Different diversity measures and genetic traits reveal different speciesgenetic diversity relationships: A case study in forest tree communities

Relationships between species diversity and genetic diversity, the two most important elements of biodiversity, have recently attracted considerable interest in the field of community genetics. The present study contributes to this issue by addressing three questions that seem to have been ignored so far, namely whether the use of (a) different diversity measures, of (b) different components of diversity, and of (c) different genetic traits may lead to different assessements of speciesgenetic diversity relationships. For this purpose, data on species composition and genetic traits were collected from the natural regeneration of nine forest communities, which consist of three pure and six mixed tree stands located in the Thuringian forest area. The genetic traits comprised one DNA (AFLP) and five isozyme traits all of which were determined in all species. In contrast to other studies, the species diversity was determined for two components, SD (species diversity) and NeS (effective number of genetically distinct species), and the genetic diversity was determined for three components, TSGD (the transspecific genetic diversity taken over all species of a community), ISGD and NGS (each describing a special average of intraspecific genetic diversity). Each component was quantified by measures of diversity representing four orders of the Renyi/Hillfamily. The orders correspond to the degree to which prevalence of types is considered in the diversity measure (at the lowest order, known as richness, prevalence is disregarded, with increasing order, the diversity measure reports prevalent types only). In our data, the diversity measured for each genetic trait separately showed a great range of variation across traits and components of diversity even in the same stand. The choice of the diversity component thus turned out to have a substantial effect on the assessment of the level of genetic diversity within stands. This prompted more detailed studies of the relationships between species and genetic diversity. Relationships were quantified with the help of the coefficient of co-variation, and the statistical significance of the co-variations was verified through permutation tests. The co-variations between SD and TSGD were found to be generally positive and in most cases significant, but the co-variation declined with increasing orders of diversity for most of the genetic traits. In contrast, the co-variation between SD and ISGD was not consistent for the four orders of diversity. In particular, the co-variations for the highest order were found to be negative for all traits. The results of our explorative study thus demonstrate that the assessment of levels of genetic diversity within stands as well as species-genetic interrelations critically depend on the choice of the diversity component, of the order of diversity, and of the genetic trait. These observations lend support to different and even opposing hypotheses on the processes potentially generating species-genetic relationships. Therefore, strategies in the conservation of biodiversity, for example, are suggested to be related more specifically to the components and orders of diversity to be safegarded and to consider the functions of genetic traits in relation to adaptationally relevant environmental factors.