Abstract
Community structure as summarized by presence–absence data is often evaluated via diversity measures by incorporating taxonomic, phylogenetic and functional information on the constituting species. Most commonly, various dissimilarity coefficients are used to express these aspects simultaneously such that the results are not comparable due to the lack of common conceptual basis behind index definitions. A new framework is needed which allows such comparisons, thus facilitating evaluation of the importance of the three sources of extra information in relation to conventional species-based representations. We define taxonomic, phylogenetic and functional beta diversity of species assemblages based on the generalized Jaccard dissimilarity index. This coefficient does not give equal weight to species, because traditional site dissimilarities are lowered by taking into account the taxonomic, phylogenetic or functional similarity of differential species in one site to the species in the other. These, together with the traditional, taxon- (species-) based beta diversity are decomposed into two additive fractions, one due to taxonomic, phylogenetic or functional excess and the other to replacement. In addition to numerical results, taxonomic, phylogenetic and functional community structure is visualized by 2D simplex or ternary plots. Redundancy with respect to taxon-based structure is expressed in terms of centroid distances between point clouds in these diagrams. The approach is illustrated by examples coming from vegetation surveys representing different ecological conditions. We found that beta diversity decreases in the following order: taxon-based, taxonomic (Linnaean), phylogenetic and functional. Therefore, we put forward the beta-redundancy hypothesis suggesting that this ordering may be most often the case in ecological communities, and discuss potential reasons and possible exceptions to this supposed rule. Whereas the pattern of change in diversity may be indicative of fundamental features of the particular community being studied, the effect of the choice of functional traits—a more or less subjective element of the framework—remains to be investigated.
Highlights
Presence–absence (p–a) indices of dissimilarity between pairs of objects have long been used for various purposes in ecology
We first overview existing proposals that allow adjustment of species weighting according to functional, taxonomic or phylogenetic relatedness. Further, that these generalized dissimilarities may be partitioned into additive fractions that have similar interpretation as those of species-based dissimilarities, and extend the functional approach suggested by Ricotta et al [17] to taxonomic and phylogenetic data
In the marshland we have a mosaic of very different environmental conditions in terms of soil composition and salinity, determining which species can persist in each site depending on their functional characteristics. It has been generally acknowledged in numerical ecology that the measurement of biodiversity in terms of the number of taxa and their abundances provides only a one-sided view on community composition
Summary
Presence–absence (p–a) indices of dissimilarity between pairs of objects (usually sites or sample plots) have long been used for various purposes in ecology. Contrariwise, differential species may be fairly unique in their functionality as well, falling quite far from all the species of the other site in this respect Such ecologically different situations are not reflected by the classical p–a coefficients: high dissimilarity based on taxon (usually species) lists does not necessarily imply high dissimilarity in ecological functionality of the assemblages. Classical p–a dissimilarity measures do not cope with these relationships, whereas it may be desirable to consider taxonomic or phylogenetic distinctness of differential species in calculating dissimilarity of sites. These modified dissimilarities may be used as a proxy for functional dissimilarity in lieu of detailed information on the functional features of species. We put forward some hypotheses regarding the mutual relationship of results generated by these methods
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