Methods in Modeling Wildlife Disease from Model Selection to Parameterization With Multi-Scale Data

The effects of emerging wildlife diseases are global and profound, resulting in loss of human life, economic and agricultural impacts, declines in wildlife populations, and ecological disturbance. The spread of wildlife diseases can be viewed as the result of two simultaneous processes: spatial spread of wildlife populations and disease spread through a population. For many diseases these processes happen at different timescales, which is reflected in available data. These data come in two flavors: high-frequency, high-resolution telemetry data (e.g. GPS collar) and low-frequency, low-resolution presence-absence disease data. The multi-scale nature of these data makes analysis of such systems challenging. Mathematical models serve as valuable tools for forecasting disease spread. To produce meaningful predictions a model must include appropriate mechanisms for both transmission and animal movement and be parameterized with data. Herein, a framework is developed for modeling wildlife disease spread. Model competition is used to select and parameterize appropriate transmission mechanisms given time-series prevalence data. For animal movement a parameterization method for a mechanistic, population-scale wildlife movement model is derived for use with individual telemetry data. Throughout, special attention is payed to computational complexity. Homogenization and other asymptotic methods are used to maintain feasibility of parameterization. In tandem, these two methods determine and parameterize the movement and transmission mechanisms that play a role in wildlife disease spread, taking into account the types of available data and inherent separation of scales between the two processes

Towards Optimal and Practical Asynchronous Byzantine Fault Tolerant Protocols

With recent advancements in blockchain technology, people expect Byzantine fault tolerant (BFT) protocols to be deployed more frequently in wide-area networks (WAN) as opposed to conventional in-house settings. Asynchronous BFT protocols, which do not rely on any form of timing assumption, are arguably robust in such a setting. Asynchronous BFT protocols have been studied since the 1980s, but these asynchronous BFT works mainly focus on understanding the theoretical limits and possibilities. Until the recent asynchronous BFT protocol, HoneyBadgerBFT (HBBFT), was proposed, the field received renewed attention. Dumbo family, a series of our works on the asynchronous BFT protocols, significantly pushed those protocols towards practice. First, all complexity metrics are pushed down to asymptotically optimal, simultaneously. Second, we identify the bottleneck in the state of the art and revisit the design methodology, identifying and utilizing the right components, and optimizing the protocol structure in various ways. Last but not least, we also open the box and optimize the critical components themselves. The resulting protocols are indeed significantly more performant, the latest protocol can have 100K tps and a few seconds of latency at a reasonable scale. This thesis focuses on the latest three members of the Dumbo family. To begin, we solved an open problem by proposing an optimal Multi-valued validated asynchronous Byzantine agreement protocol. Next, we present Dumbo-NG to address the challenge of latency-throughput tension by redesigning the methodology of asynchronous BFT protocols. Another benefit of the new methodology is that it can conquer the censorship threat without extra cost. Furthermore, we consider a realistic environment and present Bolt-Dumbo Transformer (BDT), a generic framework for practical optimistic asynchronous BFT to achieve the "best of both worlds" in terms of the advantages of deterministic BFT and randomized (asynchronous) BFT

The Reaction-Diffusion of Range Expansion of American Black Bears (Ursus Americanus) In North Carolina, USA

By the early 19th century, many big-game species were extirpated from much of their historic range. Implementation of harvest regulations or restrictions, habitat succession, and changes in land use practices have facilitated the return of many of these species. It is necessary, for proper management, to be able to estimate with precision or certainty, abundance and other demographic parameters as well as range expansion often with personnel and financial limitations. New advancements in analyses allow for greater extraction of information from commonly collected data. White oak (subgenus Leucobalanus) mast production had a strong correlation with non-harvest mortality of American black bears (Ursus americanus; r = 0.89). Using white oak mast as a surrogate for hunter effort, I used a catch-effort likelihood within statistical population reconstruction (SPR) using an N- mixture multinomial model to estimate the abundance and other demographic parameters of black bears in the Mountain region of North Carolina. Abundance was estimated at 3365 (95% B.C.I. = 3165-3569) for females and 3882 (95% B.C.I. = 3696-4080) for males in 2016, with numbers continuing to increase at a rate of approximately 5% annually. SPR estimates tracked estimates from Downing population reconstruction (DPR until approximately 2008 when DPR indicated population growth to be slowing in contrast to SPR estimates. The probability of harvest ranged from 6.7-15.6% (95% B.C.I. = 6.3-16.3%) for females and 11.6-26.1% (95% B.C.I. = 11.2-26.9%) for males. Additional parameters could be estimated with the inclusion of additional data and likelihoods. The velocity of range expansion of the Mountain and Coastal black bear populations into the Piedmont was tracked using reliable sightings, frequency and location of bear-vehicle collisions, and demographic parameters in five methods of reaction-diffusion models. The rate of expansion was approximately 4-8 km/year. Each of the five methods yielded similar velocities of range expansion, indicating the simplest method that used commonly-collected data was just as informative as more elaborate methods. Likelihoods using other food resources availability may be necessary to modify this SPR to fit other species or bear populations in agriculturally-dominated regions, but is easily adaptable. Collecting animal- vehicle mortality locations is an inexpensive way to be estimate range expansion of elusive species

Updated pest risk assessment of Phytophthora ramorum in Norway

The Norwegian Food Safety Authority has asked the Norwegian Scientific Committee for Food and Environment for an updated pest risk assessment of Phytophthora ramorum in Norway. The previous risk assessment of P. ramorum for Norway is from 2009. Since then, the pathogen has been detected repeatedly in Norway, primarily in parks, garden centres, and nurseries in southwestern Norway. The knowledge base concerning P. ramorum has changed since the last pest risk assessment, with increased genetic knowledge about different populations, lineages, and mating types. The risks associated with P. ramorum have also changed, since the disease has become epidemic in new host plants, such as larch trees in England. This updated pest risk assessment will provide important input to the Norwegian Food Safety Authority’s efforts to develop the Norwegian plant health regulation.Updated pest risk assessment of Phytophthora ramorum in NorwaypublishedVersio

Digital certificates and threshold cryptography

This dissertation discusses the use of secret sharing cryptographic protocols for distributing and sharing of secret documents, in our case PDF documents. We discuss the advantages and uses of such a system in the context of collaborative environments. Description of the cryptographic protocol involved and the necessary Public Key Infrastructure (PKI) shall be presented. We also provide an implementation of this framework as a “proof of concept” and fundament the use of a certificate extension as the basis for threshold cryptography. Details of the shared secret distribution protocol and shared secret recovery protocol shall be given as well as the associated technical implementation details. The actual secret sharing algorithm implemented at this stage is based on an existing well known secret sharing scheme that uses polynomial interpolation over a finite field. Finally we conclude with a practical assessment of our prototype

LIPIcs, Volume 274, ESA 2023, Complete Volume

LIPIcs, Volume 274, ESA 2023, Complete Volum

Quantifying and simulating movement of the predator carabid beetle Pterostichus melanarius in arable land

Keywords: landscape entomology, movement ecology, quantifying movement, population spread, habitat heterogeneity, motility, edge-behaviour, diffusion model, model selection, inverse modelling, Pterostichus melanarius, Carabidae, entomophagous arthropod Biological control provided by entomophagous arthropods is an ecosystem service with the potential to reduce pesticide use in agriculture. The distribution of entomophagous arthropods and the associated ecosystem service over crop fields is affected by their dispersal capacity and landscape heterogeneity. Current knowledge on entomophagous arthropod distribution and movement patterns, in particular for soil dwelling predators, is insufficient to provide advice on how a production landscape should be re-arranged to maximally benefit from biological pest control. Movement has mainly been measured in single habitats rather than in habitat mosaics and as a consequence little information is available on behaviour at habitat interfaces, i.e. the border between two habitats. This study contributes to insight into movement patterns of the entomophagous arthropod Pterostichus melanarius (Illiger) in an agricultural landscape as a knowledge basis for redesign of landscapes for natural pest control. Movement patterns were studied with video equipment in experimental arenas of 5 m2 and with mark-recapture at much larger scales in the field. Interpretation of the results was supported by diffusion models that accounted for habitat specific motility µ (L2 T−1), a measure for diffusion of a population in space and time, and preference behaviour at habitat interfaces. Movement of carabids has mostly been quantified as movement rate, which cannot be used for scaling-up. Available information on movement rate of carabids was made available for scaling-up by calculating motility from published data and looking for patterns through meta-analysis of data from thirteen studies, including 55 records on twelve species. Beetles had on average a three times higher motility in arable land than in forest/hedgerow habitat. The meta-analysis did not identify consistent differences in motility at the individual species level, and a grouping of species according to gender or size did not demonstrate a significant gender or size effect. A methodology to directly estimate motility from data using inverse modelling was evaluated on data of a mass mark-recapture field experiment in a single field of winter triticale (x Triticosecale Wittmack.). Inverse modelling yielded the same result as motility calculated from squared displacement distances. In the first case, motility was calculated as an average over motility of individuals, in the second case motility was estimated from a population density distribution fitted to the recapture data. The similarity in motility between these two very different approaches strengthens the confidence in motility as a suitable concept for quantifying dispersal rate of carabid beetles, and in inverse modelling as a method to retrieve movement parameters from observed patterns. The effect of habitat heterogeneity on movement behaviour was studied for P. melanarius across adjacent fields of oilseed radish (Raphanus sativus) and rye (Secale cereale) in a mark-recapture experiment. The field study was complemented by observations on movement behaviour in the experimental arena. Motility was neither significantly different between the crop species in the field nor in the arena. Overall movement in the field was significantly affected by behaviour at the interface between the crops. Beetles moved more frequently from rye to oilseed radish than in the opposite direction. The arena data indicated greater frequency of habitat entry into oilseed radish as compared to rye. Analysis of video tracking data from the arena resulted in estimates of motility that, when scaled up were close to those obtained in the field. Thus, the studies at the smaller and larger scales gave qualitatively and quantitatively similar results. The effect of habitat heterogeneity on within-season dispersal behaviour was further explored in an agricultural landscape mosaic comprising perennial strips and different crop species with distinct tillage management. Semi-natural grass margins were functionally different from the crop habitats. Motility was lower in margins than in crop habitats, and at the crop-margin interface more beetles moved towards the crop than to the margin. Margins thus effectively acted as barriers for dispersal. In the crop habitats motility differed between fields but no consistent relations were found with crop type, food availability or tillage. Based on the motility in crop habitats P. melanarius was predicted to disperse over a distance of about 100 – 160 m during a growing season in a landscape without semi-natural elements. Given this range little redistribution of beetles is expected between fields within a growing season, even more when fields are surrounded by grass margins or hedgerows, meaning that the success of biological control by this species is more dependent on field management affecting local population dynamics than on habitat heterogeneity. This thesis has resulted in a methodological approach to quantify dispersal behaviour of ground-dwelling insects from mark-recapture data in heterogeneous environments using inverse modelling. The combination of models and data proved to be powerful for studying movement and contributes to the development of predictive dynamic models for population spread of entomophagous arthropods. These models for population spread may be used as part of multi-objective assessment of alternative landscape configurations to find spatial arrangements of land use that maximize the ecosystem service of biological control as part of a wider set of landscape functions.</p

Efficient Asynchronous Byzantine Agreement without Private Setups

Efficient asynchronous Byzantine agreement (BA) protocols were mostly studied with private setups, e.g., pre-setup threshold cryptosystem. Challenges remain to reduce the large communication in the absence of such setups. Recently, Abraham et al. (PODC'21) presented the first asynchronous validated BA (VBA) with expected $O(n^3)$ messages and $O(1)$ rounds, relying on only public key infrastructure (PKI) setup, but the design still costs $O({\lambda}n^3 \log n)$ bits. Here $n$ is the number of parties, and $\lambda$ is a cryptographic security parameter. In this paper, we reduce the communication of private-setup free asynchronous BA to expected $O(\lambda n^3)$ bits. At the core of our design, we give a systematic treatment of common randomness protocols in the asynchronous network, and proceed as: - We give an efficient reasonably fair common coin protocol in the asynchronous setting with only PKI setup. It costs only $O(\lambda n^3)$ bits and $O(1)$ rounds, and ensures that with at least 1/3 probability, all honest parties can output a common bit that is as if randomly flipped. This directly renders more efficient private-setup free asynchronous binary agreement (ABA) with expected $O(\lambda n^3)$ bits and $O(1)$ rounds. - Then, we lift our common coin to attain perfect agreement by using a single ABA. This gives us a reasonably fair random leader election protocol with expected $O(\lambda n^3)$ communication and expected constant rounds. It is pluggable in all existing VBA protocols (e.g., Cachin et al., CRYPTO'01; Abraham et al., PODC'19; Lu et al., PODC'20) to remove the needed private setup or distributed key generation (DKG). As such, the communication of private-setup free VBA is reduced to expected $O(\lambda n^3)$ bits while preserving fast termination in expected $O(1)$ rounds

Mini-Workshop: Applied Koopmanism

Koopman and Perron–Frobenius operators are linear operators that encapsulate dynamics of nonlinear dynamical systems without loss of information. This is accomplished by embedding the dynamics into a larger infinite-dimensional space where the focus of study is shifted from trajectory curves to measurement functions evaluated along trajectories and densities of trajectories evolving in time. Operator-theoretic approach to dynamics shares many features with an optimization technique: the Lasserre moment–sums-of-squares (SOS) hierarchies, which was developed for numerically solving non-convex optimization problems with semialgebraic data. This technique embeds the optimization problem into a larger primal semidefinite programming (SDP) problem consisting of measure optimization over the set of globally optimal solutions, where measures are manipulated through their truncated moment sequences. The dual SDP problem uses SOS representations to certify bounds on the global optimum. This workshop highlighted the common threads between the operator-theoretic dynamical systems and moment–SOS hierarchies in optimization and explored the future directions where the synergy of the two techniques could yield results in fluid dynamics, control theory, optimization, and spectral theory

Analysis and design of multifunctional agricultural landscapes : a graph theoretic approach

This thesis deals with the development of quantitative methodologies for the evaluation of landscape functions and their interactions in multifunctional agricultural landscapes. It focuses on the spatial coherence of hedgerow networks for ecological functions and landscape character for perception of landscape identity, and on their integration in a multifunctional and multiscale trade-off analysis. Graph theory provided the basis for new methodologies that are applied in this research