Species diversity of nematode communities in the digestive tract of domestic ruminants: multivariate versus univariate estimations

Abstract

The evaluation of species diversity can be performed using species richness (number of species), diversity (number and relative proportions of species) or evenness (equitability of the proportion of each species). A large number of indices related to diversity or evenness is available but their mathematical properties remain unexplained, and hence their use is somewhat unreliable. We intended to present an array of well defined methods, based on discriminant analysis, to evaluate diversity in helminth communities of ruminants. The database used concerned seven cattle farms and seven sheep farms located in temperate areas, from which at least three necropsies were undertaken in autumn. The hosts were chosen because they had experienced nearly a complete grazing period and no anthelmintic treatment was performed for a minimum of 2 months before the necropsies were undertaken, so that the helminth communities could be considered as representative of each farm at one specific moment. We used discriminant analyses to evaluate diversity, based either on proportions of species, or on proportions of species arranged in decreasing order, or on a set of six indices of diversity selected from the most commonly used. We showed that actual proportions were the most efficient in cattle but not in lambs, and that discriminant analyses based on six indices of diversity or based on actual proportions of species ranked in decreasing order yielded very similar results in both host communities. We rejected the use of one single index for evaluating diversity in all cases and proposed the following procedure: actual proportions of species provide information on interactions between species and, when there is limited or no interaction, a combination of diversity indices or single indices could be used for estimating diversity. When interactions between species have to be taken into account, the best information will be obtained either from species proportions arranged in decreasing order or a combination of biodiversity indices.