I have broad research interests, including population and community ecology of plants and animals, insect-plant interactions, environmental toxicology, evolutionary ecology, statistical ecology, conservation biology, and ecological biogeography. Recently, I have become interested in the phenomenon of nested species distributions and in the importance of nestedness to conservation biology (Boecklen 1997, Bird and Boecklen 1998) My research methods include computer simulations, meta-analysis of literature data, molecular genetic analyses, statistical and mathematical modeling, design-based field sampling, and field experiments. I have received funding for my research from the National Science Foundation.

 

The primary focus of my research program is the evolutionary ecology of insect-plant interactions, with an emphasis on the role of host-plant variation (genetic, phenotypic, and geographic) in mediating population dynamics, community organization, and preference-performance relationships of phytophagous insects. I have worked on a variety of plant-herbivore interactions, including ant-plant mutualisms (Boecklen 1984, McClellan and Boecklen 1993), local adaptation of herbivore populations (Boecklen and Mopper 1998), and patterns of herbivory in dieocious plants. In particular, I am interested in how plant sexual dimorphism in resource allocation and defense (Boecklen et al. 1990, Boecklen et al. 1991) affects resistance to insect herbivores (Boecklen and Price 1989, Boecklen et al. 1994). I am interested also in interactions between environmental heterogeneity and plant sexual dimorphism and how these interactions affect phytophagous insect populations (Boecklen and Hoffman 1993).
 
 
 

My current interest is the structure and dynamics of phytophagous insect populations and communities in host-plant hybrid zones. For a number of years now, I have been investigating community organization, preference-performance relationships, and tri-trophic level interactions of leaf-mining moths and gall-forming wasps in oak hybrid zones. I have identified a rich set of interactions in these systems, involving host plants, herbivores, natural enemies, endophytic fungi, introgressive hybridization, and environmental heterogeneity.

 
 

This research has proceeded along several major fronts and has had a variety of objectives. I have conducted a broad-scale biogeographic analysis of hybrid susceptibility to herbivores in a number of oak hybrid zones in the Southwestern United States and northern Mexico (Boecklen and Spellenberg 1990, Aguilar and Boecklen 1992, Boecklen and Larson 1994, Boecklen and Spellenberg 1998). The objectives are to determine which of several competing patterns of hybrid susceptibility is most common, and to elucidate the factors that determine which pattern obtains in a given hybrid zone.

 
 

The second major approach involves the use of experimental crosses between oaks and molecular genetic techniques (RAPD's, AFLP’s) to characterize the structure of hybrid zones and to quantify the hybrid status of individual host plants (Howard et al. 1997, Williams et al., in prep.). The objectives are to understand the processes that lead to the formation of hybrid zones between oaks, and to develop quantitative (predictive) relationships between host hybrid status and susceptibility to phytophagous insects.

 
 

During the course of these genetic investigations, I have become interested in the statistical properties of genetic markers and the magnitude of classification errors associated with their use in assigning individuals to hybrid and parental categories (Boecklen and Howard 1997). These errors are large enough to warrant a fundamental revision of the theoretical framework underlying herbivore responses to host-plant hybridization (Boecklen and Spellenberg 1997).

 
 

The third approach is a detailed investigation of plant-herbivore interactions in Quercus grisea x Quercus gambelii hybrid zones (Preszler and Boecklen 1994, Gaylord et al. 1995, Preszler and Boecklen 1996, Preszler et al. 1996). The objectives are to elucidate the mechanisms governing herbivory in host-plant hybrid zones by characterizing preference-performance relationships, three-trophic-level interactions, and interactions between endophytic fungi and herbivores. I plan to expand these investigations by examining the population genetic structure and source-sink dynamics of herbivore populations within and outside the hybrid zones. Hybrid zones are evolutionary hot spots, and detailed analyses of herbivory in host-plant hybrid zones provides unparalleled opportunities to examine evolutionary processes important to insect-plant interactions.

 
 

I have discovered a rich set of interactions involving endophytic fungi, insect herbivores, and their natural enemies. For example, there are positive correlations between endophyte loads and early larval survival and pupal weights, negative correlations between late-instar survival and endophyte loads, and negative correlations between density-dependent parasitism of herbivores and endophyte density. Currently, I am conducting a series of fungal inoculation experiments to test these correlative patterns.

 
 

An extension of my work on hybrid zones is an examination of preference-performance relationships of herbivores along environmental gradients (Preszler and Boecklen 1996). Leaf-miner densities on Quercus gambelii exhibit significant differences along elevational gradients. In addition, larval mortality, parasitism rates, and the relative importance of top-down versus bottom-up mortality of miners also varies significantly with elevation.

 
 

Lastly, I have been examining oak hybrid zones within the context of conservation strategy and management. In particular, I have been testing the Hybrid-Zones-As-Centers-of-Biodiversity Hypothesis, which posits that plant hybrid zones should support elevated levels of biodiversity, not only of herbivores, but of higher trophic levels as well. To date, I have examined abundances of birds and reptiles in hybrid zones and in contact zones (areas of sympatry of plant species where hybridization is rare). I have little support for the Hybrid-Zones-As-Centers-of-Biodiversity Hypothesis (Campbell and Boecklen, submitted).