Research in Plant Ecology
Rich Niesenbaum - Department of Biology - Muhlenberg College

In my lab our primary interests have been in the areas of plant reproduction and plant-insect interactions.  We have worked on pollination and fruit set; genetics of inbreeding; mechanisms of non-random mating in plants; sex ratio variation; herbivory, and rarity and invasiveness. The two species that we primarily work with are Lindera benzoin and Mirabilis jalapa (below), but new projects include other species and community studies.
 
Spicebush (Lindera benzoin) and 4 O'Clock (Mirabilis jalapa)

Current Research Projects:

Linking Ecology, Leaf Chemistry, and Genetics to Assess Abiotic and Biotic Determinants of Herbivory (click here to go to the project homepage)

In nature, the degree to which insects eat plants (herbivory) can be quite variable from location to location. Scientists have traditionally hypothesized that the physical environment can influence a plant, which in turn affects the ability of that plant to defend itself against herbivory. Thus, variation in local conditions is what drives the degree to which certain plants get eaten. More recently, the focus on herbivory has shifted from these environmental influences to biological influences. This has included studies of how predators and parasites of insect herbivores can be signaled chemically by plants being eaten by those insects. In other words, plants are using aromatic or volatile chemicals to attract enemies to their enemies. This type of interaction is referred to as a tri-trophic interaction because it involves three feeding or trophic levels: the plant, the herbivore insect, and the predators or parasites of the herbivore. Other biological factors that can influence levels of herbivory include interactions with other plants, and variation in the genetic make-up of the plants

In this study, a plant ecologist, analytical chemist, insect molecular biologist, and a statistician will take an integrative approach to examine how light interacts with biotic factors in determining levels of herbivory in a natural system. Our study will focus on the caterpillar, Tulip Tree Beauty or Epimecis hortaria, and its primary food source Spicebush or Lindera benzoin. These native insects and plants are abundant in Northeastern forests. The plant, Spicebush, is easily recognizable by its aromatic condition or volatile chemistry. Feeding rates of this insect on Spicebush have been demonstrated to differ between light and shade environments. Our goal here is explore the mechanisms responsible for this variation. We will examine how differences in light influence leaf characteristics such as leaf digestibility, leaf chemicals that could serve as defense against herbivory, and leaf volatile compounds that may cue the predators or parasites of the insect herbivore. We will also examine how light environment directly and indirectly mediates insect feeding, growth, and development. We will focus on how predation and parasitism of the herbivore, and association with other plants impact our system in relation to light environment. Finally, we will incorporate molecular and plant propagation techniques to test hypotheses about the relative importance of plant genotype and environment in determining levels of herbivory in this system. In so doing, this will be the first study that simultaneously examines how both physical and biological factors, including plant genotype, intersect in the determination of insect feeding rates in a natural, woody plant system.

Collaborators: Marten Edwards, Muhlenberg College
  Christine Ingersoll, Muhlenberg College
  George Benjamin, Muhlenberg College
Students: Please click here for a link to comprehensive lists of students involved in this research in 2005 and 2006
Funding: The National Science Foundation, Cross-Disciplinary Research at Undergraduate Institutions (NSF-CRUI)

The Herbivory Uncertainty Principle - How Experimenatal Visitation and Measurement Affect Herbivory and Plant Growth

In 1927,Werner Heisenberg proposed that there are fundamental limitations to the study of subatomic particles, as the act of measuring them can affect their behavior.  Our prior work confirms that such uncertainty also occurs in ecological studies, where visiting plants to measure rates of herbivory actually changes those rates and significantly impacts the plant-insect interactions being studied. The implications of such "visitation effects" are enormous, and the proposed work will permit us to more substantially test whether visitation and measurement of plants alters rates of herbivory and plant growth, and will increase our understanding of the mechanisms responsible for these effects.  We will examine how the presence of neighboring plants and local light environment influence the occurrence of  "visitation effects", and how visitation and touch influence plant chemistry and insect foraging in the plant, Apocynum cannabinum.  Results from the proposed research will challenge the long-standing assumption that field researchers are "benign observers", as the essential act of visiting plants during an experiment could alter the performance of those plants. A significant visitation effect may motivate us to re-think the way that we measure and test hypotheses about herbivory, plant growth and productivity, and other plant-animal interactions. This work is essential to understanding possible strategies to mitigate any potential observer effect in future studies, and will provide information about the basic ecology of plant-animal interactions in natural plant communities.  An additional major goal is to advance undergraduate education by giving students primary roles in a significant ecological research project.                   
Collaborators: James Cahill, The Unversity of Alberta
Christine Ingersoll, Muhlenberg College
   
Students: Lauren Mastro, Steph Zettle, Jeff Dipple, Richard Kipp 
Funding: The National Science Foundation
Publications: Niesenbaum, R.A., J.F. Cahill, and C. Ingersoll. 2006. Light, wind, and touch influence leaf chemistry, growth, and rates of herbivory in Apocynum cannabinum (Apocynaceae). International Journal of Plant Sciences 167:969-978.

Environmental Variation in Chemical Defense and Herbivory in Lindera benzoin (spicebush)

Previous research on the plant, Lindera benzoin found rates of insect herbivory to be higher in shaded environments than in sunny, open environments (Niesenbaum 1991).  The aim of this study was to begin to better understand the effects of light environment on herbivory and defense in this species. The following questions were addressed to explore the relationship between light and herbivory in plants: Are there differences in leaf toughness of plants exposed to different light levels?  Do leaves from sun-grown plants have a higher nutritional quality than leaves removed from shade-grown plants?  Do the rates of herbivory and defoliation differ between plants grown in shaded and light environments?  Will the light intensity and its relationship with the food source have an affect on the caterpillar's development? and Do leaves from sun and shade habitats differ in their defensive chemistry?  Leaves originating from high light environments were significantly tougher and had a stronger fragrance (and perhaps more aromatic compounds) than leaves from low light environments.  However, there were no significant differences found between sunlit and shaded shrubs with respect to defoliation rates, caterpillar development, and leaf nutrition.  Future work will focus on the relationship between leaf age, light environment, and leaf defense and herbivory.
Collaborators: Dr. Charles Russell, Muhlenberg College 
Students: Emily Kluger, Melanie Ongchin, Lori Haynes 
Funding: Merck/AAAS
Publications: Niesenbaum, R.A. and E.C. Kluger*. 2006. When studying the effects of light on herbivory, should one consider temperature? The case of Epimecis hortaria F. (Lepidoptera: Geometridae) feeding on Lindera benzoin L. (Lauraceae). Environmental Entomology 35:600-606. (PDF)