Pieter deHart, Ph.D.

Research

 

My research agenda focuses around ecosystem dynamics, with an emphasis specifically on organismal foraging ecology and population biology.  I work in a wide range of systems (marine, freshwater, and terrestrial) and with a great number of collaborators to explore issues relating to global climate change.  I focus on ecological sampling techniques equally wide-ranging, from population assessments through photo-identification of individuals to stable isotope analyses of keratinous tissues and collagen.  Please read below for further description of three more specific areas of recent interest. 

 

 

Closeup of adult mantid 

 

Praying Mantid Trophic Dynamics: 

The Chinese Mantid, Tenodera aridifolia sinensis, is one of the most pervasive such species and is found in temperate habitats worldwide. These are top predators in arthropod assemblages, and can exert controlling influence on biodiversity by virtue of what is known as top-down trophic cascades that extend all the way down to the primary producers in an ecosystem. Since most animal species on earth are arthropods, these systems are appropriate models for studying the general properties of ecosystem trophic interactions. While it is known from captive studies that mantids are tritrophic predators (able to survive on three distinct known diets: herbivores, carnivores, and plant material), the degree to which these different strategies occur in nature has yet to be determined. Since the summer of 2012 I have been pursuing research to help decipher the important relationships these predators have with species on other trophic levels, thus determining both their influence on current food web structures as well as their true behavioral plasticity in the face of global climate change. In collaboration with Dr. Larry Hurd (Washington & Lee University), I have been working to explore the trophic dynamics of praying mantids using stable isotope analyses.  Analysis of the Carbon, Nitrogen, Oxygen, and Hydrogen isotope ratios in field-collected mantids from Virginia are being compared to mantids raised in the laboratory on three distinct known diets: A) grasshoppers and moths (herbivores), B) spiders and wasps (carnivores), and C) pollen (plant material) to find out the relative importance of these different trophic levels in the diet of these generalist predators during different stages of their life cycle.  This research will finally give us insight into some key life history characteristics: 1) Exactly which components of the food web are most important or essential for Mantid survival in the wild, 2) Determining the influence of Mantids on the trophic dynamics and structure of local ecosystems, and 3) highlight any inter- and intra-species variations in foraging strategy. 

Groundhog and hair trap Coyote at game cam 

 

 

Coyote Foraging Ecology: 

The coyote (Canis latrans) has increased in population throughout the east coast of North America, especially in the recent decade and particularly in Virginia.  As a consequence of this range expansion, human-coyote interactions have increased, both directly through preying on livestock and indirectly through resource competition with local hunters. Effective management of these interactions in multiple habitat interfaces can be significantly enhanced by broadening the scientific understanding of both the basic foraging ecology of the coyote, as well as the specific diet of the species in Virginia. Since Spring of 2010, I have been examining the carbon and nitrogen isotopic signature from the hairs of wild coyotes and potential prey (livestock, wild mammals, and domesticated pets) throughout Appalachia in forest, agricultural, and urban habitats in order to investigate the specific trophic role of the coyote in this ecosystem. I am currently obtaining samples from wild coyotes through noninvasive hair traps, as well as through cooperative agreements with educational, governmental, and private entities and landowners. To more precisely pinpoint which prey are utilized by coyotes in which habitats, I am incorporating delta15N and delta13C signatures from my samples into isotopic mixing models, and comparing proposed diets geographically between multiple habitats. 

 

Macroinvertebrate sampling in Kerr's Creek 

 

Macroinvertebrate diversity in Appalachian Streams 

This research endeavor is investigating the impacts of environmental change on biodiversity and trophic structure across aquatic ecosystems.  Through the survey and collection of freshwater invertebrates, I am examining the population structure of native organisms in comparison to the environment in which they reside to establish a dynamic model of trophic structure.  This work will provide essential baseline knowledge into the passage of nutrients through local ecosystems, as well as yield specific insight on the impacts of climate change on Virginia’s mountain ecosystems that will increase the state’s ability to adapt and prepare for these changes.  In addition, the results of this effort will aid the Virginia Save-Our-Streams and Maury River Watershed Monitors program in their long-term monitoring efforts through data sharing and feedback on sampling techniques.  This research is also incorporated into coursework, as it is supported by both independent research cadets and students in my Aquatic Ecosystems course.  This project provides cadets interested in ecology and conservation biology an opportunity to work hands-on in the field, learn the intricacies of environmental sampling, and further develop laboratory skills. 

 

 

Closeup of seals 

 

Marine Mammal Population Dynamics: 

            Ever since my first bit of graduate studies at Woods Hole through Boston University and the Marine Biology Laboratory, I have been interested in the population biology and physiology of marine mammals.  As critical components of the marine ecosystem, marine mammals are often both keystone species and ‘canaries in the coalmine’ for the effects of global climate change on our dynamic ecosystems.  I started my scientific endeavors in this field by exploring the Population biology of Harbor (Phoca vitulina concolor) and Gray seals (Halichoerus grypus) in Southern New England in conjunction with work through the National Marine Fisheries Service (NEFSC).  I then continued my exploration of marine mammals through an examination of Bowhead whale (Balaena mysticetus) migratory patterns and Steller sea lion (Eumetopias jubatus) feeding patterns using stable isotope analyses at the University of Alaska Fairbanks.  There, I examined seasonal and multi-year migratory patterns of the Bowhead whale through an analysis of Oxygen and Hydrogen isotopes in the baleen of harvested whales.  Connected with that project, I investigated the way in which O & H are passed through multiple trophic levels in a marine food web, from water up to whale.  Additionally, I explored the historical ecology of Steller sea lions through changes in diet recorded in individuals (growth layers in teeth) and throughout the population (bone samples).  Since 2007 I have been exploring further population dynamics of marine mammals through a field course in New Brunswick, Canada and in conjunction with the Huntsman Marine Science Centre there.  With the assistance of students from throughout Ontario, I am collecting a long-term dataset on Harbor and Gray seal population dynamics in the Passamaquoddy Bay region. 

 

Humpback whale tail- August 2012