Theoretical Ecology Lab Tea

Fall 2018 schedule

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

Wed. August 15^th – 03:00pm

Special Lab TeaMasato Yamamichi (Visitor from U. Of Tokyo)

Coevolution is relentlessly creating and maintaining biodiversity and therefore has been a central topic in evolutionary biology. Previous theoretical studies have mostly considered coevolution between genetically symmetric traits (i.e. coevolution between two continuous quantitative traits or two discrete Mendelian traits). However, recent empirical evidence indicates that coevolution can occur between genetically asymmetric traits (e.g. between quantitative and Mendelian traits). We examine consequences of antagonistic coevolution mediated by a quantitative predator trait and a Mendelian prey trait, such that predation is more intense with decreased phenotypic distance between their traits (phenotype matching). This antagonistic coevolution produces a complex pattern of bifurcations with bistability (initial state dependence) in a two-dimensional model for trait coevolution. Furthermore, with eco-evolutionary dynamics (so that the trait evolution affects predator–prey population dynamics), we find that coevolution can cause rich dynamics including anti-phase cycles, in-phase cycles, chaotic dynamics and deterministic predator extinction. Predator extinction is more likely to occur when the prey trait exhibits complete dominance rather than semidominance and when the predator trait evolves very rapidly. Our study illustrates how recognizing the genetic architectures of interacting ecological traits can be essential for understanding the population and evolutionary dynamics of coevolving species.

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Wed. September 5^th – 12:30pm

Voluntary vaccination or mandatory vaccinationXue Feng

Voluntary vaccination coexists with mandatory vaccination on a global and even national scale. For example, most states in the US use voluntary vaccination for MMR (a combined vaccine against Measles, Mumps, and Rubella); but in Mississippi, West Virginia, and California, MMR is a mandatory requirement for school entry. Meanwhile, human movements connect regions with various vaccination strategies. Therefore, the epidemic dynamics in one region is not only influenced by its own vaccination strategy but also by the vaccination strategies and epidemic dynamics in neighboring regions. Here, a meta-population model is proposed to study how two typical vaccination strategies, voluntary vaccination and mandatory vaccination, influence each other from the perspective of epidemiology and populations’ economic cost. Specifically, with voluntary vaccination, individual decision-making depends on the perceived payoffs of disease and vaccines rather than the real payoffs. Population structure on which information and diseases spread and the ability of processing information are two factors leading to the difference between perceived and real payoffs. Here, network and prospect theory are used to capture the features of these two factors, respectively.

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Wed. September 12^th – 12:30pm

Natural selection of behaviors with underlying processes for any graph structureVitor Vasconcelos

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Wed. September 19^th – 12:30pm

Daniel Cooney

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Wed. September 26^th – 12:30pm

Chadi Saad-Roy

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Wed. October 3^rd – 12:30pm

A model for growing and shrinking cities: the urban garden bridge to chaosTheresa Ong

Urban gardens are temporally dynamic systems, with many (e.g., the Victory Gardens in the U.S. following WWII), sprouting, and then quickly disappearing in history, while others (e.g. the urban and periurban gardens of Cuba and Germany) seem more resistant to change. To understand why transitions to urban gardens are more permanent in some cases than others, we develop a game dynamical model of land-use transitions where players choose between a given set of land-use strategies (vacant lots, gardens and developed land). Landowners compete for markets and grow their territories depending on the utilities of their land-use states, sometimes transitioning towards states that have higher payoffs in competition. We find that relaxing static impressions of utility so that they change with economic conditions may lead to complex dynamic consequences for urban gardens, including limit cycles and chaos. Supplementing the economy of land markets can lead to large-scale economic booms and busts and correspondingly large changes in land-use; results that are similar to trends seen during the subprime mortgage crisis of the U.S. in the early 2000s, and other cascading housing bubbles felt worldwide. Hence, simple game theoretic models can mimic the complex, large-magnitude fluctuations in urban land-use following economic collapse that have been observed to occur in many places and times in history. We find that reducing land tenure to medium levels may stabilize dominance of urban gardens in cities albeit at the cost of a slightly reduced, but more stable economy.

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Wed. October 10^th – 12:30pm

Daniel Cooney & Fernando Rossine

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Wed. October 17^th – 12:30pm

Why do most isogamous species have so few mating types, yet some have so many?George Constable

Mating types determine compatibility between the gametes of sexually reproducing eukaryotes. In anisogamous species (those with gametes of different sizes) mating types are synonymous with the two sexes. In isogamous species (those with morphologically similar gametes) the picture is more complex. Simple evolutionary reasoning suggests that a near infinite diversity of mating type classes should be observed. However, while empirical observations show that such a scenario is possible (the fungus Schizophyllum commune has a staggering 23,328 “sexes”) most species have just two. In this talk I will show how this discrepancy can be largely explained by a null model of mating type dynamics. Analytical results will be presented that support the view that much of the variety in mating type number across isogamous species can be explained by a balance between the mutation and extinction of mating type alleles.

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Wed. October 24^th – 12:30pm

Agent-Based Model of Human MigrationNicolas Choquette-Levy

Predicting international and within-country flows of human migration has been a question of interest for policymakers across multiple scales of government (international, national, and local). This is likely to increase in salience as climate change introduces greater risks to livelihoods through stronger and more frequent droughts and floods, rising sea levels, and other phenomena.1 Traditional models of migration, often termed “gravity models”, are not equipped to evaluate these concerns: they typically assume that potential migrants are economically rational actors whose decisions are dominated by considerations of income and monetary costs of migration.2 In this talk, I will present the beginnings of an agent-based model that accounts for additional decision-making factors, including the effects of migrant networks, place attachment, and variations in risk tolerance across a population. I will also demonstrate how this type of model can help distinguish the effects of different hypothesized pathways for how climate change could affect migration, which can inform more precise empirical research questions. I look forward to collecting feedback on the structure and ideas for extending the model!

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Wed. October 31^st – 12:30pm

Fall break - no lab tea

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Wed. November 7^th – 12:30pm

Emergence of life cycles during a transition to multicellularity Merlijn Staps

Multicellular organisms display a wide variety of life cycles. For example, some short-lived multicellular entities grow by aggregation and reproduce only once by generating large numbers of single cells (e.g. cellular slime molds), whereas others grow by repeated cell divisions and can reproduce continuously by releasing unicellular propagules (e.g. animals). I will present a model to study how a primitive multicellular life cycle arises from a solitary ancestor. The model shows that diverse life cycles may readily evolve, depending on the physical constraints on group formation, the benefits provided by multicellularity, and the way by which groups are constructed from single cells.

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Fri. November 9^th – 01:00pm

How do diffusion and heterogeneities affect competition? Sergio Fernández-Rincón

It has been nearly 90 years since Alfred J. Lotka and Vito Volterra proposed the models that established the basis of the study of the interaction between species. During this time, significant improvements have been achieved in this field, with the addition of stochastic techniques and the introduction of the space. In this talk, we will discuss the last point, analyzing fascinating results that arise when the diffusion of the species and the heterogeneity of the environment are incorporated into the basic Lotka-Volterra competition model for two species. Particularly, the Singular Perturbation Theorem and the Principle of Induced Instability will be established as a link between non-diffusive and diffusive models and, among other consequences, either uniqueness or multiplicity will be obtained depending on the configuration of the habitat.

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Wed. November 14^th – 12:30pm

Plants as pathogens: Predicting invasive plant spread using an epidemiological model framework Zoe Volenec

The two biggest threats facing biodiversity are habitat loss and invasive species. I am developing a model that tackles the intersection of these two problems to understand how habitat loss facilitates invasive plant spread. I am currently using an epidemiological model framework to predict invasive plant spread based on remnant habitat fragment size, the surrounding land use and the proximity of other “source” habitat fragments. In this talk I will present some preliminary results of the model and a case study I am developing for New Jersey open space areas. Ultimately I hope to use this model to conduct invasion risk assessments for the networks of habitat remnants that increasingly characterize nature reserves in populous countries and to target management to specific remnants that play key roles in facilitating invasion.

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Wed. November 21^st – 12:30pm

Thanksgiving break - no lab tea

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Wed. November 28^th – 12:30pm

Dylan Morris

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Wed. December 5^th – 12:30pm

Sam Cho

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Fri. December 7^th – 04:00pm

Ryan Chisholm (visitor from NUS)

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Wed. December 12^th – 12:30pm

George Hagstrom

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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
34. Spring 2018