Theoretical Ecology Lab Tea

The Theoretical Ecology lab teas are designed to be informal meetings for members of the research groups of Simon Levin , Steve Pacala , and Andy Dobson to give talks on their current research and receive feedback from their audience. The talks are usually 30 minutes, including the question and answer sessions, scheduled on Tuesdays at 3 PM. Additionally, other members of the Princeton University community and visitors are welcome to attend and to give presentations.

Talk schedules and email lists are maintained by Nandi Leslie and Ben Strauss. Please contact or to have your name added to the labtea email list so that you can receive reminders about upcoming lab teas. Click here for Fall 2000 schedule and summaries or Spring 2001 schedule and summaries or Fall 2001 schedule and summaries or Spring 2002 schedule and summaries or  Fall 2002 schedule and summaries


Spring 2003
Tuesday, February 4, at 3 PM
Colleen Webb
Wednesday, February 5 at 3PM Nadav Shnerb (Bar-Ilan University)
Tuesday, February 11, at 3 PM
Drew Purves
Tuesday, February 25, at 3 PM
Kai Chan
Tuesday, March 4, at 3 PM
Peter Walsh
Tuesday, March 11, at 3 PM
Somnath Roy
Tuesday, March 25, at 3 PM
Irakli Loladze
Tuesday, April 1, at 3 PM
Jim Regetz
Tuesday, April 8, at 3 PM
Tuesday, April 15, at 3 PM
Abdul-Aziz Yakubu (Howard University)
Wednesday, April 23, at 2 PM
Alain Franc
Tuesday, April 29, at 3 PM
Andy Dobson
Tuesday, May 6, at 3 PM
Nandi Leslie

Titles and abstracts most recent first (posted approximately one week before the talk):

Tuesday, February 4 @ 3 pm

Colleen Webb

Effects of spatial structure on ecosystem resilience

In a general context, robustness in complex systems may be
enhanced by intermediate levels of modularization.  When thinking about
ecosystems and spatial structure, this translates most simply to the
level of aggregation or clustering of individuals.  I will discuss
results from spatial simulations I have been running to look at how
spatial structure affects ecosystem recovery following a spatially
spreading disturbance.  The amount of clustering in my simulations is
controlled by the probability that individuals disperse locally versus
randomly.  My results suggest that the amount of random dispersal
interacts with growth rate in determining maximum resilience.  This is
due both to the higher realized birthrate with partial random dispersal
and to the changes it brings about in the spatial structure.

Wednesday, February 5 @ 3 pm

Nadav Shnerb

Adaptation and Pattern Formation in noisy reactive systems

The effect of intrinsic noise in spatially extended reactive systems
is considered. Adaptation of autocatalytic fluctuations do diffusive
noise and the formation of "reactive glass" will be discussed.

Tuesday, February 11 @ 3 pm

Drew Purves

(Root) Foraging as a spatial game

A bottom-up understanding of plant population biology is complicated by the
great flexibility of plant size and shape. This means that models based on
plants as point s in space are unlikely to reproduce the most important general
patterns observed in real populations (competition density effect, 3/2 or 4/3
thinning etc.). I've been trying to derive optimal horizintal root
distributions for plants foraging for water, b oth in isolation (an
optimisation problem) and in competition (a game theoretic problem). Some of
the results, e.g. that most space should be used exclusively by one plant
rather than being shared, should extend to foraging above-ground for light, and
als o to animals that have a spatial location (bird nest, ant colony, fish
crevices) from which they forage for a spatially diffuse resource.

Tuesday, February 25 @ 3 pm

Kai Chan

Detecting and Distinguishing between Processes Affecting Extinction
and Speciation Using the Shape of Phylogenies

The diversification of species is an epiphenomenon of many important
processes at the individual and population levels, whose patterns are
expressed at and above the species level.  This confluence of scales has
hindered a holistic understanding of this crucial biological process.  I
shall discuss some of my recent efforts to bridge these scales by
analyzing the effects of (traditionally) ecological and evolutionary
processes on the pattern of phylogenetic tree shape, and discovering
practical means of detecting and distinguishing between these processes.
I investigate the effects of several models of stochastic extinction,
including "demographic" (population size fluctuation) and
"rival-mediated" extinction (through competitive exclusion by or
hybridization with closely related species).  I contrast those
extinction-affecting processes with a speciation-affecting process by
which "new" species are inhibited from speciating (e.g., through
suppression by sister species).  In describing the phylogenetic effects
of these forces, I simultaneously derive statistics for their detection
and discrimination, and assess the relative power of these statistics.
The proximate goal is to implement these statistics in SymmeTREE, a
program that I developed with Brian Moore to detect differential rates of
diversification using the shape of phylogenies.  Assessing both within-
and between-lineage variation of diversification, SymmeTREE should
provide a toolbox for understanding the patterns of diversification and
their probable causes.

Tuesday, March 4 @ 3 pm

Peter Walsh

Density dependence, social structure and the emergence of Ebola in
African apes.

The ape Ebola crisis in Congo & Gabon continues to worsen and is now
burning through the world's highest density gorilla population. In this
talk I will discuss the role that transmission between apes may have
played in the emergence of Ebola. I will briefly present statistical
analyses suggesting that Ebola transmission between gorilla in the same
social group is common. These analyses compare the support for alternate
models of primary and secondary transmission, given survey and
observational data on gorilla group sizes. This work examines more
realistic transmission scenarios than presented in my last talk, using
Monte Carlo simulation to evaluate likelihoods for alternate models. I
will then discuss a spatially explicit, individual based simulator of
Ebola transmission dynamics that I am developing. I will present
preliminary results suggesting that Ebola exhibits density dependent
dynamics in which epidemics can only spread when ape density is above
some threshold. The model also suggests that ape group size has a strong
effect on Ebola outbreak potential that is independent of population
density. I'll finish by discussing two ways in which I plan to
parameterize the model: 1) with data from habituated gorillas and chimps,
and 2) with data from population surveys before, during, and after Ebola
epidemics. The ultimate goal is to use the model as a tool for evaluating
and optimizing intervention strategies (e.g. vaccination, barrier
construction, translocation).

Tuesday, March 11 @ 3 pm

Somnath Roy

The impact of large windfarms on local meteorology

Concerns regarding the cleanliness and long-term potential of conventional (fossil
fuel-based) sources of energy have triggered a search for alternatives. Windpower has emerged
as a viable candidate. Operational windfarms already exist in many countries. Several
environmental issues associated with windfarms have been identified and are being actively
addressed. Here we used a numerical model to simulate the impact of a large windfarm on
atmospheric and land-surface processes over short temporal and spatial scales. Results show
that under certain situations, the turbulence generated by windmills can significantly alter
the surface wind-speed, humidity and rate of evapotranspiration. Further studies are required
to investigate whether these effects can become permanent.

Tuesday, March 25 @ 3 pm

Irakli Loladze

Stoichiometric effects of rising atmospheric CO2 on humans and food webs.

The ongoing increase in atmospheric carbon dioxide concentrations (CO2),
stemming largely from fossil fuel burning, is unprecedented in the history
of human species.  Concerns about the impact of this increase on humans are
mainly linked to climate change. In this labtea, I will talk about direct,
unrelated to climate change, effects of high CO2 on the elemental
composition (stoichiometry) of plants. Plant products are the foundation of
human nutrition providing the bulk of essential nutrients and 84% of calorie
intake worldwide. Concentrations of several essential elements, such as
iron, iodine, and zinc, in modern crops are insufficient for optimal human
nutrition, thus contributing to the 'hidden hunger' problem that affects
over the half of human population. Relying on both empirical data and
modeling, I will argue that elevated CO2 has a potential to alter overall
plant stoichiometry with likely declines in the levels of essential elements
in plants. Such declines, if not counterbalanced, will intensify the already
acute and widespread problem of micronutrient malnutrition and can alter the
dynamics of natural food webs.


Tuesday, April 1 @ 3 pm

Jim Regetz 

Climatic influences on chinook salmon demography in the Pacific Northwest

Chinook salmon of the Pacific Northwest have declined on the whole during
the past century, yet individual populations exhibit substantial interannual
variability (and often no clear trend). For the purposes of implementing
management plans for these fish, an important question is to what extent
this variability is spatially correlated among populations. It is thought
that shared climatic forcing could potentially drive such correlations.
Using maximum likelihood methods, I examine geographic patterns in the
relationship between historical rainfall and observed salmon counts, and
also explore evidence for regime shifts in marine productivity. Although
there will be overlap between this talk and my recent departmental seminar,
I hope to spend more time discussing the particulars of the statistical
approach and exploring feasible model extensions.

Tuesday, April 15 @ 3 pm

Abdul-Aziz Yakubu

Asynchronous Versus Synchronous Dispersal In Discrete-time Metapopulation Models

This talk is on the role of asynchronous and synchronous
dispersal in discrete-time matapopulation dynamics where the pre-dispersal
local patch dynamics are of the same compensatory or overcompensatory
types. Single-species metapopulation models behave as single-species
single-patch models whenever all pre-dispersal local patch dynamics are
compensatory and dispersal is synchronous. However, the dynamics of the
corresponding metapopulation model connected by asynchronous dispersal
depends on the dispersal rates. The species goes extinct in at least one
patch when the asynchronous dispersal rates are high while it persists
when the rates are low. Metapopulation models with "unstructured"
overcompensatory pre-dispersal local dynamics connected by synchronous
dispersal can generate multiple attractors with fractal basin boundaries.
However, the corresponding models under asynchronous dispersal support
multiple attractors with smaller numbers of distinct attractors. That is,
dispersal asynchrony can make it easier to determine with absolute
certainty the set of initial population sizes that lead to each attractor.
Also, asynchronous dispersal is capable of altering the pre-dispersal
local patch dynamics from overcompensatory to compensatory dynamics.

Wednesday, April 23 @ 2 pm

Alain Franc

On Perfect Aggregation and Dynamic Clustering

      Any biological system has an inherent hierarchy of
      structures, each being subject to modelling. Hence, it can be
      modelled at different scales, or coarse graining levels.
      Making sure that two different models at different scales
      describe the time evolution of the same biological system can
      be achieved by perfect aggregation, pioneered in ecology in
      the late 80's. A first part of the talk will present this
      tool, and show that it displays several nice mathematical
      properties, with suggestions it can be studied with high
      level of generality, over a whole biological hierarchy. In a
      second and more speculative part, a link will be sketched
      with so called 'dynamical clustering': recent numerical
      simulations show that for large sets of maps coupled by
      diffusion on a lattice, clusters of highly correlated cells
      can emerge, such that the whole system can be analyzed as a
      spontaneous  network of clusters. These recent examples
      suggest that perfect aggregation may be more often met in
      biological systems than what could be spontaneously assumed.

Tuesday, April 29 @ 3 pm

Andy Dobson

Population dynamics of cholera and climate

Cholera is a water-borne infectious disease endemic to Bangladesh and Eastern India.   It has
spread from this region to other parts of the worlds and cholera outbreaks are synonymous
with civil strife and the breakdown of water treatment facilities.   In this talk I^Òll
describe some models I have been developing with Mercedes Pascual (Ann Arbor, Michigan) that
look at the interaction between cholera transmission and climate variation.   There is
considerable evidence linking cholera outbreaks in Bangladesh to climate, yet mechanisms
explaining this coupling are inconsistent.  The models I will describe illustrate a subset of
the subtleties and complexities that arise when we try coupling mechanistic models for
infectious diseases to climate.

Tuesday, May 6 @ 3 pm

Nandi Leslie

Spatially-Explicit Models for the Dynamic Interplay of Land Cover and Soil

Human activities have transformed many forest ecosystems into a mosaic of
forested, degraded, and used lands. The ecosystems which emerge on old
fields and abandoned sites tend to resist reestablishment of pioneer tree
species due to loss of seed viability and low propogule availability.  
The regrowth capacity is further depleted in proportion to the type,
intensity, and duration of the previous land use. We will propose a
spatially explicit model for habitat conversion that is motivated by land
cover change in tropical rain forests in Amazonia. This model examines the
landscape level impact of land use activities by utilizing the
interactions between agricultural/industrial use and soil and plant
community dynamics. With concepts from spatial statistics, we will examine
the spatio-temporal patterns that arise from our model.

[back to schedule ]