Population structure of the rare, long-lived perennial Gentiana pneumonanthe in relation to vegetation and management in The Netherlands Oostermeijer, J.G.B.; van 't Veer, R.; den Nijs, J.C.M.

Offspring fitness in relation to population size and genetic variation in the rare perennial plant species Gentiana pneumonanthe (Gentianaceae) Oostermeijer, J.G.B.; van Eijck, M.W.; den Nijs, J.C.M. Published in: Oecologia DOI:10.1007/BF00317317 Link to publication Citation for published version (APA):Oostermeijer, J. G. B., van Eijck, M. W., & den Nijs, J. C. M. (1994). Offspring fitness in relation to population size and genetic variation in the rare perennial plant species Gentiana pneumonanthe (Gentianaceae). Oecologia, 97, 289-296. DOI: 10.1007/BF00317317 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Offspring fitness in relation to population size and genetic variation in the rare perennial plant species Gentiana pneumonanthe (Gentianaceae) Received: 5 February 1993 / Accepted: 8 December 1993 Abstract Seeds were sampled from 19 populations of the rare Gentiana pneumonanthe, ranging in size from 5 to more than 50,000 flowering plants. An analysis was made of variation in a number of life-history characters in relation to population size and offspring heterozygosity (based on seven polymorphic isozyme loci). Life-history characters included seed weight, germination rate, proportion of seeds germinating, seedling mortality, seedling weight, adult weight, flower production per plant and proportion of plants flowering per family. Principal component analysis (PCA) reduced the dataset to three main fitness components. The first component was highly correlated with adult weight and flowering performance, the second with germination performance and the third component with seed and seedling weight and seedling mortality. The latter two components were considered as being maternally influenced, since these comprised life-history traits that were significantly correlated with seed weight. Multiple regression analysis showed that variation in the first fitness component was mainly associated with heterozygosity and not with population size, while the third fitness component was only correlated with population size and not with heterozygosity. The latter relationship appeared to be non-linear, which suggests a stronger loss of fitness in the smallest populations. The second (germination) component was neither correlated with population size nor with genetic variati...

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The amount of genetic variation in the rare perennial herb Gentiana pneumonanthe L. was determined to explore its relation to population size. Differences in isozyme variation between maternal plants and their offspring were used to investigate the relationship between population size and outcrossing rate. In 25 populations in The Netherlands, differing in size from 1 to more than 50,000 flowering individuals, 16 allozyme loci were analyzed on leaves of maternal plants and offspring grown in a greenhouse. Population size was significantly positively correlated with the proportion of polymorphic loci, but only marginally with heterozygosity and the mean effective number of alleles. Most of the studied populations were characterized by a complete absence of rare alleles, and F‐statistics suggest relatively high levels of genetic differentiation among populations and thus a low level of gene flow. Leaf samples (maternal) were mostly in Hardy‐Weinberg equilibrium, while several offspring samples showed an excess of homozygotes, which suggests selection favoring heterozygotes. Because most small populations consist only of adult survivors from formerly larger populations, this may partly explain the absence of a clear relationship between genetic variation of the maternal plants and population size. A significant positive correlation was found between the level of cross‐fertilization and population size. From these results, we conclude that, to some degree, small populations have a reduced level of genetic variation, while their present isolation in nature reserves has resulted in a very limited interpopulational gene flow level. At present a higher level of inbreeding in small populations contributes to a further loss of genetic variation and may also result in reduced offspring fitness.

Summary1. We need to understand how threatened plant species respond to natural or managementinduced habitat changes to conserve them successfully. Because long-term demographic studies are not feasible for large numbers of species, there is a clear need for simple short-term methods to assess demographic responses. 2. The population structure of 23 populations of the endangered perennial Salvia pratensis was studied in relation to the vegetation and management of dry floodplain grasslands along Dutch rivers. The aims of the study were to (i) evaluate the suitability of single censuses of population stage structures as a tool for quick assessments of the viability of plant populations; (ii) test whether viable populations of S. pratensis indicate sites of higher conservation value; (iii) obtain information on the viability of the remaining populations; and (iv) provide advice for optimal habitat management. 3. Using cluster analysis, we distinguished three different types of populations: (i) 'dynamic' populations, characterized by a large proportion of young individuals (seedlings, juveniles and immatures); (ii) 'normal' populations, with a relatively higher proportion of adults but still a considerable number of young individuals; and (iii) 'regressive' populations, in which adult stages, especially large flowering individuals, dominated and rejuvenation hardly occurred. The three population types differed with respect to population size and total plant density, which were highest in dynamic, intermediate in normal and lowest in regressive populations. 4. Both the structure and composition of the surrounding vegetation were associated with the type of population found. The percentage of bare soil surface (indicating an open vegetation structure) was positively related to recruitment of S. pratensis . The dynamic populations occurred in a species-rich vegetation, comprising species of nutrient-poor soils and characteristic of floodplain grasslands. The regressive populations occurred more often in species-poor vegetation, comprising mainly species of nutrient-rich conditions. 5. Salvia population structure was correlated with management. We observed that those populations with a late mowing regime had higher proportions of young stages and larger population sizes. Although we expected that recently established populations on the young river dunes formed during ecological restoration projects would be dynamic, most sampled plots were of the regressive type, which suggests that either site conditions were not yet optimal or Allee effects limited further expansion of the small founder populations. 6. We conclude that conservation of the remaining populations of S. pratensis in Dutch dry floodplain grasslands will be best achieved by late mowing with hay removal.

Summary1. Hybridization seems possible for many crop species after pollen transfer from crops to wild relatives in the surrounding vegetation. Subsequent introgression of crop-specific traits into wild relatives could lead to invasive introgressants. This process has become a public concern following the introduction of genetically modified (GM) crops. Until now, few studies have used demographic vital rates to compare the performance of hybrids with their wild relatives. 2. We created second-generation (S 1 and BC 1 ) hybrids between the non-transgenic crop Lactuca sativa and its entirely cross-fertile wild relative Lactuca serriola . Seeds of parents and hybrids were individually sown in field plots at three different locations. Next to germination and survival, we measured a range of single fitness components and morphological traits. We also compared observed phenotypes to phenotypes theoretically expected, according to different inheritance scenarios. 3. Phenotypes of both hybrid classes resembled L. serriola closely, and more than theoretically expected. However, demographic vital rates, i.e. germination and survival of hybrids were much higher than in L. serriola. 4. Our results indicate that hybrids between crop and wild Lactuca are phenotypically indistinguishable from the wild relative and thus will largely remain unnoticed when they occur. However, these hybrids could potentially become invasive because of substantial differences in vital rates and seeds returned per seed sown. Synthesis and applications.A comparative study on single fitness components, such as seed production, alone would not have revealed the performance advantage of cropwild hybrids in Lactuca . Therefore, studying demographic vital rates of hybrids and back-crosses to test for long-term consequences of hybridization should be part of any risk assessment of GM crops. Demographic vital rates are also important for the development of predictive modelling tools that can be employed to test the individual-and population-level consequences of new-to-add traits.

Summary1 Transition matrix models were used to evaluate the effects of environmental stochasticity and four different methods of grassland management on dynamics and viability of a population of the biennial Gentianella campestris (Gentianaceae) in species-rich grassland. Data were collected between 1990 and 1995. 2 Continuous summer grazing, the prevailing management strategy in Scandinavian grasslands, resulted in high recruitment of new plants, mainly because litter accumulation was prevented and gaps were created by trampling. Trampling and repeated grazing, however, caused damage which reduced seed production. Lambda for the average matrix was c . 0.77, and a stochastic matrix model yielded an extinction probability for the total population of c. 0.08 within 50 years. 3 Mowing in mid-July (used as a conservation tool) increased seed production, but litter accumulation following re-growth of the vegetation prevented establishment. Lambda and extinction risk were similar to continuous grazing. 4 Mowing in October (another conservation tool) promoted recruitment because of low litter accumulation, but the seed output decreased because plant growth was impaired by tall vegetation. Lambda was 0.64, while the extinction probability was very high ( c. 0.98 within 50 years). 5 Mid-July mowing followed by autumn grazing (the historical management regime) yielded high values for both seed production and establishment of rosettes. Lambda was 0.94 and the probability of extinction within 50 years was below detection level. 6 Log-linear analysis showed that the matrices differed significantly both between treatments and between years. The latter indicates environmental stochasticity, here caused by summer drought that increased the extinction risk. Lambda may be slightly underestimated because drought occurred in one out of five summers during the study period, which is high compared with the natural frequency. 7 We conclude that traditional grassland management is more favourable for G. campestris than the methods that prevail in Scandinavia today. This indicates a serious conservation problem, because grazing has replaced traditional management in many of the remaining semi-natural grasslands throughout Europe.