Multivariate Analysis of the Factors Influencing Changes in Colorado Grasshopper Abundances

Abstract

The correlation between grasshopper densities and environmental conditions has long been recognized. However, the relationship is not well understood and may involve very complex interactions. The objective of this study was to determine the environmental factors which are most closely linked with changes in grasshopper densities. Multiple regression and stepwise discriminant analysis (DA) were used to identify the soil and weather variables which best distinguished among changes in Colorado grasshopper densities from 1995 to 1996. Grasshopper density in 1995 was the most important variable in DA, followed by mean precipitation for April, 1993, and mean temperature in October, 1993. Our results indicate that soil characteristics are not as important to changes in density as are population level and stochastic weather events. In addition, our findings confirm the importance of time lags in the effects of weather conditions on population changes and highlight the need to incorporate weather events from previous seasons into predictive population models.