Dr. Péter Molnár – Postdoctoral Research Associate
My research focuses
on the ecological impacts of climate change and other anthropogenic influences,
such as habitat destruction and habitat restoration. I study diverse aspects of
this topic, from climate change impacts on the structure of arctic
host-parasite systems to the impacts of a melting sea ice habitat on polar bear
populations (please see below for a list of publications and a summary of my
polar bear work). Outside of the Arctic, I work on the Osa Peninsula, Costa Rica, studying how habitat fragmentation and
conservation corridors affect parasite and pathogen transmission in tropical
ecosystems, for instance, between domestic dogs and cats, feline mesopredators such as ocelot and margay, and apex predators
such as jaguar and puma. My research
blends ecological insight and field data collection with statistical analyses
and mathematical modeling to identify and quantify the biological mechanisms by
which environmental change affects ecosystems. Common to all of my projects is a focus on conservation
biology and an emphasis on applying quantitative models and empirical findings
to aid conservation managers in
proactive conservation planning. 
I have completed my
Ph.D. at the University of Alberta in 2009, supervised by Drs. Andrew Derocher
and Mark Lewis. Currently, I am based at Princeton University as a Postdoctoral
Research Associate with Dr. Andrew Dobson.
Modelling future impacts of climate change and harvest on the reproductive success of
female polar bears (Ursus maritimus) –
Ph.D. Thesis, University of Alberta, 2009,  Abstract:
Climate change and human harvest are among the most significant
threats to polar bear (Ursus maritimus) populations today. Climatic
warming and resultant sea ice reductions affect polar bears because they depend
on this substrate for most aspects of their life history, including access to
seals, their main prey. Harvest is highly sex-selective, and males have been
reduced significantly in most Canadian populations, leading to concerns that
males might eventually be depleted to a point where many females become unable
to mate (a so-called Allee effect). Few studies have attempted quantitative
predictions of polar bear population dynamics under climate change, and all
predictions are associated with large uncertainty. The conditions that would
lead to an Allee effect are similarly unclear, but sex-selective harvest is
ongoing. In this thesis I coupled mathematical models with empirical data to
understand and anticipate effects of climate change and human harvest on the
reproductive success of female polar bears. To predict conditions leading to an
Allee effect, I developed a mechanistic model for the polar bear mating system.
The model described observed mating dynamics well, predicts the proportion of
mated females from population density and operational sex ratio, and
specifically outlines conditions for an Allee effect. Female mating success was
shown to be a nonlinear function of the operational sex ratio, implying sudden
reproductive collapse if males are severely depleted. The threshold operational
sex ratio for such an Allee effect depends on population density. To predict
effects of climatic warming on female reproduction, I first developed a body
composition model that estimates the amount of energy stored in the fat and
protein reserves of a polar bear. Based on this model, I developed a dynamic
energy budget model that predicts changes in energy stores of both fasting and
feeding adults. Metabolic rates of adult polar bears were estimated using the
energy budget model, and corresponded closely to theoretically expected and
experimentally measured values. The models were then used to predict changes in
litter size of pregnant females in western Hudson Bay as a result of predicted
losses in sea ice and feeding opportunities, and consequent reductions in
female storage energy. Severe declines in litter size can be expected under
climatic warming, although the precise rates of change depend on current, to
date unobserved, summer feeding rates. Behavioural adaptation towards terrestrial feeding is unlikely to significantly compensate
for expected losses in storage energy and resultant reductions in litter size.
The results of this thesis are a significant step towards a predictive
framework for polar bear populations, and aid optimal population management and
proactive direction of conservation efforts.
Publications:
Molnár, P.K., Derocher, A.E., Klanjscek, T., Lewis, M.A. 2011.
Predicting climate change impacts on polar bear litter size. Nature Communications 2: 186 doi:
10.1038/ncomms1183.
Molnár, P.K., Derocher, A.E., Thiemann, G.W., Lewis, M.A. 2010.
Predicting survival, reproduction and abundance of polar bears under climate
change. Biological Conservation 143:
1612-1622.
Molnár, P.K., Klanjscek, T., Derocher, A.E., Obbard, M.E., Lewis, M.A.
2009. A body composition model to estimate mammalian energy stores and
metabolic rates from body mass and body length, with application to polar
bears. Journal of Experimental Biology 212:
2313-2323.
Molnár, P.K., Derocher, A.E., Lewis, M.A., Taylor, M.K. 2008.
Modelling the mating system of polar bears: a mechanistic approach to the Allee
effect. Proceedings of the Royal Society
of London Series B 275: 217-226.
Gaenssler, P., Molnár, P.K., Rost, D. 2007. On continuity and strict
increase of the cdf for the sup-functional of a Gaussian process with
applications to statistics. Results in
Mathematics 51: 51-60.

Contact:
Péter K. Molnár, Ph.D.
Department of Ecology and Evolutionary Biology
Princeton University
Princeton, NJ, 08544-2016
Email: pmolnar@princeton.edu