Why do populations fluctuate in time and space? This question is the common thread that links my various research interests. Understanding spatiotemporal population dynamics of organisms is critical to a variety of applications including 1) conservation efforts that aim to prevent extinction on a local or regional scale, and 2) prevention of pest insect outbreaks over large scales. My research approach is to work at the interface of empirical data (observational and experimental) and theoretical modeling. I analyze spatial data and build data-driven models (both deterministic and stochastic) with the aim of understanding both the pattern and the underlying mechanisms driving complex spatiotemporal population dynamics across a spatial landscape. More specifically, I am interested in metapopulation dynamics, source-sink dynamics, spatially-synchronous dynamics, traveling waves of outbreak, invasion, and their relationships to dispersal, competition, predation, herbivory, and parasitism.

My current research projects include the study of spatial dynamics of forest insect outbreaks (e.g. gypsy moth and larch budmoth, the probabilistic nature of species invasions using spruce bark beetle in Europe as a model system, and spread of the invasive grass Phragmites australis in southern Louisiana. I am also interested in tropical biology and invasion of the cactus moth (Cactoblastis cactorum) from the southeastern U.S. toward the Opuntia-rich southwestern U.S.

I am looking for bright and motivated graduate students to enter my lab in the fall of 2009. I may have research assistantships available (pending grant proposals) to work on the various projects listed above. Also, fellowships and teaching assistantships are available at the University of Louisiana. While my background is in working with insects, I am open to graduate students pursuing interesting research projects on other organisms in the realm of population ecology.

• Tobin, P.C., C. Robinet, D.M. Johnson, S.L. Whitmire, O.N. Bjørnstad & A.M. Liebhold. In press. The role of Allee effects in gypsy moth (Lymantria dispar (L.)) invasions. Population Ecology.
• Jang, S.R.-J. & D.M. Johnson. In press. Dynamics of discrete-time larch budmoth population models. Journal of Biological Dynamics.
• Haynes, K.J., A.M. Liebhold & D.M. Johnson. In press. Spatial analysis of harmonic oscillation in intensity of gypsy moth outbreaks. Oecologia.
• Bjørnstad, O.N., A.M. Liebhold & D.M. Johnson. 2008. Transient synchronization following invasion: revisiting Moran’s model and a case study. Population Ecology 50:379-389.
• Tobin, P.C., S.L.Whitmore, D.M. Johnson, O.N. Bjørnstad & A.M. Liebhold. 2007. Invasion speed is affected by geographic variation in Allee effects. Ecology Letters 10: 36-43.
• Johnson, D.M., P.C. Tobin, A.M. Liebhold & O.N. Bjørnstad. 2006. Allee effects and pulsed invasions by the gypsy moth. Nature 444: 361-363.
• Johnson, D.M., A.M. Liebhold & O.N. Bjørnstad. 2006. Geographical variation in the periodicity of gypsy moth outbreaks. Ecography 29: 367-374.
• Johnson, D.M., O.N. Bjørnstad & A.M. Liebhold. 2006. Habitat fragmentation and spread of insect outbreaks. Oecologia 148: 51-60.
• Liebhold, A.M., D.M. Johnson & O.N. Bjørnstad. 2006. Geographic variation in density dependent dynamics impacts the synchronizing effect of dispersal and regional stochasticity. Population Ecology 48: 131-138.
• Johnson, D.M. 2005. Metapopulation models: an empirical test of model assumptions and evaluation methods. Ecology 86: 3088-3098.
• Johnson, D.M., A.M. Liebhold, O.N. Bjørnstad & M.L. McManus. 2005. Circumpolar variation in periodicity and synchrony among gypsy moth populations. Journal of Animal Ecology 74: 882-892.
• Johnson, D.M. & C.C. Horvitz. 2005. Estimating post-natal dispersal: tracking the unseen dispersers. Ecology 86:1185-1190.
• Johnson, D.M., O.N. Bjørnstad & A.M. Liebhold. 2004. Landscape geometry and traveling waves in the larch budmoth. Ecology Letters 7: 967-974.
• Johnson, D.M. 2004. Source-sink dynamics in a temporally heterogeneous environment. Ecology 85: 2037-2045.
• Johnson, D.M. 2004. Life history and demography of Cephaloleia fenestrata (Hispinae: Chrysomelidae). Biotropica 36:352-361.