Evaluation of anatomical characters and the question of hybridization with domestic cats in the wildcat population of Thuringia, Germany

Germany's large population of wildcats ( Felis silvestris silvestris ) can be clearly distinguished from domestic cats on the basis of morphological characters. However, an examination of 71 specimens from Thuringia also illustrates the risks involved in using only a few such characters. The most reliable tool for identification in the field are three pelage characters (distinctness of tail bands, stripes on the nape and stripes on the shoulder). Only two morphological characters (intestine length and cranial volume) are unambiguous and demonstrate no overlap in distribution between domestic cats and wildcats. A linear discriminant analysis with forward selection of variables showed that only five skull variables are necessary to distinguish all four groups (subspecies × sex). Additionally, the high degree of correlation between most of the 49 variables examined (as indicated by Pearson's r correlation matrix) speaks against the utility of measuring such high numbers of characters in the future. Principal component analysis (PCA) enabled the subspecies to be separated clearly. The first PCA axis was highly correlated with variables characterizing overall body size, thus separating male and female into wildcats and domestic cats. Even when the chief differentiating characters are missing, the PCA still resulted in a good separation of subspecies. None of the genetically determined hybrids could have been deciphered unambiguously using the morphological characters still intact after a road death. Hybridization seems to occur whenever wildcats change their ecological function and become field cats. The impulse to hybridize seems to come much more from the wildcat side than the side of feral cats, and deforestation represents the major threat to the wildcat.     

How inbreeding and outbreeding influence the risk of extinction--a genetically explicit model

We have developed a stochastic model to explore the common effect which genetics and demography have on the extinction risk of endangered populations. The dynamics is formulated as a MARKOVian birth and death process (in continuous time), whereby selection acts through different mortalities of each genotype. With the help of this model we are able to show how inbreeding and outbreeding can influence the genetic variability and the survival of a population. Whether inbreeding or outbreeding takes place depends on the specific mating system. In our model we consider positive assortative as well as disassortative mating. In the case of additive fitness we show that inbreeding reduces the extinction risk and the genetic variability.     

Influence of geographical isolation on genetic diversity ofHimantoglossum hircinum (Orchidaceae)

Many plants live in habitats that are becoming increasingly rare and fragmented due to human disturbance. Studies of genetic diversity are necessary for understanding and evaluating the impact of habitat fragmentation, and land-use change on the dynamics of rare species to help in setting priorities for their management. We used AFLP markers to study variation in genetic structure within and among three border populations of the orchidHimantoglossum hircinum. Study sites were located in central Germany, which represents the north-eastern border of distribution, and they were separated from each other by a maximum distance of 10 km. Landscape between the populations was characterized by man-made habitat features including agricultural fields, major roads and settlements. We compared pairs of populations to evaluate genetic variation, genetic differentiation, and the current level of gene flow between them. Genetic diversity was high within the populations and higher within than between the populations. Population genetic differentiation was relatively high compared to other orchid species (G _st=0.20). Gene flow between pairs of the populations varied and appeared to be influenced by landscape characteristics separating the localities. Recommendations for conservation ofH. hircinum are provided. Management activities should concentrate on maintenance or enlargement of habitat size to prevent loss of genetic diversity due to genetic drift. Sites are genetically relatively isolated, but using stepping stones to improve gene exchange would be problematic because of the intense land-use in the area.     

Genetic diversity of Ranunculus acris L. (Ranunculaceae) populations in relation to species diversity and habitat type in grassland communities

Correlates between genetic diversity at intra- and interpopulation levels and the species diversity in plant communities are rarely investigated. Such correlates may give insights into the effect of local selective forces across different communities on the genetic diversity of local plant populations. This study has employed amplified fragment length polymorphism to assess the genetic diversity within and between 10 populations of Ranunculus acris in relation to the species diversity (richness and evenness) of grassland communities of two different habitat types, 'seminatural' and 'agriculturally improved', located in central Germany. Within-population genetic diversity estimated by Nei's unbiased gene diversity (HE) was high (0.258-0.334), and was not correlated with species richness (Pearson's r = -0.17; P = 0.64) or species evenness (Pearson's r = 0.15; P = 0.68) of the plant communities. However, the genetic differentiation between R. acris populations was significantly correlated with the difference in species evenness (Mantel's r = 0.62, P = 0.02), but not with difference in species richness of plant communities (r = -0.17, P = 0.22). Moreover, we also found that populations of R. acris from the 'seminatural' habitat were genetically different (amova, P < 0.05) from those in 'agriculturally improved' habitats, suggesting that gene flow between these habitat types is limited. The results reported in this study may indicate that habitat characteristics influence the genetic diversity of plant species.     

The clonal dependence of turion formation in the duckweed Spirodela polyrhiza—an ecogeographical approach

Formation of turions, the vegetative perennation organs, plays an important role in the survival strategy of Spirodela polyrhiza (L.) Schleiden. Turion formation [quantified as number of turions formed per frond; specific turion yield (SY)] was investigated in 27 clones collected from a wide geographical range. The Pearson correlation was tested with (1) duration of growing season (monthly average temperature of ≥10°C), (2) relative growth rate of the fronds, (3) longitude and latitude, and (4) several climatic parameters, in all possible single and multiple regressions. All single coefficients of determination were below 0.10. The highest correlation (R² = 0.61; adjusted for the number of explaining variables 0.54) was found in a multiple linear regression with the following five parameters: average temperatures over the year and during the growing season, duration of the growing season and precipitation over the year and during the growth period. All these parameters were shown to have significant contributions. This equation was used successfully to predict the SY of five newly isolated clones. Finally, on the basis of all 32 clones the following conclusions were drawn: The mean annual temperature has the highest impact. It is suggested that lower temperatures decrease the survival rate of turions and that adaptation refers to increasing SY. The different levels of SY in the clones (ranging from SY = 0.22 to 5.9) were detected even after several years of in vitro cultivation. It is therefore assumed that these adaptations to the climatic conditions are genetically determined.     

On the relationship between plant species diversity and genetic diversity of Plantago lanceolata (Plantaginaceae) within and between grassland communities

Aims and Methods The relationship between genetic diversity and species diversity and the underlying mechanisms are of both fundamental and applied interest. We used amplified fragment length polymorphism (AFLP) and vegetation records to investigate the association between genetic diversity of Plantago lanceolata and plant species diversity using 15 grassland communities in central Germany. We used correlation and partial correlation analyses to examine whether relationships between genetic and species diversity were direct or mediated by environmental differences between habitats.Important findings Both within- and between-population genetic diversity of P. lanceolata were significantly positively correlated with plant species diversity within and between sites. Simple and partial correlations revealed that the positive correlations indirectly resulted from the effects of abiotic habitat characteristics on plant species diversity and, via abundance, on genetic diversity of P. lanceolata. Thus, they did not reflect a direct causal relationship between plant species diversity and genetic diversity of P. lanceolata, as would have been expected based on the hypothesis of a positive relationship between plant species diversity and niche diversity.     

Seed bank assembly in an unmanaged ruderal grassland recovering from long-term exposure to industrial emissions

The main aim of this 3-year study was to relate the temporal patterns in seed bank composition of a ruderal grassland previously subjected to industrial pollution with the successional patterns in the above-ground vegetation. In particular, we tested whether the observed changes conformed to a paradigm of declining seed numbers and diversity and decreasing similarity between seed bank and vegetation, as previously formulated for secondary successions. We found that seed numbers and the number of species per soil sample increased during the 3 years of the study. The compositional similarity between seed bank and vegetation did increase for the 0–2 cm surface layer, and remained roughly constant for deeper soil layers. Thus, the patterns found differed from those of other secondary successional communities and do not support the tested paradigm. Rather, our findings resemble those from a number of primary successional ecosystems. We suggest that temporal patterns of similarity between seed bank and vegetation should be interpreted in terms of the factors that determine the relative rates of compositional change in vegetation and seed bank at different stages of succession. Our study also provides information about the seed bank persistence of 22 species, including several species for which such knowledge previously was scarce. In particular, this study indicates the extreme longevity of the seeds of the halophytic grass Puccinellia distans. Several years after its rapid decline in the vegetation, this species dominated the seed bank, and no measurable decline in seed density was detected during this study.     

Evolutionary classification of toxin mediated interactions in microorganisms

A trade-off between the parameters of Lotka–Volterra systems is used to give verifications of relations between intrinsic growth rate and limiting capacity and the stability type of the resulting dynamical system. The well known rock–paper–scissors game serves as a template for toxin mediated interactions, which is best represented by the bacteriocin producing Escherichia coli bacteria. There, we have three strains of the same species. The producer produces a toxin lethal to the sensitive, while the resistant is able to protect itself from that toxin. Due to the fact that there are costs for production and for resistance, a dynamics similar to the rock–paper–scissors game results. By using an adaptive dynamics approach for competitive Lotka–Volterra systems and assuming an inverse relation (trade-off) between intrinsic growth rate (IGR) and limiting capacity (LC) we obtain evolutionary and convergence stable relations between the IGR’s and the LC’s. Furthermore this evolutionary process leads to a phase topology of the population dynamics with a globally stable interior fixed point by leaving the interaction parameters constant. While the inverse trade-off stabilizes coexistence and does not allow branching, toxicity itself can promote diversification. The results are discussed in view of several biological examples indicating that the above results are structurally valid.