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. The talks are 30 minutes and are scheduled generally on Wednesdays at 12:30 pm. All talks this semester will be held in Eno 209 unless stated otherwise.

This semester, talk schedules and email lists will be maintained by Charlotte Chang and Lisa McManus. Please contact one of us to have your name added to the labtea email list so that you can receive reminders about upcoming meetings.







 
 

 

Spring 2014

Wednesday February 12th at 12:30pm Lars Hedin
Wednesday February 19th at 12:30pm Efrat Shefer
Wednesday February 26th at 12:30pm Corina Tarnita
Wednesday March 5th at 12:30pm Eric Libby
Tuesday March 11th at 2:00pm Special lab tea: Rick Durrett
Wednesday March 12th at 12:30pm David Borenstein
Wednesday March 19th at 12:30pm No lab tea: Spring Break
Wednesday March 26th at 12:30pm Simon Leblanc
Wednesday April 2nd at 12:30pm Alex Washburne and Jacob Socolar
Wednesday April 2nd at 2:00pm Special lab tea: Jeremy Van Cleve
Wednesday April 9th at 12:30pm Sarah Batterman
Wednesday April 16th at 12:30pm Vitor Vasconcelos
Wednesday April 23rd at 12:30pm Rebecca Asch
Wednesday April 30th at 12:30pm Special Seminar: No labtea
Wednesday May 7th at 12:30pm Carey Nadell
Monday May 19th at 12:30pm Special Lab tea: Astrid Dannenberg
 
 

Titles and abstracts

Wednesday February 12th at 12:30pm

Fire, Nutrients, Plants and Herbivores in South African Savanna
Lars Hedin
Abstract unavailable.

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Wednesday February 19th at 12:30pm

A game theoretic explanation of biome-specific differences in N2-fixers and fixation
Efrat Shefer
N2-fixation is the principal source of nitrogen (N) to land ecosystem, manifested in vastly different patterns across the biosphere. The abundance of symbiotic N2-fixing trees in all stages of tropical forest development is puzzling in light of their scarcity in temperate and Boreal forests, where they dominate early-successional stages and are out-competed by non-fixers at later stages. This pattern presents a paradox: why individuals that pay the costs of N2-fixation succeed in N-rich tropical forests and why not in N-poor extra-tropical forests. I will show how I used a game-theoretic analysis to find the conditions under which N2-fixation is an evolutionary stable strategy (ESS) and how different strategies of N2- fixation are governed by biome-scale climatic constraints on N cycling. We found that a facultative N2-fixation strategy (the ability to down-regulate N2-fixation in reaction to increased soil N availability) is favored in tropical ecosystems where soil N accumulates fast, and results in long-term coexistence of fixers and non-fixers. In extra-tropical forests slow soil N accumulation make the down-regulation of fixation disadvantageous, and the obligate strategy (with constant fixation rate) is favored, despite its long-term exclusion. Our analyses suggest that biome-scale patterns of N2-fixation can be explained by the indirect effect of climate-dependent N cycling on individual-based strategies.

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Wednesday February 26th at 12:30pm

Causes and consequences of regular spatial patterning in foundation species
Corina Tarnita
The increasing availability of high-resolution satellite imagery over the past decade has shown that highly regular and apparently self-organized vegetation patterns are common in nature, especially in semi-arid rangelands. However, there remains much uncertainty about exactly how these patterns form, and whether they are important in determining the stability and productivity of ecosystems. We're combining mathematical modeling with experimental field studies to understand the causes and consequences of regular pattern formation by "foundation species"-specifically, subterranean termites whose mounds are both uniformly patterned and integral to important ecosystem functions such as nutrient cycling and biomass accumulation. In this talk I will be addressing two broad questions: 1. what combination of biological and physical processes generates and maintains this kind of spatial patterning? and 2. what are the emergent effects of these patterns on the overall productivity of ecosystems and their stability in the face of perturbations such as climatic change and overgrazing?

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Wednesday March 5th at 12:30pm

Geometry shapes evolution of early multicellularity
Eric Libby
The transition from unicellularity to multicellularity marks an important shift in the level of organization and individuality of living organisms. Although this transition has occurred independently dozens of times, early steps remain poorly understood. A recent experiment with the yeast Saccharomyces cerevisiae observed the evolution of self-reproducing groups from single-celled precursors. Interestingly, these self-reproducing groups soon evolved a secondary trait: a higher rate of apoptosis. Since groups divide (reproduce) as a result of cell death, increased apoptosis leads to an increase in the number of groups, i.e. group fitness. In the context of the selective regime such a result is puzzling. How does a trait disadvantageous for individual cell fitness but advantageous for group fitness arise when groups originally formed to increase cell fitness? Here, we show that the geometric organization of the group is key to understanding how such a trait might evolve.

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Tuesday March 11th at 2:00pm

Spatial Evolutionary Games (Special Lab tea)
Rick Durrett
In 1994 Durrett and Levin suggested that the outcome of spatial competition could be predicted from properties of the mean-field PDE which is derived by pretending that adjacent sites were always independent. Using recent work of Cox, Durrett, and Perkins on voter model perturbations, I will show that this is true for evolutionary games of the form 1 + wG, where 1 is a matrix of all 1's and w is small, but one must replace assumption of independent sites by the voter model equilibrium. The take home message is simple: the effect of space is equivalent to simply changing some of the entries in the game matrix.

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Wednesday March 12th at 12:30pm

eSLIME: a novel software system for rapid individual-based modeling
David Borenstein
Developing a new model can often be an arduous task, with development times of weeks or more. Here I present eSLIME, a new-high level programming system for lattice-based ecological modeling. The system consists of a modular back-end interface for designing new behaviors and features, and a hierarchical front-end for model definition. Implementing a new model with existing features requires no software background and can be completed in hours instead of weeks. The system can run on a personal computer or a computing cluster, and is designed to run to high replicate overnight. The framework has support for individual-based (local) discrete processes, global discrete processes and reaction-diffusion solute processes, making it applicable for a variety of ecological and biophysical models at many scales. A feature-complete alpha will be available for evaluation within weeks.

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Wednesday March 19th at 12:30pm

No labtea - spring break
Have a wonderful spring break!

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Wednesday March 26th at 12:30pm

Information Flow on Interaction Networks
Simon Leblanc
Many tasks achieved collectively by groups of animals like bird flocks and fish schools involve gathering, processing and exchanging information. Individuals in a group take decisions based on information that they gather from the environment and from their neighbors who, voluntarily or not, produce information by performing actions which are the results of their own decision process. And apparently, information flows pretty fast in these groups! But the underlying mechanisms are unknown. By modeling this decision process using Bayesian updating and optimizing prior probabilities of individuals' decision process for fast and robust consensus at the group level, independently of the group's structure (which might be dynamic) or one's position on the interaction network, we hope to find general principles of synergetic information processing applicable to a wide range of groups and to groups of any size.

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Wednesday April 2nd at 12:30pm

The maintenance of prey diversity in a stochastic world
Alex Washburne and Jacob Socolar
How will introducing (or removing) a prey-switching predator affect prey diversity? Theoretical studies of infinitely-large and deterministic systems governing predator and prey interactions suggest that a prey-switching predator (a predator that preferentially targets the more abundant prey) should promote diversity among its prey. We use a Gillespie algorithm to create trajectories of non-zero-sum neutral prey communities with migration from a metacommunity, density-dependent birth and constant per-capita probabilities of death. Crucially, these simulations represent communities with finite prey and predator populations, and they capture demographic stochasticity while preserving the same expected trajectories of the underlying ODEs. We use our simulation scheme to explore the influence of prey-switching predators on finite prey populations, and our initial investigations reveal a common answer in biology: it depends. At realistic predation rates, we find that prey-switching predators do promote prey species-richness when the prey carrying capacity is high. However, for low prey carrying capacity, identical predation regimes depress prey diversity. These results are preliminary and our work is far from complete - we're excited to brainstorm with y'all about what of our simulation and its results are novel and interesting for theoreticians, and what would be relevant for wildlife managers. We also invite discussion of the pitfalls and utility the Gillespie algorithm in ecology, which can be easily (yet cautiously) applied to simulate stochastic trajectories of any system of ODEs.

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Wednesday April 2nd at 2:00pm

The evolution of bet-hedging and phenotypic plasticity (Special Lab tea)
Jeremy Van Cleve
In light of an uncertain future, organisms face a difficult trade-off. They can either specialize on a single phenotype across a range of environments, hedge their bets by randomly choosing among a set of phenotypes, or invest in physiological machinery to adjust their phenotype plastically. Understanding the evolutionary relationship between these strategies remains a puzzle. Here, we present a simple model for the evolution of specialization, bet-hedging, and plasticity that reveals how these strategies are fundamentally sensitive to the shape of the cost of plasticity. When costs accelerate with plasticity, bet-hedging is the likely outcome. In contrast, decelerating costs can lead to full adaptive plasticity, but only when initial conditions are right. The shape of the cost curve is due to the genetic and metabolic network machinery underlying plastic traits, which means that certain networks are more likely than others to evolve plasticity.

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Wednesday April 9th at 12:30pm

Biogeochemical controls of symbiotic N2 fixation across broad spatial scales
Sarah Batterman
Symbiotic N2-fixing trees fill a critical role in the nitrogen cycle, yet the abundance of fixers varies widely both within and across biomes. A dominant idea proposed to resolve this variation is that fixation and fixers are controlled by soil phosphorus, although the mechanisms of how fixers depend on phosphorus remain largely unexplored and have different consequences for the distribution of fixers. I will consider four hypotheses about the influence of phosphorus on fixers relative to non-fixers, and examine the consequences of these hypotheses for how fixers differ from non-fixers in phosphatase activity, abundance, and nutrient limitation status across a gradient in phosphorus availability. I use a theoretical plant-soil ecosystem model that includes different ideas about the phosphorus costs of fixation, competitive abilities of fixers relative to non-fixers, and phosphorus uptake strategies. If I have time, I will evaluate the predictions with empirical data from our own work and the literature and new analyses of forest inventory data from tropical forests.

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Wednesday April 16th at 12:30pm

Unknown
Vitor Vasconcelos
Abstract not yet available.

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Wednesday April 23rd at 12:30pm

TBA
Rebecca Asch
Abstract TBA.

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Wednesday April 30th at 12:30pm

Special EEB Seminar
NA
No labtea this week.

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May 7th at 12:30pm

TBA
Carey Nadell
Abstract TBA.

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May 19th at 12:30pm

TBA (Special Lab tea)
Astrid Dannenberg
Abstract TBA.

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[back to schedule]

 
 

Links to previous schedules

   Fall 2000    Spring 2001
   Fall 2001    Spring 2002
   Fall 2002    Spring 2003
   Fall 2003    Spring 2004
   Fall 2004    Spring 2005
   Fall 2005    Spring 2007
   Fall 2007    Spring 2008
   Fall 2008    Spring 2009
   Fall 2009    Spring 2010
   Fall 2010    Spring 2011
   Fall 2011    Spring 2012
   Fall 2012    Spring 2013
   Fall 2013
   




Last update: February 17, 2014
Charlotte Chang