Ecological systems are inherently complex and their responses to environmentals changes are likewise complex as well. Up to the present, our ability to analyze complex relationships using conventional statistical methods has been very limited. To try and remedy this situation, the USGS has worked to apply a new generation of multivariate statistical methods called structural equations to ecological problems. Structural equation modeling (SEM) represents a method whereby a number of interconnected hypotheses are evaluated against data, yielding a more realistic (and usually more interesting) perspective. Our group has applied structural equations to a variety of ecological problems. Synopses of these studies can be found in the following articles:

Grace, J.B. and B. Pugesek.1997. A structural equation model of plant species richness and its application to a coastal wetland. American Naturalist. 149:436-460.

Grace, J.B. 1997. Bioinformatics: Mathematical challenges and ecology. Science 275:1862-1863. (letter to the editor)

Grace, J.B. and B.H. Pugesek. 1998. On the use of path analysis and related procedures for the investigation of ecological problems. American Naturalist 152:151-159.

Pugesek, B.H. and J.B. Grace. 1998. On the utility of path modeling for ecological and evolutionary studies. Functional Ecology 12:853-856.

Grace, J.B. 1999. The factors controlling species density in herbaceous plant communities: an assessment. Perspectives in Plant Ecology, Evolution and Systematics 2:1-28.

Grace, J.B. and H. Jutila. 1999. The relationship between species density and community biomass in grazed and ungrazed coastal meadows. Oikos 85:398-408.

Grace, J.B. and G.R. Guntenspergen. 1999. The effects of landscape position on plant species density: evidence of past environmental effects in a coastal wetland. Ecoscience 6:381-391.

Gough, L. and J.B. Grace. 1999. Predicting effects of environmental change on plant species density: experimental evaluations in a coastal wetland. Ecology 80:882-890.

Grace, J.B., L. Allain, and C. Allen. 2000. Factors associated with plant species richness in a coastal tall-grass prairie. Journal of Vegetation Science 11:443-452.

Grace, J.B. 2002. Comparing groups using structural equations. In: B. Pugesek, A. Tomer, and A. von Eye (eds.) Structural Equation Modeling: Applications in Ecological and Evolutionary Biology Research. Cambridge University Press.

Grace, J.B. 2002. Examining the relationships between environmental variables and ordination axes using latent variables and structural equation modeling. In: B. Pugesek, A. Tomer, and A. von Eye (eds.) Structural Equation Modeling: Applications in Ecological and Evolutionary Biology Research. Cambridge University Press.

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