My research has focused on predator-prey systems, including the origin of cycles in these systems, augmentative biological control, and how dispersal influences predator-prey dynamics. I also have interests in statistical and quantitative ecology. Abstracts of recently funded research projects are listed below.

Collaborative Research: Linking Dispersal to Landscape-Level Dynamics of a Predator and Prey - James T. Cronin and John D. Reeve - NSF DEB

Abstract
Human induced fragmentation, modification and loss of native habitats have been implicated in the decline of biodiversity worldwide. As a consequence, connectivity among existing habitat fragments has become a special concern of ecologists and conservation biologists. Recent empirical data suggests that landscape structure, i.e. patch size and isolation, edge-to-area ratios, and the composition of the matrix can affect connectivity. Characterizing the movement behavior of organisms in the face of this landscape complexity is a daunting and laborious task, especially when considering two or more interacting species (e.g., a predator and its prey). However, it is a crucial step toward understanding the mechanistic basis of connectivity and the spatial and temporal dynamics of populations. Empirical work by Cronin over the past five years has resulted in one of the most comprehensive data sets on how landscape structure affects the movement behavior, connectivity, spatial distributions and short-term temporal population dynamics of a planthopper Prokelisia crocea and its egg parasitoid Anagrus columbi (see Fig. 1 below) that exist among discrete patches of prairie cordgrass Spartina pectinata

In this proposal, the power of empirical research will be combined with landscape-level modeling to address one of the most significant questions in ecology today - how does spatial heterogeneity affect the long-term temporal population dynamics and persistence of interacting species? The main objective is to develop a spatially realistic, landscape-level model that will reveal the mechanisms underlying the effects of habitat fragmentation and loss, and the invasion of exotic plant species, on the dynamics and persistence of a predator and its prey. The model will include both dispersal and population dynamics components in a reaction-diffusion framework. The dispersal component of the model will include patterns of movement within patches and through different matrix habitats, as well as behavior responses of organisms to patch edges. The landscape model will be parameterized with data obtained previously by Cronin: although, additional movement experiments on planthopper and parasitoid attraction to cordgrass patches, and parasitoid dispersal through different habitats will need to be conducted. Testing and refinement of the model will be made possible by fitting the model to independently derived experimental data. The final model will be used to address a number of important ecological questions including how 1) habitat fragmentation and loss affects predator and prey local and regional persistence and long-term population dynamics, 2) matrix composition influences the efficacy of corridors and stepping stones, and 3) the invasion and spread of exotic plants affect patch connectivity and predator-prey dynamics.

Interaction of Below- and Above-Ground Herbivory in Forest Gap Formation: Long-Term Analysis of Underlying Mechanisms and Spatio-temporal Patterns - Kenneth F. Raffa, Brian Aukema, Murray K. Clayton, John D. Reeve, and Jun Zhu - NSF DEB LTREB

Abstract. Interactions among below- and above-ground processes are widely recognized as important yet poorly understood components of terrestrial ecosystem functioning. This lack of understanding rises in part from practical difficulties working with subterranean organisms, and also from biologically based differences in the relevant spatial and temporal scale of various species. This research will focus on one type of interaction, effects of root-colonizing insect-fungal complexes on above-ground herbivory. In particular, it will emphasize the subcortical guilds of conifer roots and stems.

The root-colonizing guild of red pine includes six principal beetle species that partition the resource based on host histology, condition, and semiochemistry, and vector weakly phytopathogenic fungi. The stem-colonizing guild consists of two major bark beetle-fungal complexes, and several species of sapwood borers. The stem-, but not root-colonizers are strongly impacted by several species of habitat-specialist predators. Previous work from 1986-present includes field censuses of tree colonization & condition, excavation of selected stands, systematic isolation of fungi from roots, tree physiological & insect behavioral assays, and population sampling. Results lead to the proposed model: Root colonizing beetles enter and vector fungi into a few trees in new stands. These organisms do not kill mature trees, but compromise conductance between above- and below-ground tissues. This reduces trees' ability to resist lethal bark beetle attackes in the stem. Fungi spread through root grafts, exerting continued feedback to the above, and yielding a radial pattern of host mortality. Early succession plants colonize the expanding gaps, leading to faunistic changes. Several features of this interaction require further understanding before this model can be accepted: 1) High spatial autocorrelation allows for other relationships to be responsible; 2) Continual long-term data are limited to one of the 30 stands examined; 3) Observed physiological changes are consistent with the model, but pose the same limitations; 4) Stand manipulation lacks replication and detailed observations; 5) The presumption that colonization by stem insects is required for tree mortality is untested; 6) Statistical associations suggest an important role of predators, but ther is strong multi-covariance. Resolution of these issues requires long term, multidisciplinary, and hypothesis-driven research, and hence is well suited for LTREB.

The overall purpose of this research is to explore the role of one ecosystem process, herbivory, in interactions between below- and above-ground functions. Specific objectives are to 1) Evaluate the role of below-ground herbivory on susceptibility to above-ground herbivores, with particular emphasis on spatial / temporal patterns of colonization, physiological changes within trees, tree mortality & forest gaps, and vegetational changes; 2) Evaluation the degree of connectedness among forest harboring common below- and above-ground feeding guilds by measuring movement of root beetles, bark beetles, & predators; 3) Conduct manipulative experiments to test the relative importance of inciting agents, stem colonizing organisms, and predators in tree mortality and gap formation. The working hypotheses to be test by long-term sampling and repeated assays are: a) Stem colonization is more likely in trees whose roots are previously colonized by root beetles & associated fungi; b) Spatial spread is more likely in treee whose roots are previously colonized by root beetles & associated fungi; c) Colonization of root tissue compromises tree defenses agains stem colonizers; d) Interactions among below- and above-ground processes contribute to gap formation and altered vegetational pathways; e) Predator - bark beetle - host interactions show density dependence, with varying degrees of resource partitioning & weather sensitivity. The issue of connectedness will be tested by dispersal studies of root, stem, and predator insects, using mark-recapture. A test of the overall model will be conducted by stand-level treatments that either sever root grafts and remove root beetles, selectively augment predators, or serve as controls.

For further details see website for this project.

Inferring the Magnitude of Migration in Southern Pine Beetle (SPB) Using Genetic Markers and Diffusion Models - John D. Reeve and Edward J. Heist - Southern Research Station, USDA Forest Service

Migration and movement are recognized as important factors in SPB ecology, and long-range migration could potentially be a trigger for SPB outbreaks. Although there is considerable in-formation on relatively short-range ( 1 km) movement for SPB, little information exists on movement on larger spatial scales, nor has the available information been synthesized into a form useful for stakeholders. We propose the use of genetic markers (microsatellites) to obtain information on migration rates on a hierarchy of spatial scales. Existing information on move-ment will also be synthesized into a predictive model of SPB aerial densities, using as a starting point the spatial configuration of infestations. See Fig. 2-3 below.