Dr. Shannon L. LaDeau
Community Ecologist
Ph.D., 2005, Duke University

Dr. LaDeau investigates how spatially and temporally distinct population dynamics define ecological communities and ecosystem function. Ecological communities are increasingly faced with diverse ‘global change’ disturbances, including invasive species, changes in climate and weather regimes, and anthropogenic habitat modification. LaDeau’s research is focused on understanding the mechanisms that generate spatial and temporal heterogeneity in when and where ecological communities resist and succumb to global change pressures.

Current Research

Avian community response to multiple global change stressors.
Population stressors such as habitat loss, weather events, and disease are most often investigated independently but populations exist in a complex reality and most species declines can be attributed to a network of associated causes. Disease events may have large impacts on local populations of birds but extinction risk is rarely attributed to disease when species aren’t already suffering from other stressors. In collaboration with Drs. Peter Marra (Smithsonian Migratory Bird Center), Catherine Calder (The Ohio State University) and Patrick Doran (The Nature Conservancy), we are using a combination of citizen science and hierarchical Bayesian models to understand how both intrinsic and extrinsic forces shape the population dynamics of native bird species.

Understanding mechanisms behind the spatio-temporal variation in WNV intensity.
A .West Nile virus (WNV) emerged in the western hemisphere during the summer of 1999, reawakening public awareness to the potential severity of vector –borne pathogens.  Since its New World introduction, WNV has caused disease in avian, human and other mammalian communities across the continent.  American crows (Corvus brachyrhynchos) are highly sensitive to the disease, with mortality rates approaching 100%.  My collaborators (Calder, Doran, Marra) and I have quantified and used dramatic declines in abundance of this susceptible avian host as a proxy for WNV activity to explicitly examine heterogeneity in WNV intensity over a broad spatial range and across multiple land cover types. Population-wide estimates of American crow abundances declined an average 30% after the emergence of WNV.  However, the spatial pattern of where individual crows were lost varied considerably.  We documented significant declines in crow abundance after WNV emergence at 15% of Breeding Bird Survey (BBS) sites across the eastern United States. Generally, locations with more area under human development and less forested area were associated with higher odds of WNV impact. 

B. The potential effects of landscape modification and interactions with changing climate on pathogen dynamics are complex, and likely to alter the ecological processes that define spatio-temporal patterns in composition and abundance of mosquito species and human disease risk. In collaboration with Dr. John Wallace (Millersville University), I have begun field work in conjunction with the Baltimore Ecosystem Study, to test the hypothesis that urban breeding habitats support fewer mosquito species but greater abundances of vector species. We have identified ten mosquito species across the Gwynns Falls watershed in Baltimore. Four occurred in both urban and rural samples, while three potentially important bridge vectors (mosquitoes that feed on both birds and humans) were found only in urban sites (Aedes vexans, Aedes albopictus, Ochlerotatus japonicas).

Invasive insect expected to fundamentally alter northeastern forest ecosystems.
Hemlock is a “foundation” tree species in eastern forests and its presence defines the properties of a unique ecosystem that is presently declining due to the introduction and spread of an invasive insect, the hemlock woolly adelgid (HWA), which currently covers 25% of hemlock’s geographic range. However, the impacts of HWA are highly variable, causing rapid, stand-wide hemlock removal in some regions and little visible impact in others. At sites where hemlock trees succumb to HWA, ecosystem function, including water, carbon and nutrient cycles, are dramatically altered. LaDeau and colleagues, Drs. Gary Lovett and Jennifer Fraterrigo (University of Illinois) are investigating the biological mechanisms that generate spatial variability in hemlock resistance to HWA impacts across New York and the broader northeastern hemlock forest. The relationship among winter temperatures, HWA populations, and hemlock impact is generally assumed to be temperature-driven. However, in many parts of the HWA range, sites with similar climates experience diverse HWA-related impacts, ranging from apparent coexistence of HWA with hemlock for over a decade to complete collapse of the hemlock ecosystem in under five years. This research integrates experimental and field data with Bayesian data-model assimilation techniques and GIS to evaluate how multiple interacting forces, including climate, air pollution and other insect pests, generate spatio-temporal heterogeneity in hemlock forest decline.

Selected Publications

• LaDeau, S.L., P.P. Marra, Kilpatrick, A.M, and C.A. Calder. 2008. West Nile virus revisited: Consequences for North American ecology. BioScience. 58(10): 937-946.
• LaDeau, S.L., Kilpatrick, A.M, and P.P. Marra. 2007. Continental declines in bird populations and the emergence of West Nile virus. Nature. 447(7145): 710-714.
• Kilpatrick, A.M., LaDeau, and P.P. Marra. 2007. West Nile virus in the western hemisphere. Auk. 124 (4): 1121-1136.
• Clark, J.S., Dietze, M., Chakraborty, S., Agarwal, P., Ibáñez, I., LaDeau, S., and M. Wolosin. 2007 Resolving the biodiversity paradox: The dimensionality of coexistence. Ecology Letters. 10 (8): 647-662.
• Ibáñez, I. Clark, J.S., LaDeau, S. and J. HilleRisLambers. 2007. Exploiting temporal variability to understand tree recruitment response to climate change. Ecological Monographs. 77(2): 167-177.
• Ibáñez, I., J. S. Clark, M. C. Dietze, K. Feeley, M. Hersh, S. LaDeau, A. McBride, N. E. Welch, and M.S. Wolosin. 2006. Predicting biodiversity change: Outside the climate envelope, beyond the species-area curve. Ecology. 87 (8): 1896-1906.
• LaDeau, S. L. and J. S. Clark. 2006. Annual pollen production in Pinus taeda grown under elevated CO₂. Functional Ecology. 20 (3): 541-547.
• LaDeau, S. L. and J. S. Clark. 2006. Elevated CO₂ and tree fecundity: the role of tree size, inter-annual variability and population heterogeneity. Global Change Biology. 12: 822-833.
• Williams C.G., LaDeau S.L., Oren R., Katul G.G. 2006. Modeling seed dispersal distances: implications for transgenic Pinus taeda. Ecological Applications. 16 (1): 117-124.
• LaDeau, S. L. and J. S. Clark. 2001. Rising CO₂ levels and the fecundity of forest trees. Science. 292 (5514): 95-98.