Increase System Resilience Research Articles

Heterogeneity in symbiotic effects facilitates Wolbachia establishment in insect populations

Facultative vertically transmitted bacterial symbionts often manipulate its host’s reproductive biology and thus facilitate their persistence. Wolbachia is one such symbiont where frequency-dependent reproductive benefits are opposed by frequency-independent fitness costs leading to bistable dynamics. Introduction of carriers does not assure invasion unless the initial frequency is above a threshold determined by the balance of costs and benefits. Recent laboratory experiments have uncovered that Wolbachia also protects their hosts from pathogens. The expected consequence of this phenotype in natural environments is to lower the invasion threshold by a factor that increases with the extent of pathogen exposure. Here, we introduce a series of mathematical models to address how pathogen protection affects Wolbachia invasion. First, under homogeneous symbiotic effects, we obtain an analytical expression for the invasion threshold in terms of pathogen exposure, and find a regime where symbiont releases may result in elimination of the entire host population provided that abundance of virulent pathogens is high. Second, we distribute Wolbachia effects such that some carriers are totally protected and others not at all, and explore how this interplays with different pathogen intensities, to conclude that heterogeneity further lowers the threshold for Wolbachia invasion. Third, we replicate the analysis using a realistic distribution of protective effects and confirm that heterogeneity increases system resilience by reducing the odds of population collapse.

Redundancy in Disaster Response Systems: A Pathway to Resilience or a Recipe for Disaster?

Redundancy in organizational systems is often discussed as an absolute ‘truth’ as something that is always beneficial or always detrimental. Further, while it has been identified as a critical component of resilient system design in the field of disasters, we still lack empirical and theoretical clarity about the role of redundancy in incident response systems. Using three large- scale wildfire events, this paper extends the theoretical discussion of redundancy in a disaster response context to develop an integrated, multidimensional framework of redundancy and its associated capabilities and risks during incident response. Our findings suggest four principal ways redundancy can be integrated into system design: backup, cross-functionality, duplication, and cross-checking. We summarize each redundancy strategy, describe the ways in which it manifested itself on the ground, summarize evidence concerning this strategy’s contribution to promoting resilience in the disaster response system, and summarize findings concerning the risk it poses for system failure. We conclude with suggestions for managers seeking to increase system resilience while managing risks associated with introducing redundancy into the system.

Towards an agroecological assessment of dairy systems: proposal for a set of criteria suited to mountain farming

Ruminant production systems have been facing the sustainability challenge, namely, how to maintain or even increase production while reducing their environmental footprint, and improving social acceptability. One currently discussed option is to encourage farmers to follow agroecological principles, that is, to take advantage of ecological processes to reduce inputs and farm wastes, while preserving natural resources, and using this diversity to increase system resilience. However, these principles need to be made more practical. Here, we present the procedure undertaken for the collaborative construction of an agroecological diagnostic grid for dairy systems with a focus on the mountain farming relying on the use of semi-natural grasslands. This diagnosis will necessarily rely on a multicriteria evaluation as agroecology is based on a series of complementary principles. It requires defining a set of criteria, based on practices to be recommended, that should be complied with to ensure agroecological production. We present how such agroecological criteria were identified and organized to form the architecture of an evaluation model. As a basis for this work, we used five agroecological principles already proposed for animal production systems. A group of five experts of mountain production systems and of their multicriteria evaluation was selected, with a second round of consultation with five additional experts. They first split up each principle into three to four generic sub-principles. For each principle, they listed three to eight categories of state variables on which the fulfilment of the principle should have a positive impact (e.g. main health disorders for the integrated health management principle). State variables are specific for a given production, for example, dairy farms. Crossing principles with state variables enabled experts to build five matrices, with 75 cells relevant for dairy systems. In each cell, criteria are specific to the local context, for example, mountain dairy systems in this study. Finally, we discuss the opportunities offered by our methodology, and the steps remaining for the construction of the evaluation model.

Forty research issues for the redesign of animal production systems in the 21st century

Agroecology offers a scientific and operational framework for redesigning animal production systems (APS) so that they better cope with the coming challenges. Grounded in the stimulation and valorization of natural processes to reduce inputs and pollutions in agroecosystems, it opens a challenging research agenda for the animal science community. In this paper, we identify key research issues that define this agenda. We first stress the need to assess animal robustness by measurable traits, to analyze trade-offs between production and adaptation traits at within-breed and between-breed level, and to better understand how group selection, epigenetics and animal learning shape performance. Second, we propose research on the nutritive value of alternative feed resources, including the environmental impacts of producing these resources and their associated non-provisioning services. Third, we look at how the design of APS based on agroecological principles valorizes interactions between system components and promotes biological diversity at multiple scales to increase system resilience. Addressing such challenges requires a collection of theories and models (concept–knowledge theory, viability theory, companion modeling, etc.). Acknowledging the ecology of contexts and analyzing the rationales behind traditional small-scale systems will increase our understanding of mechanisms contributing to the success or failure of agroecological practices and systems. Fourth, the large-scale development of agroecological products will require analysis of resistance to change among farmers and other actors in the food chain. Certifications and market-based incentives could be an important lever for the expansion of agroecological alternatives in APS. Finally, we question the suitability of current agriculture extension services and public funding mechanisms for scaling-up agroecological practices and systems.

Regime shifts and management

Regime shifts are substantial reorganizations in system structure, functions and feedbacks, which can lead to changes in the provision of ecosystem services with significant impacts on human well-being. Recent research has documented cases of regime shifts in local and regional systems and there is mounting concern about regime shifts of global significance. In this paper we discuss management of social–ecological systems in light of the potential for regime shift. Management that increases system resilience and lowers the probability of regime shifts is beneficial when regime shifts are likely to reduce human well-being. It may not always be possible to avoid harmful regime shifts, so building capacity to adapt should a regime shift occur is beneficial too. Adaptive management can help reduce uncertainty about the likelihood of regime shifts, how this likelihood can be affected by management action, and the impact of regime shifts on well-being. Linking scientific understanding with decision-making is important but distributional consequences can impede decision making and action.

Power-Efficient Cross-Layer Design for OFDMA Systems With Heterogeneous QoS, Imperfect CSI, and Outage Considerations

Reducing power consumption subject to quality-of-service (QoS) provisions is a critical task for next-generation networking. Recent research in resource management for orthogonal frequency-division multiple-access (OFDMA) systems has generally assumed the availability of perfect channel state information at the transmitter (CSIT) or imperfect CSIT with small uncertainty. Nevertheless, such approaches deliver resource scheduling strategies with high transmitting power because, in real environments, large channel feedback delays and estimation errors cause high CSIT imperfectness. Furthermore, most existing works treat various QoS requirements from mobile users as homogenous, although they are heterogeneous in nature. In this paper, we address these issues by proposing a new power-efficient adaptive error-tolerant cross-layer scheduling scheme for OFDMA systems (PE-AETS). Our target is to minimize the transmitting power by considering heterogeneous QoS requirements and data outage due to imperfect CSIT. The proposed scheme adopts a robust power-bit loading (PBL) method that adjusts power and data rates across subcarriers with increased system resilience to channel errors. We develop a statistical queuing model to express the delay limitation of each user with an equivalent cross-layer constraint, and we apply subcarrier time-sharing relaxation to formulate a convex optimization problem. Finally, we utilize Lagrangian optimization to propose a joint power and subcarrier allocation policy with guaranteed convergence to optimal solutions and linear complexity. Various simulation scenarios confirm the superior performance of the proposed PE-AETS over relevant cross-layer approaches.

Improving Resilience of Critical Infrastructure Systems Postdisaster

The nation's capacity for maintenance and improvement of infrastructure systems and its ability to maintain and improve infrastructure systems and ensure the continued service of critical infrastructure systems are receiving special attention because recent disasters have had a significant impact on critical infrastructure. These critical infrastructure systems are the foundation of the nation's economic and social systems. Much research and many policy studies have been conducted to develop methods to improve protection of critical infrastructure with a focus on decreased vulnerability. This paper describes the development of a framework for a decision support system. The objective of the decision support system is to reduce the vulnerability of places and infrastructure systems through the use of mitigation strategies that increase system resilience and resistance to the stresses imposed by disasters. The decision support system will also provide an understanding of the many variables involved in developing strategies to improve the resilience of critical infrastructure systems. This decision support system, referred to as the Critical Infrastructure Resilience Decision Support System (CIR-DSS), uses systems dynamics and recognizes the impacts of disasters, including damage and disruption to critical infrastructure. Results include those of risk and cost–benefit analyses of alternative strategies that also recognize U.S. government policies for recovery and mitigation. A case study focused on transportation infrastructure was used to test and validate the CIR-DSS framework.

Chapter 5: Law and regulation

Chapter 5: Law and regulation

Dynamic modeling of environmental amenity-driven migration with ecological feedbacks

Environmental amenity-driven migration presents a double-edged sword to policy makers concerned with both economic and ecological sustainability. Clearly the protection of environmental amenities is important, but what is the right balance between ecosystem protection and regional economic processes that simultaneously respond to and degrade ecological resources? We consider this question in the context of households that are attracted to a region by urban and lake amenities and a lake ecosystem that becomes degraded by land development. An analytical expression for the time evolution of population is derived from households' and firms' optimizing behaviors. Numerical methods with phase plane diagrams are used to study the steady state and transient dynamics of the resulting population-phosphorus coupled system. The system is found to be bi-stable under a range of parameter values with one attractor corresponding to a desired “balanced” economy-ecology state and the other to a very small population base with fully restored ecology. We examine the dynamics and quantify the resilience of the system in and away from the balanced steady state using phase plane diagrams that demarcate the two domains of attraction. Economic-ecological interactions fundamentally alter regional economic dynamics and influence the resilience of the balanced domain of attraction. For example, a one percent increase in the loadings coefficient associated with residential land development generates a three percent decline in the resilience of the balanced state. We find that economic feedbacks often increase system resilience. Initial increases in the attraction of urban amenities spur greater population growth that increases the resilience of the balanced state. In addition, price feedbacks that arise from capitalized (dis)amenities increase the resilience of the system to bad ecological shocks.

The effects of seston food quality on planktonic food web patterns

In planktonic food webs, the conversion rate of plant material to herbivore biomass is determined by a variety of factors such as seston biochemical/elemental composition, phytoplankton cell morphology, and colony architecture. Despite the overwhelming heterogeneity characterizing the plant–animal interface, plankton population models usually misrepresent the food quality constraints imposed on zooplankton growth. In this study, we reformulate the zooplankton grazing term to include seston food quality effects on zooplankton assimilation efficiency and examine its ramifications on system stability. Using different phytoplankton parameterizations with regards to growth strategies, light requirements, sinking rates, and food quality, we examined the dynamics induced in planktonic systems under varying zooplankton mortality/fish predation, light conditions, nutrient availability, and detritus food quality levels. In general, our analysis suggests that high food quality tends to stabilize the planktonic systems, whereas unforced oscillations (limit cycles) emerge with lower seston food quality. For a given phytoplankton specification and resource availability, the amplitude of the plankton oscillations is primarily modulated from zooplankton mortality and secondarily from the nutritional quality of the alternative food source (i.e., detritus). When the phytoplankton community is parameterized as a cyanobacterium-like species, conditions of high nutrient availability combined with high zooplankton mortality led to phytoplankton biomass accumulation, whereas a diatom-like parameterization resulted in relatively low phytoplankton to zooplankton biomass ratios highlighting the notion that high phytoplankton food quality allows the zooplankton community to sustain relatively high biomass and to suppress phytoplankton biomass to low levels. During nutrient and light enrichment conditions, both phytoplankton and detritus food quality determine the extent of the limit cycle region, whereas high algal food quality increases system resilience by shifting the oscillatory region towards lower light attenuation levels. Detritus food quality seems to regulate the amplitude of the dynamic oscillations following enrichment, when algal food quality is low. These results highlight the profitability of the alternative food sources for the grazer as an important predictor for the dynamic behavior of primary producer–grazer interactions in nature.

Collaborative Cross-Checking to Enhance Resilience

There has been a longstanding consensus that supporting error detection and recovery processes is critical for very high safety levels because it increases system resilience. System resilience is defined in Resilience Engineering as successful adaptation to variations, changes, and surprises by organizations, groups, or individuals. Cross-checking is a critical component of resilience because it can enable detection of erroneous assessments or actions while negative consequences can be mitigated or eliminated. Prior studies suggest that cross-checking where an additional human with a fresh perspective breaks fixations may be an effective strategy. Nevertheless, collaborative cross-checking remains a somewhat murky concept. In this paper, we describe in detail three healthcare incidents where collaborative cross-checking played a key role. Emerging patterns that provide opportunities for follow-on research are discussed.

The SIGIR peer-to-peer information retrieval workshop

Peer-to-peer (P2P) systems have emerged as a popular way to share huge volumes of data. The P2P paradigm holds many promises: it fits naturally with the Internet, the universal knowledge and service exchange medium; it favors scalability, by allowing the seamless plugging of data, services and computational resources into the global system; it increases system resilience, by avoiding unique points of failures; and it can speed up global access by distributing the indexing and query processing tasks to multiple computing nodes. However, retrieval methods for P2P systems are still in their infancy. P2P networks are prone to congestion when messages are not routed intelligently. Many of the most effective routing or data placement methods developed recently rely on relatively simple retrieval methods and homogeneous network environments.