Fall 2008

Titles and abstracts

Wednesday September 17th at 1.30pm

Fog and the formation of patterns in desert vegetation
Daniel Stanton
I will be presenting the still rather preliminary work that Liliana Salvador and I have been doing on self-organizing pattern formation associated with fog.  We have been constructing a model of spatial patterns of what may be one of the simplest ecosystems around, bromeliad fields that live off of fog in rain-less areas of the Atacama desert.  We aim to show how directional flow of fog is sufficient to generate the striking banding patterns observed at some sites in Peru and Chile.  I will also present some work on a similar model of forest fragment dynamics in a fog-forest in Chile, in which we have begun to incorporate some fluid dynamic.

Wednesday September 24th at 1.30pm

Adaptation under molecular clock
Sergey Kryazhimskiy
The observation that the rates of evolution at the protein level are approximately constant with time at long timescales (the so called "molecular clock") was one of the major arguments presented in the 60-ies by Kimura in favor of the neutral theory. Three decades later, a remarkable constancy of amino acid substitution rates is confirmed by direct observation in the long-term evolutionary experiments in E. coli in Rich Lenski's lab. The caveat is, however, that the neutral theory is out of question: the observed substitutions are highly adaptive. In this talk I will discuss a potential explanation for how adaptation can proceed under molecular clock.

Wednesday October 1st at 1.30pm

A neutral theory of biological invasions
Ryan Chisholm
Biological invasions threaten native biodiversity and human welfare, but they also provide invaluable insights into ecology, evolution and biogeography.  The study of biological invasions has been criticised for its lack of general principles.  At a previous lab tea, I proposed a neutral theoretical framework as a null model of biological invasions against which specific hypotheses can be tested.  In this week's lab tea I will discuss ongoing development of the theory and compare the theoretical predictions to data from invasions of temperate forests and grasslands.

Tuesday October 7th from 1.30 - 2.30pm

Ecological science and tomorrow's world
Robert May

Wednesday October 15th at 1.30pm

Foraging strategies and primate grouping patterns: “Not all who wander are lost”
Liliana Salvador
Animals move to explore their environment, to search for food and to find mates, constantly making decisions about when and where to go. The success of these routine activities depends on the searching strategies that the animals adopt. From field data, there is evidence that foraging animal groups have preference for specific sites, returning to them after a time period. This indicates that they have both “cognitive maps” of the position of the resource patches, and “episodic memory” which allows them to remember past resource values and to predict future ones. There is also evidence that they share their search space with other groups, creating a contact network of overlapping home ranges. Despite a vast literature describing the statistical patterns of home range usage, very little research has addressed the behavioral mechanisms through which home range patterns emerge. To address these questions, I have been developing a spatially explicit foraging model using primates as a model system. With this model I show that the use of sophisticated cognitive skills leads to the spontaneous self-organization of home range behavior.

Wednesday October 22nd at 1.30pm

Social evolution and spatial structure in bacterial biofilms
Carey Nadell
Bacteria predominantly reside in densely packed, surface-bound communities known as biofilms. While living in groups, many microbial species also secrete compounds that affect the reproductive success of their neighbors. Predominant examples of such secreted products include nutrient-sequestering compounds and digestive enzymes, some of which are virulence factors for pathogenic bacteria. I will present the preliminary results of a model exploring the evolution of cooperative exo-product secretion in biofilms.

Wednesday November 5th at 1.30pm

Novel insights and predictions about the structure of forests across fertility and disturbance gradients 
Ray Dybzinski 
Before I arrived at Princeton, several members of the Pacala lab made, in my estimation, a tremendous advance in our understanding of height-structured competition for light with both the creation and testing of an analytically tractable, mean field model of forest dynamics. Last Spring, I presented my contribution to that model, which consists of adding a mechanistic link between capture of soil nutrients and growth rates of trees in the canopy and the understory. I will review the model and then present several of its interesting insights and predictions. ESS strategies are predicted to be “rootier” in areas of either lesser fertility or greater disturbance. The model permits invasion of sufficiently similar strategies, but sufficiently dissimilar strategies are founder controlled. Importantly, and in contrast to many of the predictions made by earlier models that use less sophisticated light competition, good nutrient competitors are never predicted to coexist with good light competitors because each must go through a life history stage (understory or canopy) in which it is limited by the resource for which it is the better competitor. Moreover, there is a suggestion that species that may initially dominate a site via founder control may “engineer” nutrient availability via litter chemistry so that they are the ESS. The model also makes predictions about the grassland/forest boundary: At low nutrients and with increasing disturbance, no closed-canopy ESS “rootiness” is predicted; rather, rootier strategies invade and drive the system into open canopy. Open-canopy “rootiness” is much greater than any closed-canopy strategy and does not vary with fertility or disturbance (although total canopy area does). 

Wednesday November 12th at 1.30pm

A metacommunity perspective on forest dynamics
Jeremy Lichstein
We have developed a model of forest dynamics that is simple enough so that
many aspects of the model's behavior can be described analytically, yet
realistic enough to make useful predictions about real forest communities.
I am developing a metacommunity version of this model to explore how habitat
loss and inter-patch dispersal rates affect local (within-patch) species
diversity.  I would like to tell you about it.  The modeling framework is
similar to that described by Ray Dybzinski in last week's labtea.  Because I
have fewer and less cool results than Ray, I will spend some time walking
through some of the basic building-blocks of the model.

Wednesday November 19th at 1.30pm

Towards a better understanding of biome distributions and vegetation structure shifts: building the first analytical and mechanistic model of biome distributions
Caroline Farrior
The distribution of biomes can largely be explained using only a few climatic variables.  Although this pattern is considered one of few ecological laws, we have no quantitative, mechanistic explanation for the specific transitions between biomes.  The Pacala research group has designed a model of forest dynamics governed by macroscopic equations that predict the outcome of height-structured competition from plant vital rates. During the past year, I worked to incorporate physiological models of light and water limited photosynthesis into the vital rates.  As I have been able to do this in a way that maintains analytical tractability, we now have a prediction for competitive ability as a function of plant physiological traits and environmental conditions.  Here I will present a plan for extending this model of forest dynamics into a treatment of general vegetation and analytic tools that will determine the late-successional dominant plant types across the globe.

Wednesday December 3rd at 1.30pm

Human gossip networks and the ecology of honesty
Mark Laidre
This talk will attempt to stimulate some constructive gossip about the topic of gossip. It will explore, in particular, the prospects for modeling networks of gossiping human agents who signal to one another in the context of an evolutionary game. I will begin by providing a sampling of some of the intriguing empirical patterns from the social sciences literature as well as from studies of our closest primate relatives. These empirical patterns will then be used to sketch a step-by-step framework for an agent-based simulation of gossip, focusing specifically on how gossip can remain reliable over evolutionary time. This is a brand new project, somewhat tangential to the rest of my thesis work, so I’ll be extremely grateful for any general feedback on the ideas as well as more specific discussion about some of the thornier compromises between realism and tractability.

Wednesday December 10th at 1.30pm

What determines the global distribution of savanna? A case for climate, soil resources and disturbance
Carla Staver
On a broad scale, how do climate and nutrient conditions of a savanna determine how disturbance impacts on vegetation dynamics? Higgins et al. (2000) consider the impacts of fire on tree cover, which can undoubtedly be significant (Bond et al. 2005). While herbivory and fire are often discussed as key local disturbances that act on an 'abiotic template' (Scholes & Archer 1997), the interactions of fire and herbivory with that template are rarely explicitly considered. Local climate and soil resources strongly influence many ecological processes in savannas--including rates of tree and grass growth, herbivore use, and the probability and extent of fires--but the ways in which these processes interact to affect vegetation structure in savannas is largely unknown.
 

Links to previous schedules

    Fall 2002     Spring 2003
    Fall 2003     Spring 2004
    Fall 2004     Spring 2005
    Fall 2005     Spring 2006     Summer 2006
    Fall 2006     Spring 2007
    Fall 2007     Spring 2008