Theoretical Ecology Lab Tea

The Theoretical Ecology Lab Teas are informal meetings where members of affiliated lab groups give talks on their current research and receive feedback from their audience. Talks are 30 minutes long and are followed by questions and discussion.

Lab Tea typically meets Wednesdays at 12:30 pm during the fall and spring semesters. All talks this semester will be held in Eno 209 unless otherwise stated.

For the spring semester of 2018, the talk schedules and email lists will be maintained by Samuel Cho and Chadi Saad-Roy. Please contact Samuel or Chadi to have your name added to the Lab Tea email list so that you can receive reminders about upcoming meetings.

Spring 2018 schedule

Click on an event to view the talk title and abstract

Date and time Speaker
Ricardo Martinez
Jobst Heitzig
Daniel Cooney
Vitor Vasconcelos / Wenying Liao
Jaime Lopez
Theresa Ong
Jude Kong
Fernando Rossine
Spring Break
George Hagstrom
Daniel Cooney
Nicolas Choquette-Levy
Cancelled due to PCTS Pattern Formation Workshop
Christopher Tokita
Kairui Feng

Note: Priority is given to graduate students. A ⊛ symbol next to the speaker's name means that approval is pending for a week and graduate students can still claim the slot.

Titles and abstracts

Biological self-organization across spatiotemporal scalesRicardo Martinez

Self-organization is a ubiquitous phenomenon in nature, underlying the emergence of population-level patterns out from individual-level interactions in complex biological systems. Instances can be found at any spatiotemporal scale, from microbial communities and tissue organization to collective animal behavior to landscape patterning. Remarkably, despite the large variety of systems driven by self-organized processes, the diversity of shapes found in the emergent patterns is strikingly low. In this context, the question naturally arises as to how seemingly identical patterns can emerge in different scenarios and from completely different interactions. One hypothesis is that all these self-organized systems could be governed, to some extent, by the same set principles. Driven by this possibility, I will discuss my work on the development of a theoretical framework that encompasses different driving forces of spatial self-organization, both in motile and sessile organisms and on several spatiotemporal scales. In particular, I will focus on self-organized cell aggregation in Dictyostelium discoideum, emphasizing on the impact that an imperfectly synchronized self-organized collective behavior has on the biodiversity of this species.

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The copan:CORE framework: from World-Earth modeling to theoretical ecology?Jobst Heitzig

I'll present a modular modeling framework recently developed at PIK for studying the planetary social ecology, involving feedback loops between biophysical, socio-metabolic, and socio-cultural processes, by means of ''World-Earth'' models. It allows to combine macroscopic and microscopic equation-based model components in discrete and/or continuous time with agent-based components at various levels of aggregation (individual, spatial grid cell, social system, planet, etc.). After speculating how it might also be used in theoretical ecology, I'll hope to engage in a lively discussion about the relationship between these fields of research. Ref.: Heitzig, Donges et al., ESDD 2018, https://doi.org/10.5194/esd-2017-126

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Evolutionary Games in MetapopulationsDaniel Cooney

We consider two models for evolutionary games in group-structured populations. In the first model, we consider a two-level Moran process for the Prisoner's Dilemma in which within-group selection favors defectors and between group-selection favors cooperation. In the second model, we explore a coordination game to explore the balance between the individual incentive to coordinate with group members and the group-level incentive for groups to coordinate on an efficient strategy.

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Envisioning future food system under climatic riskVitor Vasconcelos / Wenying Liao

Prediction suggests that global food production must double to satisfy the increasing demand of world population by 2050. Yield enhancement relies heavily on the use of nitrogen fertilizer. However, excess nitrogen fertilizer input results in diminishing return of crop yield and increased environmental pollution. In addition, the predicted increase in future climatic risk will likely further incentivize countries to increase nitrogen fertilizer use, to sustain food security. Can we design a food system that both sustains food security and reduces global nitrogen pollution? Here, in this preliminary work, we explore the utility of a central food bank, where countries voluntarily enter by paying a fixed cost. If climatic disaster affects the yield of one member country, its food production is compensated by the bank.

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Metabolic Trade-Offs in Serial Dilution CultureJaime Lopez

Microbial communities in nature typically exhibit a vast diversity of organisms. These observations clash with the predictions of resource-competition models, which allow only as many species as resources to coexist at steady state. One possible solution to this paradox is the idea that organisms are subject to trade-offs, which ensure no species has an absolute advantage over others. This concept was explored in the framework of a chemostat model by Posfai et al. (2017), who found that large regions of the nutrient supply space can support unlimited diversity if all organisms have the same fixed enzyme budget. However, while the chemostat provides a useful conceptual model, nutrient supply rates in nature are seldom steady. The other extreme corresponds to serial dilution or ''seasonal'' variation where nutrients are supplied periodically or even randomly in discrete packets. Here, we analyze how metabolic trade-offs influence diversity in such a serial dilution model. We characterize the effects of varying supply on the population dynamics, finding relationships that still permit unlimited diversity but differ qualitatively from those found in the chemostat case. We also examine connections between the chemostat and serial dilution models.

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Multiple Hysteretic Patterns from Elementary Population ModelsTheresa Ong

Critical transitions whereby small changes in conditions can cause large and irreversible changes in ecosystem states are a cause of increasing concern in ecology. Here we focus on the irreversibility of these transitions, formally known as hysteresis. We explore how simple correlations between parameters in Lotka-Volterra predator-prey equations result in a variety of complicated hysteretic patterns. These patterns include “unattainable” stable states that once lost may never be recovered. We suspect these patterns to be common in natural systems, where interactions between diverse assemblages are unavoidable. Thus, understanding underlying hysteretic structures may be necessary for rescuing lost ecosystem states and avoiding future losses.

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TBAJude Kong

Microbial metabolism of fugitive hydrocarbons produces greenhouse gas (GHG) emissions from oil sands tailings ponds (OSTP) and end pit lakes (EPL) that contain processed waste from surface-mined oil sands ores. Predicting GHG emissions, particularly methane, is important for oil sands industry and government agencies for the purpose of mitigation and regulation. In this talk, I will present a predictive model for GHG emissions from OSTP and EPL. Furthermore, the mathematical analysis and the performance of the model will be thoroughly discussed. The proposed model can be used to (1) predict the mass of methane produced in OSTP or EPL at a given timepoint; (2) calculate the time required to produce a given cumulative mass of methane; and (3) estimate the duration of methane production. The insight provided by the model may help oil sands operators manage their tailings repositories and evaluate the success of EPL reclamation scenarios.

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Til growth do us partFernando Rossine

Recently much attention has been given to non competitive interactions in microbial communities. Syntrophic chains, in which the waste of a microbe is the food for another one, are thought to be pervasive in natural and synthetic systems. Non resource mediated interactions are also possible, behavioral shifts in slime molds of co-occurring strains being a prime example. However, in order to stabilize such processes, microbial associations must persist throughout colony expansion. It has been shown in numerous systems that growth itself has a role in segregating microbial communities. I will propose ways in which the geometry on the substrate might interact with the rules of movement of microbes giving rise to counter-intuitive segregation patterns. I will then outline an experimental system to test these predictions.

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Spring Break

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Marine Gels, Motility, and Organic Matter RemineralizationGeorge Hagstrom

Heterotrophic bacteria play a key role in the biological carbon pump by processing over 50% of marine primary productivity each day. Despite their importance to ecological and biogeochemical processes, we understand little of the interactions between organic matter and marine bacteria. Several outstanding problems include explaining the factors regulating the size of the recalcitrant dissolved organic carbon pool and the ecological role of motility for heterotrophic bacteria. Here we build a simple model which combines several interesting features: a trait-based description of bacterial strategies, diversity of available organic compounds, and the formation of microgels through interactions between dissolved polymers. This model suggests an alternative mechanism which can explain both the trait-distribution of marine bacteria and properties of marine organic matter.

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Continuum Models for Population DynamicsDaniel Cooney

We will discuss two frameworks for describing the connection between individual decision-making and emergent behavior in large populations. First, we will discuss the "gradient dynamics" approach of Friedman and Ostrov, which describes learning dynamics in games with continuous strategies, and then we will illustrate an application to a social-ecological model of fisheries with peer-punishment for overfishing. Next, we will describe Medvedev's use of the theory of graph limits to understand the continuum limit of the Kuramoto model for coupled oscillators, and will explore how this approach can be used to describe social, epidemic, or ecological processes on metapopulation networks.

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Applying Ecological Models to Inform Climate PolicyNicolas Choquette-Levy

Climate change poses a set of "wicked" problems for policymakers, who must contend with uncertain ecological tipping points, tradeoffs among competing policy goals, diverse stakeholder values, and coordination issues across and within governments. Furthermore, well-intentioned policy interventions to reduce greenhouse gases or promote climate resilience may lead to long-term unintended consequences. Ecological and evolutionary models could help policymakers improve their understanding of the possible equilibria and stability of their intended policy objectives. In this talk, I will discuss three types of climate problems that could be improved by these kinds of models: promoting cooperation among heterogeneous actors, decreasing individual and collective vulnerability to extreme climate events, and deploying low-carbon energy technologies. I will introduce some initial research and ideas on how to adapt ecological models to inform these problems, and hope to gather your thoughts on potential next steps.

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Cancelled due to PCTS Pattern Formation Workshop

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The effect of social interactions on emergent behavioral specialization and social network structureChristopher Tokita

With increasing size, social systems—from social insects to humans—often exhibit increasing organizational complexity, as measured by the behavioral diversity and the structure of interactions among individuals. In order to investigate the role of social interactions in emergent organizational complexity, I will present an individual-based model that incorporates social interactions into a response threshold framework. Preliminary findings suggest that allowing individuals to (a) influence one another through interactions and (b) bias their interactions towards those with the same behavioral phenotype results in the non-linear emergence of behavioral diversity and polarized (i.e., clustered and assortative) social networks. Although the model and its results will present behavioral diversity in the context of division of labor, I will touch on how I am interested in generalizing the model further to account for broader behavioral diversity, potentially including political/opinion polarization in human groups. I look forward to hearing thoughts and suggestions for this work in progress.

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Hurricane Evacuation: Coupling Hurricane Forecast, Human Behavior, Governmental Strategy and Game Theory on TrafficKairui Feng

Hurricane evacuation couples the evacuation process and the traffic assignment together and controlled by the governmental management. Evacuation, as a collective dynamics problem, leads to researches on ODE system of particles to capture the congestion behavior and employs variation methods to figure out the optimal evacuation route of every single player under deterministic and stochastic scenarios. With the game nature of traffic, researchers developed network-based game theory solver to predict the Nash equilibrium of the traffic system and generalize that methodology to random and dynamic situations. These methodologies though elegant, are usually complex and time-consuming. When it comes to a real engineering evacuation problem, people usually fail to capture the global behavior of traffic system because of the mechanism of these two research groups introduced too many "physics and behavioristics". So "what physics to mention" becomes a problem when we start to think about predicting traffic condition during a real hurricane evacuation. In this research, the 7-million-people-involved large hurricane evacuation under IRMA last summer in Florida is studied. A simplified mean-field model succeeds in reducing the agent number from 7 million to 15 thousand while keeping the main "physics" of evacuation and able to finish the traffic simulation of the 6-evacuation-day in 9 seconds on a personal PC. With this fast model, parameter fitting for human behavior (evacuation decision, route choice, etc..) becomes possible and finally, we get the simulation result matches the real traffic data under given governmental decision. And also, by perturbation on governmental decisions, this research shows that governmental decision matters a lot on the lowest traffic speed (traffic bottleneck) during evacuation so it is worth improvement.

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Links to previous schedules

  1. Fall 2000
  2. Spring 2001
  3. Fall 2001
  4. Spring 2002
  5. Fall 2002
  6. Spring 2003
  7. Fall 2003
  8. Spring 2004
  9. Fall 2004
  10. Spring 2005
  11. Fall 2005
  12. Spring 2007
  13. Fall 2007
  14. Spring 2008
  15. Fall 2008
  16. Spring 2009
  17. Fall 2009
  18. Spring 2010
  19. Fall 2010
  20. Spring 2011
  21. Fall 2011
  22. Spring 2012
  23. Fall 2012
  24. Spring 2013
  25. Fall 2013
  26. Spring 2014
  27. Fall 2014
  28. Spring 2015
  29. Fall 2015
  30. Spring 2016
  31. Fall 2016
  32. Spring 2017
  33. Fall 2017