Simon Levin

Characterizing the relationship between disease testing behaviors and infectious disease dynamics is of great importance for public health. Tests for both current and past infection can influence disease-related behaviors at the individual level, while population-level knowledge of an epidemic’s course may feed back to affect one’s likelihood of taking a test. The COVID-19 pandemic has generated testing data on an unprecedented scale for tests detecting both current infection (PCR, antigen) and past infection (serology); this opens the way to characterizing the complex relationship between testing behavior and infection dynamics. Leveraging a rich database of individualized COVID-19 testing histories in New Jersey, we analyze the behavioral relationships between PCR and serology tests, infection, and vaccination. We quantify interactions between individuals’ test-taking tendencies and their past testing and …

We analyze a spatially extended version of a well-known model of forest-savanna dynamics, which presents as a system of nonlinear partial integro-differential equations, and study necessary conditions for pattern-forming bifurcations. Homogeneous solutions dominate the dynamics of the standard forest-savanna model, regardless of the length scales of the various spatial processes considered. However, several different pattern-forming scenarios are possible upon including spatial resource limitation, such as competition for water, soil nutrients, or herbivory effects. Using numerical simulations and continuation, we study the nature of the resulting patterns as a function of system parameters and length scales, uncovering subcritical pattern-forming bifurcations and observing significant regions of multistability for realistic parameter regimes. Finally, we discuss our results in the context of extant savanna-forest …

When individuals form social organizations around shared interests or common goals, they can generate new ideas and accomplish complex tasks. To understand why some organizations are more successful than others at attracting supporters and reaching their goals, we need a model of organizations that can be experimentally validated. We identify Reddit's r/place experiment as a model system in which we can study organizations and their ability to achieve a collective goal. In this unique experiment, different groups on Reddit compete to craft pixel art on a size-limited canvas of pixels, which allows us to observe the behavior of communities and their individuals as they compete for space on the canvas. Using the pixel and user data, we examine scaling laws that relate the community size to variables that describe their art and user dynamics. We find categories of variables that scale sub-linearly, linearly, and …

In Somalia, extreme droughts, floods, and conflicts have generated a great wave of internally displaced persons (IDPs) involuntarily moving within the country’s boundaries. Despite increasing concerns about the IDP problem, we still do not fully understand the emergent properties of IDP flows from the network perspective. Particularly lacking is quantitative information on how natural disasters and conflicts differently or similarly shape IDP networks. These knowledge gaps are critical for IDP studies with complex interactions because the gaps may misconnect IDP flows with socio-environmental data at inappropriate spatial scales. To address these gaps, this study applies a series of network analyses to compare emergent patterns in disaster-induced and conflict-induced IDP networks. Push patterns were random without hub formation in both cases. Social connections were critical to incoming IDP flows but not to …

G31. 00007: Learning about early warning signals and the structure of collaborations with a large-scale experiment on Reddit

Achieving global sustainability in the face of climate change, pandemics, and other global systemic threats will require collective intelligence and collective action beyond what we are currently experiencing. Increasing polarization within nations and populist trends that undercut international cooperation make the problem even harder. Allegiance within groups is often strengthened because of conflict among groups, leading to a form of polarization termed “affective.” Hope for addressing these global problems will require recognition of the commonality in threats facing all groups collective intelligence that integrates relevant inputs from all sources but fights misinformation and coordinated, cooperative collective action. Elinor Ostrom’s notion of polycentric governance, involving centers of decision-making from the local to the global in a complex interacting framework, may provide a possible pathway to achieve these …

Several governments have tested formal index-based insurance to build climate resilience among smallholder farmers. Yet, adoption of such programmes has generated concerns that insurance may crowd out long-established informal risk transfer arrangements. Understanding this phenomenon requires new analytic approaches that capture dynamics of human social behaviour when facing risky events. Here we develop a modelling framework, based on evolutionary game theory and empirical data from Nepal and Ethiopia, to demonstrate that insurance may introduce a new social dilemma in farmer risk management strategies. We find that while socially optimal risk management is achieved when all farmers pursue a combination of formal and informal risk transfer, a community of self-interested agents is unable to maintain this co-existence under rising climate risks. We find that a combination of prosocial …

The dynamics of ecological communities in nature are typically characterized by probabilistic processes involving invasion dynamics. Because of technical challenges, however, the majority of theoretical and experimental studies have focused on coexistence dynamics. Therefore, it has become central to understand the extent to which coexistence outcomes can be used to predict analogous invasion outcomes relevant to systems in nature. Here, we study the limits to this predictability under a geometric and probabilistic Lotka–Volterra framework. We show that while individual survival probability in coexistence dynamics can be fairly closely translated into invader colonization probability in invasion dynamics, the translation is less precise between community persistence and community augmentation, and worse between exclusion probability and replacement probability. These results provide a guiding and …