The relationship between genetic diversity and species diversity – impact of parallel processes in isolated plant populations

Chapter 1: The relationship between genetic diversity (GD) and species diversity (SD) is still not clearly understood. By now, many theoretical and experimental studies on this essential issue of biodiversity research exist and different hypotheses have been developed that predict either positive or...

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Bibliographic Details
Main Author: Hornemann, Gitte
Contributors: Ziegenhagen, Birgit (Prof.Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2012
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Summary:Chapter 1: The relationship between genetic diversity (GD) and species diversity (SD) is still not clearly understood. By now, many theoretical and experimental studies on this essential issue of biodiversity research exist and different hypotheses have been developed that predict either positive or negative GD-SD correlations. Especially processes like drift and selection are believed to indirectly create positive GD-SD correlations by acting similarly and in parallel on both levels. In this study we analyze the impact of parallel processes on genetic diversity of eight dry grassland plant species in central Germany. We used amplified fragment length polymorphism (AFLP) to determine genetic diversity within species. In total 31 isolated grassland patches differing in species richness (range: 43 to 126 dry grassland species per site) and habitat heterogeneity were studied. Drift and selection are expected to be strong determinants of GD and SD in this study system because of long term habitat isolation and restricted gene flow among populations and plant communities. We found high genetic diversity within populations throughout all study species. In three of the eight species we found a positive GD-SD correlation. However, effects of drift and selection are generally low within our study system and probably did not create the observed patterns. Although gene flow appears to be restricted in some cases, species specific responses to habitat isolation are strongly dependent on the species’ life history traits, such as breeding system and dispersal strategy. Single species studies may thus not be able to draw general conclusions about the processes acting in such study systems. Therefore, our study highlights the importance for multi species studies. Chapter 2: The conservation of endangered species critically depends on the understanding to which degree short-term fitness and long-term trends are affected by intrinsic local conditions and external global dynamics. However, studies combining long-term demographic data with population level analyses of site conditions, GD and reproduction as well as with climatic data are still rare. Here we studied the endangered orchid Anacamptis morio, representative for species with a sub-mediterranean distribution. For populations at the northern range edge, we combined long-term monitoring data (1977-2010) with climatic data and analyzed reproductive fitness components, GD and abiotic site conditions. Reproduction was generally low as expected from the deceptive pollination system, and was positively influenced by population size and xerothermic site quality. The majority of populations showed a positive population trend, which was paralleled by an increase in spring temperature and which was positively affected by site quality. High levels of GD were found in the populations which were at gene flow-drift equilibrium. A. morio may profit from increasing spring temperatures because of increased reproductive output. Nevertheless, whether climate change results in fitness increase may depend on the maintenance and provision of optimal site quality, i.e. xerothermic and nutrient poor conditions. Chapter 3: In plant populations a positive correlation between population size, genetic variation and fitness components is often found, due to increased pollen limitation or reduced genetic variation and inbreeding depression in smaller populations. However, components of fitness also depend on environmental factors which can vary strongly between years. The dry grassland species Muscari tenuiflorum experiences long term habitat isolation and small population sizes. We analyzed seed production of M. tenuiflorum in four years and its dependence on population size and genetic variation. Genetic diversity within populations was high (AFLP: HE = 0.245; allozymes: HE = 0.348). An analysis of molecular variance revealed considerable population differentiation (AFLP: 26 %; allozyme: 17 %). An overall pattern of isolation by distance was found, which, however was not present at distances below 20 km indicating stronger effects of genetic drift. Genetic diversity was positively correlated to population size. Self pollination reduced seed set by 24 % indicating inbreeding depression. Reproductive fitness was not correlated to genetic diversity and a positive correlation with population size was present in two of four study years. The absence of a general pattern stresses the importance for multi-year studies. Overall the results show that despite long term habitat isolation M. tenuiflorum maintains seed production in many years independent of population size. The long term persistence of populations is thus expected to depend less on intrinsic genetic or demographic properties affecting seed production but on successful plant establishment and persistence which are based on conservation and protection of suitable habitat.