Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Sampling / growing transplants

For sampling purposes c. 120 sites in Germany within an area of 30 x 25 km were visited and studied. About 80 sites containing populations of different size and degree of isolation of the target species (Carlina vulgaris, Hypochoeris radicata, Pimpinella saxifraga, Tragopogon pratensis, and Succisa pratensis and Daucus carota for other WPs) were then selected. Seeds were sampled in each population for the common garden studies (results: 9382) and the reciprocal transplant experiments (results: 9380), and also for studies performed by WP1 (crossing experiments), WP3 (demography studies) and WP5 (recruitment experiments, seed burial experiments, terminal velocity studies). Leaf samples were collected for WP1 (genetic variation). Biotic (e.g. species composition) and abiotic variables were recorded to characterise the sites, and soil samples were collected to carry out a bioassay in order to assess soil fertility. Seeds for the common garden study and the transplants experiments were collected and other seeds received from WP3, WP4, WP5 and WP6.

The seeds were counted and weighed and batches of seeds were prepared for the transplant experiments. In spring 2001 batches of seeds containing random samples of equal size from each population were sent back to the project partners who carried out the reciprocal transplant experiments (WP3, WP4; WP6). Seeds were germinated, raised in nutrient-poor gardening soil in each study region for a few weeks and then the seedlings were transplanted into natural field populations either at their site of origin ("home site") or at one of the other regions ("away sites").

To study the effect of population size on reproduction and performance at the field sites, the number of seeds per plant and plant size was determined in a number of German populations of Carlina, Hypochoeris, Pimpinella and Tragopogon. These four species differ in the two traits dispersability and longevity: Hypochoeris and Tragopogon are well and Carlina and Pimpinella poorly dispersed, Carlina and Tragopogon are short-lived (monocarpic), whereas Hypochoeris and Pimpinella are perennial. Because of their short-generation time, short-lived species are thought to suffer faster from the negative genetic effects of small population size, and poorly dispersed plants are presumably more strongly isolated. However, we found that the number of seeds per plant increased with population size in the two obligate outcrossing species Carlina and Hypochoeris, but not in Pimpinella and Tragopogon.

Thus, there were no consistent differences between well and poorly dispersed, and between short- and long-lived species. Instead, the results suggest that the breeding system is a better predictor of the effects of small population size on plants than longevity or dispersability: Reproduction of obligate outcrossers (Carlina and Hypochoeris) was more strongly affected by population size than that of self-compatible plants (Pimpinella and Tragopogon), presumably because of pollination limitation. In contrast to reproduction, plant performance in the field was not influenced by population size, the effects of habitat type were far more important. In conclusion, fragmentation has already negative effects on the reproduction of plants in natural populations, which could present a particular problem for monocarpic plants like Carlina that have to re-establish frequently from seeds.

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