South Africa. In the region, African buffaloes (Syncerus caffer) act as reservoirs of the virus and spread the infection to domestic cattle bordering the park. We tested the sensitivity of various factors influencing contact rate between buffaloes and cattle, and thus the risk of foot-and-mouth disease transmission. Results show that cattle-buffalo contacts mostly depend on the range of displacements of cattle and buffaloes, as influenced by the landscape configuration, and on the number of fence breakages multiplied by the time between breakage and repair. Contacts take place not only close to water-points but also in grazing areas, within an area up to 6 km from the fence.     

Resource allocation in two species systems: Is it worth acknowledging species interactions?

It is becoming increasingly popular to consider species interactions when managing ecological foodwebs. Such an approach is useful in determining how management can affect multiple species, with either beneficial or detrimental consequences. Identifying such actions is particularly valuable in the context of conservation decision making as funding is severely limited. This paper outlines a new approach that simplifies the resource allocation problem in a two species system for a range of species interactions: independent, mutualism, predator-prey, and competitive exclusion. We assume that both species are endangered and we do not account for decisions over time. We find that optimal funding allocation is to the conservation of the species with the highest marginal gain in expected probability of survival and that, across all except mutualist interaction types, optimal conservation funding allocation differs between species. Loss in efficiency from ignoring species interactions was most severe in predator-prey systems. The funding problem we address, where an ecosystem includes multiple threatened species, will only become more commonplace as increasing numbers of species worldwide become threatened.     

Evaluating the success of functional restoration after reintroduction of a lost avian pollinator

Conservation translocation is a common method for species recovery, for which one increasingly frequent objective is restoring lost ecological functions to promote ecosystem recovery. However, few conservation translocation programs explicitly state or monitor function as an objective, limiting the ability to test assumptions, learn from past efforts, and improve management. We evaluated whether translocations of hihi (Notiomystis cincta), a threatened New Zealand passerine, achieved their implicit objective of restoring lost pollination function. Through a pollinator-exclusion experiment, we quantified, with log response ratios (lnR), the effects of birds on fruit set and seed quality in hangehange (Geniostoma ligustrifolium), a native flowering shrub. We isolated the contributions of hihi by making comparisons across sites with and without hihi. Birds improved fruit set more at sites without hihi (lnR = 1.27) than sites with hihi (lnR = 0.50), suggesting other avian pollinators compensated for and even exceeded hihi contributions to fruit set. Although birds improved seed germination only at hihi sites (lnR = 0.22–0.41), plants at sites without hihi had germination rates similar to hihi sites because they produced 26% more filled seeds, regardless of pollination condition. Therefore, although our results showed hihi improved seed quality, they also highlighted the complexity of ecological functions. When an important species is lost, ecosystems may be able to achieve similar function through different means. Our results underscore the importance of stating and monitoring the ecological benefits of conservation translocations when functional restoration is a motivation to ensure these programs are achieving their objectives.     

A CFD study of the transport and fate of airborne droplets in a ventilated office: The role of droplet−droplet interactions

• Coulomb and Lennard−Jones forces were considered for droplet interactions. • The net droplet interactions were repulsive. • Repulsive droplet interactions increased the transport of droplets. • Repulsive droplet interactions significantly modified the fate of droplets. Previous studies reported that specially designed ventilation systems provide good air quality and safe environment by removing airborne droplets that contain viruses expelled by infected people. These water droplets can be stable in the environment and remain suspended in air for prolonged periods. Encounters between droplets may occur and droplet interactions should be considered. However, the previous studies focused on other physical phenomena (air flow, drag force, evaporation) for droplet transport and neglected droplet interactions. In this work, we used computational fluid dynamics (CFD) to simulate the transport and fate of airborne droplets expelled by an asymptomatic person and considered droplet interactions. Droplet drag with turbulence for prediction of transport and fate of droplets indicated that the turbulence increased the transport of 1 μm droplets, whereas it decreased the transport of 50 μm droplets. In contrast to only considering drag and turbulence, consideration of droplet interactions tended to increase both the transport and fate. Although the length scale of the office is much larger than the droplet sizes, the droplet interactions, which occurred at the initial stages of release when droplet separation distances were shorter, had a significant effect in droplet fate by considerably manipulating the final locations on surfaces where droplets adhered. Therefore, it is proposed that when an exact prediction of transport and fate is required, especially for high droplet concentrations, the effects of droplet interactions should not be ignored.     

Testing the Stochastic Dynamic Methodology (StDM) as a management tool in a shallow temperate estuary of south Europe (Mondego, Portugal)

A long-term monitoring program has been carried out since the early 1990s in the Mondego estuary, on Portugal's west coast, which is presently under heavy human pressure. In this shallow warm-temperate estuary, a significant macroalgal proliferation has been observed, which is a clear sign of nutrient enrichment. As a result of competition with algae, the extension of the seagrass meadows (mainly Zostera noltii) has been reduced. The present paper examined the applicability of a holistic Stochastic Dynamic Methodology (StDM) in predicting the tendencies of trophic key-components (macrophytes, macroalgae, benthic macroinvertebrate and wading birds) as a response to the changes in estuarine environmental conditions. The StDM is a sequential modelling process developed in order to predict the ecological status of changed ecosystems, from which management strategies can be designed. The data used in the dynamic model construction included true gradients of environmental changes and was sampled from January 1993 to September 1995 and from December 1998 to December 2005. The dynamic model developed was preceded by a conventional multivariate statistical procedure performed to discriminate the significant relationships between the selected ecological components. The model validation was based on independent data collected from January 1996 to January 1997 and from February 1999 to April 2000 for all the state variables considered. Overall, the simulation results are encouraging since they seem to demonstrate the StDM reliability in capturing the trophic dynamics of the studied estuary, by predicting the behavioural pattern for the most part of the components selected, with a focus on the Zostera noltii meadows recovery after the implementation of important management measures.     

Efficient and Practical Approaches to Ground‐Water Right Transfers Under the Prior Appropriation Doctrine and the Snake River Example1

Abstract: Water right transfers are one of the basic means of implementing changes in water use in the highly appropriated water resource systems of the western United States. Many of these systems are governed by the Prior Appropriation Doctrine, which was not originally intended for application to ground‐water pumping and the conjunctive management of ground water and surface water, and thus creates an administrative challenge. That challenge results from the fact that ground‐water pumping can affect all interconnected surface‐water bodies and the effects may be immeasurably small relative to surface water discharge and greatly attenuated in time. Although we may have the ability to calculate the effects of ground‐water pumping and transfers of pumping location on surface‐water bodies, mitigating for all the impacts of each individual transfer is sufficiently inefficient that it impedes the transfer process, frustrates water users, and consequently inhibits economic development. A more holistic approach to ground‐water right transfers, such as a ground‐water accounting or banking scheme, may adequately control transfer third‐party effects while reducing mitigation requirements on individual transfers. Acceptance of an accounting scheme can accelerate the transfer process, and possibly reduce the administrative burden.     

Modification of the biochemical pathways of plants induced by ozone: what are the varied routes to change?

When plants are observed under a low dose of ozone, some physiological and metabolic shifts occur. Barring extreme injury such as tissue damage or stomata closure, most of these disruptive changes are likely to have been initiated at the level of gene expression. The belief is oxidative products formed in ozone exposed leaves, e.g. hydrogen peroxide, are responsible for much of the biochemical adjustments. The first line of defense is a range of antioxidants, such as ascorbate and glutathione, but if this defense is overwhelmed, subsequent actions occur, similar to systemic acquired resistance or general wounding. Yet there are seemingly unrelated metabolic responses which are also triggered, such as early senescence. We discuss here the current understanding of gene control and signal transduction/control in order to increase our comprehension of how ozone alters the basic metabolism of plants and how plants counteract or cope with ozone.     

Seaweed sex pheromones and their degradation products frequently suppress amphipod feeding but rarely suppress sea urchin feeding

Summary. A diverse group of brown seaweeds produce bouquets of C₁₁ metabolites, some of which act as pheromones that cue gamete release or attract sperm to eggs following release. We demonstrate that these C₁₁ metabolites and their degradation products also frequently and strongly deter feeding by the herbivorous amphipod Ampithoe longimana, but rarely by the herbivorous sea urchin Arbacia punctulata. Across the range of concentrations tested, seven of twelve C₁₁ metabolites or mixtures that we tested deterred feeding by the amphipod, but only two of eleven deterred the sea urchin. For those compounds where we could rigorously contrast the magnitude of deterrence against the amphipod with the magnitude of deterrence against the urchin, the amphipod was deterred significantly more than the urchin by five of six metabolites. Thus, C₁₁ compounds were more frequently and more strongly deterrent to the amphipod than to the sea urchin. These findings for C₁₁ metabolites conflict with previous investigations, where other classes of seaweed chemical defenses have been shown to deter feeding by large mobile herbivores like urchins and fishes but to be relatively ineffective against mesograzers, especially the species of amphipod that we used here. Our results suggest that C₁₁ metabolites are unusual among the known seaweed chemical defenses in that they are especially effective against mesograzers, which often consume seaweed spores, zygotes, and juveniles. The high concentrations of C₁₁ metabolites in brown algal eggs could allow these defenses to be especially important in defending gametes, zygotes, or young sporelings from herbivorous mesograzers. Received 26 February 1998; accepted 9 April 1998.     

Negative effects of nitrogen deposition on Swiss butterflies

Nitrogen (N) deposition from agriculture and combustion of fossil fuels is a major threat to plant diversity, but its effects on organisms at higher trophic levels are unclear. We investigated how N deposition may affect species richness and abundance (number of individuals per species) in butterflies. We reviewed the peer-reviewed literature on variables used to explain spatial variation in butterfly species richness and found that vegetation variables appeared to be as important as climate and habitat variables in explaining butterfly species richness. It thus seemed likely that increased N deposition could indirectly affect butterfly communities via its influence on plant communities. To test this prediction, we analyzed data from the Swiss biodiversity monitoring program for vascular plants and butterflies in 383 study sites of 1 km² that are evenly distributed throughout Switzerland. The area has a modeled N deposition gradient of 2–44 kg N ha⁻¹ year⁻¹. We used traditional linear models and structural equation models to infer the drivers of the spatial variation in butterfly species richness across Switzerland. High N deposition was consistently linked to low butterfly diversity, suggesting a net loss of butterfly diversity through increased N deposition. We hypothesize that at low elevations, N deposition may contribute to a reduction in butterfly species richness via microclimatic cooling due to increased plant biomass. At higher elevations, negative effects of N deposition on butterfly species richness may also be mediated by reduced plant species richness. In most butterfly species, abundance was negatively related to N deposition, but the strongest negative effects were found for species of conservation concern. We conclude that in addition to factors such as intensified agriculture, habitat fragmentation, and climate change, N deposition is likely to play a key role in negatively affecting butterfly diversity and abundance.     

IMPACT OF IRRIGATION WELLS ON BASEFLOW OF THE BIG BLUE RWER,NEBRASKA1

ABSTRACT: The Kansas-Nebraska Big Blue River compact requires that the state of Nebraska insure a minimum flow of the Big Blue River across the state line. There are two options that the state of Nebraska may use to ensure minimum flows. The obvious option is to limit surface-water irrigators along the river. However, under the terms of the compact, a second option may be to regulate irrigation wells that are within one mile of the river and were installed after November 1, 1968. The objective of this study is to quantify the effects of 17 irrigation wells that may be regulated on baseflow of the Big Blue River. A finite-element model is used to study the hydrogeologic system between DeWitt and Beatrice, Nebraska. The 17 wells that may be regulated are located between these towns and are developed in sediments deposited in a cross-cutting paleovalley anchor alluvium associated with the Big Blue River. While there wore considerable existing data, additional data were gathered by drilling an additional nine test holes, conducting several aquifer tests, stream-stage measurements, and baseflow calculation through extensive stream-discharge measurements, establishment of a ground water-level monitoring network, determining the amount of water pumped for irrigation and municipal use in the area, and a short-term precipitation network. The model was calibrated using observed baseflow and ground water level data. The model clearly shows that regulating the 17 wells to maintain baseflow would have a minimal effect on the overall water budget. This is reasonable, especially considering that there are over 250 irrigation wells in the project area. The 17 wells considered pumped only 6 percent of the total pumpage within the modeled area during the irrigation season of 1984. The computer model provides the documentation needed to demonstrate this fact. Although much of the resources spent and a significant amount of hydrogeologic data are being collected over a period of three years on a relatively small area, the simulation model could be improved through further field testing of the aquifer and stream-bed sediment characteristics and quantification of ground water recharge, discharge, and evapotranspiration rates.