Péter Molnár

Email: pmolnar@ualberta.ca

Péter is currently an Assistant Professor at the University of Toronto in Scarborough, Ontario.

Dr. Péter Molnár – Postdoctoral Research Associate

My research focused on the ecological impacts of climate change and other anthropogenic influences, such as habitat destruction and habitat restoration. I studied 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.


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.

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