COMPARATIVE-ANALYSIS OF 2 METHODS USED TO SHOW INTERSPECIFIC ASSOCIATIONS IN NATURALLY ACQUIRED PARASITE NEMATODE COMMUNITIES FROM THE ABOMASUM OF EWES

The aim of our study was to compare a multivariate and a univariate me thod to evaluate the associations between nematode species in natural infections. We used a data set based on the 3-year study of the commun ity of abomasal nematodes in ewes of the middle-Atlas region of Morocc o. Frequency data (percentage of each species in the individual host c ommunity) were processed by principal component analysis. Euclidean di stances between species (D-2) were calculated from projections of prin cipal component analysis on three axes and compared to a bivariate est imate (1-correlation coefficient R). Low distances were recorded betwe en morphs of the same species (Teladorsagia circumcincta and T. trifur cata, for example), which indicates a positive association. Only two s pecies, Trichostrongylus axei and T. circumcincta, were negatively ass ociated having D-2 values much over 1. The distances D-2, i.e., multiv ariate measure of association intensity were similar in most cases to 1-R estimates, indicating probably the absence of strong multispecies association. The D-2 fitted a Motomura geometric progression model ind icating that associations were arranged in a continuum from low to hig h values, but they did not depart much from what could be expected fro m random associations for most species. The D-2 interest is mostly to relate associations with environmental variables: and comparing with 1 -R, to assess the degree of interaction in the community. (C) 1998 Els evier Science B.V.