Theoretical Ecology lab teas are informal talks to the lab group(s) of Simon Levin, Steve Pacala, Andy Dobson, and other interested folks around Princeton or visiting.  The speakers come from that same set.  The talks are  limited to 30 minutes including the usual questions and interruptions.  Of course, lively discussion often continues beyond 30 minutes -- after the talk is concluded.

Talk schedules and email lists are maintained by Joshua Plotkin; food is provided by Eduardo Zea and Juan Keymer.  Contact plotkin@ias.edu  to have your name added to the labtea email list so you too can receive reminders about upcoming lab teas. Click here for Spring 2001 schedule and summaries or Fall 2000 schedule and summaries.
 

Wednesday, September 19	Stephen Pratt
Wednesday, September 26	Ellis McKenzie (NIH)
Wednesday, October 3	Junling Ma
Wednesday, October 10	Tom Reichert (NIH)
Wednesday, October 17	Mayuko Nakamaru
Wednesday, October 24	Nandi Leslie
Wednesday, October 31	Akiko Satake (Kyushu University)
Thursday, November 8	Chris Weaver (Rutgers)
Wednesday, November 14	Chis Klausmeier
Wednesday, November 21	-- thanksgiving recess--
Wednesday, November 28	Martin Nowak
Wednesday, December 5	Lee Worden
Wednesday, December 12	Helene Muller-Landau
Wednesday, December 19	-- winter recess--
Wednesday, December 26	-- winter recess--
Wednesday, January 2	-- winter recess--
Wednesday, January 9	Kai Chan
Wednesday, January 16	Ian Rozdilsky
Wednesday, January 23	Jonathan Dushoff

 

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

Stephen Pratt:
Quorum sensing and collective decision-making during colony emigration by the ant Leptothorax albipennis

In a notable example of collective decision-making, emigrating colonies of the ant Leptothorax albipennis can
choose the better of two nest sites, even when few individual ants visit both sites.  This study investigated how
this ability emerges from the behaviors used by ants to recruit nestmates to potential homes.  We found that, in a
given emigration, only one-third of the colony's workers ever recruit.  At first, they summon fellow recruiters
via tandem runs, in which a single follower is physically led all the way to the new site.  They later switch to
recruiting the passive majority of the colony via transports, in which nestmates are simply carried to the site.
Recruitment accelerates with the start of transport, which proceeds at a rate three times greater than that of
tandem runs.  The recruitment switch is triggered by population increase at the new site, such that ants lead
tandem runs when the site is relatively empty, but change to transport once a quorum of nestmates is present.  A
simple model shows that the quorum requirement can help a colony choose the best available site, even when few
ants have the opportunity to compare sites directly, because recruiters to a given site launch the rapid transport
of the bulk of the colony only if enough active ants have been ``convinced'' of the worth of the site.  This
exemplifies how insect societies can achieve adaptive colony-level behaviors from the decentralized interactions
of relatively poorly-informed insects, each combining her own limited direct information with indirect cues about
the experience of her nestmates.

Ellis McKenzie
Population dynamics of the malaria parasite
 
 

Junling Ma
Adaptive dynamics and its application to resource partitioning.

Adaptive dynamics depicts the evolution of species in a trait space. In
this talk, we are using adaptive dynamics to study evolutionary
branching, an important phenomenon that tells us how new species may
evolve from their ancestor species. There is much work in this area,
particularly by Metz, Geritz, Dieckmann, Kisdi et al. But their work does
not answer questions of how the interaction between multiple species or
multiple traits affects coevolution and branching.

Our research addresses this problem, and we give a geometric view of
what happens in trait dynamics at branching points.  Our method
successfully handles multiple species and multiple dimensional trait
spaces.

We will then discuss several applications, such as evolutionary
partitioning of a resource distributed along a continuous trait axis,
and interactions between evolutionary dynamics and foodweb dynamics.

Tom Reichert

Mayuko Nakamaru
Extinction Risk to Bird Populations Caused by DDT Exposure

The impact of toxic chemicals on wild animals and plants can be quantified
in terms of the enhanced risk of population extinction.  To illustrate a
method for doing this, we estimated such impact for two bird species:
herring gull (Larus argentatus) in Long Island, NY, and sparrowhawk
(Accipiter nisus) in easthern England, when they were exposed to DDT (p,
p'-dichlorodiphenyltrichloroethane) and its metabolites (called DDTs).  The
method we used is based on a formula of the mean time to population
extinction derived for a stochastic differential equation (the canonical
model).  The intrinsic rate of natural population growth was estimated from
an exponentially growing population, and the intensity of the environmental
fluctuation was estimated from the magnitude of population size
fluctuation.  The effect of exposure to DDTs in reducing the population
growth rate was evaluated based on an age-structured population model, by
assuming that age-specific fertility is density-dependent and sensitive to
DDTs exposure, but age-specific survivorship is not.  The results are
expressed in terms of the risk equivalent -- the decrease in carrying
capacity K that causes the same enhancement of extinction risk as chemical
exposure at a given level.  The risk equivalent can be used in mitigation
banking.

Nandi Leslie

The forest ecosystem of the Brazilian Amazon is undergoing transformation from tropical forest into agricultural and industrial landscapes. Following site abandonment, the new ecosystems are degraded and often resist forest re-establishment. The recovery process in these abandoned sites is inversely related to the intensity of the previous land use. I will present a model that connects forest regrowth dynamics to land use intensity. 

Akiko Satake

We studied coupled map models for the dynamics of individual energy reserve to explain the synchronized and intermittent reproduction of trees (mast seeding), widely observed in mature forests. We assume that trees accumulate photosynthate every year, produce flowers when the energy reserve level exceeds a threshold, and set seeds and fruits at a rate limited by pollen availability. The trees can show a large periodic or chaotic fluctuation in seed crops between years in a constant environment, and they can be synchronized over the forest if their fruit production is limited by the availability of out-cross pollen. Two different types of pollen dispersal, global pollen coupling and local pollen coupling, were examined. When pollen dispersal is limited to the neighbors, it was more difficult to realize synchronized reproduction, and perfect synchrony did not occur although strong synchrony was created when the resource depletion after reproduction was small. We also investigated the effect of correlated environmental fluctuation experienced by different individuals. Without pollen coupling, strongly correlated environmental fluctuation failed to produce a clearly positive correlation of seed production between individual trees. Positive correlation was maintained at a high level if both pollen coupling and correlated environmental fluctuation were at work.
 

Chris Weaver

Abstract: This talk will be an overview of issues relating to better
understanding the interactions between the land surface and the atmosphere
and better representing these interactions at the large space and time
scales of global climate models.  The context will be the recent, ongoing
work in our group using a high-resolution, regional coupled
land-atmosphere model. Questions to be considered include: How important
are processes and/or variability happening at small scales, in both the
land system (e.g., ecosystem dynamics and vegetation distribution, human
modification of the land surface) and the atmosphere (e.g., vertical
transport, clouds, precipitation) at large scales?  What are potential
feedbacks that might nonlinearly "scale up" these small-scale interactions
over larger areas and longer time periods?  How can high-resolution
numerical models help us to investigate these things and (maybe) improve
our climate models?

Chris Klausmeier

Lake plankton communities are ideal systems for theoretically minded
community ecologists.  I will give an overview of my past, current, and
future work in three domains of organization in plankton communities:
spatial, temporal, and structural.  1) Spatial patterns occur in poorly
mixed water columns, and include thin layers of phytoplankton at depth
or on the surface or bottom.  I've used an ESS approach to modelling
these vertical distributions.  2) Lakes undergo seasonal succession,
with broad similarities from year to year.  I'm using periodically
forced models to understand these successional pathways.  3) Community
structure (species traits and diversity) depends on abiotic
characteristics of the lake.  I'm using adaptive dynamics to understand
how community assembly maps environmental conditions into patterns of
community organization.

Martin Nowak

TBA.

Lee Worden

Helene Muller-Landau

TBA.
[back to schedule]

Kai Chan

Ian Rozdilsky

Jonathan Dushoff

TBA
 
 

plotkin@eno.princeton.edu