Structural Equation Modeling in Support of Conservation
Science Center Objects
Understanding systems sometimes requires approaches that allow for both the discovery of the a system's structure and the estimation of its implications. Structural Equation Modeling - SEM - is one tool scientists use to better understand the complex world in which we live.
The Science Issue and Relevance: Ecology and society are moving from a historical emphasis on individual processes to a concern about entire systems. The complexities of the world in which we live, along with the increased level of our ambitions, now drive us to want to understand systems and predict, as much as we can, their behavior. Understanding systems sometimes requires approaches that permit both the discovery of system structure and estimation of its implications. Analytically, systems are often represented as networks of interacting elements, thus the business of studying systems can be approached using methods for studying causal networks.
Methodology for Addressing the Issue: One approach to studying causal networks is structural equation modeling (SEM). From an historical perspective, the SEM currently practiced can be called “Second Generation” SEM. The first phase of development, “First Generation SEM”, was based on the path analysis methodology developed by Sewell Wright. The “Second Generation” of SEM commenced with the LISREL synthesis in the early 1970’s and continues as the dominant form of application to the present. We believe there is now a need for a “Third Generation” of SEM that is more fundamental, more flexible, and a more complete scientific system. The goal of current WARC research is to develop this third-generation capability and utilize it to develop more comprehensive perspectives of systems from the analysis of data.
Future Steps: The three major thrusts of this project are (a) methods development, (b) methods application, and (c) education. Regarding methods development, we are working on several fronts to extend the range of conditions under which SEM principles can be applied. Regarding methods application, one of our core applications deals with disentangling the mechanisms regulating coastal wetland sustainability in the face of rising sea levels. A second core application involves working with the National Park Service to develop causal models from their monitoring data so as to inform both protection and restoration efforts. Regarding education, we have developed a SEM training webpage to enable our collaborators (as well as all other interested partners) to develop their own applications. Many resources now reside at www.nwrc.usgs.gov/SEM.
- Improving our ability to forecast the responses of coastal wetlands to rising sea levels.
- Modeling landscape-scale habitat relations for land birds during migration (Wylie Barrow).
- Evaluating the ecological implications of climate change along a gradient in macroclimatic drivers of coastal wetland ecosystems (Mike Osland).
- Understanding impacts of salinity intrusion on amphibians in coastal environments (Hardin Waddle).