Research Interests
My
general interests are in theoretical population biology and evolutionary
ecology. The research typically combines modeling, mathematics, and
simulations, and is usually in collaboration with experimental biologists. I am
especially interested in the interface between theory, modeling, and empirical
ecology, and using dynamic models as a tool for identifying the mechanisms that
drive the dynamics of ecological systems. I believe that useful theory must be
grounded in real data, and must prove itself by leading to greater
understanding of empirical results.
If
my research group had a motto, it might be (paraphrasing Benjamin Franklin): "Nothing
is certain but predators and parasites". Nature abhors an
uneaten meal, so the fundamental links in ecosystems are between organisms and
the other organisms that try to consume them all at once (predators) or slowly
(parasites). Our other motto might be "Evolution changes
everything". These are not unrelated. Becoming somebody else's dinner,
or being turned into a factory for producing the next generation of Plasmodium (the
protozoan that causes malaria), are very strong natural selection. It is hard
to imagine these events occurring without significant evolutionary
consequences. But exactly that thinking is embedded in most of the ecological
theory underpinning environmental and natural resource management. Models for
host-pathogen dynamics have started to include pathogen evolution, but still
ignore host evolution. We need broadened theories that let us take account of
the fact that we are studying and managing a moving target.
My current projects include:
1. Ecology and Evolution in an Experimental
Predator-prey System (1997-present)
For
about a decade we have trying to understand the mechanisms driving population
dynamics in a simple experimental system: a chemostat (flow-through glass
vessel) in which predators (rotifers) consume prey (algae) who require a
limiting nutrient (N supplied as nitrate) that is supplied in the inflowing
culture medium. This was our introduction to the importance of rapid evolution
and how it could literally "change everything" about one of the most
classic (and "well understood") 
phenomena in 
ecology: predator-prey
cycles.
Research support
Evaluating Complex Dynamics and Chaos in Natural
Ecological Systems: Experimental, Statistical, and Modeling Approaches (co-PI Nelson G. Hairston, Jr.), Andrew W. Mellon Foundation,
1997- 2002.
The Evolutionary Ecology of Population Dynamics: Experimental and
Modeling Approaches (co-PI Nelson G.
Hairston, Jr.), Andrew W. Mellon Foundation, 2003-2007.
Contemporary Rapid Evolution: Dynamics and Persistence
in Complex Ecological Communities
(co-PIs Nelson G. Hairston, Jr., Laura E. Jones, and G.F. Fussmann), James S
McDonnell Foundation, 2008-2011.
Selected Publications
2007
T.
Yoshida, S. P. Ellner, L. E. Jones, B. J. M. Bohannan, R. E. Lenski, N. G.
Hairston Jr. 2007. Cryptic population dynamics: rapid evolution masks trophic
interactions. PloS Biology 5:
e235.
doi:10.1371/journal.pbio.0050235
L.E.
Jones and S.P. Ellner. Effects of rapid prey evolution on predator-prey cycles.
Journal of Mathematical Biology 55:541–573.
2006
J.R.
Meyer, Stephen P. Ellner, Nelson G. Hairston, Jr., Laura E. Jones, and Takehito
Yoshida. Prey evolution on the time scale of predator–prey dynamics
revealed by allele-specific quantitative PCR. Proceedings of the
2005
Gregor
F. Fussman, Stephen P. Ellner, Nelson G. Hairston, Jr., Laura E. Jones, Kyle W.
Shertzer and Takehito Yoshida. Ecological and evolutionary dynamics of
experimental plankton communities. Advances
in Ecological Research 37: 221-243.
N.
G. Hairston, Jr., S. P. Ellner, M. A. Geber, T. Yoshida, and J. A. Fox. Rapid
evolution and the convergence of ecological and evolutionary time. Ecology Letters 8: 1114-1127.
2004
L.E.
Jones and S.P. Ellner. Evolutionary tradeoff and equilibrium in an aquatic
predator-prey system. Bulletin of
Mathematical Biology 66: 1547-1573.
T.Y.
Yoshida, N.G. Hairston, Jr., and S.P. Ellner. Evolutionary tradeoff between
defence against grazing and competetive ability in a simple unicellular alga,
Chlorella vulgaris. Proceedings of the
Royal Society of
2003
T.
Yoshida, L.E. Jones, S.P. Ellner, G.F. Fussmann, and N. G. Hairston, Jr. Rapid
evolution drives ecological dynamics in a predator-prey system. Nature 424: 303-306.
G.
F. Fussmann, S.P. Ellner, and N.G. Hairston, Jr. Evolution as a critical
component of plankton dynamics. Proceedings
of the Royal Society of
S.P.
Ellner and G.F. Fussmann. Effects of successional dynamics on metapopulation
persistence. Ecology, 84: 882–889.
2002
G.
F. Fussmann and G. Heber. Food web complexity and chaotic population dynamics.
Ecology Letters 5: 394-401.
S.
P. Ellner, Y. Seifu, and Robert H. Smith. Fitting population models to time
series data by gradient matching. Ecology 83: 2256-2270.
K.W.
Shertzer and S.P. Ellner. Energy storage and the evolution of population
dynamics. Journal of Theoretical Biology 215: 183–200.
K.W.
Shertzer and S.P. Ellner. State-dependent energy allocation in variable
environments: life history evolution of a rotifer. Ecology 83: 2181–2193.
K.
W. Shertzer, S.P. Ellner, G.F. Fussmann, and N.G. Hairston, Jr. Predator-prey
cycles in an aquatic microcosm: testing hypotheses of mechanism. Journal of
Animal Ecology 71: 802–815.
2001
P.
Schliekelman and S.P. Ellner. Egg size evolution and energetic constraints on
population dynamics. Theoretical Population Biology 60: 73-92.
2000
G.
F. Fussmann, S.P. Ellner, K.W. Shertzer, and N.G. Hairston, Jr. Crossing the
Hopf bifurcation in a live predator-prey system. Science 290: 1358-1360.
Origins and Spread of the Aspergillus-Gorgonian Coral Epizootic: Role of
Climate and Environmental Facilitators (2003-2007)
This multi-investigator,
multi-instutution project, was funded by NSF under the
"Ecology of Infectious Diseases" program. Other participants at
Cornell are C. Drew Harvell (PI), Laura Jones (Research Associate), and Laura
Mydlarz (University of Texas Arlington).
Coral reefs worldwide have
seen major declines in recent decades, and infectious diseases are one of the
most important factors in this decline. Aspergillosis
is a fungal pathogen affecting seafan corals in the
1) Determine the origins of
the aspergillosis outbreak in sea fans, using microsatellite markers,
2) Evaluate the role of host
resistance through development of immunological assays,
3) Evaluate the role of
environmental stressors in the outbreak, and
4) Develop models for the
within-individual and population level impacts of the disease.
My
group has been involved primarily in items 3) and 4). We have developed a novel
PDE model for the spread of a fungal pathogen within a coral host, which
includes the hosts' natural immune response (mediated primarily by chemical
signaling and mobile amoebocytes). The paper, currently in press at American
Naturalist, shows that key factors determining the outcome of an infection are
the rate at which fungus can consume host tissue and reproduce, and the rate at
which the host can produce immune cells to replace those lost while battling
the infection. Another important factor is whether the host is concurrently
fighting several infections, each drawing on the limited supply of host immune
cells. So coral vs. fungus is like long-term trench warfare: speed and ingenuity
are much less important than the number of troops that can be thrown into
battle. Consequently, any stresses that diminish even slightly the host's
ability to regenerate immune cells, or its ability to chemically inhibit fungal
growth and reproduction, could tip the balance in favor of the infection. There
are many other lesion-forming infections of corals, so the results of this
study may also be useful for understanding disease outbreaks in corals.
I am currently working with
co-PI John Bruno (UNC-Chapel Hill) on development of an Integral Projection
Model (IPM) for the population-level impacts of the disease. Population in
which 60% of individuals are uninfected nonetheless have near-zero reproductive
output, according to population surveys in the