Select Faculty Member Mark R. Brown Donald E. Champagne Daniel G. Colley Harry W. Dickerson, Jr. Roberto Docampo Stephen L. Hajduk Jessica Kissinger Patrick J. Lammie Kojo A. Mensa-Wilmot Julie M. Moore Silvia N.J. Moreno Ynes R. Ortega David S. Peterson Pejman Rohani Robert Sabatini Mike R. Strand Boris Striepen Rick L. Tarleton

Associate Professor, School of Ecology
Ph.D., 1995, Imperial College, University of London

Telephone: 706-542-9249
E-mail: rohani(at)uga.edu

Lab Homepage

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Research

In our lab, we are interested in addressing population ecological questions using a combination of experimental work, data mining and mathematical modelling and the development of theory. Broadly speaking, this research is focused on four key issues in contemporary population ecology:

• The consequences of spatial structure for metapopulation persistence, species coexistence and population dynamics
• The interaction between non-linearity and (environmental and demographic) stochasticity
• The role of temporal heterogeneity in determining the dynamics and coexistence likelihoods of communities
• The interplay between ecological and evolutionary forces in shaping communities

To study these broad topics, we concentrate on a range of host-natural enemy interactions. In particular, research in the lab can be readily split into the study of host-(micro) parasite and insect host-parasitoid systems:

Host-(micro)parasite systems

Much of current research in the lab is based on understanding long term data sets on the spatio-temporal patterns of morbidity and mortality caused by the great childhood microparasitic infections (such as measles and whooping cough). The analyses of these data have provided interesting insights into the mechanisms of disease transmission and the ecology of infectious diseases. This work has demonstrated:

Epidemics of measles are strongly driven by the interaction between the recruitment rate of susceptibles and seasonal changes in contact rates. Taking into account systematic trends in per capita population birth rates or the onset of large scale immunization programmes explains the dynamical transitions observed in measles data in England & Wales (Earn et al. 2000) and the Niakhar region of Senegal (Broutin et al. in review).

Whooping cough epidemics show the opposite spatio-temporal pattern to measles both before mass vaccination and in the vaccine era (Rohani et al. 1999). This has been suggested to be due to increased susceptibility of whooping cough dynamics to stochasticity, arising from its differing life-history traits (Keeling et al. 2001;Rohani et al. 2002).

In contrast to the generally accepted wisdom that whooping cough vaccines only protect against disease (and not infection), our ecological analyses of data from England & Wales (Rohani et al. 2000) and Senegal (Broutin et al. 2004) both show strong signatures of dramatically reduced whooping cough transmission in response to vaccination.

Possible ecological interactions between unrelated infections, arising from unavailability to contract a disease following infection with another. Theoretical analyses of such mechanisms predict pronounced phase-differences between different disease (or strains of the same disease), which are consistent with observed patterns in mortality data. We are currently exploring a number of aspects of this phenomenon, as relating to childhood infections, antigenically polymorphic infections (with Dr Helen Wearing, University of New Mexico), and the development of statistically robust methodology for the detection of interference effects (Dan Vasco).

Using game theoretic approaches to study co-evolutionary dynamics in host-pathogen systems, we have demonstrated that infectious diseases can give rise to increased sociality in the host population (Bonds et al., 2005).

 Host-parasitoid assemblages

In collaboration with Dr Steve Sait (Department of Biology, University of Leeds, UK) we are studying laboratory populations of insect host-parasitoid-pathogen assemblages. Specifically, the system is centered on the Indian meal moth, Plodia interpunctella (a stored-product pest) and its competitor, the Almond moth, Ephestia cautella. Both species are subject to attack by a suite of natural enemies, including a solitary ichneumonid wasp (Venturia canescens) and two species of baculoviruses (the P. interpunctella granulovirus and E. cautella nucleopolyhedrovirus; PiGV and EcNPV respectively).

Using this system, we have explored a number of ecological questions, typically by testing model predictions in the laboratory population assemblages. These topics include:

Understanding the dynamical consequences of specialized versus generalist natural enemies (Rohani et al. 2003; Wearing et al. 2004a)

Exploring the importance of development variability and demographic noise in determining the fluctuations observed in our laboratory populations (Wearing et al. 2004b).

Examining the role of periodic resource dynamics in generating cycles of different periods (Wearing et al., in prep).

Understanding the co-evolutionary consequences of seasonality. We are exploring seasonality in two separate mechanisms: (i) periodic changes in pathogen transmission and parasitism, and (ii) temporally varying environment.

Work on host-parasitoid-pathogen assemblages has been funded by two grants from the UKs Natural Environment Research Council.