Muskox bulls      Svalbard reindeer   Arctic fox      

Eric Post

Associate Professor of Biology, Penn State University
  Honorary Professor, Department of Arctic Environment, Aarhus University, Denmark

In general, I'm interested in ecological dynamics at many levels of organization and across multiple scales of space and time.  I find the most fundamental questions in ecology to be the most intriguing.  For example, what combination of biotic and abiotic factors determines whether an individual survives and reproduces from one year to the next; how do those same factors interact to influence population dynamics; how does community composition vary in time and space in relation to species interactions and environmental conditions; and how do interactions across trophic levels, and between the abiotic environment and organisms at different trophic levels, influence ecosystem function?  Most of my research relates to climate change, and is conducted almost exclusively in the Arctic.  In my research group, we employ an array of approaches, including mathematical and statistical modeling, observation, and experimentation.


My current major research topics include:

Variation in the distribution and abundance of organisms.  How is spatial and temporal variation in population size influenced by intrinsic factors, such as density dependence, and extrinsic factors, such as predation, interspecific competition, and environmental variability in time and space?  Along this line of research, my colleagues and I have worked for the past several years to develop linear and non-linear models of single and multi-species population dynamics and apply them to long-term data on birds and mammals.  Most recently, we have advocated a "global population dynamics" approach to undertanding species-level responses to climate change (Post et al. 2009 BioScience 59:489-497).  


Yearling caribou                  Muskox bull               snow bunting 

                                Caribou yearlings                                                   Muskox bull                                                   Male snow bunting



Community structure and dynamics in relation to species interactions and climate change.  How are trophic interactions among predators and herbivores, and among herbivores and plants, influenced by climatic variation and change?  How do abiotic conditions and species interactions shape plant community composition and primary productivity?  To answer these questions, my colleagues and I have conducted extensive analyses of long-term data and simulation modeling. 

Beginning in 2002, I adopted an empirical approach to investigating these questions by initiating a large-scale, long-term field experiment in West Greenland involving the use of multiple herbivore exclosures and passive warming devices.  My students, assistants, and I erected 6, 800m2 permanent exclosures designed to eliminate herbivory by caribou and muskoxen in order to quantify the impact of these herbivores on productivity and species composition of arctic plant communities. 

Exclosure 2002                   Exclosure 2003     Muskox bulls and exclosure

Erecting an exclosure at the study site in June, 2002.           The same exclosure in June, 2003.               Muskoxen grazing outside the same exclosure in June, 2009


Inside and outside of these exclosures we employ open-topped, passive warming chambers designed according to the protocols of the International Tundra Experiment (ITEX) to quantify short- and long-term vegetation community composition and productivity responses to warming and herbivory.  Recently, we reported that plant biomass responses to warming are opposed by responses to herbivory, suggesting that a warmer Arctic without large herbivores would look very different from a warmer Arctic with large herbivores (Post & Pedersen 2008 PNAS 105:12353-12358).

Cones              Mason and Eric                muskox ITEX cone

ITEX open-top chambers.                              Getting some valuable help from my son, Mason, while                       Muskoxen grazing adjacent to two of our exclosures and an ITEX chamber.
                                                                        estimating biomass with the non-destructive
                                                                        point-intercept method.



Life history variation in relation to environment and conspecifics.  What factors influence the seasonal timing of reproduction, age at first reproduction, production of offspring, and variation in fitness-related traits such as body size of organisms in northern environments, where the growing season is short but also variable on inter-annual and longer-term scales?  On this subject, my colleagues and I have devoted considerable effort to analyzing long-term data on body size variation and fecundity in large herbivores, plant phenology, and timing of migration by several species of birds.  We have also developed models of the timing of reproduction in relation to climate change and biotic interactions. 

At my study site in West Greenland, we've been conducting a long-term, observational study on the timing of calving by caribou, and offspring production by caribou and muskoxen, in relation to plant phenology since 1993.  These date have allowed us to examine natural variation in timing and synchrony of parturition and plant phenology in relation to climate change, and have shown that while plant phenology has advanced considerably in relation to recent warming, caribou calving has not.  This "trophic mismatch" has contributed to a severe decline in offspring production by caribou at my study site (Post & Forchhammer 2008 Phil. Trans. Roy. Soc. Lond. B 363:2369-2375; Post et al. 2008 Proc. Roy. Soc. Lond. B 275:2005-2013).

muskox calves       caribou      Muskox and calf

                                        Muskox calves                                                                Female caribou and calf                                                                    Muskox with calves


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