Discriminant analysis of vegetational and topographical factors associated with the focal distribution of Rocky Mountain wood ticks, Dermacentor andersoni (Acari: Ixodidae), on cattle range.

Abstract

Discriminant analysis can be a useful statistical tool for identifying indicators of the presence or absence of a species in an area. In a 2-year study in south-central British Columbia, Canada, the presence or absence of Rocky Mountain wood ticks was compared with indices of abundance of certain trees, shrubs, grasses, and topographical features, and also with presence or absence of host animal signs in sampling quadrats. Discriminant analysis was used to identify and assess combinations of these indices to be used in predicting tick presence or absence. Although the analysis selected a different set of indicator variables for each year, there was agreement that saskatoon (Amelanchier) abundance, rose (Rosa) abundance, and aspen (Populus) absence were useful as predictors. When the predictive functions for each year were used to classify the other year's plots, at least 76% were correctly classified as to tick presence or absence. A discriminant analysis of the combined data added absence of domestic animal signs and presence of Agropyron spicatum as indicators of tick presence, and used all of the indicators to classify 77% of the quadrats correctly. The results have potential application in improving sampling procedures and control of tick infestations of cattle by range management.