Spring 2017 schedule
Click on an event to view the talk title and abstract
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
The interplay between environmental flow and extracellular matrix production determines lineage segregation during bacterial surface colonizationRicardo Martinez-Garcia Biofilms are extracellular matrix formations grown at a solid-liquid interface. These formations increase cell adhesiveness and allow bacterial cells to remain attached to each other and to the surface after cell division. Thus, as part of a biofilm, cells are protected against shear forces induced by flows at the interface, their resource exploitation rate increases, and their dispersal probability decreases. Therefore, biofilm formation not only influences the spatial structure of the bacterial colony, but it can also determine its survival in different environmental conditions, for example in the presence of flows. Surprisingly, the influence that the latter may have on bacterial spatial organization has received little attention in the literature. With this project, we aim to fill this gap by studying experimental and theoretically the surface colonization patterns of a population of the bacterium Vibrio Cholerae growing in microfluidic devices. Our results suggest that adhesiveness plays a key role in the surface colonization pattern, with flow playing an important role even under controlled environments such as the microfluidic chamber. We use spatial correlation functions to quantify the differences between the emergent lineage segregation patterns, as well as to determine with numerical models the dependence of the competitive ability of the cells on both adhesiveness and strength of the flow in the chamber. Finally, I will discuss the evolutionary implications of matrix formation for the colonization strategies of founding cells, with a main focus in public good production. Our results emphasize the importance of considering both flow and adhesiveness when estimating the virulence of pathogens such as V.Cholerae which colonize environments that, like the human gut, are intrinsically affected by flows of different strengths.
Back to scheduleNitrogen fixation: an interaction between bacteria and plasmidsFlavia Darcie Marquitti What is the importance of the reproduction method to the existence and persistence of mutualism? In my work, I am exploring this question using the interaction between plasmids and bacteria involved in the nitrogen fixation at the roots of some plants. I am exploring how the horizontal gene transfer (sexual reproduction) and the vertical transmission (asexual reproduction) play role in the interaction of plasmids carrying the nodulation (NOD) and Nitrogen fixation (NIF) genes and their bacteria hosts. I face the problem of the plasmid paradox: “non-beneficial plasmids should be lost to purifying selection, whereas beneficial genes carried on plasmids should be integrated into the bacterial chromosome” and I try to understand the plasmid-bacteria interaction from the coevolutionary point of view. I will discuss my future steps on this theoretical work and also about future experiments.
Back to scheduleRelationships between cooperation and population densityEdward Tekwa Selection acting above the individual level may lead to an increase in cooperation. While experiments have shown that cooperation increases population density - a higher-than-individual level property - the relationship may be reversed in nature. The extent to which cooperation between individuals benefits the population may be chiefly determined by spatial mixing, which spreads the positive effect of cooperation across the population, but may also inhibit the evolution of cooperation by overexposure to defection. Using individual-based simulations and a simple mathematical model, we found that spatial factors affecting mixing lead to a negative relationship between cooperation and population density, while non-spatial factors (such as intrinsic growth rate and competition) lead to a positive relationship. I don’t really know what this means.
Back to scheduleRevenue sharing in fisheries and the emergence of sustainabilityAndrew Tilman Fishers are subject to risk in the form of variability in catch day-to-day and season-to-season. I will present a model that explores the conditions under which revenue sharing among fishers can emerge as a method to mitigate the risk inherent in harvesting a biotic resource. The talk will also assess the consequences of revenue sharing not only for risk mitigation but also for improved management. Bottom-up governance in fisheries has the potential to improve the management of fisheries especially is places where strong external management is weak or ineffective. A revenue sharing agreement among fishers is one such bottom-up mechanism that may lead to improvements in fisheries harvesting practices.
Back to scheduleCooperation and reputations in finite populationsFernando Santos The prevalence of altruistic cooperation is considered a paradox: why is that people are selfless and often incur costs to help unrelated others? Reputations are intimately linked with the answer to this question, and so are the social norms that dictate what should be considered a good or a bad action. Traditionally, the relation between cooperation and reputations has been studied in models of Indirect Reciprocity (IR) that consider infinitely sized populations. This contrasts with the fact that cooperation, norms, reciprocity and the art of managing reputations are features that go along with humans from their pre-historic existence in small-scale societies. In this presentation, I will describe a mathematical framework of IR that allows us to analyze the cooperation levels associated with different social norms, in populations of arbitrary sizes. We will see that population size is indeed relevant when evaluating the merits of each social norm. I will further discuss the role of behavioral errors, high exploration (aka mutation) rates and possible extensions to the model.
Back to scheduleTBA Back to scheduleTrees as a limiting resource in the spatial spread of an invasive antJessica Zung & Dylan Morris Pheidole megacephala, the “big-headed ant”, is a remarkably successful invasive species. Colonies of Pheidole are spreading rapidly across the savanna landscape at Mpala Research Centre in Laikipia, Kenya. Though ground-dwelling, Pheidole forage on trees and displace any tree-dwelling ants they encounter. We mapped a snapshot of Pheidole foraging presence on trees at the invasion wavefront. By modeling the spatial pattern of the wavefront and comparing ant presence on trees to presence on the ground, we will argue that trees act as a limiting resource in the ants’ spatial spread. We will propose that lower afternoon temperatures on trees relative to the ground are a key component of trees’ value to Pheidole.
Back to scheduleFeedbacks between loss of biosphere integrity and climate changeSteven Lade The terrestrial and marine biospheres sink substantial fractions of human fossil fuel emissions. How the biosphere's capacity to sink carbon depends on biodiversity and other measures of biosphere integrity is however poorly understood. Here, we (1): review hypotheses from literature regarding the relationships between the carbon cycle and the terrestrial and marine biospheres; and (2) explore the consequences of these different hypotheses for climate feedbacks using a stylised carbon cycle model. We find that response lag in terrestrial ecosystems, biodiversity loss in terrestrial ecosystems, and changes to marine biodiversity could all amplify climate change. This study constitutes the first detailed study of the interactions between climate change and biosphere integrity, two of the 'planetary boundaries'.
Back to scheduleDan Cooney Back to scheduleCharlotte Chang Back to scheduleRenewable resources in diverse market environmentsLaura & Sarah Renewable resources markets are associated with the rapid decline of biomass in the oceans and on land. The proportion of internationally traded fish and seafood are the highest for food commodities globally- and thus our system of choice. Bio-economics is to date the most comprehensively used tool to assess and manage fisheries. Market dynamics in these models are usually represented as single lumped parameters. We introduce different price dynamics of global and local market prices and observe changes in optimality and equilibria over three market scenarios. Income maxima shift towards the larger fish stock from local to global markets and extreme values are less critical from local to global markets. We welcome you to our Lab Tea and are excited to discuss your ideas and thoughts!
Back to scheduleAn Interdisciplinary Approach to Conflict Reversion Sara Usher Why do some intrastate conflict-affected states revert back to conflict, while others do not? This presentation aims to answer this question by proposing an interdisciplinary and multi-method approach to analyze the phenomenon of intrastate conflict reversion. I begin my analysis by highlighting the problematic approach of examining conflict reversion as ‘frozen’ or ‘stuck’ in equilibrium. Then, I address the shortcomings of applying 2-actor game theory models to the study of conflict reversion by linking ecological and social sciences under the theoretical framework of complexity theory. I introduce a novel model called the Competitive Efficiency Model (CEM) that embraces international relations (IR), ecology and complexity theory to simulate intrastate conflict dynamics through statistical and numerical modeling. I explain the applicability of the CEM by demonstrating mathematical principles of the model to both hypothetical scenarios and scenarios with real data. The presentation contributes to existing knowledge in three core areas of conflict dynamics within the IR discipline: (1) how the misconception of equilibrium to describe conflict dynamics can be detrimental to IR and conflict scholars’ ability to interpret conflict processes; (2) how an interdisciplinary approach coalesced with IR, ecology, and complexity theory, can increase our understanding of conflict reversion; and (3) how population dynamics from ecology theory can be applied to better understand conflict reversion.
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