Evan Preisser

Evan PreisserPersonal Information
  • B.A. (Biology and English), 1993, Williams College
  • M.F.S. (Forest Science), 1998, Yale School of Forestry and Environmental Studies
  • M.S. (Population Biology), 2000, University of California at Davis
  • Ph.D. (Population Biology), 2004, University of California at Davis
  • Curriculum Vitae
Research Interests

The effects of predation risk on community dynamics

Non-lethal interactions between predators and their prey can profoundly affect food webs and alter community dynamics. Many organisms are capable of altering phenotypic traits (behavior, development, morphology, etc.) to reduce their risk of predation; changes occurring via the ‘non-consumptive effect’ (NCE) of predators on their prey can nonetheless incur significant demographic and fitness-level costs. I worked with several co-authors on an analysis of published literature in which we found that the magnitude of the effect of NCEs on prey population growth was roughly equal to the direct lethal effect of predators. This led to a working group at the National Center for Ecological Analysis and Synthesis, where I coordinated a group of theoreticians, modelers, and field ecologists in answering when, where, and under what conditions NCEs might be important. I continue to collaborate with several group members on research addressing the effects of resource dynamics on NCE strength (published in 2009) as well as synthetic work exploring the impact of species invasions and spatial structure on NCEs (both published in 2010). I have also begun empirical research on how ontogenetic niche shifts (i.e., changes in predator hunting mode during an organism’s development) alter the direct and indirect impacts of predation on prey populations.

Factors affecting range expansion of invasive herbivores sharing a common host

The hemlock woolly adelgid, Adelges tsugae, has been implicated in the decline of hemlock throughout the eastern United States. Eastern hemlock is also attacked by the elongate hemlock scale, Fiorinia externa, which has invaded at least 10 states in the northeast. The interactions between the adelgid and scale, and the role of dispersal and cold tolerance in their range expansion, have never been studied; the results are increasingly important as hemlock stands decline in health and the scale expands its range into that of the adelgid. My work addresses both basic and applied ecological questions in this system and aims at understanding the spread of these invasive species. Some of my research in this area involves assessing the intensity and outcome of adelgid-scale competition occurring when both species colonize the same host plant. The results of these experiments are of considerable practical significance, since understanding how these invasive species interact is essential for predicting their individual and joint effects on hemlock health.

Naturally-occurring adelgid resistance in eastern hemlock

My work surveying hemlock forests led me to become interested in whether rare eastern hemlock individuals might possess some degree of innate resistance to the hemlock woolly adelgid A. tsugae. I helped develop a citizens’ science program that involved environmental groups throughout the east coast in the search for healthy hemlock trees growing in adelgid-devastated forests. This initiative turned up a number of potentially resistant trees, growing both individually or in small stands; my collaborators and I took cuttings from the most promising individuals and treated them to induce rooting in order to experimentally assess their adelgid resistance in a controlled environment. We have a number of promising candidate trees in cultivation, and four years of testing both grafted and clonally-propagated accessions derived from ‘putatively resistant’ individuals have shown a clear pattern: lower adelgid settlement and increased adelgid mortality relative to cuttings from control trees.